Repo created

app/storage/src/main/java/com/fsck/k9/preferences/K9StorageEditor.java

@@ -0,0 +1,114 @@
+package com.fsck.k9.preferences;
+
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Map.Entry;
+
+import android.os.SystemClock;
+
+import com.fsck.k9.preferences.K9StoragePersister.StoragePersistOperationCallback;
+import com.fsck.k9.preferences.K9StoragePersister.StoragePersistOperations;
+import timber.log.Timber;
+
+
+public class K9StorageEditor implements StorageEditor {
+    private StorageUpdater storageUpdater;
+    private K9StoragePersister storagePersister;
+
+    private Map<String, String> changes = new HashMap<>();
+    private List<String> removals = new ArrayList<>();
+
+
+    public K9StorageEditor(StorageUpdater storageUpdater, K9StoragePersister storagePersister) {
+        this.storageUpdater = storageUpdater;
+        this.storagePersister = storagePersister;
+    }
+
+    @Override
+    public boolean commit() {
+        try {
+            storageUpdater.updateStorage(this::commitChanges);
+            return true;
+        } catch (Exception e) {
+            Timber.e(e, "Failed to save preferences");
+            return false;
+        }
+    }
+
+    private Storage commitChanges(Storage storage) {
+        long startTime = SystemClock.elapsedRealtime();
+        Timber.i("Committing preference changes");
+
+        Map<String, String> newValues = new HashMap<>();
+        Map<String, String> oldValues = storage.getAll();
+        StoragePersistOperationCallback committer = new StoragePersistOperationCallback() {
+            @Override
+            public void beforePersistTransaction(Map<String, String> workingStorage) {
+                workingStorage.putAll(oldValues);
+            }
+
+            @Override
+            public void persist(StoragePersistOperations ops) {
+                for (String removeKey : removals) {
+                    ops.remove(removeKey);
+                }
+                for (Entry<String, String> entry : changes.entrySet()) {
+                    String key = entry.getKey();
+                    String newValue = entry.getValue();
+                    String oldValue = oldValues.get(key);
+                    if (removals.contains(key) || !newValue.equals(oldValue)) {
+                        ops.put(key, newValue);
+                    }
+                }
+            }
+
+            @Override
+            public void onPersistTransactionSuccess(Map<String, String> workingStorage) {
+                newValues.putAll(workingStorage);
+            }
+        };
+        storagePersister.doInTransaction(committer);
+        long endTime = SystemClock.elapsedRealtime();
+        Timber.i("Preferences commit took %d ms", endTime - startTime);
+
+        return new Storage(newValues);
+    }
+
+    @Override
+    public StorageEditor putBoolean(String key,
+            boolean value) {
+        changes.put(key, "" + value);
+        return this;
+    }
+
+    @Override
+    public StorageEditor putInt(String key, int value) {
+        changes.put(key, "" + value);
+        return this;
+    }
+
+    @Override
+    public StorageEditor putLong(String key, long value) {
+        changes.put(key, "" + value);
+        return this;
+    }
+
+    @Override
+    public StorageEditor putString(String key, String value) {
+        if (value == null) {
+            remove(key);
+        } else {
+            changes.put(key, value);
+        }
+        return this;
+    }
+
+    @Override
+    public StorageEditor remove(String key) {
+        removals.add(key);
+        return this;
+    }
+}

app/storage/src/main/java/com/fsck/k9/preferences/K9StoragePersister.java

@@ -0,0 +1,251 @@
+package com.fsck.k9.preferences;
+
+
+import java.util.HashMap;
+import java.util.Map;
+
+import android.content.ContentValues;
+import android.content.Context;
+import android.database.Cursor;
+import android.database.sqlite.SQLiteDatabase;
+import android.database.sqlite.SQLiteStatement;
+import android.os.SystemClock;
+
+import androidx.annotation.NonNull;
+import com.fsck.k9.helper.Utility;
+import com.fsck.k9.preferences.migrations.StorageMigrations;
+import com.fsck.k9.preferences.migrations.StorageMigrationsHelper;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+import timber.log.Timber;
+
+
+public class K9StoragePersister implements StoragePersister {
+    private static final int DB_VERSION = 19;
+    private static final String DB_NAME = "preferences_storage";
+
+    private final Context context;
+
+    public K9StoragePersister(Context context) {
+        this.context = context;
+    }
+
+    private SQLiteDatabase openDB() {
+        SQLiteDatabase db = context.openOrCreateDatabase(DB_NAME, Context.MODE_PRIVATE, null);
+
+        db.beginTransaction();
+        try {
+            if (db.getVersion() > DB_VERSION) {
+                throw new AssertionError("Database downgrades are not supported. " +
+                        "Please fix the database '" + DB_NAME + "' manually or clear app data.");
+            }
+
+            if (db.getVersion() < 1) {
+                createStorageDatabase(db);
+            } else {
+                StorageMigrations.upgradeDatabase(db, migrationsHelper);
+            }
+
+            db.setVersion(DB_VERSION);
+            db.setTransactionSuccessful();
+        } finally {
+            db.endTransaction();
+        }
+
+        if (db.getVersion() != DB_VERSION) {
+            throw new RuntimeException("Storage database upgrade failed!");
+        }
+
+        return db;
+    }
+
+    private void createStorageDatabase(SQLiteDatabase db) {
+        Timber.i("Creating Storage database");
+
+        db.execSQL("DROP TABLE IF EXISTS preferences_storage");
+        db.execSQL("CREATE TABLE preferences_storage " +
+                "(primkey TEXT PRIMARY KEY ON CONFLICT REPLACE, value TEXT)");
+        db.setVersion(DB_VERSION);
+    }
+
+    void doInTransaction(StoragePersistOperationCallback operationCallback) {
+        HashMap<String, String> workingStorage = new HashMap<>();
+        SQLiteDatabase workingDb = openDB();
+
+        try {
+            operationCallback.beforePersistTransaction(workingStorage);
+
+            StoragePersistOperations storagePersistOperations = new StoragePersistOperations(workingStorage, workingDb);
+            workingDb.beginTransaction();
+            operationCallback.persist(storagePersistOperations);
+            storagePersistOperations.close();
+            workingDb.setTransactionSuccessful();
+
+            operationCallback.onPersistTransactionSuccess(workingStorage);
+        } finally {
+            workingDb.endTransaction();
+            workingDb.close();
+        }
+    }
+
+    @NonNull
+    @Override
+    public StorageEditor createStorageEditor(@NonNull StorageUpdater storageUpdater) {
+        return new K9StorageEditor(storageUpdater, this);
+    }
+
+    static class StoragePersistOperations {
+        private Map<String, String> workingStorage;
+        private final SQLiteStatement deleteStatement;
+        private final SQLiteStatement insertStatement;
+
+        private StoragePersistOperations(Map<String, String> workingStorage, SQLiteDatabase database) {
+            this.workingStorage = workingStorage;
+
+            insertStatement = database.compileStatement(
+                    "INSERT INTO preferences_storage (primkey, value) VALUES (?, ?)");
+            deleteStatement = database.compileStatement(
+                    "DELETE FROM preferences_storage WHERE primkey = ?");
+        }
+
+        void put(String key, String value) {
+            insertStatement.bindString(1, key);
+            insertStatement.bindString(2, value);
+            insertStatement.execute();
+            insertStatement.clearBindings();
+
+            workingStorage.put(key, value);
+        }
+
+        void remove(String key) {
+            deleteStatement.bindString(1, key);
+            deleteStatement.executeUpdateDelete();
+            deleteStatement.clearBindings();
+
+            workingStorage.remove(key);
+        }
+
+        private void close() {
+            insertStatement.close();
+            deleteStatement.close();
+        }
+    }
+
+    interface StoragePersistOperationCallback {
+        void beforePersistTransaction(Map<String, String> workingStorage);
+        void persist(StoragePersistOperations ops);
+        void onPersistTransactionSuccess(Map<String, String> workingStorage);
+    }
+
+    @NonNull
+    @Override
+    public Storage loadValues() {
+        long startTime = SystemClock.elapsedRealtime();
+        Timber.i("Loading preferences from DB into Storage");
+
+        try (SQLiteDatabase database = openDB()) {
+            return new Storage(readAllValues(database));
+        } finally {
+            long endTime = SystemClock.elapsedRealtime();
+            Timber.i("Preferences load took %d ms", endTime - startTime);
+        }
+    }
+
+    private Map<String, String> readAllValues(SQLiteDatabase database) {
+        HashMap<String, String> loadedValues = new HashMap<>();
+        Cursor cursor = null;
+        try {
+            cursor = database.rawQuery("SELECT primkey, value FROM preferences_storage", null);
+            while (cursor.moveToNext()) {
+                String key = cursor.getString(0);
+                String value = cursor.getString(1);
+                Timber.d("Loading key '%s', value = '%s'", key, value);
+                loadedValues.put(key, value);
+            }
+        } finally {
+            Utility.closeQuietly(cursor);
+        }
+
+        return loadedValues;
+    }
+
+    private String readValue(SQLiteDatabase mDb, String key) {
+        Cursor cursor = null;
+        String value = null;
+        try {
+            cursor = mDb.query(
+                    "preferences_storage",
+                    new String[] {"value"},
+                    "primkey = ?",
+                    new String[] {key},
+                    null,
+                    null,
+                    null);
+
+            if (cursor.moveToNext()) {
+                value = cursor.getString(0);
+                Timber.d("Loading key '%s', value = '%s'", key, value);
+            }
+        } finally {
+            Utility.closeQuietly(cursor);
+        }
+
+        return value;
+    }
+
+    private void writeValue(SQLiteDatabase mDb, String key, String value) {
+        if (value == null) {
+            mDb.delete("preferences_storage", "primkey = ?", new String[] { key });
+            return;
+        }
+
+        ContentValues cv = new ContentValues();
+        cv.put("primkey", key);
+        cv.put("value", value);
+
+        long result = mDb.update("preferences_storage", cv, "primkey = ?", new String[] { key });
+
+        if (result == -1) {
+            Timber.e("Error writing key '%s', value = '%s'", key, value);
+        }
+    }
+
+    private void insertValue(SQLiteDatabase mDb, String key, String value) {
+        if (value == null) {
+            return;
+        }
+
+        ContentValues cv = new ContentValues();
+        cv.put("primkey", key);
+        cv.put("value", value);
+
+        long result = mDb.insert("preferences_storage", null, cv);
+
+        if (result == -1) {
+            Timber.e("Error writing key '%s', value = '%s'", key, value);
+        }
+    }
+
+    private StorageMigrationsHelper migrationsHelper = new StorageMigrationsHelper() {
+        @Override
+        public void writeValue(@NotNull SQLiteDatabase db, @NotNull String key, String value) {
+            K9StoragePersister.this.writeValue(db, key, value);
+        }
+
+        @NotNull
+        @Override
+        public Map<String, String> readAllValues(@NotNull SQLiteDatabase db) {
+            return K9StoragePersister.this.readAllValues(db);
+        }
+
+        @Override
+        public String readValue(@NotNull SQLiteDatabase db, @NotNull String key) {
+            return K9StoragePersister.this.readValue(db, key);
+        }
+
+        @Override
+        public void insertValue(@NotNull SQLiteDatabase db, @NotNull String key, @Nullable String value) {
+            K9StoragePersister.this.insertValue(db, key, value);
+        }
+    };
+}

app/storage/src/main/java/com/fsck/k9/preferences/migrations/StorageMigrationTo10.kt

@@ -0,0 +1,37 @@
+package com.fsck.k9.preferences.migrations
+
+import android.database.sqlite.SQLiteDatabase
+
+/**
+ * Remove saved folder settings
+ *
+ * Folder settings are now only written to 'Storage' when settings are imported. The saved settings will be used when
+ * folders are first created and then the saved settings are discarded.
+ * Since this wasn't the procedure in earlier app versions, we remove any saved folder settings in this migration.
+ */
+class StorageMigrationTo10(
+    private val db: SQLiteDatabase,
+    private val migrationsHelper: StorageMigrationsHelper
+) {
+    private val folderKeyPattern = Regex("[^.]+\\..+\\.([^.]+)")
+    private val folderSettingKeys = setOf(
+        "displayMode",
+        "notifyMode",
+        "syncMode",
+        "pushMode",
+        "inTopGroup",
+        "integrate"
+    )
+
+    fun removeSavedFolderSettings() {
+        val loadedValues = migrationsHelper.readAllValues(db)
+
+        for (key in loadedValues.keys) {
+            val matches = folderKeyPattern.matchEntire(key) ?: continue
+            val folderKey = matches.groupValues[1]
+            if (folderKey in folderSettingKeys) {
+                migrationsHelper.writeValue(db, key, null)
+            }
+        }
+    }
+}

app/storage/src/main/java/com/fsck/k9/preferences/migrations/StorageMigrationTo11.kt

@@ -0,0 +1,26 @@
+package com.fsck.k9.preferences.migrations
+
+import android.database.sqlite.SQLiteDatabase
+import com.fsck.k9.preferences.GeneralSettingsDescriptions
+
+/**
+ * Convert old value for message view content font size to new format.
+ *
+ * This change in formats has been made a long time ago. But never in a migration. So it's possible there are still
+ * installations out there that have the old version in the database. And they would work just fine, because this
+ * conversion was done when loading font size values.
+ */
+class StorageMigrationTo11(
+    private val db: SQLiteDatabase,
+    private val migrationsHelper: StorageMigrationsHelper
+) {
+    fun upgradeMessageViewContentFontSize() {
+        val newFontSizeValue = migrationsHelper.readValue(db, "fontSizeMessageViewContentPercent")
+        if (newFontSizeValue != null) return
+
+        val oldFontSizeValue = migrationsHelper.readValue(db, "fontSizeMessageViewContent")?.toIntOrNull() ?: 3
+        val fontSizeValue = GeneralSettingsDescriptions.SettingsUpgraderV31.convertFromOldSize(oldFontSizeValue)
+        migrationsHelper.writeValue(db, "fontSizeMessageViewContentPercent", fontSizeValue.toString())
+        migrationsHelper.writeValue(db, "fontSizeMessageViewContent", null)
+    }
+}

app/storage/src/main/java/com/fsck/k9/preferences/migrations/StorageMigrationTo12.kt

@@ -0,0 +1,65 @@
+package com.fsck.k9.preferences.migrations
+
+import android.database.sqlite.SQLiteDatabase
+import com.fsck.k9.ServerSettingsSerializer
+import com.fsck.k9.mail.filter.Base64
+import com.fsck.k9.preferences.migrations.migration12.ImapStoreUriDecoder
+import com.fsck.k9.preferences.migrations.migration12.Pop3StoreUriDecoder
+import com.fsck.k9.preferences.migrations.migration12.SmtpTransportUriDecoder
+import com.fsck.k9.preferences.migrations.migration12.WebDavStoreUriDecoder
+
+/**
+ * Convert server settings from the old URI format to the new JSON format
+ */
+class StorageMigrationTo12(
+    private val db: SQLiteDatabase,
+    private val migrationsHelper: StorageMigrationsHelper
+) {
+    private val serverSettingsSerializer = ServerSettingsSerializer()
+
+    fun removeStoreAndTransportUri() {
+        val accountUuidsListValue = migrationsHelper.readValue(db, "accountUuids")
+        if (accountUuidsListValue == null || accountUuidsListValue.isEmpty()) {
+            return
+        }
+
+        val accountUuids = accountUuidsListValue.split(",")
+        for (accountUuid in accountUuids) {
+            convertStoreUri(accountUuid)
+            convertTransportUri(accountUuid)
+        }
+    }
+
+    private fun convertStoreUri(accountUuid: String) {
+        val storeUri = migrationsHelper.readValue(db, "$accountUuid.storeUri")?.base64Decode() ?: return
+
+        val serverSettings = when {
+            storeUri.startsWith("imap") -> ImapStoreUriDecoder.decode(storeUri)
+            storeUri.startsWith("pop3") -> Pop3StoreUriDecoder.decode(storeUri)
+            storeUri.startsWith("webdav") -> WebDavStoreUriDecoder.decode(storeUri)
+            else -> error("Unsupported account type")
+        }
+
+        val json = serverSettingsSerializer.serialize(serverSettings)
+
+        migrationsHelper.insertValue(db, "$accountUuid.incomingServerSettings", json)
+        migrationsHelper.writeValue(db, "$accountUuid.storeUri", null)
+    }
+
+    private fun convertTransportUri(accountUuid: String) {
+        val transportUri = migrationsHelper.readValue(db, "$accountUuid.transportUri")?.base64Decode() ?: return
+
+        val serverSettings = when {
+            transportUri.startsWith("smtp") -> SmtpTransportUriDecoder.decodeSmtpUri(transportUri)
+            transportUri.startsWith("webdav") -> WebDavStoreUriDecoder.decode(transportUri)
+            else -> error("Unsupported account type")
+        }
+
+        val json = serverSettingsSerializer.serialize(serverSettings)
+
+        migrationsHelper.insertValue(db, "$accountUuid.outgoingServerSettings", json)
+        migrationsHelper.writeValue(db, "$accountUuid.transportUri", null)
+    }
+
+    private fun String.base64Decode() = Base64.decode(this)
+}

app/storage/src/main/java/com/fsck/k9/preferences/migrations/StorageMigrationTo13.kt

@@ -0,0 +1,18 @@
+package com.fsck.k9.preferences.migrations
+
+import android.database.sqlite.SQLiteDatabase
+
+/**
+ * Rename `hideSpecialAccounts` to `showUnifiedInbox` (and invert value).
+ */
+class StorageMigrationTo13(
+    private val db: SQLiteDatabase,
+    private val migrationsHelper: StorageMigrationsHelper
+) {
+    fun renameHideSpecialAccounts() {
+        val hideSpecialAccounts = migrationsHelper.readValue(db, "hideSpecialAccounts")?.toBoolean() ?: false
+        val showUnifiedInbox = !hideSpecialAccounts
+        migrationsHelper.insertValue(db, "showUnifiedInbox", showUnifiedInbox.toString())
+        migrationsHelper.writeValue(db, "hideSpecialAccounts", null)
+    }
+}

app/storage/src/main/java/com/fsck/k9/preferences/migrations/StorageMigrationTo14.kt

@@ -0,0 +1,35 @@
+package com.fsck.k9.preferences.migrations
+
+import android.database.sqlite.SQLiteDatabase
+import com.fsck.k9.ServerSettingsSerializer
+import com.fsck.k9.preferences.Protocols
+
+/**
+ * Rewrite 'folderPushMode' value of non-IMAP accounts to 'NONE'.
+ */
+class StorageMigrationTo14(
+    private val db: SQLiteDatabase,
+    private val migrationsHelper: StorageMigrationsHelper
+) {
+    private val serverSettingsSerializer = ServerSettingsSerializer()
+
+    fun disablePushFoldersForNonImapAccounts() {
+        val accountUuidsListValue = migrationsHelper.readValue(db, "accountUuids")
+        if (accountUuidsListValue == null || accountUuidsListValue.isEmpty()) {
+            return
+        }
+
+        val accountUuids = accountUuidsListValue.split(",")
+        for (accountUuid in accountUuids) {
+            disablePushFolders(accountUuid)
+        }
+    }
+
+    private fun disablePushFolders(accountUuid: String) {
+        val json = migrationsHelper.readValue(db, "$accountUuid.incomingServerSettings") ?: return
+        val serverSettings = serverSettingsSerializer.deserialize(json)
+        if (serverSettings.type != Protocols.IMAP) {
+            migrationsHelper.writeValue(db, "$accountUuid.folderPushMode", "NONE")
+        }
+    }
+}

app/storage/src/main/java/com/fsck/k9/preferences/migrations/StorageMigrationTo15.kt

@@ -0,0 +1,36 @@
+package com.fsck.k9.preferences.migrations
+
+import android.database.sqlite.SQLiteDatabase
+
+private const val DEFAULT_IDLE_REFRESH_MINUTES = 24
+private const val MINIMUM_IDLE_REFRESH_MINUTES = 2
+
+/**
+ * Rewrite 'idleRefreshMinutes' to make sure the minimum value is 2 minutes.
+ */
+class StorageMigrationTo15(
+    private val db: SQLiteDatabase,
+    private val migrationsHelper: StorageMigrationsHelper
+) {
+    fun rewriteIdleRefreshInterval() {
+        val accountUuidsListValue = migrationsHelper.readValue(db, "accountUuids")
+        if (accountUuidsListValue == null || accountUuidsListValue.isEmpty()) {
+            return
+        }
+
+        val accountUuids = accountUuidsListValue.split(",")
+        for (accountUuid in accountUuids) {
+            rewriteIdleRefreshInterval(accountUuid)
+        }
+    }
+
+    private fun rewriteIdleRefreshInterval(accountUuid: String) {
+        val idleRefreshMinutes = migrationsHelper.readValue(db, "$accountUuid.idleRefreshMinutes")?.toIntOrNull()
+            ?: DEFAULT_IDLE_REFRESH_MINUTES
+
+        val newIdleRefreshMinutes = idleRefreshMinutes.coerceAtLeast(MINIMUM_IDLE_REFRESH_MINUTES)
+        if (newIdleRefreshMinutes != idleRefreshMinutes) {
+            migrationsHelper.writeValue(db, "$accountUuid.idleRefreshMinutes", newIdleRefreshMinutes.toString())
+        }
+    }
+}

app/storage/src/main/java/com/fsck/k9/preferences/migrations/StorageMigrationTo16.kt

@@ -0,0 +1,18 @@
+package com.fsck.k9.preferences.migrations
+
+import android.database.sqlite.SQLiteDatabase
+
+/**
+ * Change default value of `registeredNameColor` to have enough contrast in both the light and dark theme.
+ */
+class StorageMigrationTo16(
+    private val db: SQLiteDatabase,
+    private val migrationsHelper: StorageMigrationsHelper
+) {
+    fun changeDefaultRegisteredNameColor() {
+        val registeredNameColorValue = migrationsHelper.readValue(db, "registeredNameColor")?.toInt()
+        if (registeredNameColorValue == 0xFF00008F.toInt()) {
+            migrationsHelper.writeValue(db, "registeredNameColor", 0xFF1093F5.toInt().toString())
+        }
+    }
+}

app/storage/src/main/java/com/fsck/k9/preferences/migrations/StorageMigrationTo17.kt

@@ -0,0 +1,54 @@
+package com.fsck.k9.preferences.migrations
+
+import android.database.sqlite.SQLiteDatabase
+
+/**
+ * Rewrite 'led' and 'ledColor' values to 'notificationLight'.
+ */
+class StorageMigrationTo17(
+    private val db: SQLiteDatabase,
+    private val migrationsHelper: StorageMigrationsHelper
+) {
+    fun rewriteNotificationLightSettings() {
+        val accountUuidsListValue = migrationsHelper.readValue(db, "accountUuids")
+        if (accountUuidsListValue == null || accountUuidsListValue.isEmpty()) {
+            return
+        }
+
+        val accountUuids = accountUuidsListValue.split(",")
+        for (accountUuid in accountUuids) {
+            rewriteNotificationLightSettings(accountUuid)
+        }
+    }
+
+    private fun rewriteNotificationLightSettings(accountUuid: String) {
+        val isLedEnabled = migrationsHelper.readValue(db, "$accountUuid.led").toBoolean()
+        val ledColor = migrationsHelper.readValue(db, "$accountUuid.ledColor")?.toInt() ?: 0
+        val accountColor = migrationsHelper.readValue(db, "$accountUuid.chipColor")?.toInt() ?: 0
+
+        val notificationLight = convertToNotificationLightValue(isLedEnabled, ledColor, accountColor)
+
+        migrationsHelper.writeValue(db, "$accountUuid.notificationLight", notificationLight)
+        migrationsHelper.writeValue(db, "$accountUuid.led", null)
+        migrationsHelper.writeValue(db, "$accountUuid.ledColor", null)
+    }
+
+    private fun convertToNotificationLightValue(isLedEnabled: Boolean, ledColor: Int, accountColor: Int): String {
+        if (!isLedEnabled) return "Disabled"
+
+        return when (ledColor.rgb) {
+            accountColor.rgb -> "AccountColor"
+            0xFFFFFF -> "White"
+            0xFF0000 -> "Red"
+            0x00FF00 -> "Green"
+            0x0000FF -> "Blue"
+            0xFFFF00 -> "Yellow"
+            0x00FFFF -> "Cyan"
+            0xFF00FF -> "Magenta"
+            else -> "SystemDefaultColor"
+        }
+    }
+
+    private val Int.rgb
+        get() = this and 0x00FFFFFF
+}

app/storage/src/main/java/com/fsck/k9/preferences/migrations/StorageMigrationTo18.kt

@@ -0,0 +1,36 @@
+package com.fsck.k9.preferences.migrations
+
+import android.database.sqlite.SQLiteDatabase
+
+/**
+ * Rewrite the per-network type IMAP compression settings to a single setting.
+ */
+class StorageMigrationTo18(
+    private val db: SQLiteDatabase,
+    private val migrationsHelper: StorageMigrationsHelper
+) {
+    fun rewriteImapCompressionSettings() {
+        val accountUuidsListValue = migrationsHelper.readValue(db, "accountUuids")
+        if (accountUuidsListValue == null || accountUuidsListValue.isEmpty()) {
+            return
+        }
+
+        val accountUuids = accountUuidsListValue.split(",")
+        for (accountUuid in accountUuids) {
+            rewriteImapCompressionSetting(accountUuid)
+        }
+    }
+
+    private fun rewriteImapCompressionSetting(accountUuid: String) {
+        val useCompressionWifi = migrationsHelper.readValue(db, "$accountUuid.useCompression.WIFI").toBoolean()
+        val useCompressionMobile = migrationsHelper.readValue(db, "$accountUuid.useCompression.MOBILE").toBoolean()
+        val useCompressionOther = migrationsHelper.readValue(db, "$accountUuid.useCompression.OTHER").toBoolean()
+
+        val useCompression = useCompressionWifi && useCompressionMobile && useCompressionOther
+        migrationsHelper.writeValue(db, "$accountUuid.useCompression", useCompression.toString())
+
+        migrationsHelper.writeValue(db, "$accountUuid.useCompression.WIFI", null)
+        migrationsHelper.writeValue(db, "$accountUuid.useCompression.MOBILE", null)
+        migrationsHelper.writeValue(db, "$accountUuid.useCompression.OTHER", null)
+    }
+}

app/storage/src/main/java/com/fsck/k9/preferences/migrations/StorageMigrationTo19.kt

@@ -0,0 +1,54 @@
+package com.fsck.k9.preferences.migrations
+
+import android.database.sqlite.SQLiteDatabase
+import com.squareup.moshi.Moshi
+import com.squareup.moshi.Types
+
+/**
+ * Mark Gmail accounts.
+ *
+ * Gmail has stopped allowing clients to use the Google account password to authenticate via IMAP/POP3/SMTP. We want to
+ * automatically update the server settings to use OAuth 2.0 for users who can no longer access Gmail because of the
+ * change. However, we don't want to touch accounts that are using an app-specific password and still work fine. Since
+ * we can't distinguish an app-specific password from an account password, we only switch accounts to using OAuth after
+ * an authentication failure. We usually want to avoid automatically changing the user's settings like this. So we only
+ * do it for existing accounts, and only after the first authentication failure.
+ */
+class StorageMigrationTo19(
+    private val db: SQLiteDatabase,
+    private val migrationsHelper: StorageMigrationsHelper
+) {
+    fun markGmailAccounts() {
+        val accountUuidsListValue = migrationsHelper.readValue(db, "accountUuids")
+        if (accountUuidsListValue == null || accountUuidsListValue.isEmpty()) {
+            return
+        }
+
+        val accountUuids = accountUuidsListValue.split(",")
+        for (accountUuid in accountUuids) {
+            markIfGmailAccount(accountUuid)
+        }
+    }
+
+    private fun markIfGmailAccount(accountUuid: String) {
+        val incomingServerSettingsJson = migrationsHelper.readValue(db, "$accountUuid.incomingServerSettings") ?: return
+        val outgoingServerSettingsJson = migrationsHelper.readValue(db, "$accountUuid.outgoingServerSettings") ?: return
+
+        val moshi = Moshi.Builder().build()
+        val adapter = moshi.adapter<Map<String, Any?>>(
+            Types.newParameterizedType(Map::class.java, String::class.java, Any::class.java)
+        )
+
+        val incomingServerSettings = adapter.fromJson(incomingServerSettingsJson) ?: return
+        val outgoingServerSettings = adapter.fromJson(outgoingServerSettingsJson) ?: return
+
+        if (incomingServerSettings["type"] == "imap" &&
+            incomingServerSettings["host"] in setOf("imap.gmail.com", "imap.googlemail.com") &&
+            incomingServerSettings["authenticationType"] != "XOAUTH2" ||
+            outgoingServerSettings["host"] in setOf("smtp.gmail.com", "smtp.googlemail.com") &&
+            outgoingServerSettings["authenticationType"] != "XOAUTH2"
+        ) {
+            migrationsHelper.insertValue(db, "$accountUuid.migrateToOAuth", "true")
+        }
+    }
+}

app/storage/src/main/java/com/fsck/k9/preferences/migrations/StorageMigrationTo2.java

@@ -0,0 +1,100 @@
+package com.fsck.k9.preferences.migrations;
+
+
+import java.net.URI;
+
+import android.database.sqlite.SQLiteDatabase;
+
+import com.fsck.k9.helper.UrlEncodingHelper;
+import com.fsck.k9.mail.filter.Base64;
+import timber.log.Timber;
+
+
+public class StorageMigrationTo2 {
+    public static void urlEncodeUserNameAndPassword(SQLiteDatabase db, StorageMigrationsHelper migrationsHelper) {
+        Timber.i("Updating preferences to urlencoded username/password");
+
+        String accountUuids = migrationsHelper.readValue(db, "accountUuids");
+        if (accountUuids != null && accountUuids.length() != 0) {
+            String[] uuids = accountUuids.split(",");
+            for (String uuid : uuids) {
+                try {
+                    String storeUriStr = Base64.decode(migrationsHelper.readValue(db, uuid + ".storeUri"));
+                    String transportUriStr = Base64.decode(migrationsHelper.readValue(db, uuid + ".transportUri"));
+
+                    URI uri = new URI(transportUriStr);
+                    String newUserInfo = null;
+                    if (transportUriStr != null) {
+                        String[] userInfoParts = uri.getUserInfo().split(":");
+
+                        String usernameEnc = UrlEncodingHelper.encodeUtf8(userInfoParts[0]);
+                        String passwordEnc = "";
+                        String authType = "";
+                        if (userInfoParts.length > 1) {
+                            passwordEnc = ":" + UrlEncodingHelper.encodeUtf8(userInfoParts[1]);
+                        }
+                        if (userInfoParts.length > 2) {
+                            authType = ":" + userInfoParts[2];
+                        }
+
+                        newUserInfo = usernameEnc + passwordEnc + authType;
+                    }
+
+                    if (newUserInfo != null) {
+                        URI newUri = new URI(uri.getScheme(), newUserInfo, uri.getHost(), uri.getPort(), uri.getPath(),
+                                uri.getQuery(), uri.getFragment());
+                        String newTransportUriStr = Base64.encode(newUri.toString());
+                        migrationsHelper.writeValue(db, uuid + ".transportUri", newTransportUriStr);
+                    }
+
+                    uri = new URI(storeUriStr);
+                    newUserInfo = null;
+                    if (storeUriStr.startsWith("imap")) {
+                        String[] userInfoParts = uri.getUserInfo().split(":");
+                        if (userInfoParts.length == 2) {
+                            String usernameEnc = UrlEncodingHelper.encodeUtf8(userInfoParts[0]);
+                            String passwordEnc = UrlEncodingHelper.encodeUtf8(userInfoParts[1]);
+
+                            newUserInfo = usernameEnc + ":" + passwordEnc;
+                        } else {
+                            String authType = userInfoParts[0];
+                            String usernameEnc = UrlEncodingHelper.encodeUtf8(userInfoParts[1]);
+                            String passwordEnc = UrlEncodingHelper.encodeUtf8(userInfoParts[2]);
+
+                            newUserInfo = authType + ":" + usernameEnc + ":" + passwordEnc;
+                        }
+                    } else if (storeUriStr.startsWith("pop3")) {
+                        String[] userInfoParts = uri.getUserInfo().split(":", 2);
+                        String usernameEnc = UrlEncodingHelper.encodeUtf8(userInfoParts[0]);
+
+                        String passwordEnc = "";
+                        if (userInfoParts.length > 1) {
+                            passwordEnc = ":" + UrlEncodingHelper.encodeUtf8(userInfoParts[1]);
+                        }
+
+                        newUserInfo = usernameEnc + passwordEnc;
+                    } else if (storeUriStr.startsWith("webdav")) {
+                        String[] userInfoParts = uri.getUserInfo().split(":", 2);
+                        String usernameEnc = UrlEncodingHelper.encodeUtf8(userInfoParts[0]);
+
+                        String passwordEnc = "";
+                        if (userInfoParts.length > 1) {
+                            passwordEnc = ":" + UrlEncodingHelper.encodeUtf8(userInfoParts[1]);
+                        }
+
+                        newUserInfo = usernameEnc + passwordEnc;
+                    }
+
+                    if (newUserInfo != null) {
+                        URI newUri = new URI(uri.getScheme(), newUserInfo, uri.getHost(), uri.getPort(), uri.getPath(),
+                                uri.getQuery(), uri.getFragment());
+                        String newStoreUriStr = Base64.encode(newUri.toString());
+                        migrationsHelper.writeValue(db, uuid + ".storeUri", newStoreUriStr);
+                    }
+                } catch (Exception e) {
+                    Timber.e(e, "ooops");
+                }
+            }
+        }
+    }
+}

app/storage/src/main/java/com/fsck/k9/preferences/migrations/StorageMigrationTo3.kt

@@ -0,0 +1,44 @@
+package com.fsck.k9.preferences.migrations
+
+import android.database.sqlite.SQLiteDatabase
+
+/**
+ * Rewrite folder name values of "-NONE-" to `null`
+ */
+class StorageMigrationTo3(
+    private val db: SQLiteDatabase,
+    private val migrationsHelper: StorageMigrationsHelper
+) {
+    fun rewriteFolderNone() {
+        val accountUuidsListValue = migrationsHelper.readValue(db, "accountUuids")
+        if (accountUuidsListValue == null || accountUuidsListValue.isEmpty()) {
+            return
+        }
+
+        val accountUuids = accountUuidsListValue.split(",")
+        for (accountUuid in accountUuids) {
+            rewriteAccount(accountUuid)
+        }
+    }
+
+    private fun rewriteAccount(accountUuid: String) {
+        rewriteFolderValue("$accountUuid.archiveFolderName")
+        rewriteFolderValue("$accountUuid.autoExpandFolderName")
+        rewriteFolderValue("$accountUuid.draftsFolderName")
+        rewriteFolderValue("$accountUuid.sentFolderName")
+        rewriteFolderValue("$accountUuid.spamFolderName")
+        rewriteFolderValue("$accountUuid.trashFolderName")
+    }
+
+    private fun rewriteFolderValue(key: String) {
+        val folderValue = migrationsHelper.readValue(db, key)
+        if (folderValue == OLD_FOLDER_VALUE) {
+            migrationsHelper.writeValue(db, key, NEW_FOLDER_VALUE)
+        }
+    }
+
+    companion object {
+        private const val OLD_FOLDER_VALUE = "-NONE-"
+        private val NEW_FOLDER_VALUE = null
+    }
+}

app/storage/src/main/java/com/fsck/k9/preferences/migrations/StorageMigrationTo4.kt

@@ -0,0 +1,31 @@
+package com.fsck.k9.preferences.migrations
+
+import android.database.sqlite.SQLiteDatabase
+
+/**
+ * Add `*FolderSelection` values of "MANUAL" for existing accounts (default for new accounts is "AUTOMATIC").
+ */
+class StorageMigrationTo4(
+    private val db: SQLiteDatabase,
+    private val migrationsHelper: StorageMigrationsHelper
+) {
+    fun insertSpecialFolderSelectionValues() {
+        val accountUuidsListValue = migrationsHelper.readValue(db, "accountUuids")
+        if (accountUuidsListValue == null || accountUuidsListValue.isEmpty()) {
+            return
+        }
+
+        val accountUuids = accountUuidsListValue.split(",")
+        for (accountUuid in accountUuids) {
+            insertSpecialFolderSelectionValues(accountUuid)
+        }
+    }
+
+    private fun insertSpecialFolderSelectionValues(accountUuid: String) {
+        migrationsHelper.insertValue(db, "$accountUuid.archiveFolderSelection", "MANUAL")
+        migrationsHelper.insertValue(db, "$accountUuid.draftsFolderSelection", "MANUAL")
+        migrationsHelper.insertValue(db, "$accountUuid.sentFolderSelection", "MANUAL")
+        migrationsHelper.insertValue(db, "$accountUuid.spamFolderSelection", "MANUAL")
+        migrationsHelper.insertValue(db, "$accountUuid.trashFolderSelection", "MANUAL")
+    }
+}

app/storage/src/main/java/com/fsck/k9/preferences/migrations/StorageMigrationTo5.kt

@@ -0,0 +1,36 @@
+package com.fsck.k9.preferences.migrations
+
+import android.database.sqlite.SQLiteDatabase
+
+/**
+ * Rewrite frequencies lower than LOWEST_FREQUENCY_SUPPORTED
+ */
+class StorageMigrationTo5(
+    private val db: SQLiteDatabase,
+    private val migrationsHelper: StorageMigrationsHelper
+) {
+    fun fixMailCheckFrequencies() {
+        val accountUuidsListValue = migrationsHelper.readValue(db, "accountUuids")
+        if (accountUuidsListValue == null || accountUuidsListValue.isEmpty()) {
+            return
+        }
+
+        val accountUuids = accountUuidsListValue.split(",")
+        for (accountUuid in accountUuids) {
+            fixFrequencyForAccount(accountUuid)
+        }
+    }
+
+    private fun fixFrequencyForAccount(accountUuid: String) {
+        val key = "$accountUuid.automaticCheckIntervalMinutes"
+        val frequencyValue = migrationsHelper.readValue(db, key)?.toIntOrNull()
+        if (frequencyValue != null && frequencyValue > -1 && frequencyValue < LOWEST_FREQUENCY_SUPPORTED) {
+            migrationsHelper.writeValue(db, key, LOWEST_FREQUENCY_SUPPORTED.toString())
+        }
+    }
+
+    companion object {
+        // see: https://github.com/evernote/android-job/wiki/FAQ#why-cant-an-interval-be-smaller-than-15-minutes-for-periodic-jobs
+        private const val LOWEST_FREQUENCY_SUPPORTED = 15
+    }
+}

app/storage/src/main/java/com/fsck/k9/preferences/migrations/StorageMigrationTo6.kt

@@ -0,0 +1,54 @@
+package com.fsck.k9.preferences.migrations
+
+import android.database.sqlite.SQLiteDatabase
+
+/**
+ * Perform legacy conversions that previously lived in `K9`.
+ */
+class StorageMigrationTo6(
+    private val db: SQLiteDatabase,
+    private val migrationsHelper: StorageMigrationsHelper
+) {
+    fun performLegacyMigrations() {
+        rewriteTheme()
+        migrateOpenPgpGlobalToAccountSettings()
+    }
+
+    private fun rewriteTheme() {
+        val theme = migrationsHelper.readValue(db, "theme")?.toInt()
+
+        // We used to save the resource ID of the theme. So convert that to the new format if necessary.
+        val newTheme = if (theme == THEME_ORDINAL_DARK || theme == android.R.style.Theme) {
+            THEME_ORDINAL_DARK
+        } else {
+            THEME_ORDINAL_LIGHT
+        }
+
+        migrationsHelper.writeValue(db, "theme", newTheme.toString())
+    }
+
+    private fun migrateOpenPgpGlobalToAccountSettings() {
+        val accountUuidsListValue = migrationsHelper.readValue(db, "accountUuids")
+        if (accountUuidsListValue == null || accountUuidsListValue.isEmpty()) {
+            return
+        }
+
+        val openPgpProvider = migrationsHelper.readValue(db, "openPgpProvider") ?: ""
+        val openPgpSupportSignOnly = migrationsHelper.readValue(db, "openPgpSupportSignOnly")?.toBoolean() ?: false
+        val openPgpHideSignOnly = (!openPgpSupportSignOnly).toString()
+
+        val accountUuids = accountUuidsListValue.split(",")
+        for (accountUuid in accountUuids) {
+            migrationsHelper.writeValue(db, "$accountUuid.openPgpProvider", openPgpProvider)
+            migrationsHelper.writeValue(db, "$accountUuid.openPgpHideSignOnly", openPgpHideSignOnly)
+        }
+
+        migrationsHelper.writeValue(db, "openPgpProvider", null)
+        migrationsHelper.writeValue(db, "openPgpSupportSignOnly", null)
+    }
+
+    companion object {
+        private const val THEME_ORDINAL_LIGHT = 0
+        private const val THEME_ORDINAL_DARK = 1
+    }
+}

app/storage/src/main/java/com/fsck/k9/preferences/migrations/StorageMigrationTo7.kt

@@ -0,0 +1,54 @@
+package com.fsck.k9.preferences.migrations
+
+import android.database.sqlite.SQLiteDatabase
+
+/**
+ * Rewrite settings to use enum names instead of ordinals.
+ */
+class StorageMigrationTo7(
+    private val db: SQLiteDatabase,
+    private val migrationsHelper: StorageMigrationsHelper
+) {
+    fun rewriteEnumOrdinalsToNames() {
+        rewriteTheme()
+        rewriteMessageViewTheme()
+        rewriteMessageComposeTheme()
+    }
+
+    private fun rewriteTheme() {
+        val theme = migrationsHelper.readValue(db, "theme")?.toInt()
+        val newTheme = if (theme == THEME_ORDINAL_DARK) {
+            THEME_DARK
+        } else {
+            THEME_LIGHT
+        }
+
+        migrationsHelper.writeValue(db, "theme", newTheme)
+    }
+
+    private fun rewriteMessageViewTheme() {
+        rewriteScreenTheme("messageViewTheme")
+    }
+
+    private fun rewriteMessageComposeTheme() {
+        rewriteScreenTheme("messageComposeTheme")
+    }
+
+    private fun rewriteScreenTheme(key: String) {
+        val newTheme = when (migrationsHelper.readValue(db, key)?.toInt()) {
+            THEME_ORDINAL_DARK -> THEME_DARK
+            THEME_ORDINAL_USE_GLOBAL -> THEME_USE_GLOBAL
+            else -> THEME_LIGHT
+        }
+
+        migrationsHelper.writeValue(db, key, newTheme)
+    }
+
+    companion object {
+        private const val THEME_ORDINAL_DARK = 1
+        private const val THEME_ORDINAL_USE_GLOBAL = 2
+        private const val THEME_LIGHT = "LIGHT"
+        private const val THEME_DARK = "DARK"
+        private const val THEME_USE_GLOBAL = "USE_GLOBAL"
+    }
+}

app/storage/src/main/java/com/fsck/k9/preferences/migrations/StorageMigrationTo8.kt

@@ -0,0 +1,23 @@
+package com.fsck.k9.preferences.migrations
+
+import android.database.sqlite.SQLiteDatabase
+
+/**
+ * Rewrite theme setting to use `FOLLOW_SYSTEM` when it's currently set to `LIGHT`.
+ */
+class StorageMigrationTo8(
+    private val db: SQLiteDatabase,
+    private val migrationsHelper: StorageMigrationsHelper
+) {
+    fun rewriteTheme() {
+        val theme = migrationsHelper.readValue(db, "theme")
+        if (theme == THEME_LIGHT) {
+            migrationsHelper.writeValue(db, "theme", THEME_FOLLOW_SYSTEM)
+        }
+    }
+
+    companion object {
+        private const val THEME_LIGHT = "LIGHT"
+        private const val THEME_FOLLOW_SYSTEM = "FOLLOW_SYSTEM"
+    }
+}

app/storage/src/main/java/com/fsck/k9/preferences/migrations/StorageMigrations.kt

@@ -0,0 +1,29 @@
+package com.fsck.k9.preferences.migrations
+
+import android.database.sqlite.SQLiteDatabase
+
+internal object StorageMigrations {
+    @JvmStatic
+    fun upgradeDatabase(db: SQLiteDatabase, migrationsHelper: StorageMigrationsHelper) {
+        val oldVersion = db.version
+
+        if (oldVersion < 2) StorageMigrationTo2.urlEncodeUserNameAndPassword(db, migrationsHelper)
+        if (oldVersion < 3) StorageMigrationTo3(db, migrationsHelper).rewriteFolderNone()
+        if (oldVersion < 4) StorageMigrationTo4(db, migrationsHelper).insertSpecialFolderSelectionValues()
+        if (oldVersion < 5) StorageMigrationTo5(db, migrationsHelper).fixMailCheckFrequencies()
+        if (oldVersion < 6) StorageMigrationTo6(db, migrationsHelper).performLegacyMigrations()
+        if (oldVersion < 7) StorageMigrationTo7(db, migrationsHelper).rewriteEnumOrdinalsToNames()
+        if (oldVersion < 8) StorageMigrationTo8(db, migrationsHelper).rewriteTheme()
+        // 9: "Temporarily disable Push" is no longer necessary
+        if (oldVersion < 10) StorageMigrationTo10(db, migrationsHelper).removeSavedFolderSettings()
+        if (oldVersion < 11) StorageMigrationTo11(db, migrationsHelper).upgradeMessageViewContentFontSize()
+        if (oldVersion < 12) StorageMigrationTo12(db, migrationsHelper).removeStoreAndTransportUri()
+        if (oldVersion < 13) StorageMigrationTo13(db, migrationsHelper).renameHideSpecialAccounts()
+        if (oldVersion < 14) StorageMigrationTo14(db, migrationsHelper).disablePushFoldersForNonImapAccounts()
+        if (oldVersion < 15) StorageMigrationTo15(db, migrationsHelper).rewriteIdleRefreshInterval()
+        if (oldVersion < 16) StorageMigrationTo16(db, migrationsHelper).changeDefaultRegisteredNameColor()
+        if (oldVersion < 17) StorageMigrationTo17(db, migrationsHelper).rewriteNotificationLightSettings()
+        if (oldVersion < 18) StorageMigrationTo18(db, migrationsHelper).rewriteImapCompressionSettings()
+        if (oldVersion < 19) StorageMigrationTo19(db, migrationsHelper).markGmailAccounts()
+    }
+}

app/storage/src/main/java/com/fsck/k9/preferences/migrations/StorageMigrationsHelper.kt

@@ -0,0 +1,10 @@
+package com.fsck.k9.preferences.migrations
+
+import android.database.sqlite.SQLiteDatabase
+
+interface StorageMigrationsHelper {
+    fun readAllValues(db: SQLiteDatabase): Map<String, String>
+    fun readValue(db: SQLiteDatabase, key: String): String?
+    fun writeValue(db: SQLiteDatabase, key: String, value: String?)
+    fun insertValue(db: SQLiteDatabase, key: String, value: String?)
+}

app/storage/src/main/java/com/fsck/k9/preferences/migrations/migration12/ImapStoreUriDecoder.java

@@ -0,0 +1,144 @@
+package com.fsck.k9.preferences.migrations.migration12;
+
+
+import java.net.URI;
+import java.net.URISyntaxException;
+import java.util.HashMap;
+import java.util.Map;
+
+import com.fsck.k9.mail.AuthType;
+import com.fsck.k9.mail.ConnectionSecurity;
+import com.fsck.k9.mail.ServerSettings;
+
+import static com.fsck.k9.mail.helper.UrlEncodingHelper.decodeUtf8;
+
+
+public class ImapStoreUriDecoder {
+    private static final int DEFAULT_PORT = 143;
+    private static final int DEFAULT_TLS_PORT = 993;
+
+    /**
+     * Decodes an ImapStore URI.
+     *
+     * <p>Possible forms:</p>
+     * <pre>
+     * imap://auth:user:password@server:port ConnectionSecurity.NONE
+     * imap+tls+://auth:user:password@server:port ConnectionSecurity.STARTTLS_REQUIRED
+     * imap+ssl+://auth:user:password@server:port ConnectionSecurity.SSL_TLS_REQUIRED
+     * </pre>
+     *
+     * NOTE: this method expects the userinfo part of the URI to be encoded twice, due to a bug in the URI creation
+     * code.
+     *
+     * @param uri the store uri.
+     */
+    public static ServerSettings decode(String uri) {
+        String host;
+        int port;
+        ConnectionSecurity connectionSecurity;
+        AuthType authenticationType = AuthType.PLAIN;
+        String username = "";
+        String password = null;
+        String clientCertificateAlias = null;
+        String pathPrefix = null;
+        boolean autoDetectNamespace = true;
+
+        URI imapUri;
+        try {
+            imapUri = new URI(uri);
+        } catch (URISyntaxException use) {
+            throw new IllegalArgumentException("Invalid ImapStore URI", use);
+        }
+
+        String scheme = imapUri.getScheme();
+        /*
+         * Currently available schemes are:
+         * imap
+         * imap+tls+
+         * imap+ssl+
+         *
+         * The following are obsolete schemes that may be found in pre-existing
+         * settings from earlier versions or that may be found when imported. We
+         * continue to recognize them and re-map them appropriately:
+         * imap+tls
+         * imap+ssl
+         */
+        if (scheme.equals("imap")) {
+            connectionSecurity = ConnectionSecurity.NONE;
+            port = DEFAULT_PORT;
+        } else if (scheme.startsWith("imap+tls")) {
+            connectionSecurity = ConnectionSecurity.STARTTLS_REQUIRED;
+            port = DEFAULT_PORT;
+        } else if (scheme.startsWith("imap+ssl")) {
+            connectionSecurity = ConnectionSecurity.SSL_TLS_REQUIRED;
+            port = DEFAULT_TLS_PORT;
+        } else {
+            throw new IllegalArgumentException("Unsupported protocol (" + scheme + ")");
+        }
+
+        host = imapUri.getHost();
+
+        if (imapUri.getPort() != -1) {
+            port = imapUri.getPort();
+        }
+
+        if (imapUri.getUserInfo() != null) {
+            String userinfo = imapUri.getUserInfo();
+            String[] userInfoParts = userinfo.split(":");
+
+            if (userinfo.endsWith(":")) {
+                // Last field (password/certAlias) is empty.
+                // For imports e.g.: PLAIN:username: or username:
+                // Or XOAUTH2 where it's a valid config - XOAUTH:username:
+                if (userInfoParts.length > 1) {
+                    authenticationType = AuthType.valueOf(userInfoParts[0]);
+                    username = decodeUtf8(userInfoParts[1]);
+                } else {
+                    username = decodeUtf8(userInfoParts[0]);
+                }
+            } else if (userInfoParts.length == 2) {
+                // Old/standard style of encoding - PLAIN auth only:
+                // username:password
+                username = decodeUtf8(userInfoParts[0]);
+                password = decodeUtf8(userInfoParts[1]);
+            } else if (userInfoParts.length == 3) {
+                // Standard encoding
+                // PLAIN:username:password
+                // EXTERNAL:username:certAlias
+                authenticationType = AuthType.valueOf(userInfoParts[0]);
+                username = decodeUtf8(userInfoParts[1]);
+
+                if (AuthType.EXTERNAL == authenticationType) {
+                    clientCertificateAlias = decodeUtf8(userInfoParts[2]);
+                } else {
+                    password = decodeUtf8(userInfoParts[2]);
+                }
+            }
+        }
+
+        String path = imapUri.getPath();
+        if (path != null && path.length() > 1) {
+            // Strip off the leading "/"
+            String cleanPath = path.substring(1);
+
+            if (cleanPath.length() >= 2 && cleanPath.charAt(1) == '|') {
+                autoDetectNamespace = cleanPath.charAt(0) == '1';
+                if (!autoDetectNamespace) {
+                    pathPrefix = cleanPath.substring(2);
+                }
+            } else {
+                if (cleanPath.length() > 0) {
+                    pathPrefix = cleanPath;
+                    autoDetectNamespace = false;
+                }
+            }
+        }
+
+        Map<String, String> extra = new HashMap<>();
+        extra.put("autoDetectNamespace", Boolean.toString(autoDetectNamespace));
+        extra.put("pathPrefix", pathPrefix);
+
+        return new ServerSettings("imap", host, port, connectionSecurity, authenticationType, username,
+                password, clientCertificateAlias, extra);
+    }
+}

app/storage/src/main/java/com/fsck/k9/preferences/migrations/migration12/Pop3StoreUriDecoder.java

@@ -0,0 +1,106 @@
+package com.fsck.k9.preferences.migrations.migration12;
+
+
+import java.net.URI;
+import java.net.URISyntaxException;
+
+import com.fsck.k9.mail.AuthType;
+import com.fsck.k9.mail.ConnectionSecurity;
+import com.fsck.k9.mail.ServerSettings;
+
+import static com.fsck.k9.mail.helper.UrlEncodingHelper.decodeUtf8;
+
+
+public class Pop3StoreUriDecoder {
+    private static final int DEFAULT_PORT = 110;
+    private static final int DEFAULT_TLS_PORT = 995;
+
+    /**
+     * Decodes a Pop3Store URI.
+     *
+     * <p>Possible forms:</p>
+     * <pre>
+     * pop3://authType:user:password@server:port
+     *      ConnectionSecurity.NONE
+     * pop3+tls+://authType:user:password@server:port
+     *      ConnectionSecurity.STARTTLS_REQUIRED
+     * pop3+ssl+://authType:user:password@server:port
+     *      ConnectionSecurity.SSL_TLS_REQUIRED
+     * </pre>
+     *
+     * e.g.
+     * <pre>pop3://PLAIN:admin:pass123@example.org:12345</pre>
+     */
+    public static ServerSettings decode(String uri) {
+        String host;
+        int port;
+        ConnectionSecurity connectionSecurity;
+        String username = "";
+        String password = null;
+        String clientCertificateAlias = null;
+
+        URI pop3Uri;
+        try {
+            pop3Uri = new URI(uri);
+        } catch (URISyntaxException use) {
+            throw new IllegalArgumentException("Invalid Pop3Store URI", use);
+        }
+
+        String scheme = pop3Uri.getScheme();
+        /*
+         * Currently available schemes are:
+         * pop3
+         * pop3+tls+
+         * pop3+ssl+
+         *
+         * The following are obsolete schemes that may be found in pre-existing
+         * settings from earlier versions or that may be found when imported. We
+         * continue to recognize them and re-map them appropriately:
+         * pop3+tls
+         * pop3+ssl
+         */
+        if (scheme.equals("pop3")) {
+            connectionSecurity = ConnectionSecurity.NONE;
+            port = DEFAULT_PORT;
+        } else if (scheme.startsWith("pop3+tls")) {
+            connectionSecurity = ConnectionSecurity.STARTTLS_REQUIRED;
+            port = DEFAULT_PORT;
+        } else if (scheme.startsWith("pop3+ssl")) {
+            connectionSecurity = ConnectionSecurity.SSL_TLS_REQUIRED;
+            port = DEFAULT_TLS_PORT;
+        } else {
+            throw new IllegalArgumentException("Unsupported protocol (" + scheme + ")");
+        }
+
+        host = pop3Uri.getHost();
+
+        if (pop3Uri.getPort() != -1) {
+            port = pop3Uri.getPort();
+        }
+
+        AuthType authType = AuthType.PLAIN;
+        if (pop3Uri.getUserInfo() != null) {
+            int userIndex = 0, passwordIndex = 1;
+            String userinfo = pop3Uri.getUserInfo();
+            String[] userInfoParts = userinfo.split(":");
+            if (userInfoParts.length > 2 || userinfo.endsWith(":") ) {
+                // If 'userinfo' ends with ":" the password is empty. This can only happen
+                // after an account was imported (so authType and username are present).
+                userIndex++;
+                passwordIndex++;
+                authType = AuthType.valueOf(userInfoParts[0]);
+            }
+            username = decodeUtf8(userInfoParts[userIndex]);
+            if (userInfoParts.length > passwordIndex) {
+                if (authType == AuthType.EXTERNAL) {
+                    clientCertificateAlias = decodeUtf8(userInfoParts[passwordIndex]);
+                } else {
+                    password = decodeUtf8(userInfoParts[passwordIndex]);
+                }
+            }
+        }
+
+        return new ServerSettings("pop3", host, port, connectionSecurity, authType, username,
+                password, clientCertificateAlias);
+    }
+}

app/storage/src/main/java/com/fsck/k9/preferences/migrations/migration12/SmtpTransportUriDecoder.java

@@ -0,0 +1,108 @@
+package com.fsck.k9.preferences.migrations.migration12;
+
+
+import java.io.UnsupportedEncodingException;
+import java.net.URI;
+import java.net.URISyntaxException;
+import java.net.URLDecoder;
+
+import com.fsck.k9.mail.AuthType;
+import com.fsck.k9.mail.ConnectionSecurity;
+import com.fsck.k9.mail.ServerSettings;
+
+
+public class SmtpTransportUriDecoder {
+    private static final int DEFAULT_PORT = 587;
+    private static final int DEFAULT_TLS_PORT = 465;
+
+    /**
+     * Decodes a SmtpTransport URI.
+     *
+     * NOTE: In contrast to ImapStore and Pop3Store, the authType is appended at the end!
+     *
+     * <p>Possible forms:</p>
+     * <pre>
+     * smtp://user:password:auth@server:port ConnectionSecurity.NONE
+     * smtp+tls+://user:password:auth@server:port ConnectionSecurity.STARTTLS_REQUIRED
+     * smtp+ssl+://user:password:auth@server:port ConnectionSecurity.SSL_TLS_REQUIRED
+     * </pre>
+     */
+    public static ServerSettings decodeSmtpUri(String uri) {
+        String host;
+        int port;
+        ConnectionSecurity connectionSecurity;
+        AuthType authType = AuthType.PLAIN;
+        String username = "";
+        String password = null;
+        String clientCertificateAlias = null;
+
+        URI smtpUri;
+        try {
+            smtpUri = new URI(uri);
+        } catch (URISyntaxException use) {
+            throw new IllegalArgumentException("Invalid SmtpTransport URI", use);
+        }
+
+        String scheme = smtpUri.getScheme();
+        /*
+         * Currently available schemes are:
+         * smtp
+         * smtp+tls+
+         * smtp+ssl+
+         *
+         * The following are obsolete schemes that may be found in pre-existing
+         * settings from earlier versions or that may be found when imported. We
+         * continue to recognize them and re-map them appropriately:
+         * smtp+tls
+         * smtp+ssl
+         */
+        if (scheme.equals("smtp")) {
+            connectionSecurity = ConnectionSecurity.NONE;
+            port = DEFAULT_PORT;
+        } else if (scheme.startsWith("smtp+tls")) {
+            connectionSecurity = ConnectionSecurity.STARTTLS_REQUIRED;
+            port = DEFAULT_PORT;
+        } else if (scheme.startsWith("smtp+ssl")) {
+            connectionSecurity = ConnectionSecurity.SSL_TLS_REQUIRED;
+            port = DEFAULT_TLS_PORT;
+        } else {
+            throw new IllegalArgumentException("Unsupported protocol (" + scheme + ")");
+        }
+
+        host = smtpUri.getHost();
+
+        if (smtpUri.getPort() != -1) {
+            port = smtpUri.getPort();
+        }
+
+        if (smtpUri.getUserInfo() != null) {
+            String[] userInfoParts = smtpUri.getUserInfo().split(":");
+            if (userInfoParts.length == 1) {
+                username = decodeUtf8(userInfoParts[0]);
+            } else if (userInfoParts.length == 2) {
+                username = decodeUtf8(userInfoParts[0]);
+                password = decodeUtf8(userInfoParts[1]);
+            } else if (userInfoParts.length == 3) {
+                // NOTE: In SmtpTransport URIs, the authType comes last!
+                authType = AuthType.valueOf(userInfoParts[2]);
+                username = decodeUtf8(userInfoParts[0]);
+                if (authType == AuthType.EXTERNAL) {
+                    clientCertificateAlias = decodeUtf8(userInfoParts[1]);
+                } else {
+                    password = decodeUtf8(userInfoParts[1]);
+                }
+            }
+        }
+
+        return new ServerSettings("smtp", host, port, connectionSecurity,
+                authType, username, password, clientCertificateAlias);
+    }
+
+    private static String decodeUtf8(String s) {
+        try {
+            return URLDecoder.decode(s, "UTF-8");
+        } catch (UnsupportedEncodingException e) {
+            throw new RuntimeException("UTF-8 not found");
+        }
+    }
+}

app/storage/src/main/java/com/fsck/k9/preferences/migrations/migration12/WebDavStoreUriDecoder.java

@@ -0,0 +1,120 @@
+package com.fsck.k9.preferences.migrations.migration12;
+
+
+import com.fsck.k9.mail.AuthType;
+import com.fsck.k9.mail.ConnectionSecurity;
+import com.fsck.k9.mail.ServerSettings;
+
+import java.net.URI;
+import java.net.URISyntaxException;
+import java.util.HashMap;
+import java.util.Map;
+
+import static com.fsck.k9.mail.helper.UrlEncodingHelper.decodeUtf8;
+
+public class WebDavStoreUriDecoder {
+
+    /**
+     * Decodes a WebDavStore URI.
+     * <p/>
+     * <p>Possible forms:</p>
+     * <pre>
+     * webdav://user:password@server:port ConnectionSecurity.NONE
+     * webdav+ssl+://user:password@server:port ConnectionSecurity.SSL_TLS_REQUIRED
+     * </pre>
+     */
+    public static ServerSettings decode(String uri) {
+        String host;
+        int port;
+        ConnectionSecurity connectionSecurity;
+        String username = null;
+        String password = null;
+        String alias = null;
+        String path = null;
+        String authPath = null;
+        String mailboxPath = null;
+
+
+        URI webDavUri;
+        try {
+            webDavUri = new URI(uri);
+        } catch (URISyntaxException use) {
+            throw new IllegalArgumentException("Invalid WebDavStore URI", use);
+        }
+
+        String scheme = webDavUri.getScheme();
+        /*
+         * Currently available schemes are:
+         * webdav
+         * webdav+ssl+
+         *
+         * The following are obsolete schemes that may be found in pre-existing
+         * settings from earlier versions or that may be found when imported. We
+         * continue to recognize them and re-map them appropriately:
+         * webdav+tls
+         * webdav+tls+
+         * webdav+ssl
+         */
+        if (scheme.equals("webdav")) {
+            connectionSecurity = ConnectionSecurity.NONE;
+        } else if (scheme.startsWith("webdav+")) {
+            connectionSecurity = ConnectionSecurity.SSL_TLS_REQUIRED;
+        } else {
+            throw new IllegalArgumentException("Unsupported protocol (" + scheme + ")");
+        }
+
+        host = webDavUri.getHost();
+        if (host.startsWith("http")) {
+            String[] hostParts = host.split("://", 2);
+            if (hostParts.length > 1) {
+                host = hostParts[1];
+            }
+        }
+
+        port = webDavUri.getPort();
+
+        String userInfo = webDavUri.getUserInfo();
+        if (userInfo != null) {
+            String[] userInfoParts = userInfo.split(":");
+            username = decodeUtf8(userInfoParts[0]);
+            String userParts[] = username.split("\\\\", 2);
+
+            if (userParts.length > 1) {
+                alias = userParts[1];
+            } else {
+                alias = username;
+            }
+            if (userInfoParts.length > 1) {
+                password = decodeUtf8(userInfoParts[1]);
+            }
+        }
+
+        String[] pathParts = webDavUri.getPath().split("\\|");
+        for (int i = 0, count = pathParts.length; i < count; i++) {
+            if (i == 0) {
+                if (pathParts[0] != null &&
+                        pathParts[0].length() > 1) {
+                    path = pathParts[0];
+                }
+            } else if (i == 1) {
+                if (pathParts[1] != null &&
+                        pathParts[1].length() > 1) {
+                    authPath = pathParts[1];
+                }
+            } else if (i == 2) {
+                if (pathParts[2] != null &&
+                        pathParts[2].length() > 1) {
+                    mailboxPath = pathParts[2];
+                }
+            }
+        }
+
+        Map<String, String> extra = new HashMap<>();
+        extra.put("alias", alias);
+        extra.put("path", path);
+        extra.put("authPath", authPath);
+        extra.put("mailboxPath", mailboxPath);
+
+        return new ServerSettings("webdav", host, port, connectionSecurity, AuthType.PLAIN, username, password, null, extra);
+    }
+}

app/storage/src/main/java/com/fsck/k9/storage/K9SchemaDefinitionFactory.kt

@@ -0,0 +1,13 @@
+package com.fsck.k9.storage
+
+import com.fsck.k9.mailstore.LockableDatabase
+import com.fsck.k9.mailstore.MigrationsHelper
+import com.fsck.k9.mailstore.SchemaDefinitionFactory
+
+class K9SchemaDefinitionFactory : SchemaDefinitionFactory {
+    override val databaseVersion = StoreSchemaDefinition.DB_VERSION
+
+    override fun createSchemaDefinition(migrationsHelper: MigrationsHelper): LockableDatabase.SchemaDefinition {
+        return StoreSchemaDefinition(migrationsHelper)
+    }
+}

app/storage/src/main/java/com/fsck/k9/storage/KoinModule.kt

@@ -0,0 +1,18 @@
+package com.fsck.k9.storage
+
+import com.fsck.k9.mailstore.MessageStoreFactory
+import com.fsck.k9.mailstore.SchemaDefinitionFactory
+import com.fsck.k9.notification.NotificationStoreProvider
+import com.fsck.k9.storage.messages.K9MessageStoreFactory
+import com.fsck.k9.storage.notifications.K9NotificationStoreProvider
+import org.koin.dsl.module
+
+val storageModule = module {
+    single<SchemaDefinitionFactory> { K9SchemaDefinitionFactory() }
+    single<MessageStoreFactory> {
+        K9MessageStoreFactory(localStoreProvider = get(), storageManager = get(), basicPartInfoExtractor = get())
+    }
+    single<NotificationStoreProvider> {
+        K9NotificationStoreProvider(localStoreProvider = get())
+    }
+}

app/storage/src/main/java/com/fsck/k9/storage/StoreSchemaDefinition.java

@@ -0,0 +1,273 @@
+package com.fsck.k9.storage;
+
+
+import android.database.sqlite.SQLiteDatabase;
+
+import com.fsck.k9.K9;
+import com.fsck.k9.mail.FolderClass;
+import com.fsck.k9.mailstore.LockableDatabase.SchemaDefinition;
+import com.fsck.k9.mailstore.MigrationsHelper;
+import com.fsck.k9.storage.migrations.Migrations;
+import timber.log.Timber;
+
+
+class StoreSchemaDefinition implements SchemaDefinition {
+    static final int DB_VERSION = 84;
+
+    private final MigrationsHelper migrationsHelper;
+
+
+    StoreSchemaDefinition(MigrationsHelper migrationsHelper) {
+        this.migrationsHelper = migrationsHelper;
+    }
+
+    @Override
+    public int getVersion() {
+        return DB_VERSION;
+    }
+
+    @Override
+    public void doDbUpgrade(final SQLiteDatabase db) {
+        try {
+            upgradeDatabase(db);
+        } catch (Exception e) {
+            if (K9.DEVELOPER_MODE) {
+                throw new Error("Exception while upgrading database", e);
+            }
+
+            Timber.e(e, "Exception while upgrading database. Resetting the DB to v0");
+            db.setVersion(0);
+            upgradeDatabase(db);
+        }
+    }
+
+    private void upgradeDatabase(final SQLiteDatabase db) {
+        Timber.i("Upgrading database from version %d to version %d", db.getVersion(), DB_VERSION);
+
+        db.beginTransaction();
+        try {
+            if (db.getVersion() > DB_VERSION) {
+                String accountUuid = migrationsHelper.getAccount().getUuid();
+                throw new AssertionError("Database downgrades are not supported. " +
+                        "Please fix the account database '" + accountUuid + "' manually or " +
+                        "clear app data.");
+            }
+
+            // We only support upgrades from K-9 Mail 5.301. For upgrades from earlier versions we start from scratch.
+            if (db.getVersion() < 61) {
+                dbCreateDatabaseFromScratch(db);
+            } else {
+                Migrations.upgradeDatabase(db, migrationsHelper);
+            }
+
+            db.setVersion(DB_VERSION);
+
+            db.setTransactionSuccessful();
+        } finally {
+            db.endTransaction();
+        }
+
+        if (db.getVersion() != DB_VERSION) {
+            throw new RuntimeException("Database upgrade failed!");
+        }
+    }
+
+    private static void dbCreateDatabaseFromScratch(SQLiteDatabase db) {
+        db.execSQL("DROP TABLE IF EXISTS account_extra_values");
+        db.execSQL("CREATE TABLE account_extra_values (" +
+                "name TEXT NOT NULL PRIMARY KEY, " +
+                "value_text TEXT, " +
+                "value_integer INTEGER " +
+                ")");
+
+        db.execSQL("DROP TABLE IF EXISTS folders");
+        db.execSQL("CREATE TABLE folders (" +
+                "id INTEGER PRIMARY KEY," +
+                "name TEXT, " +
+                "last_updated INTEGER, " +
+                "unread_count INTEGER, " +
+                "visible_limit INTEGER, " +
+                "status TEXT, " +
+                "flagged_count INTEGER default 0, " +
+                "integrate INTEGER, " +
+                "top_group INTEGER, " +
+                "poll_class TEXT, " +
+                "push_class TEXT, " +
+                "display_class TEXT, " +
+                "notify_class TEXT default '"+ FolderClass.INHERITED.name() + "', " +
+                "more_messages TEXT default \"unknown\", " +
+                "server_id TEXT, " +
+                "local_only INTEGER, " +
+                "type TEXT DEFAULT \"regular\"" +
+                ")");
+
+        db.execSQL("DROP INDEX IF EXISTS folder_server_id");
+        db.execSQL("CREATE INDEX folder_server_id ON folders (server_id)");
+
+        db.execSQL("DROP TABLE IF EXISTS folder_extra_values");
+        db.execSQL("CREATE TABLE folder_extra_values (" +
+                "folder_id INTEGER NOT NULL, " +
+                "name TEXT NOT NULL, " +
+                "value_text TEXT, " +
+                "value_integer INTEGER, " +
+                "PRIMARY KEY (folder_id, name)" +
+                ")");
+
+        db.execSQL("DROP TABLE IF EXISTS messages");
+        db.execSQL("CREATE TABLE messages (" +
+                "id INTEGER PRIMARY KEY, " +
+                "deleted INTEGER default 0, " +
+                "folder_id INTEGER, " +
+                "uid TEXT, " +
+                "subject TEXT, " +
+                "date INTEGER, " +
+                "flags TEXT, " +
+                "sender_list TEXT, " +
+                "to_list TEXT, " +
+                "cc_list TEXT, " +
+                "bcc_list TEXT, " +
+                "reply_to_list TEXT, " +
+                "attachment_count INTEGER, " +
+                "internal_date INTEGER, " +
+                "message_id TEXT, " +
+                "preview_type TEXT default \"none\", " +
+                "preview TEXT, " +
+                "mime_type TEXT, "+
+                "normalized_subject_hash INTEGER, " +
+                "empty INTEGER default 0, " +
+                "read INTEGER default 0, " +
+                "flagged INTEGER default 0, " +
+                "answered INTEGER default 0, " +
+                "forwarded INTEGER default 0, " +
+                "message_part_id INTEGER," +
+                "encryption_type TEXT," +
+                "new_message INTEGER DEFAULT 0" +
+                ")");
+
+        db.execSQL("DROP INDEX IF EXISTS new_messages");
+        db.execSQL("CREATE INDEX IF NOT EXISTS new_messages ON messages(new_message)");
+
+        db.execSQL("CREATE TRIGGER new_message_reset " +
+                "AFTER UPDATE OF read ON messages " +
+                "FOR EACH ROW WHEN NEW.read = 1 AND NEW.new_message = 1 " +
+                "BEGIN " +
+                "UPDATE messages SET new_message = 0 WHERE ROWID = NEW.ROWID; " +
+                "END");
+
+        db.execSQL("DROP TABLE IF EXISTS message_parts");
+        db.execSQL("CREATE TABLE message_parts (" +
+                "id INTEGER PRIMARY KEY, " +
+                "type INTEGER NOT NULL, " +
+                "root INTEGER, " +
+                "parent INTEGER NOT NULL, " +
+                "seq INTEGER NOT NULL, " +
+                "mime_type TEXT, " +
+                "decoded_body_size INTEGER, " +
+                "display_name TEXT, " +
+                "header TEXT, " +
+                "encoding TEXT, " +
+                "charset TEXT, " +
+                "data_location INTEGER NOT NULL, " +
+                "data BLOB, " +
+                "preamble TEXT, " +
+                "epilogue TEXT, " +
+                "boundary TEXT, " +
+                "content_id TEXT, " +
+                "server_extra TEXT" +
+                ")");
+
+        db.execSQL("CREATE TRIGGER set_message_part_root " +
+                "AFTER INSERT ON message_parts " +
+                "BEGIN " +
+                "UPDATE message_parts SET root=id WHERE root IS NULL AND ROWID = NEW.ROWID; " +
+                "END");
+
+        db.execSQL("CREATE INDEX IF NOT EXISTS msg_uid ON messages (uid, folder_id)");
+        db.execSQL("DROP INDEX IF EXISTS msg_folder_id");
+        db.execSQL("DROP INDEX IF EXISTS msg_folder_id_date");
+        db.execSQL("CREATE INDEX IF NOT EXISTS msg_folder_id_deleted_date ON messages (folder_id,deleted,internal_date)");
+
+        db.execSQL("DROP INDEX IF EXISTS msg_empty");
+        db.execSQL("CREATE INDEX IF NOT EXISTS msg_empty ON messages (empty)");
+
+        db.execSQL("DROP INDEX IF EXISTS msg_read");
+        db.execSQL("CREATE INDEX IF NOT EXISTS msg_read ON messages (read)");
+
+        db.execSQL("DROP INDEX IF EXISTS msg_flagged");
+        db.execSQL("CREATE INDEX IF NOT EXISTS msg_flagged ON messages (flagged)");
+
+        db.execSQL("DROP INDEX IF EXISTS msg_composite");
+        db.execSQL("CREATE INDEX IF NOT EXISTS msg_composite ON messages (deleted, empty,folder_id,flagged,read)");
+
+        db.execSQL("DROP INDEX IF EXISTS message_parts_root");
+        db.execSQL("CREATE INDEX IF NOT EXISTS message_parts_root ON message_parts (root)");
+
+        db.execSQL("DROP TABLE IF EXISTS threads");
+        db.execSQL("CREATE TABLE threads (" +
+                "id INTEGER PRIMARY KEY, " +
+                "message_id INTEGER, " +
+                "root INTEGER, " +
+                "parent INTEGER" +
+                ")");
+
+        db.execSQL("DROP INDEX IF EXISTS threads_message_id");
+        db.execSQL("CREATE INDEX IF NOT EXISTS threads_message_id ON threads (message_id)");
+
+        db.execSQL("DROP INDEX IF EXISTS threads_root");
+        db.execSQL("CREATE INDEX IF NOT EXISTS threads_root ON threads (root)");
+
+        db.execSQL("DROP INDEX IF EXISTS threads_parent");
+        db.execSQL("CREATE INDEX IF NOT EXISTS threads_parent ON threads (parent)");
+
+        db.execSQL("DROP TRIGGER IF EXISTS set_thread_root");
+        db.execSQL("CREATE TRIGGER set_thread_root " +
+                "AFTER INSERT ON threads " +
+                "BEGIN " +
+                "UPDATE threads SET root=id WHERE root IS NULL AND ROWID = NEW.ROWID; " +
+                "END");
+
+        db.execSQL("DROP TABLE IF EXISTS outbox_state");
+        db.execSQL("CREATE TABLE outbox_state (" +
+                "message_id INTEGER PRIMARY KEY NOT NULL REFERENCES messages(id) ON DELETE CASCADE," +
+                "send_state TEXT," +
+                "number_of_send_attempts INTEGER DEFAULT 0," +
+                "error_timestamp INTEGER DEFAULT 0," +
+                "error TEXT)");
+
+        db.execSQL("DROP TABLE IF EXISTS pending_commands");
+        db.execSQL("CREATE TABLE pending_commands " +
+                "(id INTEGER PRIMARY KEY, command TEXT, data TEXT)");
+
+        db.execSQL("DROP TRIGGER IF EXISTS delete_folder");
+        db.execSQL("CREATE TRIGGER delete_folder BEFORE DELETE ON folders BEGIN DELETE FROM messages WHERE old.id = folder_id; END;");
+
+        db.execSQL("DROP TRIGGER IF EXISTS delete_folder_extra_values");
+        db.execSQL("CREATE TRIGGER delete_folder_extra_values " +
+                "BEFORE DELETE ON folders " +
+                "BEGIN " +
+                "DELETE FROM folder_extra_values WHERE old.id = folder_id; " +
+                "END;");
+
+        db.execSQL("DROP TRIGGER IF EXISTS delete_message");
+        db.execSQL("CREATE TRIGGER delete_message " +
+                "BEFORE DELETE ON messages " +
+                "BEGIN " +
+                "DELETE FROM message_parts WHERE root = OLD.message_part_id; " +
+                "DELETE FROM messages_fulltext WHERE docid = OLD.id; " +
+                "DELETE FROM threads WHERE message_id = OLD.id; " +
+                "END");
+
+        db.execSQL("DROP TABLE IF EXISTS messages_fulltext");
+        db.execSQL("CREATE VIRTUAL TABLE messages_fulltext USING fts4 (fulltext)");
+
+        db.execSQL("DROP TABLE IF EXISTS notifications");
+        db.execSQL("CREATE TABLE notifications (" +
+                "message_id INTEGER PRIMARY KEY NOT NULL REFERENCES messages(id) ON DELETE CASCADE," +
+                "notification_id INTEGER UNIQUE," +
+                "timestamp INTEGER NOT NULL" +
+                ")");
+
+        db.execSQL("DROP INDEX IF EXISTS notifications_timestamp");
+        db.execSQL("CREATE INDEX IF NOT EXISTS notifications_timestamp ON notifications(timestamp)");
+    }
+}

app/storage/src/main/java/com/fsck/k9/storage/messages/AttachmentFileManager.kt

@@ -0,0 +1,36 @@
+package com.fsck.k9.storage.messages
+
+import com.fsck.k9.K9
+import com.fsck.k9.helper.FileHelper
+import com.fsck.k9.mailstore.StorageManager
+import com.fsck.k9.mailstore.StorageManager.InternalStorageProvider
+import java.io.File
+import timber.log.Timber
+
+internal class AttachmentFileManager(
+    private val storageManager: StorageManager,
+    private val accountUuid: String
+) {
+    fun deleteFile(messagePartId: Long) {
+        val file = getAttachmentFile(messagePartId)
+        if (file.exists() && !file.delete() && K9.isDebugLoggingEnabled) {
+            Timber.w("Couldn't delete message part file: %s", file.absolutePath)
+        }
+    }
+
+    fun moveTemporaryFile(temporaryFile: File, messagePartId: Long) {
+        val destinationFile = getAttachmentFile(messagePartId)
+        FileHelper.renameOrMoveByCopying(temporaryFile, destinationFile)
+    }
+
+    fun copyFile(sourceMessagePartId: Long, destinationMessagePartId: Long) {
+        val sourceFile = getAttachmentFile(sourceMessagePartId)
+        val destinationFile = getAttachmentFile(destinationMessagePartId)
+        sourceFile.copyTo(destinationFile)
+    }
+
+    fun getAttachmentFile(messagePartId: Long): File {
+        val attachmentDirectory = storageManager.getAttachmentDirectory(accountUuid, InternalStorageProvider.ID)
+        return File(attachmentDirectory, messagePartId.toString())
+    }
+}

app/storage/src/main/java/com/fsck/k9/storage/messages/CheckFolderOperations.kt

@@ -0,0 +1,34 @@
+package com.fsck.k9.storage.messages
+
+import com.fsck.k9.mailstore.LockableDatabase
+
+internal class CheckFolderOperations(private val lockableDatabase: LockableDatabase) {
+    fun areAllIncludedInUnifiedInbox(folderIds: Collection<Long>): Boolean {
+        return lockableDatabase.execute(false) { database ->
+            var allIncludedInUnifiedInbox = true
+
+            performChunkedOperation(
+                arguments = folderIds,
+                argumentTransformation = Long::toString
+            ) { selectionSet, selectionArguments ->
+                if (allIncludedInUnifiedInbox) {
+                    database.rawQuery(
+                        "SELECT COUNT(id) FROM folders WHERE integrate = 1 AND id $selectionSet",
+                        selectionArguments
+                    ).use { cursor ->
+                        if (cursor.moveToFirst()) {
+                            val count = cursor.getInt(0)
+                            if (count != selectionArguments.size) {
+                                allIncludedInUnifiedInbox = false
+                            }
+                        } else {
+                            allIncludedInUnifiedInbox = false
+                        }
+                    }
+                }
+            }
+
+            allIncludedInUnifiedInbox
+        }
+    }
+}

app/storage/src/main/java/com/fsck/k9/storage/messages/ChunkedDatabaseOperations.kt

@@ -0,0 +1,21 @@
+package com.fsck.k9.storage.messages
+
+internal fun <T> performChunkedOperation(
+    arguments: Collection<T>,
+    argumentTransformation: (T) -> String,
+    chunkSize: Int = 500,
+    operation: (selectionSet: String, selectionArguments: Array<String>) -> Unit
+) {
+    require(arguments.isNotEmpty()) { "'arguments' must not be empty" }
+    require(chunkSize in 1..1000) { "'chunkSize' needs to be in 1..1000" }
+
+    arguments.asSequence()
+        .map(argumentTransformation)
+        .chunked(chunkSize)
+        .forEach { selectionArguments ->
+            val selectionSet = selectionArguments.indices
+                .joinToString(separator = ",", prefix = "IN (", postfix = ")") { "?" }
+
+            operation(selectionSet, selectionArguments.toTypedArray())
+        }
+}

app/storage/src/main/java/com/fsck/k9/storage/messages/CopyMessageOperations.kt

@@ -0,0 +1,315 @@
+package com.fsck.k9.storage.messages
+
+import android.content.ContentValues
+import android.database.Cursor
+import android.database.sqlite.SQLiteDatabase
+import androidx.core.database.getBlobOrNull
+import androidx.core.database.getLongOrNull
+import androidx.core.database.getStringOrNull
+import com.fsck.k9.K9
+import com.fsck.k9.mailstore.LockableDatabase
+import java.util.UUID
+
+internal class CopyMessageOperations(
+    private val lockableDatabase: LockableDatabase,
+    private val attachmentFileManager: AttachmentFileManager,
+    private val threadMessageOperations: ThreadMessageOperations
+) {
+    fun copyMessage(messageId: Long, destinationFolderId: Long): Long {
+        return lockableDatabase.execute(true) { database ->
+            val newMessageId = copyMessage(database, messageId, destinationFolderId)
+
+            copyFulltextEntry(database, newMessageId, messageId)
+
+            newMessageId
+        }
+    }
+
+    private fun copyMessage(
+        database: SQLiteDatabase,
+        messageId: Long,
+        destinationFolderId: Long
+    ): Long {
+        val rootMessagePart = copyMessageParts(database, messageId)
+
+        val threadInfo = threadMessageOperations.doMessageThreading(
+            database,
+            folderId = destinationFolderId,
+            threadHeaders = threadMessageOperations.getMessageThreadHeaders(database, messageId)
+        )
+
+        return if (threadInfo?.messageId != null) {
+            updateMessageRow(
+                database,
+                sourceMessageId = messageId,
+                destinationMessageId = threadInfo.messageId,
+                destinationFolderId,
+                rootMessagePart
+            )
+        } else {
+            val newMessageId = insertMessageRow(
+                database,
+                sourceMessageId = messageId,
+                destinationFolderId = destinationFolderId,
+                rootMessagePartId = rootMessagePart
+            )
+
+            if (threadInfo?.threadId == null) {
+                threadMessageOperations.createThreadEntry(
+                    database,
+                    newMessageId,
+                    threadInfo?.rootId,
+                    threadInfo?.parentId
+                )
+            }
+
+            newMessageId
+        }
+    }
+
+    private fun copyMessageParts(database: SQLiteDatabase, messageId: Long): Long {
+        return database.rawQuery(
+            """
+SELECT
+  message_parts.id,
+  message_parts.type,
+  message_parts.root,
+  message_parts.parent,
+  message_parts.seq,
+  message_parts.mime_type,
+  message_parts.decoded_body_size,
+  message_parts.display_name,
+  message_parts.header,
+  message_parts.encoding,
+  message_parts.charset,
+  message_parts.data_location,
+  message_parts.data,
+  message_parts.preamble,
+  message_parts.epilogue,
+  message_parts.boundary,
+  message_parts.content_id,
+  message_parts.server_extra 
+FROM messages 
+JOIN message_parts ON (message_parts.root = messages.message_part_id) 
+WHERE messages.id = ? 
+ORDER BY message_parts.seq
+            """,
+            arrayOf(messageId.toString())
+        ).use { cursor ->
+            if (!cursor.moveToNext()) error("No message part found for message with ID $messageId")
+
+            val rootMessagePart = cursor.readMessagePart()
+
+            val rootMessagePartId = writeMessagePart(
+                database = database,
+                databaseMessagePart = rootMessagePart,
+                newRootId = null,
+                newParentId = -1
+            )
+
+            val messagePartIdMapping = mutableMapOf<Long, Long>()
+            messagePartIdMapping[rootMessagePart.id] = rootMessagePartId
+
+            while (cursor.moveToNext()) {
+                val messagePart = cursor.readMessagePart()
+
+                messagePartIdMapping[messagePart.id] = writeMessagePart(
+                    database = database,
+                    databaseMessagePart = messagePart,
+                    newRootId = rootMessagePartId,
+                    newParentId = messagePartIdMapping[messagePart.parent] ?: error("parent ID not found")
+                )
+            }
+
+            rootMessagePartId
+        }
+    }
+
+    private fun writeMessagePart(
+        database: SQLiteDatabase,
+        databaseMessagePart: DatabaseMessagePart,
+        newRootId: Long?,
+        newParentId: Long
+    ): Long {
+        val values = ContentValues().apply {
+            put("type", databaseMessagePart.type)
+            put("root", newRootId)
+            put("parent", newParentId)
+            put("seq", databaseMessagePart.seq)
+            put("mime_type", databaseMessagePart.mimeType)
+            put("decoded_body_size", databaseMessagePart.decodedBodySize)
+            put("display_name", databaseMessagePart.displayName)
+            put("header", databaseMessagePart.header)
+            put("encoding", databaseMessagePart.encoding)
+            put("charset", databaseMessagePart.charset)
+            put("data_location", databaseMessagePart.dataLocation)
+            put("data", databaseMessagePart.data)
+            put("preamble", databaseMessagePart.preamble)
+            put("epilogue", databaseMessagePart.epilogue)
+            put("boundary", databaseMessagePart.boundary)
+            put("content_id", databaseMessagePart.contentId)
+            put("server_extra", databaseMessagePart.serverExtra)
+        }
+
+        val messagePartId = database.insert("message_parts", null, values)
+
+        if (databaseMessagePart.dataLocation == DataLocation.ON_DISK) {
+            attachmentFileManager.copyFile(databaseMessagePart.id, messagePartId)
+        }
+
+        return messagePartId
+    }
+
+    private fun updateMessageRow(
+        database: SQLiteDatabase,
+        sourceMessageId: Long,
+        destinationMessageId: Long,
+        destinationFolderId: Long,
+        rootMessagePartId: Long
+    ): Long {
+        val values = readMessageToContentValues(database, sourceMessageId, destinationFolderId, rootMessagePartId)
+
+        database.update("messages", values, "id = ?", arrayOf(destinationMessageId.toString()))
+        return destinationMessageId
+    }
+
+    private fun insertMessageRow(
+        database: SQLiteDatabase,
+        sourceMessageId: Long,
+        destinationFolderId: Long,
+        rootMessagePartId: Long
+    ): Long {
+        val values = readMessageToContentValues(database, sourceMessageId, destinationFolderId, rootMessagePartId)
+
+        return database.insert("messages", null, values)
+    }
+
+    private fun readMessageToContentValues(
+        database: SQLiteDatabase,
+        sourceMessageId: Long,
+        destinationFolderId: Long,
+        rootMessagePartId: Long
+    ): ContentValues {
+        val values = readMessageToContentValues(database, sourceMessageId)
+
+        return values.apply {
+            put("folder_id", destinationFolderId)
+            put("uid", K9.LOCAL_UID_PREFIX + UUID.randomUUID().toString())
+            put("message_part_id", rootMessagePartId)
+        }
+    }
+
+    private fun copyFulltextEntry(database: SQLiteDatabase, newMessageId: Long, messageId: Long) {
+        database.execSQL(
+            "INSERT OR REPLACE INTO messages_fulltext (docid, fulltext) " +
+                "SELECT ?, fulltext FROM messages_fulltext WHERE docid = ?",
+            arrayOf(newMessageId.toString(), messageId.toString())
+        )
+    }
+
+    private fun readMessageToContentValues(database: SQLiteDatabase, messageId: Long): ContentValues {
+        return database.query(
+            "messages",
+            arrayOf(
+                "deleted",
+                "subject",
+                "date",
+                "flags",
+                "sender_list",
+                "to_list",
+                "cc_list",
+                "bcc_list",
+                "reply_to_list",
+                "attachment_count",
+                "internal_date",
+                "message_id",
+                "preview_type",
+                "preview",
+                "mime_type",
+                "normalized_subject_hash",
+                "empty",
+                "read",
+                "flagged",
+                "answered",
+                "forwarded",
+                "encryption_type"
+            ),
+            "id = ?",
+            arrayOf(messageId.toString()),
+            null,
+            null,
+            null
+        ).use { cursor ->
+            if (!cursor.moveToNext()) error("Message with ID $messageId not found")
+
+            ContentValues().apply {
+                put("deleted", cursor.getInt(0))
+                put("subject", cursor.getStringOrNull(1))
+                put("date", cursor.getLong(2))
+                put("flags", cursor.getStringOrNull(3))
+                put("sender_list", cursor.getStringOrNull(4))
+                put("to_list", cursor.getStringOrNull(5))
+                put("cc_list", cursor.getStringOrNull(6))
+                put("bcc_list", cursor.getStringOrNull(7))
+                put("reply_to_list", cursor.getStringOrNull(8))
+                put("attachment_count", cursor.getInt(9))
+                put("internal_date", cursor.getLong(10))
+                put("message_id", cursor.getStringOrNull(11))
+                put("preview_type", cursor.getStringOrNull(12))
+                put("preview", cursor.getStringOrNull(13))
+                put("mime_type", cursor.getStringOrNull(14))
+                put("normalized_subject_hash", cursor.getLong(15))
+                put("empty", cursor.getInt(16))
+                put("read", cursor.getInt(17))
+                put("flagged", cursor.getInt(18))
+                put("answered", cursor.getInt(19))
+                put("forwarded", cursor.getInt(20))
+                put("encryption_type", cursor.getStringOrNull(21))
+            }
+        }
+    }
+
+    private fun Cursor.readMessagePart(): DatabaseMessagePart {
+        return DatabaseMessagePart(
+            id = getLong(0),
+            type = getInt(1),
+            root = getLong(2),
+            parent = getLong(3),
+            seq = getInt(4),
+            mimeType = getString(5),
+            decodedBodySize = getLongOrNull(6),
+            displayName = getStringOrNull(7),
+            header = getBlobOrNull(8),
+            encoding = getStringOrNull(9),
+            charset = getStringOrNull(10),
+            dataLocation = getInt(11),
+            data = getBlobOrNull(12),
+            preamble = getBlobOrNull(13),
+            epilogue = getBlobOrNull(14),
+            boundary = getStringOrNull(15),
+            contentId = getStringOrNull(16),
+            serverExtra = getStringOrNull(17)
+        )
+    }
+}
+
+private class DatabaseMessagePart(
+    val id: Long,
+    val type: Int,
+    val root: Long,
+    val parent: Long,
+    val seq: Int,
+    val mimeType: String?,
+    val decodedBodySize: Long?,
+    val displayName: String?,
+    val header: ByteArray?,
+    val encoding: String?,
+    val charset: String?,
+    val dataLocation: Int,
+    val data: ByteArray?,
+    val preamble: ByteArray?,
+    val epilogue: ByteArray?,
+    val boundary: String?,
+    val contentId: String?,
+    val serverExtra: String?
+)

app/storage/src/main/java/com/fsck/k9/storage/messages/CreateFolderOperations.kt

@@ -0,0 +1,31 @@
+package com.fsck.k9.storage.messages
+
+import android.content.ContentValues
+import com.fsck.k9.mailstore.CreateFolderInfo
+import com.fsck.k9.mailstore.LockableDatabase
+import com.fsck.k9.mailstore.toDatabaseFolderType
+
+internal class CreateFolderOperations(private val lockableDatabase: LockableDatabase) {
+    fun createFolders(folders: List<CreateFolderInfo>) {
+        lockableDatabase.execute(true) { db ->
+            for (folder in folders) {
+                val folderSettings = folder.settings
+                val values = ContentValues().apply {
+                    put("name", folder.name)
+                    put("visible_limit", folderSettings.visibleLimit)
+                    put("integrate", folderSettings.integrate)
+                    put("top_group", folderSettings.inTopGroup)
+                    put("poll_class", folderSettings.syncClass.name)
+                    put("push_class", folderSettings.pushClass.name)
+                    put("display_class", folderSettings.displayClass.name)
+                    put("notify_class", folderSettings.notifyClass.name)
+                    put("server_id", folder.serverId)
+                    put("local_only", false)
+                    put("type", folder.type.toDatabaseFolderType())
+                }
+
+                db.insert("folders", null, values)
+            }
+        }
+    }
+}

app/storage/src/main/java/com/fsck/k9/storage/messages/DataLocation.kt

@@ -0,0 +1,3 @@
+package com.fsck.k9.storage.messages
+
+internal const val DATA_LOCATION_ON_DISK = 2

app/storage/src/main/java/com/fsck/k9/storage/messages/DatabaseOperations.kt

@@ -0,0 +1,40 @@
+package com.fsck.k9.storage.messages
+
+import com.fsck.k9.mailstore.LockableDatabase
+import com.fsck.k9.mailstore.StorageManager
+import timber.log.Timber
+
+internal class DatabaseOperations(
+    private val lockableDatabase: LockableDatabase,
+    val storageManager: StorageManager,
+    val accountUuid: String
+) {
+    fun getSize(): Long {
+        val storageProviderId = lockableDatabase.storageProviderId
+        val attachmentDirectory = storageManager.getAttachmentDirectory(accountUuid, storageProviderId)
+
+        return lockableDatabase.execute(false) {
+            val attachmentFiles = attachmentDirectory.listFiles() ?: emptyArray()
+            val attachmentsSize = attachmentFiles.asSequence()
+                .filter { file -> file.exists() }
+                .fold(initial = 0L) { accumulatedSize, file ->
+                    accumulatedSize + file.length()
+                }
+
+            val databaseFile = storageManager.getDatabase(accountUuid, storageProviderId)
+            val databaseSize = databaseFile.length()
+
+            databaseSize + attachmentsSize
+        }
+    }
+
+    fun compact() {
+        Timber.i("Before compaction size = %d", getSize())
+
+        lockableDatabase.execute(false) { database ->
+            database.execSQL("VACUUM")
+        }
+
+        Timber.i("After compaction size = %d", getSize())
+    }
+}

app/storage/src/main/java/com/fsck/k9/storage/messages/DeleteFolderOperations.kt

@@ -0,0 +1,44 @@
+package com.fsck.k9.storage.messages
+
+import android.database.sqlite.SQLiteDatabase
+import com.fsck.k9.mailstore.LockableDatabase
+
+internal class DeleteFolderOperations(
+    private val lockableDatabase: LockableDatabase,
+    private val attachmentFileManager: AttachmentFileManager
+) {
+    fun deleteFolders(folderServerIds: List<String>) {
+        lockableDatabase.execute(true) { db ->
+            for (folderServerId in folderServerIds) {
+                db.deleteMessagePartFiles(folderServerId)
+                db.deleteFolder(folderServerId)
+            }
+        }
+    }
+
+    private fun SQLiteDatabase.deleteMessagePartFiles(folderServerId: String) {
+        rawQuery(
+            """
+SELECT message_parts.id 
+FROM folders 
+JOIN messages ON (messages.folder_id = folders.id) 
+JOIN message_parts ON (
+  message_parts.root = messages.message_part_id 
+  AND 
+  message_parts.data_location = $DATA_LOCATION_ON_DISK
+) 
+WHERE folders.server_id = ?
+            """,
+            arrayOf(folderServerId)
+        ).use { cursor ->
+            while (cursor.moveToNext()) {
+                val messagePartId = cursor.getLong(0)
+                attachmentFileManager.deleteFile(messagePartId)
+            }
+        }
+    }
+
+    private fun SQLiteDatabase.deleteFolder(folderServerId: String) {
+        delete("folders", "server_id = ?", arrayOf(folderServerId))
+    }
+}

app/storage/src/main/java/com/fsck/k9/storage/messages/DeleteMessageOperations.kt

@@ -0,0 +1,170 @@
+package com.fsck.k9.storage.messages
+
+import android.content.ContentValues
+import android.database.sqlite.SQLiteDatabase
+import com.fsck.k9.mailstore.LockableDatabase
+
+internal class DeleteMessageOperations(
+    private val lockableDatabase: LockableDatabase,
+    private val attachmentFileManager: AttachmentFileManager
+) {
+    fun destroyMessages(folderId: Long, messageServerIds: Collection<String>) {
+        for (messageServerId in messageServerIds) {
+            destroyMessage(folderId, messageServerId)
+        }
+    }
+
+    private fun destroyMessage(folderId: Long, messageServerId: String) {
+        val (messageId, rootMessagePartId, hasThreadChildren) = getMessageData(folderId, messageServerId) ?: return
+
+        lockableDatabase.execute(true) { database ->
+            database.deleteMessagePartFiles(rootMessagePartId)
+
+            if (hasThreadChildren) {
+                // We're not deleting the 'messages' row so we'll have to manually delete the associated
+                // 'message_parts' and 'messages_fulltext' rows.
+                database.deleteMessagePartRows(rootMessagePartId)
+                database.deleteFulltextIndexEntry(messageId)
+
+                // This message has children in the thread structure so we need to make it an empty message.
+                database.convertToEmptyMessage(messageId)
+            } else {
+                database.deleteMessageRows(messageId)
+            }
+        }
+    }
+
+    private fun getMessageData(folderId: Long, messageServerId: String): MessageData? {
+        return lockableDatabase.execute(false) { database ->
+            database.rawQuery(
+                """
+SELECT messages.id, messages.message_part_id, COUNT(threads2.id) 
+FROM messages 
+LEFT JOIN threads threads1 ON (threads1.message_id = messages.id)  
+LEFT JOIN threads threads2 ON (threads2.parent = threads1.id) 
+WHERE folder_id = ? AND uid = ?
+                """,
+                arrayOf(folderId.toString(), messageServerId)
+            ).use { cursor ->
+                if (cursor.moveToFirst()) {
+                    MessageData(
+                        messageId = cursor.getLong(0),
+                        messagePartId = cursor.getLong(1),
+                        hasThreadChildren = !cursor.isNull(2) && cursor.getInt(2) > 0
+                    )
+                } else {
+                    null
+                }
+            }
+        }
+    }
+
+    private fun SQLiteDatabase.deleteMessagePartFiles(rootMessagePartId: Long) {
+        query(
+            "message_parts",
+            arrayOf("id"),
+            "root = ? AND data_location = $DATA_LOCATION_ON_DISK",
+            arrayOf(rootMessagePartId.toString()),
+            null,
+            null,
+            null
+        ).use { cursor ->
+            while (cursor.moveToNext()) {
+                val messagePartId = cursor.getLong(0)
+                attachmentFileManager.deleteFile(messagePartId)
+            }
+        }
+    }
+
+    private fun SQLiteDatabase.deleteMessagePartRows(rootMessagePartId: Long) {
+        delete("message_parts", "root = ?", arrayOf(rootMessagePartId.toString()))
+    }
+
+    private fun SQLiteDatabase.deleteFulltextIndexEntry(messageId: Long) {
+        delete("messages_fulltext", "docid = ?", arrayOf(messageId.toString()))
+    }
+
+    private fun SQLiteDatabase.convertToEmptyMessage(messageId: Long) {
+        val values = ContentValues().apply {
+            put("deleted", 0)
+            put("empty", 1)
+            putNull("subject")
+            putNull("date")
+            putNull("flags")
+            putNull("sender_list")
+            putNull("to_list")
+            putNull("cc_list")
+            putNull("bcc_list")
+            putNull("reply_to_list")
+            putNull("attachment_count")
+            putNull("internal_date")
+            put("preview_type", "none")
+            putNull("preview")
+            putNull("mime_type")
+            putNull("normalized_subject_hash")
+            putNull("message_part_id")
+            putNull("encryption_type")
+        }
+
+        update("messages", values, "id = ?", arrayOf(messageId.toString()))
+    }
+
+    private fun SQLiteDatabase.deleteMessageRows(messageId: Long) {
+        // Delete the message and all empty parent messages that have no other children in the thread structure
+        var currentMessageId: Long? = messageId
+        while (currentMessageId != null) {
+            val nextMessageId = getEmptyThreadParent(currentMessageId)
+
+            deleteMessageRow(currentMessageId)
+
+            if (nextMessageId == null || hasThreadChildren(nextMessageId)) {
+                return
+            }
+
+            currentMessageId = nextMessageId
+        }
+    }
+
+    private fun SQLiteDatabase.getEmptyThreadParent(messageId: Long): Long? {
+        return rawQuery(
+            """
+SELECT messages.id 
+FROM threads threads1 
+JOIN threads threads2 ON (threads1.parent = threads2.id) 
+JOIN messages ON (threads2.message_id = messages.id AND messages.empty = 1) 
+WHERE threads1.message_id = ?
+            """,
+            arrayOf(messageId.toString())
+        ).use { cursor ->
+            if (cursor.moveToFirst() && !cursor.isNull(0)) {
+                cursor.getLong(0)
+            } else {
+                null
+            }
+        }
+    }
+
+    private fun SQLiteDatabase.deleteMessageRow(messageId: Long) {
+        delete("messages", "id = ?", arrayOf(messageId.toString()))
+    }
+
+    private fun SQLiteDatabase.hasThreadChildren(messageId: Long): Boolean {
+        return rawQuery(
+            """
+SELECT COUNT(threads2.id) 
+FROM threads threads1 
+JOIN threads threads2 ON (threads2.parent = threads1.id) 
+WHERE threads1.message_id = ?
+            """,
+            arrayOf(messageId.toString())
+        ).use { cursor ->
+            cursor.moveToFirst() && !cursor.isNull(0) && cursor.getLong(0) > 0L
+        }
+    }
+}
+
+private data class MessageData(
+    val messageId: Long,
+    val messagePartId: Long,
+    val hasThreadChildren: Boolean
+)

app/storage/src/main/java/com/fsck/k9/storage/messages/FlagMessageOperations.kt

@@ -0,0 +1,111 @@
+package com.fsck.k9.storage.messages
+
+import android.content.ContentValues
+import android.database.sqlite.SQLiteDatabase
+import com.fsck.k9.mail.Flag
+import com.fsck.k9.mailstore.LockableDatabase
+
+internal val SPECIAL_FLAGS = setOf(Flag.SEEN, Flag.FLAGGED, Flag.ANSWERED, Flag.FORWARDED)
+
+internal class FlagMessageOperations(private val lockableDatabase: LockableDatabase) {
+
+    fun setFlag(messageIds: Collection<Long>, flag: Flag, set: Boolean) {
+        require(messageIds.isNotEmpty()) { "'messageIds' must not be empty" }
+
+        if (flag in SPECIAL_FLAGS) {
+            setSpecialFlags(messageIds, flag, set)
+        } else {
+            throw UnsupportedOperationException("not implemented")
+        }
+    }
+
+    fun setMessageFlag(folderId: Long, messageServerId: String, flag: Flag, set: Boolean) {
+        when (flag) {
+            Flag.DELETED -> setBoolean(folderId, messageServerId, "deleted", set)
+            Flag.SEEN -> setBoolean(folderId, messageServerId, "read", set)
+            Flag.FLAGGED -> setBoolean(folderId, messageServerId, "flagged", set)
+            Flag.ANSWERED -> setBoolean(folderId, messageServerId, "answered", set)
+            Flag.FORWARDED -> setBoolean(folderId, messageServerId, "forwarded", set)
+            else -> rebuildFlagsColumnValue(folderId, messageServerId, flag, set)
+        }
+    }
+
+    private fun setSpecialFlags(messageIds: Collection<Long>, flag: Flag, set: Boolean) {
+        val columnName = when (flag) {
+            Flag.SEEN -> "read"
+            Flag.FLAGGED -> "flagged"
+            Flag.ANSWERED -> "answered"
+            Flag.FORWARDED -> "forwarded"
+            else -> error("Unsupported flag: $flag")
+        }
+        val columnValue = if (set) 1 else 0
+
+        val contentValues = ContentValues().apply {
+            put(columnName, columnValue)
+        }
+
+        lockableDatabase.execute(true) { database ->
+            performChunkedOperation(
+                arguments = messageIds,
+                argumentTransformation = Long::toString
+            ) { selectionSet, selectionArguments ->
+                database.update("messages", contentValues, "id $selectionSet", selectionArguments)
+            }
+        }
+    }
+
+    private fun rebuildFlagsColumnValue(folderId: Long, messageServerId: String, flag: Flag, set: Boolean) {
+        lockableDatabase.execute(true) { database ->
+            val oldFlags = database.readFlagsColumn(folderId, messageServerId)
+
+            val newFlags = if (set) oldFlags + flag else oldFlags - flag
+            val newFlagsString = newFlags.joinToString(separator = ",")
+
+            val values = ContentValues().apply {
+                put("flags", newFlagsString)
+            }
+
+            database.update(
+                "messages",
+                values,
+                "folder_id = ? AND uid = ?",
+                arrayOf(folderId.toString(), messageServerId)
+            )
+        }
+    }
+
+    private fun SQLiteDatabase.readFlagsColumn(folderId: Long, messageServerId: String): Set<Flag> {
+        return query(
+            "messages",
+            arrayOf("flags"),
+            "folder_id = ? AND uid = ?",
+            arrayOf(folderId.toString(), messageServerId),
+            null,
+            null,
+            null
+        ).use { cursor ->
+            if (!cursor.moveToFirst()) error("Message not found $folderId:$messageServerId")
+
+            if (!cursor.isNull(0)) {
+                cursor.getString(0).split(',').map { flagString -> Flag.valueOf(flagString) }.toSet()
+            } else {
+                emptySet()
+            }
+        }
+    }
+
+    private fun setBoolean(folderId: Long, messageServerId: String, columnName: String, value: Boolean) {
+        lockableDatabase.execute(false) { database ->
+            val values = ContentValues().apply {
+                put(columnName, if (value) 1 else 0)
+            }
+
+            database.update(
+                "messages",
+                values,
+                "folder_id = ? AND uid = ?",
+                arrayOf(folderId.toString(), messageServerId)
+            )
+        }
+    }
+}

app/storage/src/main/java/com/fsck/k9/storage/messages/K9MessageStore.kt

@@ -0,0 +1,287 @@
+package com.fsck.k9.storage.messages
+
+import com.fsck.k9.Account.FolderMode
+import com.fsck.k9.mail.Flag
+import com.fsck.k9.mail.FolderClass
+import com.fsck.k9.mail.FolderType
+import com.fsck.k9.mail.Header
+import com.fsck.k9.mailstore.CreateFolderInfo
+import com.fsck.k9.mailstore.FolderDetails
+import com.fsck.k9.mailstore.FolderMapper
+import com.fsck.k9.mailstore.LockableDatabase
+import com.fsck.k9.mailstore.MessageMapper
+import com.fsck.k9.mailstore.MessageStore
+import com.fsck.k9.mailstore.MoreMessages
+import com.fsck.k9.mailstore.SaveMessageData
+import com.fsck.k9.mailstore.StorageManager
+import com.fsck.k9.message.extractors.BasicPartInfoExtractor
+import com.fsck.k9.search.ConditionsTreeNode
+import java.util.Date
+
+class K9MessageStore(
+    database: LockableDatabase,
+    storageManager: StorageManager,
+    basicPartInfoExtractor: BasicPartInfoExtractor,
+    accountUuid: String
+) : MessageStore {
+    private val attachmentFileManager = AttachmentFileManager(storageManager, accountUuid)
+    private val threadMessageOperations = ThreadMessageOperations()
+    private val saveMessageOperations = SaveMessageOperations(
+        database,
+        attachmentFileManager,
+        basicPartInfoExtractor,
+        threadMessageOperations
+    )
+    private val copyMessageOperations = CopyMessageOperations(database, attachmentFileManager, threadMessageOperations)
+    private val moveMessageOperations = MoveMessageOperations(database, threadMessageOperations)
+    private val flagMessageOperations = FlagMessageOperations(database)
+    private val updateMessageOperations = UpdateMessageOperations(database)
+    private val retrieveMessageOperations = RetrieveMessageOperations(database)
+    private val retrieveMessageListOperations = RetrieveMessageListOperations(database)
+    private val deleteMessageOperations = DeleteMessageOperations(database, attachmentFileManager)
+    private val createFolderOperations = CreateFolderOperations(database)
+    private val retrieveFolderOperations = RetrieveFolderOperations(database)
+    private val checkFolderOperations = CheckFolderOperations(database)
+    private val updateFolderOperations = UpdateFolderOperations(database)
+    private val deleteFolderOperations = DeleteFolderOperations(database, attachmentFileManager)
+    private val keyValueStoreOperations = KeyValueStoreOperations(database)
+    private val databaseOperations = DatabaseOperations(database, storageManager, accountUuid)
+
+    override fun saveRemoteMessage(folderId: Long, messageServerId: String, messageData: SaveMessageData) {
+        saveMessageOperations.saveRemoteMessage(folderId, messageServerId, messageData)
+    }
+
+    override fun saveLocalMessage(folderId: Long, messageData: SaveMessageData, existingMessageId: Long?): Long {
+        return saveMessageOperations.saveLocalMessage(folderId, messageData, existingMessageId)
+    }
+
+    override fun copyMessage(messageId: Long, destinationFolderId: Long): Long {
+        return copyMessageOperations.copyMessage(messageId, destinationFolderId)
+    }
+
+    override fun moveMessage(messageId: Long, destinationFolderId: Long): Long {
+        return moveMessageOperations.moveMessage(messageId, destinationFolderId)
+    }
+
+    override fun setFlag(messageIds: Collection<Long>, flag: Flag, set: Boolean) {
+        flagMessageOperations.setFlag(messageIds, flag, set)
+    }
+
+    override fun setMessageFlag(folderId: Long, messageServerId: String, flag: Flag, set: Boolean) {
+        flagMessageOperations.setMessageFlag(folderId, messageServerId, flag, set)
+    }
+
+    override fun setNewMessageState(folderId: Long, messageServerId: String, newMessage: Boolean) {
+        updateMessageOperations.setNewMessageState(folderId, messageServerId, newMessage)
+    }
+
+    override fun clearNewMessageState() {
+        updateMessageOperations.clearNewMessageState()
+    }
+
+    override fun getMessageServerId(messageId: Long): String? {
+        return retrieveMessageOperations.getMessageServerId(messageId)
+    }
+
+    override fun getMessageServerIds(messageIds: Collection<Long>): Map<Long, String> {
+        return retrieveMessageOperations.getMessageServerIds(messageIds)
+    }
+
+    override fun getMessageServerIds(folderId: Long): Set<String> {
+        return retrieveMessageOperations.getMessageServerIds(folderId)
+    }
+
+    override fun isMessagePresent(folderId: Long, messageServerId: String): Boolean {
+        return retrieveMessageOperations.isMessagePresent(folderId, messageServerId)
+    }
+
+    override fun getMessageFlags(folderId: Long, messageServerId: String): Set<Flag> {
+        return retrieveMessageOperations.getMessageFlags(folderId, messageServerId)
+    }
+
+    override fun getAllMessagesAndEffectiveDates(folderId: Long): Map<String, Long?> {
+        return retrieveMessageOperations.getAllMessagesAndEffectiveDates(folderId)
+    }
+
+    override fun <T> getMessages(
+        selection: String,
+        selectionArgs: Array<String>,
+        sortOrder: String,
+        messageMapper: MessageMapper<out T?>
+    ): List<T> {
+        return retrieveMessageListOperations.getMessages(selection, selectionArgs, sortOrder, messageMapper)
+    }
+
+    override fun <T> getThreadedMessages(
+        selection: String,
+        selectionArgs: Array<String>,
+        sortOrder: String,
+        messageMapper: MessageMapper<out T?>
+    ): List<T> {
+        return retrieveMessageListOperations.getThreadedMessages(selection, selectionArgs, sortOrder, messageMapper)
+    }
+
+    override fun <T> getThread(threadId: Long, sortOrder: String, messageMapper: MessageMapper<out T?>): List<T> {
+        return retrieveMessageListOperations.getThread(threadId, sortOrder, messageMapper)
+    }
+
+    override fun getOldestMessageDate(folderId: Long): Date? {
+        return retrieveMessageOperations.getOldestMessageDate(folderId)
+    }
+
+    override fun getHeaders(folderId: Long, messageServerId: String): List<Header> {
+        return retrieveMessageOperations.getHeaders(folderId, messageServerId)
+    }
+
+    override fun getHeaders(folderId: Long, messageServerId: String, headerNames: Set<String>): List<Header> {
+        return retrieveMessageOperations.getHeaders(folderId, messageServerId, headerNames)
+    }
+
+    override fun destroyMessages(folderId: Long, messageServerIds: Collection<String>) {
+        deleteMessageOperations.destroyMessages(folderId, messageServerIds)
+    }
+
+    override fun createFolders(folders: List<CreateFolderInfo>) {
+        createFolderOperations.createFolders(folders)
+    }
+
+    override fun <T> getFolder(folderId: Long, mapper: FolderMapper<T>): T? {
+        return retrieveFolderOperations.getFolder(folderId, mapper)
+    }
+
+    override fun <T> getFolder(folderServerId: String, mapper: FolderMapper<T>): T? {
+        return retrieveFolderOperations.getFolder(folderServerId, mapper)
+    }
+
+    override fun <T> getFolders(excludeLocalOnly: Boolean, mapper: FolderMapper<T>): List<T> {
+        return retrieveFolderOperations.getFolders(excludeLocalOnly, mapper)
+    }
+
+    override fun <T> getDisplayFolders(
+        displayMode: FolderMode,
+        outboxFolderId: Long?,
+        mapper: FolderMapper<T>
+    ): List<T> {
+        return retrieveFolderOperations.getDisplayFolders(displayMode, outboxFolderId, mapper)
+    }
+
+    override fun areAllIncludedInUnifiedInbox(folderIds: Collection<Long>): Boolean {
+        return checkFolderOperations.areAllIncludedInUnifiedInbox(folderIds)
+    }
+
+    override fun getFolderId(folderServerId: String): Long? {
+        return retrieveFolderOperations.getFolderId(folderServerId)
+    }
+
+    override fun getFolderServerId(folderId: Long): String? {
+        return retrieveFolderOperations.getFolderServerId(folderId)
+    }
+
+    override fun getMessageCount(folderId: Long): Int {
+        return retrieveFolderOperations.getMessageCount(folderId)
+    }
+
+    override fun getUnreadMessageCount(folderId: Long): Int {
+        return retrieveFolderOperations.getUnreadMessageCount(folderId)
+    }
+
+    override fun getUnreadMessageCount(conditions: ConditionsTreeNode?): Int {
+        return retrieveFolderOperations.getUnreadMessageCount(conditions)
+    }
+
+    override fun getStarredMessageCount(conditions: ConditionsTreeNode?): Int {
+        return retrieveFolderOperations.getStarredMessageCount(conditions)
+    }
+
+    override fun getSize(): Long {
+        return databaseOperations.getSize()
+    }
+
+    override fun changeFolder(folderServerId: String, name: String, type: FolderType) {
+        updateFolderOperations.changeFolder(folderServerId, name, type)
+    }
+
+    override fun updateFolderSettings(folderDetails: FolderDetails) {
+        updateFolderOperations.updateFolderSettings(folderDetails)
+    }
+
+    override fun setIncludeInUnifiedInbox(folderId: Long, includeInUnifiedInbox: Boolean) {
+        updateFolderOperations.setIncludeInUnifiedInbox(folderId, includeInUnifiedInbox)
+    }
+
+    override fun setDisplayClass(folderId: Long, folderClass: FolderClass) {
+        updateFolderOperations.setDisplayClass(folderId, folderClass)
+    }
+
+    override fun setSyncClass(folderId: Long, folderClass: FolderClass) {
+        updateFolderOperations.setSyncClass(folderId, folderClass)
+    }
+
+    override fun setPushClass(folderId: Long, folderClass: FolderClass) {
+        updateFolderOperations.setPushClass(folderId, folderClass)
+    }
+
+    override fun setNotificationClass(folderId: Long, folderClass: FolderClass) {
+        updateFolderOperations.setNotificationClass(folderId, folderClass)
+    }
+
+    override fun hasMoreMessages(folderId: Long): MoreMessages {
+        return retrieveFolderOperations.hasMoreMessages(folderId)
+    }
+
+    override fun setMoreMessages(folderId: Long, moreMessages: MoreMessages) {
+        updateFolderOperations.setMoreMessages(folderId, moreMessages)
+    }
+
+    override fun setLastChecked(folderId: Long, timestamp: Long) {
+        updateFolderOperations.setLastChecked(folderId, timestamp)
+    }
+
+    override fun setStatus(folderId: Long, status: String?) {
+        updateFolderOperations.setStatus(folderId, status)
+    }
+
+    override fun setVisibleLimit(folderId: Long, visibleLimit: Int) {
+        updateFolderOperations.setVisibleLimit(folderId, visibleLimit)
+    }
+
+    override fun deleteFolders(folderServerIds: List<String>) {
+        deleteFolderOperations.deleteFolders(folderServerIds)
+    }
+
+    override fun getExtraString(name: String): String? {
+        return keyValueStoreOperations.getExtraString(name)
+    }
+
+    override fun setExtraString(name: String, value: String) {
+        keyValueStoreOperations.setExtraString(name, value)
+    }
+
+    override fun getExtraNumber(name: String): Long? {
+        return keyValueStoreOperations.getExtraNumber(name)
+    }
+
+    override fun setExtraNumber(name: String, value: Long) {
+        keyValueStoreOperations.setExtraNumber(name, value)
+    }
+
+    override fun getFolderExtraString(folderId: Long, name: String): String? {
+        return keyValueStoreOperations.getFolderExtraString(folderId, name)
+    }
+
+    override fun setFolderExtraString(folderId: Long, name: String, value: String?) {
+        return keyValueStoreOperations.setFolderExtraString(folderId, name, value)
+    }
+
+    override fun getFolderExtraNumber(folderId: Long, name: String): Long? {
+        return keyValueStoreOperations.getFolderExtraNumber(folderId, name)
+    }
+
+    override fun setFolderExtraNumber(folderId: Long, name: String, value: Long) {
+        return keyValueStoreOperations.setFolderExtraNumber(folderId, name, value)
+    }
+
+    override fun compact() {
+        return databaseOperations.compact()
+    }
+}

app/storage/src/main/java/com/fsck/k9/storage/messages/K9MessageStoreFactory.kt

@@ -0,0 +1,22 @@
+package com.fsck.k9.storage.messages
+
+import com.fsck.k9.Account
+import com.fsck.k9.mailstore.ListenableMessageStore
+import com.fsck.k9.mailstore.LocalStoreProvider
+import com.fsck.k9.mailstore.MessageStoreFactory
+import com.fsck.k9.mailstore.NotifierMessageStore
+import com.fsck.k9.mailstore.StorageManager
+import com.fsck.k9.message.extractors.BasicPartInfoExtractor
+
+class K9MessageStoreFactory(
+    private val localStoreProvider: LocalStoreProvider,
+    private val storageManager: StorageManager,
+    private val basicPartInfoExtractor: BasicPartInfoExtractor
+) : MessageStoreFactory {
+    override fun create(account: Account): ListenableMessageStore {
+        val localStore = localStoreProvider.getInstance(account)
+        val messageStore = K9MessageStore(localStore.database, storageManager, basicPartInfoExtractor, account.uuid)
+        val notifierMessageStore = NotifierMessageStore(messageStore, localStore)
+        return ListenableMessageStore(notifierMessageStore)
+    }
+}

app/storage/src/main/java/com/fsck/k9/storage/messages/KeyValueStoreOperations.kt

@@ -0,0 +1,131 @@
+package com.fsck.k9.storage.messages
+
+import android.content.ContentValues
+import android.database.sqlite.SQLiteDatabase
+import androidx.core.database.getLongOrNull
+import androidx.core.database.getStringOrNull
+import com.fsck.k9.mailstore.LockableDatabase
+
+internal class KeyValueStoreOperations(private val lockableDatabase: LockableDatabase) {
+    fun getExtraString(name: String): String? {
+        return lockableDatabase.execute(false) { db ->
+            db.query(
+                "account_extra_values",
+                arrayOf("value_text"),
+                "name = ?",
+                arrayOf(name),
+                null,
+                null,
+                null
+            ).use { cursor ->
+                if (cursor.moveToFirst()) {
+                    cursor.getStringOrNull(0)
+                } else {
+                    null
+                }
+            }
+        }
+    }
+
+    fun setExtraString(name: String, value: String) {
+        lockableDatabase.execute(false) { db ->
+            val contentValues = ContentValues().apply {
+                put("name", name)
+                put("value_text", value)
+            }
+            db.insertWithOnConflict("account_extra_values", null, contentValues, SQLiteDatabase.CONFLICT_REPLACE)
+        }
+    }
+
+    fun getExtraNumber(name: String): Long? {
+        return lockableDatabase.execute(false) { db ->
+            db.query(
+                "account_extra_values",
+                arrayOf("value_integer"),
+                "name = ?",
+                arrayOf(name),
+                null,
+                null,
+                null
+            ).use { cursor ->
+                if (cursor.moveToFirst()) {
+                    cursor.getLongOrNull(0)
+                } else {
+                    null
+                }
+            }
+        }
+    }
+
+    fun setExtraNumber(name: String, value: Long) {
+        lockableDatabase.execute(false) { db ->
+            val contentValues = ContentValues().apply {
+                put("name", name)
+                put("value_integer", value)
+            }
+            db.insertWithOnConflict("account_extra_values", null, contentValues, SQLiteDatabase.CONFLICT_REPLACE)
+        }
+    }
+
+    fun getFolderExtraString(folderId: Long, name: String): String? {
+        return lockableDatabase.execute(false) { db ->
+            db.query(
+                "folder_extra_values",
+                arrayOf("value_text"),
+                "name = ? AND folder_id = ?",
+                arrayOf(name, folderId.toString()),
+                null,
+                null,
+                null
+            ).use { cursor ->
+                if (cursor.moveToFirst()) {
+                    cursor.getStringOrNull(0)
+                } else {
+                    null
+                }
+            }
+        }
+    }
+
+    fun setFolderExtraString(folderId: Long, name: String, value: String?) {
+        lockableDatabase.execute(false) { db ->
+            val contentValues = ContentValues().apply {
+                put("folder_id", folderId)
+                put("name", name)
+                put("value_text", value)
+            }
+            db.insertWithOnConflict("folder_extra_values", null, contentValues, SQLiteDatabase.CONFLICT_REPLACE)
+        }
+    }
+
+    fun getFolderExtraNumber(folderId: Long, name: String): Long? {
+        return lockableDatabase.execute(false) { db ->
+            db.query(
+                "folder_extra_values",
+                arrayOf("value_integer"),
+                "name = ? AND folder_id = ?",
+                arrayOf(name, folderId.toString()),
+                null,
+                null,
+                null
+            ).use { cursor ->
+                if (cursor.moveToFirst()) {
+                    cursor.getLongOrNull(0)
+                } else {
+                    null
+                }
+            }
+        }
+    }
+
+    fun setFolderExtraNumber(folderId: Long, name: String, value: Long) {
+        lockableDatabase.execute(false) { db ->
+            val contentValues = ContentValues().apply {
+                put("folder_id", folderId)
+                put("name", name)
+                put("value_integer", value)
+            }
+            db.insertWithOnConflict("folder_extra_values", null, contentValues, SQLiteDatabase.CONFLICT_REPLACE)
+        }
+    }
+}

app/storage/src/main/java/com/fsck/k9/storage/messages/MoveMessageOperations.kt

@@ -0,0 +1,132 @@
+package com.fsck.k9.storage.messages
+
+import android.content.ContentValues
+import android.database.sqlite.SQLiteDatabase
+import app.k9mail.core.android.common.database.getIntOrNull
+import app.k9mail.core.android.common.database.getLongOrNull
+import app.k9mail.core.android.common.database.getStringOrNull
+import com.fsck.k9.K9
+import com.fsck.k9.mailstore.LockableDatabase
+import java.util.UUID
+import timber.log.Timber
+
+internal class MoveMessageOperations(
+    private val database: LockableDatabase,
+    private val threadMessageOperations: ThreadMessageOperations
+) {
+    fun moveMessage(messageId: Long, destinationFolderId: Long): Long {
+        Timber.d("Moving message [ID: $messageId] to folder [ID: $destinationFolderId]")
+
+        return database.execute(true) { database ->
+            val threadInfo = threadMessageOperations.createOrUpdateParentThreadEntries(database, messageId, destinationFolderId)
+            val destinationMessageId = createMessageEntry(database, messageId, destinationFolderId, threadInfo)
+            threadMessageOperations.createThreadEntryIfNecessary(database, destinationMessageId, threadInfo)
+
+            convertOriginalMessageEntryToPlaceholderEntry(database, messageId)
+            moveFulltextEntry(database, messageId, destinationMessageId)
+
+            destinationMessageId
+        }
+    }
+
+    private fun moveFulltextEntry(database: SQLiteDatabase, messageId: Long, destinationMessageId: Long) {
+        val values = ContentValues().apply {
+            put("docid", destinationMessageId)
+        }
+
+        database.update("messages_fulltext", values, "docid = ?", arrayOf(messageId.toString()))
+    }
+
+    private fun createMessageEntry(
+        database: SQLiteDatabase,
+        messageId: Long,
+        destinationFolderId: Long,
+        threadInfo: ThreadInfo?
+    ): Long {
+        val destinationUid = K9.LOCAL_UID_PREFIX + UUID.randomUUID().toString()
+
+        val contentValues = database.query(
+            "messages",
+            arrayOf(
+                "subject", "date", "flags", "sender_list", "to_list", "cc_list", "bcc_list", "reply_to_list",
+                "attachment_count", "internal_date", "message_id", "preview_type", "preview", "mime_type",
+                "normalized_subject_hash", "read", "flagged", "answered", "forwarded", "message_part_id",
+                "encryption_type"
+            ),
+            "id = ?",
+            arrayOf(messageId.toString()),
+            null,
+            null,
+            null
+        ).use { cursor ->
+            if (!cursor.moveToFirst()) {
+                error("Couldn't find local message [ID: $messageId]")
+            }
+
+            ContentValues().apply {
+                put("uid", destinationUid)
+                put("folder_id", destinationFolderId)
+                put("deleted", 0)
+                put("empty", 0)
+                put("subject", cursor.getStringOrNull("subject"))
+                put("date", cursor.getLongOrNull("date"))
+                put("flags", cursor.getStringOrNull("flags"))
+                put("sender_list", cursor.getStringOrNull("sender_list"))
+                put("to_list", cursor.getStringOrNull("to_list"))
+                put("cc_list", cursor.getStringOrNull("cc_list"))
+                put("bcc_list", cursor.getStringOrNull("bcc_list"))
+                put("reply_to_list", cursor.getStringOrNull("reply_to_list"))
+                put("attachment_count", cursor.getIntOrNull("attachment_count"))
+                put("internal_date", cursor.getLongOrNull("internal_date"))
+                put("message_id", cursor.getStringOrNull("message_id"))
+                put("preview_type", cursor.getStringOrNull("preview_type"))
+                put("preview", cursor.getStringOrNull("preview"))
+                put("mime_type", cursor.getStringOrNull("mime_type"))
+                put("normalized_subject_hash", cursor.getLongOrNull("normalized_subject_hash"))
+                put("read", cursor.getIntOrNull("read"))
+                put("flagged", cursor.getIntOrNull("flagged"))
+                put("answered", cursor.getIntOrNull("answered"))
+                put("forwarded", cursor.getIntOrNull("forwarded"))
+                put("message_part_id", cursor.getLongOrNull("message_part_id"))
+                put("encryption_type", cursor.getStringOrNull("encryption_type"))
+            }
+        }
+
+        val placeHolderMessageId = threadInfo?.messageId
+        return if (placeHolderMessageId != null) {
+            database.update("messages", contentValues, "id = ?", arrayOf(placeHolderMessageId.toString()))
+            placeHolderMessageId
+        } else {
+            database.insert("messages", null, contentValues)
+        }
+    }
+
+    private fun convertOriginalMessageEntryToPlaceholderEntry(database: SQLiteDatabase, messageId: Long) {
+        val contentValues = ContentValues().apply {
+            put("deleted", 1)
+            put("empty", 0)
+            put("read", 1)
+            putNull("subject")
+            putNull("date")
+            putNull("flags")
+            putNull("sender_list")
+            putNull("to_list")
+            putNull("cc_list")
+            putNull("bcc_list")
+            putNull("reply_to_list")
+            putNull("attachment_count")
+            putNull("internal_date")
+            put("preview_type", "none")
+            putNull("preview")
+            putNull("mime_type")
+            putNull("normalized_subject_hash")
+            putNull("flagged")
+            putNull("answered")
+            putNull("forwarded")
+            putNull("message_part_id")
+            putNull("encryption_type")
+        }
+
+        database.update("messages", contentValues, "id = ?", arrayOf(messageId.toString()))
+    }
+}

app/storage/src/main/java/com/fsck/k9/storage/messages/RetrieveFolderOperations.kt

@@ -0,0 +1,284 @@
+package com.fsck.k9.storage.messages
+
+import android.database.Cursor
+import androidx.core.database.getLongOrNull
+import app.k9mail.core.android.common.database.map
+import com.fsck.k9.Account.FolderMode
+import com.fsck.k9.mail.FolderClass
+import com.fsck.k9.mail.FolderType
+import com.fsck.k9.mailstore.FolderDetailsAccessor
+import com.fsck.k9.mailstore.FolderMapper
+import com.fsck.k9.mailstore.FolderNotFoundException
+import com.fsck.k9.mailstore.LockableDatabase
+import com.fsck.k9.mailstore.MoreMessages
+import com.fsck.k9.mailstore.toFolderType
+import com.fsck.k9.search.ConditionsTreeNode
+import com.fsck.k9.search.SqlQueryBuilder
+
+internal class RetrieveFolderOperations(private val lockableDatabase: LockableDatabase) {
+    fun <T> getFolder(folderId: Long, mapper: FolderMapper<T>): T? {
+        return getFolder(
+            selection = "id = ?",
+            selectionArguments = arrayOf(folderId.toString()),
+            mapper = mapper
+        )
+    }
+
+    fun <T> getFolder(folderServerId: String, mapper: FolderMapper<T>): T? {
+        return getFolder(
+            selection = "server_id = ?",
+            selectionArguments = arrayOf(folderServerId),
+            mapper = mapper
+        )
+    }
+
+    private fun <T> getFolder(selection: String, selectionArguments: Array<String>, mapper: FolderMapper<T>): T? {
+        return lockableDatabase.execute(false) { db ->
+            db.query(
+                "folders",
+                FOLDER_COLUMNS,
+                selection,
+                selectionArguments,
+                null,
+                null,
+                null
+            ).use { cursor ->
+                if (cursor.moveToFirst()) {
+                    val cursorFolderAccessor = CursorFolderAccessor(cursor)
+                    mapper.map(cursorFolderAccessor)
+                } else {
+                    null
+                }
+            }
+        }
+    }
+
+    fun <T> getFolders(excludeLocalOnly: Boolean = false, mapper: FolderMapper<T>): List<T> {
+        val selection = if (excludeLocalOnly) "local_only = 0" else null
+        return lockableDatabase.execute(false) { db ->
+            db.query("folders", FOLDER_COLUMNS, selection, null, null, null, "id").use { cursor ->
+                val cursorFolderAccessor = CursorFolderAccessor(cursor)
+                cursor.map {
+                    mapper.map(cursorFolderAccessor)
+                }
+            }
+        }
+    }
+
+    fun <T> getDisplayFolders(displayMode: FolderMode, outboxFolderId: Long?, mapper: FolderMapper<T>): List<T> {
+        return lockableDatabase.execute(false) { db ->
+            val displayModeSelection = getDisplayModeSelection(displayMode)
+            val outboxFolderIdOrZero = outboxFolderId ?: 0
+
+            val query =
+                """
+SELECT ${FOLDER_COLUMNS.joinToString()}, (
+  SELECT COUNT(messages.id) 
+  FROM messages 
+  WHERE messages.folder_id = folders.id 
+    AND messages.empty = 0 AND messages.deleted = 0 
+    AND (messages.read = 0 OR folders.id = ?)
+), (
+  SELECT COUNT(messages.id) 
+  FROM messages 
+  WHERE messages.folder_id = folders.id 
+    AND messages.empty = 0 AND messages.deleted = 0 
+    AND messages.flagged = 1
+)
+FROM folders
+$displayModeSelection
+                """
+
+            db.rawQuery(query, arrayOf(outboxFolderIdOrZero.toString())).use { cursor ->
+                val cursorFolderAccessor = CursorFolderAccessor(cursor)
+                cursor.map {
+                    mapper.map(cursorFolderAccessor)
+                }
+            }
+        }
+    }
+
+    private fun getDisplayModeSelection(displayMode: FolderMode): String {
+        return when (displayMode) {
+            FolderMode.ALL -> {
+                ""
+            }
+            FolderMode.FIRST_CLASS -> {
+                "WHERE display_class = '${FolderClass.FIRST_CLASS.name}'"
+            }
+            FolderMode.FIRST_AND_SECOND_CLASS -> {
+                "WHERE display_class IN ('${FolderClass.FIRST_CLASS.name}', '${FolderClass.SECOND_CLASS.name}')"
+            }
+            FolderMode.NOT_SECOND_CLASS -> {
+                "WHERE display_class != '${FolderClass.SECOND_CLASS.name}'"
+            }
+            FolderMode.NONE -> {
+                throw AssertionError("Invalid folder display mode: $displayMode")
+            }
+        }
+    }
+
+    fun getFolderId(folderServerId: String): Long? {
+        return lockableDatabase.execute(false) { db ->
+            db.query(
+                "folders",
+                arrayOf("id"),
+                "server_id = ?",
+                arrayOf(folderServerId),
+                null,
+                null,
+                null
+            ).use { cursor ->
+                if (cursor.moveToFirst()) cursor.getLong(0) else null
+            }
+        }
+    }
+
+    fun getFolderServerId(folderId: Long): String? {
+        return lockableDatabase.execute(false) { db ->
+            db.query(
+                "folders",
+                arrayOf("server_id"),
+                "id = ?",
+                arrayOf(folderId.toString()),
+                null,
+                null,
+                null
+            ).use { cursor ->
+                if (cursor.moveToFirst()) cursor.getString(0) else null
+            }
+        }
+    }
+
+    fun getMessageCount(folderId: Long): Int {
+        return lockableDatabase.execute(false) { db ->
+            db.rawQuery(
+                "SELECT COUNT(id) FROM messages WHERE empty = 0 AND deleted = 0 AND folder_id = ?",
+                arrayOf(folderId.toString())
+            ).use { cursor ->
+                if (cursor.moveToFirst()) cursor.getInt(0) else 0
+            }
+        }
+    }
+
+    fun getUnreadMessageCount(folderId: Long): Int {
+        return lockableDatabase.execute(false) { db ->
+            db.rawQuery(
+                "SELECT COUNT(id) FROM messages WHERE empty = 0 AND deleted = 0 AND read = 0 AND folder_id = ?",
+                arrayOf(folderId.toString())
+            ).use { cursor ->
+                if (cursor.moveToFirst()) cursor.getInt(0) else 0
+            }
+        }
+    }
+
+    fun getUnreadMessageCount(conditions: ConditionsTreeNode?): Int {
+        return getMessageCount(condition = "messages.read = 0", conditions)
+    }
+
+    fun getStarredMessageCount(conditions: ConditionsTreeNode?): Int {
+        return getMessageCount(condition = "messages.flagged = 1", conditions)
+    }
+
+    private fun getMessageCount(condition: String, extraConditions: ConditionsTreeNode?): Int {
+        val whereBuilder = StringBuilder()
+        val queryArgs = mutableListOf<String>()
+        SqlQueryBuilder.buildWhereClause(extraConditions, whereBuilder, queryArgs)
+
+        val where = if (whereBuilder.isNotEmpty()) "AND ($whereBuilder)" else ""
+        val selectionArgs = queryArgs.toTypedArray()
+
+        val query =
+            """
+SELECT COUNT(messages.id) 
+FROM messages 
+JOIN folders ON (folders.id = messages.folder_id) 
+WHERE (messages.empty = 0 AND messages.deleted = 0 AND $condition) $where
+            """
+
+        return lockableDatabase.execute(false) { db ->
+            db.rawQuery(query, selectionArgs).use { cursor ->
+                if (cursor.moveToFirst()) cursor.getInt(0) else 0
+            }
+        }
+    }
+
+    fun hasMoreMessages(folderId: Long): MoreMessages {
+        return getFolder(folderId) { it.moreMessages } ?: throw FolderNotFoundException(folderId)
+    }
+}
+
+private class CursorFolderAccessor(val cursor: Cursor) : FolderDetailsAccessor {
+    override val id: Long
+        get() = cursor.getLong(0)
+
+    override val name: String
+        get() = cursor.getString(1)
+
+    override val type: FolderType
+        get() = cursor.getString(2).toFolderType()
+
+    override val serverId: String?
+        get() = cursor.getString(3)
+
+    override val isLocalOnly: Boolean
+        get() = cursor.getInt(4) == 1
+
+    override val isInTopGroup: Boolean
+        get() = cursor.getInt(5) == 1
+
+    override val isIntegrate: Boolean
+        get() = cursor.getInt(6) == 1
+
+    override val syncClass: FolderClass
+        get() = cursor.getString(7).toFolderClass(FolderClass.INHERITED)
+
+    override val displayClass: FolderClass
+        get() = cursor.getString(8).toFolderClass(FolderClass.NO_CLASS)
+
+    override val notifyClass: FolderClass
+        get() = cursor.getString(9).toFolderClass(FolderClass.INHERITED)
+
+    override val pushClass: FolderClass
+        get() = cursor.getString(10).toFolderClass(FolderClass.SECOND_CLASS)
+
+    override val visibleLimit: Int
+        get() = cursor.getInt(11)
+
+    override val moreMessages: MoreMessages
+        get() = MoreMessages.fromDatabaseName(cursor.getString(12))
+
+    override val lastChecked: Long?
+        get() = cursor.getLongOrNull(13)
+
+    override val unreadMessageCount: Int
+        get() = cursor.getInt(14)
+
+    override val starredMessageCount: Int
+        get() = cursor.getInt(15)
+
+    override fun serverIdOrThrow(): String {
+        return serverId ?: error("No server ID found for folder '$name' ($id)")
+    }
+}
+
+private fun String?.toFolderClass(defaultValue: FolderClass): FolderClass {
+    return if (this == null) defaultValue else FolderClass.valueOf(this)
+}
+
+private val FOLDER_COLUMNS = arrayOf(
+    "id",
+    "name",
+    "type",
+    "server_id",
+    "local_only",
+    "top_group",
+    "integrate",
+    "poll_class",
+    "display_class",
+    "notify_class",
+    "push_class",
+    "visible_limit",
+    "more_messages",
+    "last_updated"
+)

app/storage/src/main/java/com/fsck/k9/storage/messages/RetrieveMessageListOperations.kt

@@ -0,0 +1,242 @@
+package com.fsck.k9.storage.messages
+
+import android.database.Cursor
+import com.fsck.k9.mail.Address
+import com.fsck.k9.mailstore.DatabasePreviewType
+import com.fsck.k9.mailstore.LockableDatabase
+import com.fsck.k9.mailstore.MessageDetailsAccessor
+import com.fsck.k9.mailstore.MessageMapper
+import com.fsck.k9.message.extractors.PreviewResult
+import com.fsck.k9.search.SqlQueryBuilder
+
+internal class RetrieveMessageListOperations(private val lockableDatabase: LockableDatabase) {
+
+    fun <T> getMessages(
+        selection: String,
+        selectionArgs: Array<String>,
+        sortOrder: String,
+        mapper: MessageMapper<out T?>
+    ): List<T> {
+        return lockableDatabase.execute(false) { database ->
+            database.rawQuery(
+                """
+SELECT 
+  messages.id AS id, 
+  uid, 
+  folder_id, 
+  sender_list, 
+  to_list, 
+  cc_list, 
+  date, 
+  internal_date, 
+  subject, 
+  preview_type,
+  preview, 
+  read, 
+  flagged, 
+  answered, 
+  forwarded, 
+  attachment_count, 
+  root
+FROM messages
+JOIN threads ON (threads.message_id = messages.id)
+LEFT JOIN FOLDERS ON (folders.id = messages.folder_id)
+WHERE
+  ($selection)
+  AND empty = 0 AND deleted = 0
+ORDER BY $sortOrder
+                """,
+                selectionArgs
+            ).use { cursor ->
+                val cursorMessageAccessor = CursorMessageAccessor(cursor, includesThreadCount = false)
+                buildList {
+                    while (cursor.moveToNext()) {
+                        val value = mapper.map(cursorMessageAccessor)
+                        if (value != null) {
+                            add(value)
+                        }
+                    }
+                }
+            }
+        }
+    }
+
+    fun <T> getThreadedMessages(
+        selection: String,
+        selectionArgs: Array<String>,
+        sortOrder: String,
+        mapper: MessageMapper<out T?>
+    ): List<T> {
+        val orderBy = SqlQueryBuilder.addPrefixToSelection(AGGREGATED_MESSAGES_COLUMNS, "aggregated.", sortOrder)
+
+        return lockableDatabase.execute(false) { database ->
+            database.rawQuery(
+                """
+SELECT 
+  messages.id AS id, 
+  uid, 
+  folder_id, 
+  sender_list, 
+  to_list, 
+  cc_list, 
+  aggregated.date AS date, 
+  aggregated.internal_date AS internal_date, 
+  subject, 
+  preview_type,
+  preview, 
+  aggregated.read AS read, 
+  aggregated.flagged AS flagged, 
+  aggregated.answered AS answered, 
+  aggregated.forwarded AS forwarded, 
+  aggregated.attachment_count AS attachment_count, 
+  root, 
+  aggregated.thread_count AS thread_count
+FROM (
+  SELECT 
+    threads.root AS thread_root,
+    MAX(date) AS date,
+    MAX(internal_date) AS internal_date,
+    MIN(read) AS read,
+    MAX(flagged) AS flagged,
+    MIN(answered) AS answered,
+    MIN(forwarded) AS forwarded,
+    SUM(attachment_count) AS attachment_count,
+    COUNT(threads.root) AS thread_count                        
+  FROM messages
+  JOIN threads ON (threads.message_id = messages.id)
+  JOIN folders ON (folders.id = messages.folder_id)
+  WHERE
+    threads.root IN (
+      SELECT threads.root 
+      FROM messages
+      JOIN threads ON (threads.message_id = messages.id)
+      WHERE messages.empty = 0 AND messages.deleted = 0
+    )
+    AND ($selection)
+    AND messages.empty = 0 AND messages.deleted = 0
+  GROUP BY threads.root
+) aggregated
+JOIN threads ON (threads.root = aggregated.thread_root)
+JOIN messages ON (
+  messages.id = threads.message_id
+  AND messages.empty = 0 AND messages.deleted = 0
+  AND messages.date = aggregated.date
+)
+JOIN folders ON (folders.id = messages.folder_id)
+GROUP BY threads.root
+ORDER BY $orderBy
+                """,
+                selectionArgs
+            ).use { cursor ->
+                val cursorMessageAccessor = CursorMessageAccessor(cursor, includesThreadCount = true)
+                buildList {
+                    while (cursor.moveToNext()) {
+                        val value = mapper.map(cursorMessageAccessor)
+                        if (value != null) {
+                            add(value)
+                        }
+                    }
+                }
+            }
+        }
+    }
+
+    fun <T> getThread(threadId: Long, sortOrder: String, mapper: MessageMapper<out T?>): List<T> {
+        return lockableDatabase.execute(false) { database ->
+            database.rawQuery(
+                """
+SELECT 
+  messages.id AS id, 
+  uid, 
+  folder_id, 
+  sender_list, 
+  to_list, 
+  cc_list, 
+  date, 
+  internal_date, 
+  subject, 
+  preview_type,
+  preview, 
+  read, 
+  flagged, 
+  answered, 
+  forwarded, 
+  attachment_count, 
+  root
+FROM threads 
+JOIN messages ON (messages.id = threads.message_id)
+LEFT JOIN FOLDERS ON (folders.id = messages.folder_id)
+WHERE
+  root = ?
+  AND empty = 0 AND deleted = 0
+ORDER BY $sortOrder
+                """,
+                arrayOf(threadId.toString())
+            ).use { cursor ->
+                val cursorMessageAccessor = CursorMessageAccessor(cursor, includesThreadCount = false)
+                buildList {
+                    while (cursor.moveToNext()) {
+                        val value = mapper.map(cursorMessageAccessor)
+                        if (value != null) {
+                            add(value)
+                        }
+                    }
+                }
+            }
+        }
+    }
+}
+
+private class CursorMessageAccessor(val cursor: Cursor, val includesThreadCount: Boolean) : MessageDetailsAccessor {
+    override val id: Long
+        get() = cursor.getLong(0)
+    override val messageServerId: String
+        get() = cursor.getString(1)
+    override val folderId: Long
+        get() = cursor.getLong(2)
+    override val fromAddresses: List<Address>
+        get() = Address.unpack(cursor.getString(3)).toList()
+    override val toAddresses: List<Address>
+        get() = Address.unpack(cursor.getString(4)).toList()
+    override val ccAddresses: List<Address>
+        get() = Address.unpack(cursor.getString(5)).toList()
+    override val messageDate: Long
+        get() = cursor.getLong(6)
+    override val internalDate: Long
+        get() = cursor.getLong(7)
+    override val subject: String?
+        get() = cursor.getString(8)
+    override val preview: PreviewResult
+        get() {
+            return when (DatabasePreviewType.fromDatabaseValue(cursor.getString(9))) {
+                DatabasePreviewType.NONE -> PreviewResult.none()
+                DatabasePreviewType.TEXT -> PreviewResult.text(cursor.getString(10))
+                DatabasePreviewType.ENCRYPTED -> PreviewResult.encrypted()
+                DatabasePreviewType.ERROR -> PreviewResult.error()
+            }
+        }
+    override val isRead: Boolean
+        get() = cursor.getInt(11) == 1
+    override val isStarred: Boolean
+        get() = cursor.getInt(12) == 1
+    override val isAnswered: Boolean
+        get() = cursor.getInt(13) == 1
+    override val isForwarded: Boolean
+        get() = cursor.getInt(14) == 1
+    override val hasAttachments: Boolean
+        get() = cursor.getInt(15) > 0
+    override val threadRoot: Long
+        get() = cursor.getLong(16)
+    override val threadCount: Int
+        get() = if (includesThreadCount) cursor.getInt(17) else 0
+}
+
+private val AGGREGATED_MESSAGES_COLUMNS = arrayOf(
+    "date",
+    "internal_date",
+    "attachment_count",
+    "read",
+    "flagged",
+    "answered",
+    "forwarded"
+)

app/storage/src/main/java/com/fsck/k9/storage/messages/RetrieveMessageOperations.kt

@@ -0,0 +1,197 @@
+package com.fsck.k9.storage.messages
+
+import androidx.core.database.getLongOrNull
+import com.fsck.k9.K9
+import com.fsck.k9.helper.mapToSet
+import com.fsck.k9.mail.Flag
+import com.fsck.k9.mail.Header
+import com.fsck.k9.mail.internet.MimeHeader
+import com.fsck.k9.mail.message.MessageHeaderParser
+import com.fsck.k9.mailstore.LockableDatabase
+import com.fsck.k9.mailstore.MessageNotFoundException
+import java.util.Date
+
+internal class RetrieveMessageOperations(private val lockableDatabase: LockableDatabase) {
+
+    fun getMessageServerId(messageId: Long): String? {
+        return lockableDatabase.execute(false) { database ->
+            database.query(
+                "messages",
+                arrayOf("uid"),
+                "id = ?",
+                arrayOf(messageId.toString()),
+                null,
+                null,
+                null
+            ).use { cursor ->
+                if (cursor.moveToFirst()) {
+                    cursor.getString(0)
+                } else {
+                    null
+                }
+            }
+        }
+    }
+
+    fun getMessageServerIds(messageIds: Collection<Long>): Map<Long, String> {
+        if (messageIds.isEmpty()) return emptyMap()
+
+        return lockableDatabase.execute(false) { database ->
+            val databaseIdToServerIdMapping = mutableMapOf<Long, String>()
+            performChunkedOperation(
+                arguments = messageIds,
+                argumentTransformation = Long::toString
+            ) { selectionSet, selectionArguments ->
+                database.query(
+                    "messages",
+                    arrayOf("id", "uid"),
+                    "id $selectionSet",
+                    selectionArguments,
+                    null,
+                    null,
+                    null
+                ).use { cursor ->
+                    while (cursor.moveToNext()) {
+                        val databaseId = cursor.getLong(0)
+                        val serverId = cursor.getString(1)
+
+                        databaseIdToServerIdMapping[databaseId] = serverId
+                    }
+                }
+            }
+
+            databaseIdToServerIdMapping
+        }
+    }
+
+    fun getMessageServerIds(folderId: Long): Set<String> {
+        return lockableDatabase.execute(false) { database ->
+            database.rawQuery(
+                "SELECT uid FROM messages" +
+                    " WHERE empty = 0 AND deleted = 0 AND folder_id = ? AND uid NOT LIKE '${K9.LOCAL_UID_PREFIX}%'",
+                arrayOf(folderId.toString())
+            ).use { cursor ->
+                val result = mutableSetOf<String>()
+                while (cursor.moveToNext()) {
+                    val uid = cursor.getString(0)
+                    result.add(uid)
+                }
+                result
+            }
+        }
+    }
+
+    fun isMessagePresent(folderId: Long, messageServerId: String): Boolean {
+        return lockableDatabase.execute(false) { db ->
+            db.query(
+                "messages",
+                arrayOf("id"),
+                "folder_id = ? AND uid = ?",
+                arrayOf(folderId.toString(), messageServerId),
+                null,
+                null,
+                null
+            ).use { cursor ->
+                cursor.moveToFirst()
+            }
+        }
+    }
+
+    fun getMessageFlags(folderId: Long, messageServerId: String): Set<Flag> {
+        return lockableDatabase.execute(false) { db ->
+            db.query(
+                "messages",
+                arrayOf("deleted", "read", "flagged", "answered", "forwarded", "flags"),
+                "folder_id = ? AND uid = ?",
+                arrayOf(folderId.toString(), messageServerId),
+                null,
+                null,
+                null
+            ).use { cursor ->
+                if (!cursor.moveToFirst()) error("Couldn't read flags for $folderId:$messageServerId")
+
+                val deleted = cursor.getInt(0) == 1
+                val read = cursor.getInt(1) == 1
+                val flagged = cursor.getInt(2) == 1
+                val answered = cursor.getInt(3) == 1
+                val forwarded = cursor.getInt(4) == 1
+                val flagsColumnValue = cursor.getString(5)
+
+                val otherFlags = if (flagsColumnValue.isNullOrBlank()) {
+                    emptySet()
+                } else {
+                    flagsColumnValue.split(',').map { Flag.valueOf(it) }
+                }
+
+                otherFlags
+                    .toMutableSet()
+                    .apply {
+                        if (deleted) add(Flag.DELETED)
+                        if (read) add(Flag.SEEN)
+                        if (flagged) add(Flag.FLAGGED)
+                        if (answered) add(Flag.ANSWERED)
+                        if (forwarded) add(Flag.FORWARDED)
+                    }
+            }
+        }
+    }
+
+    fun getAllMessagesAndEffectiveDates(folderId: Long): Map<String, Long?> {
+        return lockableDatabase.execute(false) { database ->
+            database.rawQuery(
+                "SELECT uid, date FROM messages" +
+                    " WHERE empty = 0 AND deleted = 0 AND folder_id = ? AND uid NOT LIKE '${K9.LOCAL_UID_PREFIX}%'",
+                arrayOf(folderId.toString())
+            ).use { cursor ->
+                val result = mutableMapOf<String, Long?>()
+                while (cursor.moveToNext()) {
+                    val uid = cursor.getString(0)
+                    val date = cursor.getLongOrNull(1)
+                    result[uid] = date
+                }
+                result
+            }
+        }
+    }
+
+    fun getOldestMessageDate(folderId: Long): Date? {
+        return lockableDatabase.execute(false) { database ->
+            database.rawQuery(
+                "SELECT MIN(date) FROM messages WHERE folder_id = ?",
+                arrayOf(folderId.toString())
+            ).use { cursor ->
+                if (cursor.moveToFirst()) {
+                    val timestamp = cursor.getLong(0)
+                    if (timestamp != 0L) Date(timestamp) else null
+                } else {
+                    null
+                }
+            }
+        }
+    }
+
+    fun getHeaders(folderId: Long, messageServerId: String, headerNames: Set<String>? = null): List<Header> {
+        return lockableDatabase.execute(false) { database ->
+            database.rawQuery(
+                "SELECT message_parts.header FROM messages" +
+                    " LEFT JOIN message_parts ON (messages.message_part_id = message_parts.id)" +
+                    " WHERE messages.folder_id = ? AND messages.uid = ?",
+                arrayOf(folderId.toString(), messageServerId)
+            ).use { cursor ->
+                if (!cursor.moveToFirst()) throw MessageNotFoundException(folderId, messageServerId)
+
+                val headerBytes = cursor.getBlob(0)
+                val lowercaseHeaderNames = headerNames?.mapToSet(headerNames.size) { it.lowercase() }
+
+                val header = MimeHeader()
+                MessageHeaderParser.parse(headerBytes.inputStream()) { name, value ->
+                    if (lowercaseHeaderNames == null || name.lowercase() in lowercaseHeaderNames) {
+                        header.addRawHeader(name, value)
+                    }
+                }
+
+                header.headers
+            }
+        }
+    }
+}

app/storage/src/main/java/com/fsck/k9/storage/messages/SaveMessageOperations.kt

@@ -0,0 +1,539 @@
+package com.fsck.k9.storage.messages
+
+import android.content.ContentValues
+import android.database.sqlite.SQLiteDatabase
+import com.fsck.k9.K9
+import com.fsck.k9.mail.Address
+import com.fsck.k9.mail.Body
+import com.fsck.k9.mail.BoundaryGenerator
+import com.fsck.k9.mail.Flag
+import com.fsck.k9.mail.Message
+import com.fsck.k9.mail.Message.RecipientType
+import com.fsck.k9.mail.MessageDownloadState
+import com.fsck.k9.mail.Multipart
+import com.fsck.k9.mail.Part
+import com.fsck.k9.mail.filter.CountingOutputStream
+import com.fsck.k9.mail.internet.BinaryTempFileBody
+import com.fsck.k9.mail.internet.MimeHeader
+import com.fsck.k9.mail.internet.MimeUtility
+import com.fsck.k9.mail.internet.SizeAware
+import com.fsck.k9.mailstore.DatabasePreviewType
+import com.fsck.k9.mailstore.LockableDatabase
+import com.fsck.k9.mailstore.SaveMessageData
+import com.fsck.k9.message.extractors.BasicPartInfoExtractor
+import com.fsck.k9.message.extractors.PreviewResult.PreviewType
+import java.io.ByteArrayOutputStream
+import java.io.File
+import java.io.FileInputStream
+import java.io.FileOutputStream
+import java.io.IOException
+import java.io.InputStream
+import java.util.Stack
+import java.util.UUID
+import org.apache.commons.io.IOUtils
+import org.apache.james.mime4j.codec.Base64InputStream
+import org.apache.james.mime4j.codec.QuotedPrintableInputStream
+import org.apache.james.mime4j.util.MimeUtil
+
+internal const val MAX_BODY_SIZE_FOR_DATABASE = 16 * 1024L
+
+internal class SaveMessageOperations(
+    private val lockableDatabase: LockableDatabase,
+    private val attachmentFileManager: AttachmentFileManager,
+    private val partInfoExtractor: BasicPartInfoExtractor,
+    private val threadMessageOperations: ThreadMessageOperations
+) {
+    fun saveRemoteMessage(folderId: Long, messageServerId: String, messageData: SaveMessageData) {
+        saveMessage(folderId, messageServerId, messageData)
+    }
+
+    fun saveLocalMessage(folderId: Long, messageData: SaveMessageData, existingMessageId: Long?): Long {
+        return if (existingMessageId == null) {
+            saveLocalMessage(folderId, messageData)
+        } else {
+            replaceLocalMessage(folderId, existingMessageId, messageData)
+        }
+    }
+
+    private fun saveLocalMessage(folderId: Long, messageData: SaveMessageData): Long {
+        val fakeServerId = K9.LOCAL_UID_PREFIX + UUID.randomUUID().toString()
+        return saveMessage(folderId, fakeServerId, messageData)
+    }
+
+    private fun replaceLocalMessage(folderId: Long, messageId: Long, messageData: SaveMessageData): Long {
+        return lockableDatabase.execute(true) { database ->
+            val (messageServerId, rootMessagePartId) = getLocalMessageInfo(folderId, messageId)
+
+            replaceMessage(
+                database,
+                folderId,
+                messageServerId,
+                existingMessageId = messageId,
+                existingRootMessagePartId = rootMessagePartId,
+                messageData
+            )
+
+            messageId
+        }
+    }
+
+    private fun saveMessage(folderId: Long, messageServerId: String, messageData: SaveMessageData): Long {
+        return lockableDatabase.execute(true) { database ->
+            val message = messageData.message
+
+            val existingMessageInfo = getMessage(folderId, messageServerId)
+            return@execute if (existingMessageInfo != null) {
+                val (existingMessageId, existingRootMessagePartId) = existingMessageInfo
+                replaceMessage(
+                    database,
+                    folderId,
+                    messageServerId,
+                    existingMessageId,
+                    existingRootMessagePartId,
+                    messageData
+                )
+
+                existingMessageId
+            } else {
+                insertMessage(database, folderId, messageServerId, message, messageData)
+            }
+        }
+    }
+
+    private fun insertMessage(
+        database: SQLiteDatabase,
+        folderId: Long,
+        messageServerId: String,
+        message: Message,
+        messageData: SaveMessageData
+    ): Long {
+        val threadInfo = threadMessageOperations.doMessageThreading(database, folderId, message.toThreadHeaders())
+
+        val rootMessagePartId = saveMessageParts(database, message)
+        val messageId = saveMessage(
+            database,
+            folderId,
+            messageServerId,
+            rootMessagePartId,
+            messageData,
+            replaceMessageId = threadInfo?.messageId
+        )
+
+        if (threadInfo?.threadId == null) {
+            threadMessageOperations.createThreadEntry(database, messageId, threadInfo?.rootId, threadInfo?.parentId)
+        }
+
+        createOrReplaceFulltextEntry(database, messageId, messageData)
+
+        return messageId
+    }
+
+    private fun replaceMessage(
+        database: SQLiteDatabase,
+        folderId: Long,
+        messageServerId: String,
+        existingMessageId: Long,
+        existingRootMessagePartId: Long?,
+        messageData: SaveMessageData
+    ) {
+        if (existingRootMessagePartId != null) {
+            deleteMessagePartsAndDataFromDisk(database, existingRootMessagePartId)
+        }
+
+        val rootMessagePartId = saveMessageParts(database, messageData.message)
+        val messageId = saveMessage(
+            database,
+            folderId,
+            messageServerId,
+            rootMessagePartId,
+            messageData,
+            replaceMessageId = existingMessageId
+        )
+
+        createOrReplaceFulltextEntry(database, messageId, messageData)
+    }
+
+    private fun saveMessageParts(database: SQLiteDatabase, message: Message): Long {
+        val rootPartContainer = PartContainer(parentId = null, part = message)
+        val rootId = saveMessagePart(database, rootPartContainer, rootId = null, order = 0)
+
+        val partsToSave = Stack<PartContainer>()
+        addChildrenToStack(partsToSave, part = message, parentId = rootId)
+
+        var order = 1
+        while (partsToSave.isNotEmpty()) {
+            val partContainer = partsToSave.pop()
+            val messagePartId = saveMessagePart(database, partContainer, rootId, order)
+            order++
+            addChildrenToStack(partsToSave, partContainer.part, parentId = messagePartId)
+        }
+
+        return rootId
+    }
+
+    private fun saveMessagePart(
+        database: SQLiteDatabase,
+        partContainer: PartContainer,
+        rootId: Long?,
+        order: Int
+    ): Long {
+        val part = partContainer.part
+        val values = ContentValues().apply {
+            put("root", rootId)
+            put("parent", partContainer.parentId ?: -1) // -1 for compatibility with previous code
+            put("seq", order)
+            put("server_extra", part.serverExtra)
+        }
+
+        return updateOrInsertMessagePart(database, values, part, existingMessagePartId = null)
+    }
+
+    private fun updateOrInsertMessagePart(
+        database: SQLiteDatabase,
+        values: ContentValues,
+        part: Part,
+        existingMessagePartId: Long?
+    ): Long {
+        val headerBytes = getHeaderBytes(part)
+        values.put("mime_type", part.mimeType)
+        values.put("header", headerBytes)
+        values.put("type", MessagePartType.UNKNOWN)
+
+        val file: File? = when (val body = part.body) {
+            is Multipart -> multipartToContentValues(values, body)
+            is Message -> messageMarkerToContentValues(values)
+            null -> missingPartToContentValues(values, part)
+            else -> leafPartToContentValues(values, part, body)
+        }
+
+        val messagePartId = if (existingMessagePartId != null) {
+            database.update("message_parts", values, "id = ?", arrayOf(existingMessagePartId.toString()))
+            existingMessagePartId
+        } else {
+            database.insertOrThrow("message_parts", null, values)
+        }
+
+        if (file != null) {
+            attachmentFileManager.moveTemporaryFile(file, messagePartId)
+        }
+
+        return messagePartId
+    }
+
+    private fun multipartToContentValues(values: ContentValues, multipart: Multipart): File? {
+        values.put("data_location", DataLocation.CHILD_PART_CONTAINS_DATA)
+        values.put("preamble", multipart.preamble)
+        values.put("epilogue", multipart.epilogue)
+        values.put("boundary", multipart.boundary)
+
+        return null
+    }
+
+    private fun messageMarkerToContentValues(cv: ContentValues): File? {
+        cv.put("data_location", DataLocation.CHILD_PART_CONTAINS_DATA)
+
+        return null
+    }
+
+    private fun missingPartToContentValues(values: ContentValues, part: Part): File? {
+        val partInfo = partInfoExtractor.extractPartInfo(part)
+        values.put("display_name", partInfo.displayName)
+        values.put("data_location", DataLocation.MISSING)
+        values.put("decoded_body_size", partInfo.size)
+
+        if (MimeUtility.isMultipart(part.mimeType)) {
+            values.put("boundary", BoundaryGenerator.getInstance().generateBoundary())
+        }
+
+        return null
+    }
+
+    private fun leafPartToContentValues(values: ContentValues, part: Part, body: Body): File? {
+        val displayName = partInfoExtractor.extractDisplayName(part)
+        values.put("display_name", displayName)
+
+        val encoding = getTransferEncoding(part)
+        values.put("encoding", encoding)
+        values.put("content_id", part.contentId)
+
+        check(body is SizeAware) { "Body needs to implement SizeAware" }
+        val sizeAwareBody = body as SizeAware
+        val fileSize = sizeAwareBody.size
+
+        return if (fileSize > MAX_BODY_SIZE_FOR_DATABASE) {
+            values.put("data_location", DataLocation.ON_DISK)
+            val file = writeBodyToDiskIfNecessary(part)
+            val size = decodeAndCountBytes(file, encoding, fileSize)
+            values.put("decoded_body_size", size)
+
+            file
+        } else {
+            values.put("data_location", DataLocation.IN_DATABASE)
+            val bodyData = getBodyBytes(body)
+            values.put("data", bodyData)
+            val size = decodeAndCountBytes(bodyData.inputStream(), encoding, bodyData.size.toLong())
+            values.put("decoded_body_size", size)
+
+            null
+        }
+    }
+
+    private fun writeBodyToDiskIfNecessary(part: Part): File? {
+        val body = part.body
+        return if (body is BinaryTempFileBody) {
+            body.file
+        } else {
+            writeBodyToDisk(body)
+        }
+    }
+
+    private fun writeBodyToDisk(body: Body): File? {
+        val file = File.createTempFile("body", null, BinaryTempFileBody.getTempDirectory())
+        FileOutputStream(file).use { outputStream ->
+            body.writeTo(outputStream)
+        }
+
+        return file
+    }
+
+    private fun decodeAndCountBytes(file: File?, encoding: String, fallbackValue: Long): Long {
+        return FileInputStream(file).use { inputStream ->
+            decodeAndCountBytes(inputStream, encoding, fallbackValue)
+        }
+    }
+
+    private fun decodeAndCountBytes(rawInputStream: InputStream, encoding: String, fallbackValue: Long): Long {
+        return try {
+            getDecodingInputStream(rawInputStream, encoding).use { decodingInputStream ->
+                CountingOutputStream().use { countingOutputStream ->
+                    IOUtils.copy(decodingInputStream, countingOutputStream)
+                    countingOutputStream.count
+                }
+            }
+        } catch (e: IOException) {
+            fallbackValue
+        }
+    }
+
+    private fun getDecodingInputStream(rawInputStream: InputStream, encoding: String?): InputStream {
+        return when (encoding) {
+            MimeUtil.ENC_BASE64 -> {
+                object : Base64InputStream(rawInputStream) {
+                    override fun close() {
+                        super.close()
+                        rawInputStream.close()
+                    }
+                }
+            }
+            MimeUtil.ENC_QUOTED_PRINTABLE -> {
+                object : QuotedPrintableInputStream(rawInputStream) {
+                    override fun close() {
+                        super.close()
+                        rawInputStream.close()
+                    }
+                }
+            }
+            else -> {
+                rawInputStream
+            }
+        }
+    }
+
+    private fun getHeaderBytes(part: Part): ByteArray {
+        val output = ByteArrayOutputStream()
+        part.writeHeaderTo(output)
+
+        return output.toByteArray()
+    }
+
+    private fun getBodyBytes(body: Body): ByteArray {
+        val output = ByteArrayOutputStream()
+        body.writeTo(output)
+
+        return output.toByteArray()
+    }
+
+    private fun getTransferEncoding(part: Part): String {
+        val contentTransferEncoding = part.getHeader(MimeHeader.HEADER_CONTENT_TRANSFER_ENCODING).firstOrNull()
+        return contentTransferEncoding?.lowercase() ?: MimeUtil.ENC_7BIT
+    }
+
+    private fun addChildrenToStack(stack: Stack<PartContainer>, part: Part, parentId: Long) {
+        when (val body = part.body) {
+            is Multipart -> {
+                for (i in body.count - 1 downTo 0) {
+                    val childPart = body.getBodyPart(i)
+                    stack.push(PartContainer(parentId, childPart))
+                }
+            }
+            is Message -> {
+                stack.push(PartContainer(parentId, body))
+            }
+        }
+    }
+
+    private fun saveMessage(
+        database: SQLiteDatabase,
+        folderId: Long,
+        messageServerId: String,
+        rootMessagePartId: Long,
+        messageData: SaveMessageData,
+        replaceMessageId: Long?
+    ): Long {
+        val message = messageData.message
+
+        when (messageData.downloadState) {
+            MessageDownloadState.ENVELOPE -> Unit
+            MessageDownloadState.PARTIAL -> message.setFlag(Flag.X_DOWNLOADED_PARTIAL, true)
+            MessageDownloadState.FULL -> message.setFlag(Flag.X_DOWNLOADED_FULL, true)
+        }
+
+        val values = ContentValues().apply {
+            put("folder_id", folderId)
+            put("uid", messageServerId)
+            put("deleted", 0)
+            put("empty", 0)
+            put("message_part_id", rootMessagePartId)
+            put("date", messageData.date)
+            put("internal_date", messageData.internalDate)
+            put("subject", messageData.subject)
+            put("flags", message.flags.toDatabaseValue())
+            put("read", message.isSet(Flag.SEEN).toDatabaseValue())
+            put("flagged", message.isSet(Flag.FLAGGED).toDatabaseValue())
+            put("answered", message.isSet(Flag.ANSWERED).toDatabaseValue())
+            put("forwarded", message.isSet(Flag.FORWARDED).toDatabaseValue())
+            put("sender_list", Address.pack(message.from))
+            put("to_list", Address.pack(message.getRecipients(RecipientType.TO)))
+            put("cc_list", Address.pack(message.getRecipients(RecipientType.CC)))
+            put("bcc_list", Address.pack(message.getRecipients(RecipientType.BCC)))
+            put("reply_to_list", Address.pack(message.replyTo))
+            put("attachment_count", messageData.attachmentCount)
+            put("message_id", message.messageId)
+            put("mime_type", message.mimeType)
+            put("encryption_type", messageData.encryptionType)
+
+            val previewResult = messageData.previewResult
+            put("preview_type", previewResult.previewType.toDatabaseValue())
+            if (previewResult.isPreviewTextAvailable) {
+                put("preview", previewResult.previewText)
+            } else {
+                putNull("preview")
+            }
+        }
+
+        return if (replaceMessageId != null) {
+            values.put("id", replaceMessageId)
+            database.replace("messages", null, values)
+            replaceMessageId
+        } else {
+            database.insert("messages", null, values)
+        }
+    }
+
+    private fun createOrReplaceFulltextEntry(database: SQLiteDatabase, messageId: Long, messageData: SaveMessageData) {
+        val fulltext = messageData.textForSearchIndex ?: return
+
+        val values = ContentValues().apply {
+            put("docid", messageId)
+            put("fulltext", fulltext)
+        }
+
+        database.replace("messages_fulltext", null, values)
+    }
+
+    private fun getMessage(folderId: Long, messageServerId: String): Pair<Long, Long?>? {
+        return lockableDatabase.execute(false) { db ->
+            db.query(
+                "messages",
+                arrayOf("id", "message_part_id"),
+                "folder_id = ? AND uid = ?",
+                arrayOf(folderId.toString(), messageServerId),
+                null,
+                null,
+                null
+            ).use { cursor ->
+                if (cursor.moveToFirst()) {
+                    val messageId = cursor.getLong(0)
+                    val messagePartId = cursor.getLong(1)
+                    messageId to messagePartId
+                } else {
+                    null
+                }
+            }
+        }
+    }
+
+    private fun getLocalMessageInfo(folderId: Long, messageId: Long): Pair<String, Long?> {
+        return lockableDatabase.execute(false) { db ->
+            db.query(
+                "messages",
+                arrayOf("uid", "message_part_id"),
+                "folder_id = ? AND id = ?",
+                arrayOf(folderId.toString(), messageId.toString()),
+                null,
+                null,
+                null
+            ).use { cursor ->
+                if (!cursor.moveToFirst()) error("Local message not found $folderId:$messageId")
+
+                val messageServerId = cursor.getString(0)!!
+                val messagePartId = cursor.getLong(1)
+                messageServerId to messagePartId
+            }
+        }
+    }
+
+    private fun deleteMessagePartsAndDataFromDisk(database: SQLiteDatabase, rootMessagePartId: Long) {
+        deleteMessageDataFromDisk(database, rootMessagePartId)
+        deleteMessageParts(database, rootMessagePartId)
+    }
+
+    private fun deleteMessageDataFromDisk(database: SQLiteDatabase, rootMessagePartId: Long) {
+        database.query(
+            "message_parts",
+            arrayOf("id"),
+            "root = ? AND data_location = " + DataLocation.ON_DISK,
+            arrayOf(rootMessagePartId.toString()),
+            null,
+            null,
+            null
+        ).use { cursor ->
+            while (cursor.moveToNext()) {
+                val messagePartId = cursor.getLong(0)
+                attachmentFileManager.deleteFile(messagePartId)
+            }
+        }
+    }
+
+    private fun deleteMessageParts(database: SQLiteDatabase, rootMessagePartId: Long) {
+        database.delete("message_parts", "root = ?", arrayOf(rootMessagePartId.toString()))
+    }
+}
+
+private fun Set<Flag>.toDatabaseValue(): String {
+    return this
+        .filter { it !in SPECIAL_FLAGS }
+        .joinToString(separator = ",")
+}
+
+private fun Boolean.toDatabaseValue() = if (this) 1 else 0
+
+private fun PreviewType.toDatabaseValue(): String {
+    return DatabasePreviewType.fromPreviewType(this).databaseValue
+}
+
+// Note: The contents of the 'message_parts' table depend on these values.
+// TODO: currently unused, might be used for caching at a later point
+internal object MessagePartType {
+    const val UNKNOWN = 0
+}
+
+// Note: The contents of the 'message_parts' table depend on these values.
+internal object DataLocation {
+    const val MISSING = 0
+    const val IN_DATABASE = 1
+    const val ON_DISK = 2
+    const val CHILD_PART_CONTAINS_DATA = 3
+}
+
+private data class PartContainer(val parentId: Long?, val part: Part)

app/storage/src/main/java/com/fsck/k9/storage/messages/ThreadMessageOperations.kt

@@ -0,0 +1,223 @@
+package com.fsck.k9.storage.messages
+
+import android.content.ContentValues
+import android.database.sqlite.SQLiteDatabase
+import com.fsck.k9.helper.Utility
+import com.fsck.k9.mail.Message
+import com.fsck.k9.mail.message.MessageHeaderParser
+
+internal class ThreadMessageOperations {
+
+    fun createOrUpdateParentThreadEntries(
+        database: SQLiteDatabase,
+        messageId: Long,
+        destinationFolderId: Long
+    ): ThreadInfo? {
+        val threadHeaders = getMessageThreadHeaders(database, messageId)
+        return doMessageThreading(database, destinationFolderId, threadHeaders)
+    }
+
+    fun getMessageThreadHeaders(database: SQLiteDatabase, messageId: Long): ThreadHeaders {
+        return database.rawQuery(
+            """
+SELECT messages.message_id, message_parts.header 
+FROM messages 
+LEFT JOIN message_parts ON (messages.message_part_id = message_parts.id) 
+WHERE messages.id = ?
+            """,
+            arrayOf(messageId.toString())
+        ).use { cursor ->
+            if (!cursor.moveToFirst()) error("Message not found: $messageId")
+
+            val messageIdHeader = cursor.getString(0)
+            val headerBytes = cursor.getBlob(1)
+
+            var inReplyToHeader: String? = null
+            var referencesHeader: String? = null
+            if (headerBytes != null) {
+                MessageHeaderParser.parse(headerBytes.inputStream()) { name, value ->
+                    when (name.lowercase()) {
+                        "in-reply-to" -> inReplyToHeader = value
+                        "references" -> referencesHeader = value
+                    }
+                }
+            }
+
+            ThreadHeaders(messageIdHeader, inReplyToHeader, referencesHeader)
+        }
+    }
+
+    fun createThreadEntryIfNecessary(database: SQLiteDatabase, messageId: Long, threadInfo: ThreadInfo?) {
+        if (threadInfo?.threadId == null) {
+            createThreadEntry(database, messageId, threadInfo?.rootId, threadInfo?.parentId)
+        }
+    }
+
+    fun createThreadEntry(database: SQLiteDatabase, messageId: Long, rootId: Long?, parentId: Long?): Long {
+        val values = ContentValues().apply {
+            put("message_id", messageId)
+            put("root", rootId)
+            put("parent", parentId)
+        }
+
+        return database.insert("threads", null, values)
+    }
+
+    // TODO: Use MessageIdParser
+    fun doMessageThreading(database: SQLiteDatabase, folderId: Long, threadHeaders: ThreadHeaders): ThreadInfo? {
+        val messageIdHeader = threadHeaders.messageIdHeader
+        val msgThreadInfo = getThreadInfo(database, folderId, messageIdHeader, onlyEmpty = true)
+
+        val references = threadHeaders.referencesHeader.extractMessageIdValues()
+        val inReplyTo = threadHeaders.inReplyToHeader.extractMessageIdValue()
+
+        val messageIdValues = if (inReplyTo == null || inReplyTo in references) {
+            references
+        } else {
+            references + inReplyTo
+        }
+
+        if (messageIdValues.isEmpty()) {
+            // This is not a reply, nothing to do for us.
+            return msgThreadInfo
+        }
+
+        var rootId: Long? = null
+        var parentId: Long? = null
+        for (reference in messageIdValues) {
+            val threadInfo = getThreadInfo(database, folderId, reference, onlyEmpty = false)
+            if (threadInfo == null) {
+                parentId = createEmptyMessage(database, folderId, reference, rootId, parentId)
+                if (rootId == null) {
+                    rootId = parentId
+                }
+            } else {
+                if (rootId == null) {
+                    rootId = threadInfo.rootId
+                } else if (threadInfo.rootId != rootId) {
+                    // Merge this thread into our thread
+                    updateThreadToNewRoot(database, threadInfo.rootId, rootId, parentId)
+                }
+                parentId = threadInfo.threadId
+            }
+        }
+
+        msgThreadInfo?.threadId?.let { threadId ->
+            // msgThreadInfo.rootId might be outdated. Fetch current value.
+            val oldRootId = getThreadRoot(database, threadId)
+            if (oldRootId != rootId) {
+                // Connect the existing thread to the newly created thread
+                updateThreadToNewRoot(database, oldRootId, rootId!!, parentId)
+            }
+        }
+
+        return ThreadInfo(msgThreadInfo?.threadId, msgThreadInfo?.messageId, rootId!!, parentId)
+    }
+
+    private fun updateThreadToNewRoot(database: SQLiteDatabase, oldRootId: Long, rootId: Long, parentId: Long?) {
+        // Let all children know who's the new root
+        val values = ContentValues()
+        values.put("root", rootId)
+        database.update("threads", values, "root = ?", arrayOf(oldRootId.toString()))
+
+        // Connect the message to the current parent
+        values.put("parent", parentId)
+        database.update("threads", values, "id = ?", arrayOf(oldRootId.toString()))
+    }
+
+    private fun createEmptyMessage(
+        database: SQLiteDatabase,
+        folderId: Long,
+        messageIdHeader: String,
+        rootId: Long?,
+        parentId: Long?
+    ): Long {
+        val messageValues = ContentValues().apply {
+            put("message_id", messageIdHeader)
+            put("folder_id", folderId)
+            put("empty", 1)
+        }
+        val messageId = database.insert("messages", null, messageValues)
+
+        val threadValues = ContentValues().apply {
+            put("message_id", messageId)
+            put("root", rootId)
+            put("parent", parentId)
+        }
+        return database.insert("threads", null, threadValues)
+    }
+
+    private fun getThreadInfo(
+        db: SQLiteDatabase,
+        folderId: Long,
+        messageIdHeader: String?,
+        onlyEmpty: Boolean
+    ): ThreadInfo? {
+        if (messageIdHeader == null) return null
+
+        return db.rawQuery(
+            """
+SELECT t.id, t.message_id, t.root, t.parent 
+FROM messages m 
+LEFT JOIN threads t ON (t.message_id = m.id) 
+WHERE m.folder_id = ? AND m.message_id = ? 
+${if (onlyEmpty) "AND m.empty = 1 " else ""}
+ORDER BY m.id 
+LIMIT 1
+            """,
+            arrayOf(folderId.toString(), messageIdHeader)
+        ).use { cursor ->
+            if (cursor.moveToFirst()) {
+                val threadId = cursor.getLong(0)
+                val messageId = cursor.getLong(1)
+                val rootId = cursor.getLong(2)
+                val parentId = if (cursor.isNull(3)) null else cursor.getLong(3)
+                ThreadInfo(threadId, messageId, rootId, parentId)
+            } else {
+                null
+            }
+        }
+    }
+
+    private fun getThreadRoot(database: SQLiteDatabase, threadId: Long): Long {
+        return database.rawQuery(
+            "SELECT root FROM threads WHERE id = ?",
+            arrayOf(threadId.toString())
+        ).use { cursor ->
+            if (cursor.moveToFirst()) {
+                cursor.getLong(0)
+            } else {
+                error("Thread with ID $threadId not found")
+            }
+        }
+    }
+
+    private fun String?.extractMessageIdValues(): List<String> {
+        return this?.let { headerValue -> Utility.extractMessageIds(headerValue) } ?: emptyList()
+    }
+
+    private fun String?.extractMessageIdValue(): String? {
+        return this?.let { headerValue -> Utility.extractMessageId(headerValue) }
+    }
+}
+
+internal data class ThreadInfo(
+    val threadId: Long?,
+    val messageId: Long?,
+    val rootId: Long,
+    val parentId: Long?
+)
+
+internal data class ThreadHeaders(
+    val messageIdHeader: String?,
+    val inReplyToHeader: String?,
+    val referencesHeader: String?
+)
+
+internal fun Message.toThreadHeaders(): ThreadHeaders {
+    return ThreadHeaders(
+        messageIdHeader = messageId,
+        inReplyToHeader = getHeader("In-Reply-To").firstOrNull(),
+        referencesHeader = getHeader("References").firstOrNull()
+    )
+}

app/storage/src/main/java/com/fsck/k9/storage/messages/UpdateFolderOperations.kt

@@ -0,0 +1,105 @@
+package com.fsck.k9.storage.messages
+
+import android.content.ContentValues
+import com.fsck.k9.mail.FolderClass
+import com.fsck.k9.mail.FolderType
+import com.fsck.k9.mailstore.FolderDetails
+import com.fsck.k9.mailstore.LockableDatabase
+import com.fsck.k9.mailstore.MoreMessages
+import com.fsck.k9.mailstore.toDatabaseFolderType
+
+internal class UpdateFolderOperations(private val lockableDatabase: LockableDatabase) {
+    fun changeFolder(folderServerId: String, name: String, type: FolderType) {
+        lockableDatabase.execute(false) { db ->
+            val values = ContentValues().apply {
+                put("name", name)
+                put("type", type.toDatabaseFolderType())
+            }
+
+            db.update("folders", values, "server_id = ?", arrayOf(folderServerId))
+        }
+    }
+
+    fun updateFolderSettings(folderDetails: FolderDetails) {
+        lockableDatabase.execute(false) { db ->
+            val contentValues = ContentValues().apply {
+                put("top_group", folderDetails.isInTopGroup)
+                put("integrate", folderDetails.isIntegrate)
+                put("poll_class", folderDetails.syncClass.name)
+                put("display_class", folderDetails.displayClass.name)
+                put("notify_class", folderDetails.notifyClass.name)
+                put("push_class", folderDetails.pushClass.name)
+            }
+
+            db.update("folders", contentValues, "id = ?", arrayOf(folderDetails.folder.id.toString()))
+        }
+    }
+
+    fun setIncludeInUnifiedInbox(folderId: Long, includeInUnifiedInbox: Boolean) {
+        lockableDatabase.execute(false) { db ->
+            val contentValues = ContentValues().apply {
+                put("integrate", includeInUnifiedInbox)
+            }
+
+            db.update("folders", contentValues, "id = ?", arrayOf(folderId.toString()))
+        }
+    }
+
+    fun setDisplayClass(folderId: Long, folderClass: FolderClass) {
+        setString(folderId = folderId, columnName = "display_class", value = folderClass.name)
+    }
+
+    fun setSyncClass(folderId: Long, folderClass: FolderClass) {
+        setString(folderId = folderId, columnName = "poll_class", value = folderClass.name)
+    }
+
+    fun setPushClass(folderId: Long, folderClass: FolderClass) {
+        setString(folderId = folderId, columnName = "push_class", value = folderClass.name)
+    }
+
+    fun setNotificationClass(folderId: Long, folderClass: FolderClass) {
+        setString(folderId = folderId, columnName = "notify_class", value = folderClass.name)
+    }
+
+    fun setMoreMessages(folderId: Long, moreMessages: MoreMessages) {
+        setString(folderId = folderId, columnName = "more_messages", value = moreMessages.databaseName)
+    }
+
+    fun setLastChecked(folderId: Long, timestamp: Long) {
+        lockableDatabase.execute(false) { db ->
+            val contentValues = ContentValues().apply {
+                put("last_updated", timestamp)
+            }
+
+            db.update("folders", contentValues, "id = ?", arrayOf(folderId.toString()))
+        }
+    }
+
+    fun setStatus(folderId: Long, status: String?) {
+        setString(folderId = folderId, columnName = "status", value = status)
+    }
+
+    fun setVisibleLimit(folderId: Long, visibleLimit: Int) {
+        lockableDatabase.execute(false) { db ->
+            val contentValues = ContentValues().apply {
+                put("visible_limit", visibleLimit)
+            }
+
+            db.update("folders", contentValues, "id = ?", arrayOf(folderId.toString()))
+        }
+    }
+
+    private fun setString(folderId: Long, columnName: String, value: String?) {
+        lockableDatabase.execute(false) { db ->
+            val contentValues = ContentValues().apply {
+                if (value == null) {
+                    putNull(columnName)
+                } else {
+                    put(columnName, value)
+                }
+            }
+
+            db.update("folders", contentValues, "id = ?", arrayOf(folderId.toString()))
+        }
+    }
+}

app/storage/src/main/java/com/fsck/k9/storage/messages/UpdateMessageOperations.kt

@@ -0,0 +1,28 @@
+package com.fsck.k9.storage.messages
+
+import android.content.ContentValues
+import com.fsck.k9.mailstore.LockableDatabase
+
+internal class UpdateMessageOperations(private val lockableDatabase: LockableDatabase) {
+
+    fun setNewMessageState(folderId: Long, messageServerId: String, newMessage: Boolean) {
+        lockableDatabase.execute(false) { database ->
+            val values = ContentValues().apply {
+                put("new_message", if (newMessage) 1 else 0)
+            }
+
+            database.update(
+                "messages",
+                values,
+                "folder_id = ? AND uid = ?",
+                arrayOf(folderId.toString(), messageServerId)
+            )
+        }
+    }
+
+    fun clearNewMessageState() {
+        lockableDatabase.execute(false) { database ->
+            database.execSQL("UPDATE messages SET new_message = 0")
+        }
+    }
+}

app/storage/src/main/java/com/fsck/k9/storage/migrations/LegacyPendingAppend.java

@@ -0,0 +1,6 @@
+package com.fsck.k9.storage.migrations;
+
+class LegacyPendingAppend extends LegacyPendingCommand {
+    public String folder;
+    public String uid;
+}

app/storage/src/main/java/com/fsck/k9/storage/migrations/LegacyPendingCommand.java

@@ -0,0 +1,4 @@
+package com.fsck.k9.storage.migrations;
+
+abstract class LegacyPendingCommand {
+}

app/storage/src/main/java/com/fsck/k9/storage/migrations/LegacyPendingDelete.java

@@ -0,0 +1,24 @@
+package com.fsck.k9.storage.migrations;
+
+import java.util.List;
+
+import static com.fsck.k9.controller.Preconditions.requireNotNull;
+import static com.fsck.k9.controller.Preconditions.requireValidUids;
+
+
+class LegacyPendingDelete extends LegacyPendingCommand {
+    public final String folder;
+    public final List<String> uids;
+
+
+    static LegacyPendingDelete create(String folder, List<String> uids) {
+        requireNotNull(folder);
+        requireValidUids(uids);
+        return new LegacyPendingDelete(folder, uids);
+    }
+
+    private LegacyPendingDelete(String folder, List<String> uids) {
+        this.folder = folder;
+        this.uids = uids;
+    }
+}

app/storage/src/main/java/com/fsck/k9/storage/migrations/LegacyPendingExpunge.java

@@ -0,0 +1,5 @@
+package com.fsck.k9.storage.migrations;
+
+class LegacyPendingExpunge extends LegacyPendingCommand {
+    public String folder;
+}

app/storage/src/main/java/com/fsck/k9/storage/migrations/LegacyPendingMarkAllAsRead.java

@@ -0,0 +1,5 @@
+package com.fsck.k9.storage.migrations;
+
+class LegacyPendingMarkAllAsRead extends LegacyPendingCommand {
+    public String folder;
+}

app/storage/src/main/java/com/fsck/k9/storage/migrations/LegacyPendingMoveAndMarkAsRead.java

@@ -0,0 +1,9 @@
+package com.fsck.k9.storage.migrations;
+
+import java.util.Map;
+
+class LegacyPendingMoveAndMarkAsRead extends LegacyPendingCommand {
+    public String srcFolder;
+    public String destFolder;
+    public Map<String, String> newUidMap;
+}

app/storage/src/main/java/com/fsck/k9/storage/migrations/LegacyPendingMoveOrCopy.java

@@ -0,0 +1,10 @@
+package com.fsck.k9.storage.migrations;
+
+import java.util.Map;
+
+class LegacyPendingMoveOrCopy extends LegacyPendingCommand {
+    public String srcFolder;
+    public String destFolder;
+    public boolean isCopy;
+    public Map<String, String> newUidMap;
+}

app/storage/src/main/java/com/fsck/k9/storage/migrations/LegacyPendingSetFlag.java

@@ -0,0 +1,12 @@
+package com.fsck.k9.storage.migrations;
+
+import com.fsck.k9.mail.Flag;
+
+import java.util.List;
+
+class LegacyPendingSetFlag extends LegacyPendingCommand {
+    public String folder;
+    public boolean newState;
+    public Flag flag;
+    public List<String> uids;
+}

app/storage/src/main/java/com/fsck/k9/storage/migrations/MigrationTo62.java

@@ -0,0 +1,15 @@
+package com.fsck.k9.storage.migrations;
+
+
+import android.database.sqlite.SQLiteDatabase;
+
+
+class MigrationTo62 {
+    public static void addServerIdColumnToFoldersTable(SQLiteDatabase db) {
+        db.execSQL("ALTER TABLE folders ADD server_id TEXT");
+        db.execSQL("UPDATE folders SET server_id = name");
+
+        db.execSQL("DROP INDEX IF EXISTS folder_name");
+        db.execSQL("CREATE INDEX folder_server_id ON folders (server_id)");
+    }
+}

app/storage/src/main/java/com/fsck/k9/storage/migrations/MigrationTo64.kt

@@ -0,0 +1,34 @@
+package com.fsck.k9.storage.migrations
+
+import android.database.sqlite.SQLiteDatabase
+
+internal object MigrationTo64 {
+    @JvmStatic
+    fun addExtraValuesTables(db: SQLiteDatabase) {
+        db.execSQL(
+            "CREATE TABLE account_extra_values (" +
+                "name TEXT NOT NULL PRIMARY KEY, " +
+                "value_text TEXT, " +
+                "value_integer INTEGER " +
+                ")"
+        )
+
+        db.execSQL(
+            "CREATE TABLE folder_extra_values (" +
+                "folder_id INTEGER NOT NULL, " +
+                "name TEXT NOT NULL, " +
+                "value_text TEXT, " +
+                "value_integer INTEGER, " +
+                "PRIMARY KEY (folder_id, name)" +
+                ")"
+        )
+
+        db.execSQL(
+            "CREATE TRIGGER delete_folder_extra_values " +
+                "BEFORE DELETE ON folders " +
+                "BEGIN " +
+                "DELETE FROM folder_extra_values WHERE old.id = folder_id; " +
+                "END;"
+        )
+    }
+}

app/storage/src/main/java/com/fsck/k9/storage/migrations/MigrationTo65.kt

@@ -0,0 +1,22 @@
+package com.fsck.k9.storage.migrations
+
+import android.database.sqlite.SQLiteDatabase
+import com.fsck.k9.mailstore.MigrationsHelper
+import com.fsck.k9.preferences.Protocols
+
+internal object MigrationTo65 {
+    @JvmStatic
+    fun addLocalOnlyColumnToFoldersTable(db: SQLiteDatabase, migrationsHelper: MigrationsHelper) {
+        db.execSQL("ALTER TABLE folders ADD local_only INTEGER")
+
+        if (isPop3Account(migrationsHelper)) {
+            db.execSQL("UPDATE folders SET local_only = CASE server_id WHEN 'INBOX' THEN 0 ELSE 1 END")
+        } else {
+            db.execSQL("UPDATE folders SET local_only = CASE server_id WHEN 'K9MAIL_INTERNAL_OUTBOX' THEN 1 ELSE 0 END")
+        }
+    }
+
+    private fun isPop3Account(migrationsHelper: MigrationsHelper): Boolean {
+        return migrationsHelper.account.incomingServerSettings.type == Protocols.POP3
+    }
+}

app/storage/src/main/java/com/fsck/k9/storage/migrations/MigrationTo66.kt

@@ -0,0 +1,12 @@
+package com.fsck.k9.storage.migrations
+
+import android.database.sqlite.SQLiteDatabase
+
+internal object MigrationTo66 {
+    @JvmStatic
+    fun addEncryptionTypeColumnToMessagesTable(db: SQLiteDatabase) {
+        db.execSQL("ALTER TABLE messages ADD encryption_type TEXT")
+
+        db.execSQL("UPDATE messages SET encryption_type = 'openpgp' WHERE preview_type = 'encrypted'")
+    }
+}

app/storage/src/main/java/com/fsck/k9/storage/migrations/MigrationTo67.kt

@@ -0,0 +1,26 @@
+package com.fsck.k9.storage.migrations
+
+import android.database.sqlite.SQLiteDatabase
+import com.fsck.k9.mailstore.MigrationsHelper
+
+internal object MigrationTo67 {
+    @JvmStatic
+    fun addTypeColumnToFoldersTable(db: SQLiteDatabase, migrationsHelper: MigrationsHelper) {
+        db.execSQL("ALTER TABLE folders ADD type TEXT DEFAULT \"regular\"")
+
+        val account = migrationsHelper.account
+        setFolderType(db, account.legacyInboxFolder, "inbox")
+        setFolderType(db, "K9MAIL_INTERNAL_OUTBOX", "outbox")
+        setFolderType(db, account.importedTrashFolder, "trash")
+        setFolderType(db, account.importedDraftsFolder, "drafts")
+        setFolderType(db, account.importedSpamFolder, "spam")
+        setFolderType(db, account.importedSentFolder, "sent")
+        setFolderType(db, account.importedArchiveFolder, "archive")
+    }
+
+    private fun setFolderType(db: SQLiteDatabase, serverId: String?, type: String) {
+        if (serverId != null) {
+            db.execSQL("UPDATE folders SET type = ? WHERE server_id = ?", arrayOf(type, serverId))
+        }
+    }
+}

app/storage/src/main/java/com/fsck/k9/storage/migrations/MigrationTo68.kt

@@ -0,0 +1,33 @@
+package com.fsck.k9.storage.migrations
+
+import android.database.sqlite.SQLiteDatabase
+
+internal object MigrationTo68 {
+    @JvmStatic
+    fun addOutboxStateTable(db: SQLiteDatabase) {
+        createOutboxStateTable(db)
+        createOutboxStateEntries(db)
+    }
+
+    private fun createOutboxStateTable(db: SQLiteDatabase) {
+        db.execSQL(
+            "CREATE TABLE outbox_state (" +
+                "message_id INTEGER PRIMARY KEY NOT NULL REFERENCES messages(id) ON DELETE CASCADE," +
+                "send_state TEXT," +
+                "number_of_send_attempts INTEGER DEFAULT 0," +
+                "error_timestamp INTEGER DEFAULT 0," +
+                "error TEXT)"
+        )
+    }
+
+    private fun createOutboxStateEntries(db: SQLiteDatabase) {
+        db.execSQL(
+            """
+            INSERT INTO outbox_state (message_id, send_state)
+              SELECT messages.id, 'ready' FROM folders
+                JOIN messages ON (folders.id = messages.folder_id)
+                WHERE folders.server_id = 'K9MAIL_INTERNAL_OUTBOX'
+            """.trimIndent()
+        )
+    }
+}

app/storage/src/main/java/com/fsck/k9/storage/migrations/MigrationTo69.kt

@@ -0,0 +1,39 @@
+package com.fsck.k9.storage.migrations
+
+import android.content.ContentValues
+import android.database.sqlite.SQLiteDatabase
+import com.fsck.k9.mail.Flag
+import com.squareup.moshi.Moshi
+
+internal class MigrationTo69(private val db: SQLiteDatabase) {
+    fun createPendingDelete() {
+        val moshi = Moshi.Builder().build()
+        val pendingSetFlagAdapter = moshi.adapter(LegacyPendingSetFlag::class.java)
+
+        val pendingSetFlagsToConvert = mutableMapOf<Long, LegacyPendingSetFlag>()
+
+        db.rawQuery("SELECT id, data FROM pending_commands WHERE command = 'set_flag'", null).use { cursor ->
+            while (cursor.moveToNext()) {
+                val databaseId = cursor.getLong(0)
+                val data = cursor.getString(1)
+
+                val pendingSetFlag = pendingSetFlagAdapter.fromJson(data) ?: error("Can't deserialize pending command")
+                if (pendingSetFlag.flag == Flag.DELETED && pendingSetFlag.newState) {
+                    pendingSetFlagsToConvert[databaseId] = pendingSetFlag
+                }
+            }
+        }
+
+        val pendingDeleteAdapter = moshi.adapter(LegacyPendingDelete::class.java)
+
+        for ((databaseId, pendingSetFlag) in pendingSetFlagsToConvert) {
+            val pendingDelete = LegacyPendingDelete.create(pendingSetFlag.folder, pendingSetFlag.uids)
+            val contentValues = ContentValues().apply {
+                put("command", "delete")
+                put("data", pendingDeleteAdapter.toJson(pendingDelete))
+            }
+
+            db.update("pending_commands", contentValues, "id = ?", arrayOf(databaseId.toString()))
+        }
+    }
+}

app/storage/src/main/java/com/fsck/k9/storage/migrations/MigrationTo70.kt

@@ -0,0 +1,93 @@
+package com.fsck.k9.storage.migrations
+
+import android.database.sqlite.SQLiteDatabase
+import com.fsck.k9.mail.FolderClass
+
+internal class MigrationTo70(private val db: SQLiteDatabase) {
+    fun removePushState() {
+        renameFoldersTable()
+        createNewFoldersTable()
+        copyFoldersData()
+        dropOldFoldersTable()
+        recreateFoldersIndex()
+        recreateFoldersTriggers()
+    }
+
+    private fun renameFoldersTable() {
+        db.execSQL("ALTER TABLE folders RENAME TO folders_old")
+    }
+
+    private fun createNewFoldersTable() {
+        db.execSQL(
+            "CREATE TABLE folders (" +
+                "id INTEGER PRIMARY KEY," +
+                "name TEXT, " +
+                "last_updated INTEGER, " +
+                "unread_count INTEGER, " +
+                "visible_limit INTEGER, " +
+                "status TEXT, " +
+                "flagged_count INTEGER default 0, " +
+                "integrate INTEGER, " +
+                "top_group INTEGER, " +
+                "poll_class TEXT, " +
+                "push_class TEXT, " +
+                "display_class TEXT, " +
+                "notify_class TEXT default '" + FolderClass.INHERITED.name + "', " +
+                "more_messages TEXT default \"unknown\", " +
+                "server_id TEXT, " +
+                "local_only INTEGER, " +
+                "type TEXT DEFAULT \"regular\"" +
+                ")"
+        )
+    }
+
+    private fun copyFoldersData() {
+        db.execSQL(
+            """
+            INSERT INTO folders 
+            SELECT 
+                id,
+                name,
+                last_updated, 
+                unread_count,
+                visible_limit,
+                status,
+                flagged_count,
+                integrate,
+                top_group,
+                poll_class,
+                push_class,
+                display_class,
+                notify_class,
+                more_messages,
+                server_id,
+                local_only,
+                type
+            FROM folders_old 
+            """.trimIndent()
+        )
+    }
+
+    private fun dropOldFoldersTable() {
+        db.execSQL("DROP TABLE folders_old")
+    }
+
+    private fun recreateFoldersIndex() {
+        db.execSQL("DROP INDEX IF EXISTS folder_server_id")
+        db.execSQL("CREATE INDEX folder_server_id ON folders (server_id)")
+    }
+
+    private fun recreateFoldersTriggers() {
+        db.execSQL("DROP TRIGGER IF EXISTS delete_folder")
+        db.execSQL("CREATE TRIGGER delete_folder BEFORE DELETE ON folders BEGIN DELETE FROM messages WHERE old.id = folder_id; END;")
+
+        db.execSQL("DROP TRIGGER IF EXISTS delete_folder_extra_values")
+        db.execSQL(
+            "CREATE TRIGGER delete_folder_extra_values " +
+                "BEFORE DELETE ON folders " +
+                "BEGIN " +
+                "DELETE FROM folder_extra_values WHERE old.id = folder_id; " +
+                "END;"
+        )
+    }
+}

app/storage/src/main/java/com/fsck/k9/storage/migrations/MigrationTo71.kt

@@ -0,0 +1,24 @@
+package com.fsck.k9.storage.migrations
+
+import android.database.sqlite.SQLiteDatabase
+
+internal class MigrationTo71(private val db: SQLiteDatabase) {
+    fun cleanUpFolderClass() {
+        db.execSQL(
+            "UPDATE folders SET poll_class = 'NO_CLASS' " +
+                "WHERE poll_class NOT IN ('NO_CLASS', 'INHERITED', 'FIRST_CLASS', 'SECOND_CLASS')"
+        )
+        db.execSQL(
+            "UPDATE folders SET push_class = 'NO_CLASS' " +
+                "WHERE push_class NOT IN ('NO_CLASS', 'INHERITED', 'FIRST_CLASS', 'SECOND_CLASS')"
+        )
+        db.execSQL(
+            "UPDATE folders SET display_class = 'NO_CLASS' " +
+                "WHERE display_class NOT IN ('NO_CLASS', 'INHERITED', 'FIRST_CLASS', 'SECOND_CLASS')"
+        )
+        db.execSQL(
+            "UPDATE folders SET notify_class = 'NO_CLASS' " +
+                "WHERE notify_class NOT IN ('NO_CLASS', 'INHERITED', 'FIRST_CLASS', 'SECOND_CLASS')"
+        )
+    }
+}

app/storage/src/main/java/com/fsck/k9/storage/migrations/MigrationTo72.kt

@@ -0,0 +1,10 @@
+package com.fsck.k9.storage.migrations
+
+import android.database.sqlite.SQLiteDatabase
+
+internal class MigrationTo72(private val db: SQLiteDatabase) {
+    fun createMessagePartsRootIndex() {
+        db.execSQL("DROP INDEX IF EXISTS message_parts_root")
+        db.execSQL("CREATE INDEX IF NOT EXISTS message_parts_root ON message_parts (root)")
+    }
+}

app/storage/src/main/java/com/fsck/k9/storage/migrations/MigrationTo73.kt

@@ -0,0 +1,169 @@
+package com.fsck.k9.storage.migrations
+
+import android.content.ContentValues
+import android.database.sqlite.SQLiteDatabase
+import app.k9mail.core.android.common.database.map
+import com.fsck.k9.controller.MessagingControllerCommands.PendingAppend
+import com.fsck.k9.controller.MessagingControllerCommands.PendingCommand
+import com.fsck.k9.controller.MessagingControllerCommands.PendingDelete
+import com.fsck.k9.controller.MessagingControllerCommands.PendingExpunge
+import com.fsck.k9.controller.MessagingControllerCommands.PendingMarkAllAsRead
+import com.fsck.k9.controller.MessagingControllerCommands.PendingMoveAndMarkAsRead
+import com.fsck.k9.controller.MessagingControllerCommands.PendingMoveOrCopy
+import com.fsck.k9.controller.MessagingControllerCommands.PendingSetFlag
+import com.fsck.k9.controller.PendingCommandSerializer
+import com.squareup.moshi.Moshi
+import timber.log.Timber
+
+internal class MigrationTo73(private val db: SQLiteDatabase) {
+    private val serializer = PendingCommandSerializer.getInstance()
+    private val moshi = Moshi.Builder().build()
+    private val legacyAdapters = listOf(
+        "append" to moshi.adapter(LegacyPendingAppend::class.java),
+        "mark_all_as_read" to moshi.adapter(LegacyPendingMarkAllAsRead::class.java),
+        "set_flag" to moshi.adapter(LegacyPendingSetFlag::class.java),
+        "delete" to moshi.adapter(LegacyPendingDelete::class.java),
+        "expunge" to moshi.adapter(LegacyPendingExpunge::class.java),
+        "move_or_copy" to moshi.adapter(LegacyPendingMoveOrCopy::class.java),
+        "move_and_mark_as_read" to moshi.adapter(LegacyPendingMoveAndMarkAsRead::class.java)
+    ).toMap()
+
+    fun rewritePendingCommandsToUseFolderIds() {
+        val pendingCommands = loadPendingCommands()
+        rewritePendingCommands(pendingCommands)
+    }
+
+    private fun loadPendingCommands(): Map<Long, LegacyPendingCommand> {
+        return db.rawQuery(
+            "SELECT id, command, data FROM pending_commands WHERE command != 'empty_trash'",
+            null
+        ).use { cursor ->
+            cursor.map {
+                val commandId = cursor.getLong(0)
+                val command = cursor.getString(1)
+                val data = cursor.getString(2)
+
+                val pendingCommand = deserialize(command, data)
+                commandId to pendingCommand
+            }.toMap()
+        }
+    }
+
+    private fun rewritePendingCommands(pendingCommands: Map<Long, LegacyPendingCommand>) {
+        for ((commandId, pendingCommand) in pendingCommands) {
+            when (pendingCommand) {
+                is LegacyPendingAppend -> rewritePendingAppend(commandId, pendingCommand)
+                is LegacyPendingMarkAllAsRead -> rewritePendingMarkAllAsRead(commandId, pendingCommand)
+                is LegacyPendingSetFlag -> rewritePendingSetFlag(commandId, pendingCommand)
+                is LegacyPendingDelete -> rewritePendingDelete(commandId, pendingCommand)
+                is LegacyPendingExpunge -> rewritePendingExpunge(commandId, pendingCommand)
+                is LegacyPendingMoveOrCopy -> rewritePendingMoveOrCopy(commandId, pendingCommand)
+                is LegacyPendingMoveAndMarkAsRead -> rewritePendingMoveAndMarkAsRead(commandId, pendingCommand)
+            }
+        }
+    }
+
+    private fun rewritePendingAppend(commandId: Long, legacyPendingCommand: LegacyPendingAppend) {
+        rewriteOrRemovePendingCommand(commandId, legacyPendingCommand.folder) { (folderId) ->
+            PendingAppend.create(folderId, legacyPendingCommand.uid)
+        }
+    }
+
+    private fun rewritePendingMarkAllAsRead(commandId: Long, legacyPendingCommand: LegacyPendingMarkAllAsRead) {
+        rewriteOrRemovePendingCommand(commandId, legacyPendingCommand.folder) { (folderId) ->
+            PendingMarkAllAsRead.create(folderId)
+        }
+    }
+
+    private fun rewritePendingSetFlag(commandId: Long, legacyPendingCommand: LegacyPendingSetFlag) {
+        rewriteOrRemovePendingCommand(commandId, legacyPendingCommand.folder) { (folderId) ->
+            PendingSetFlag.create(
+                folderId,
+                legacyPendingCommand.newState,
+                legacyPendingCommand.flag,
+                legacyPendingCommand.uids
+            )
+        }
+    }
+
+    private fun rewritePendingDelete(commandId: Long, legacyPendingCommand: LegacyPendingDelete) {
+        rewriteOrRemovePendingCommand(commandId, legacyPendingCommand.folder) { (folderId) ->
+            PendingDelete.create(folderId, legacyPendingCommand.uids)
+        }
+    }
+
+    private fun rewritePendingExpunge(commandId: Long, legacyPendingCommand: LegacyPendingExpunge) {
+        rewriteOrRemovePendingCommand(commandId, legacyPendingCommand.folder) { (folderId) ->
+            PendingExpunge.create(folderId)
+        }
+    }
+
+    private fun rewritePendingMoveOrCopy(commandId: Long, legacyPendingCommand: LegacyPendingMoveOrCopy) {
+        rewriteOrRemovePendingCommand(
+            commandId,
+            legacyPendingCommand.srcFolder,
+            legacyPendingCommand.destFolder
+        ) { (srcFolderId, destFolderId) ->
+            PendingMoveOrCopy.create(
+                srcFolderId,
+                destFolderId,
+                legacyPendingCommand.isCopy,
+                legacyPendingCommand.newUidMap
+            )
+        }
+    }
+
+    private fun rewritePendingMoveAndMarkAsRead(commandId: Long, legacyPendingCommand: LegacyPendingMoveAndMarkAsRead) {
+        rewriteOrRemovePendingCommand(
+            commandId,
+            legacyPendingCommand.srcFolder,
+            legacyPendingCommand.destFolder
+        ) { (srcFolderId, destFolderId) ->
+            PendingMoveAndMarkAsRead.create(srcFolderId, destFolderId, legacyPendingCommand.newUidMap)
+        }
+    }
+
+    private fun rewriteOrRemovePendingCommand(
+        commandId: Long,
+        vararg folderServerIds: String,
+        convertPendingCommand: (folderIds: List<Long>) -> PendingCommand
+    ) {
+        val folderIds = folderServerIds.map {
+            loadFolderId(it)
+        }
+
+        if (folderIds.any { it == null }) {
+            Timber.w("Couldn't find folder ID for pending command with database ID $commandId. Removing entry.")
+            removePendingCommand(commandId)
+        } else {
+            val pendingCommand = convertPendingCommand(folderIds.filterNotNull())
+            updatePendingCommand(commandId, pendingCommand)
+        }
+    }
+
+    private fun updatePendingCommand(commandId: Long, pendingCommand: PendingCommand) {
+        val contentValues = ContentValues().apply {
+            put("data", serializer.serialize(pendingCommand))
+        }
+        db.update("pending_commands", contentValues, "id = ?", arrayOf(commandId.toString()))
+    }
+
+    private fun removePendingCommand(commandId: Long) {
+        db.delete("pending_commands", "id = ?", arrayOf(commandId.toString()))
+    }
+
+    private fun loadFolderId(folderServerId: String): Long? {
+        return db.rawQuery("SELECT id from folders WHERE server_id = ?", arrayOf(folderServerId)).use { cursor ->
+            if (cursor.moveToFirst()) {
+                cursor.getLong(0)
+            } else {
+                null
+            }
+        }
+    }
+
+    private fun deserialize(commandName: String, data: String): LegacyPendingCommand {
+        val adapter = legacyAdapters[commandName] ?: error("Unsupported pending command type!")
+        return adapter.fromJson(data) ?: error("Error deserializing pending command")
+    }
+}

app/storage/src/main/java/com/fsck/k9/storage/migrations/MigrationTo74.kt

@@ -0,0 +1,124 @@
+package com.fsck.k9.storage.migrations
+
+import android.content.ContentValues
+import android.database.sqlite.SQLiteDatabase
+import com.fsck.k9.Account
+import com.fsck.k9.Account.DeletePolicy
+
+/**
+ * Remove all placeholder entries in 'messages' table
+ *
+ * When the user moves or deletes an email, the row in the 'messages' table is first updated with 'deleted = 1', turning
+ * it into a placeholder message. After the remote operation has completed, the row is removed.
+ *
+ * Placeholder messages are created to prevent an email from being downloaded again during a sync before the remote
+ * operation has finished. The placeholder message is also necessary to remember deleted messages when using a delete
+ * policy other than "delete from server".
+ *
+ * Previously these placeholder messages often weren't removed when they should have been. This will slowly grow the
+ * database.
+ * Here we remove all placeholder messages when the delete policy is "delete from server". This might also include
+ * placeholder messages that shouldn't be removed, because the remote operation hasn't been performed yet.
+ * However, since the app tries to execute all pending remote operations before doing a message sync, it's unlikely that
+ * deleted messages are re-downloaded. And if they are, the next sync after the remote operation has completed will
+ * remove them again.
+ */
+internal class MigrationTo74(private val db: SQLiteDatabase, private val account: Account) {
+
+    fun removeDeletedMessages() {
+        if (account.deletePolicy != DeletePolicy.ON_DELETE) return
+
+        db.query("messages", arrayOf("id"), "deleted = 1", null, null, null, null).use { cursor ->
+            while (cursor.moveToNext()) {
+                destroyMessage(messageId = cursor.getLong(0))
+            }
+        }
+    }
+
+    private fun destroyMessage(messageId: Long) {
+        if (hasThreadChildren(messageId)) {
+            // This message has children in the thread structure so we need to make it an empty message.
+            val cv = ContentValues().apply {
+                put("deleted", 0)
+                put("empty", 1)
+                put("preview_type", "none")
+                put("read", 0)
+                put("flagged", 0)
+                put("answered", 0)
+                put("forwarded", 0)
+                putNull("subject")
+                putNull("sender_list")
+                putNull("date")
+                putNull("to_list")
+                putNull("cc_list")
+                putNull("bcc_list")
+                putNull("preview")
+                putNull("reply_to_list")
+                putNull("message_part_id")
+                putNull("flags")
+                putNull("attachment_count")
+                putNull("internal_date")
+                putNull("mime_type")
+                putNull("encryption_type")
+            }
+            db.update("messages", cv, "id = ?", arrayOf(messageId.toString()))
+
+            // Nothing else to do
+            return
+        }
+
+        // Get the message ID of the parent message if it's empty
+        var currentId = getEmptyThreadParent(messageId)
+
+        // Delete the placeholder message
+        deleteMessageRow(messageId)
+
+        // Walk the thread tree to delete all empty parents without children
+        while (currentId != -1L) {
+            if (hasThreadChildren(currentId)) {
+                // We made sure there are no empty leaf nodes and can stop now.
+                break
+            }
+
+            // Get ID of the (empty) parent for the next iteration
+            val newId = getEmptyThreadParent(currentId)
+
+            // Delete the empty message
+            deleteMessageRow(currentId)
+            currentId = newId
+        }
+    }
+
+    private fun hasThreadChildren(messageId: Long): Boolean {
+        return db.rawQuery(
+            "SELECT COUNT(t2.id) " +
+                "FROM threads t1 " +
+                "JOIN threads t2 ON (t2.parent = t1.id) " +
+                "WHERE t1.message_id = ?",
+            arrayOf(messageId.toString())
+        ).use { cursor ->
+            cursor.moveToFirst() && !cursor.isNull(0) && cursor.getLong(0) > 0L
+        }
+    }
+
+    private fun getEmptyThreadParent(messageId: Long): Long {
+        return db.rawQuery(
+            "SELECT m.id " +
+                "FROM threads t1 " +
+                "JOIN threads t2 ON (t1.parent = t2.id) " +
+                "LEFT JOIN messages m ON (t2.message_id = m.id) " +
+                "WHERE t1.message_id = ? AND m.empty = 1",
+            arrayOf(messageId.toString())
+        ).use { cursor ->
+            if (cursor.moveToFirst() && !cursor.isNull(0)) cursor.getLong(0) else -1
+        }
+    }
+
+    private fun deleteMessageRow(messageId: Long) {
+        // Delete the message
+        db.delete("messages", "id = ?", arrayOf(messageId.toString()))
+
+        // Delete row in 'threads' table
+        db.delete("threads", "message_id = ?", arrayOf(messageId.toString()))
+    }
+}

app/storage/src/main/java/com/fsck/k9/storage/migrations/MigrationTo75.kt

@@ -0,0 +1,36 @@
+package com.fsck.k9.storage.migrations
+
+import android.database.sqlite.SQLiteDatabase
+import com.fsck.k9.mailstore.MigrationsHelper
+
+internal class MigrationTo75(private val db: SQLiteDatabase, private val migrationsHelper: MigrationsHelper) {
+    fun updateAccountWithSpecialFolderIds() {
+        val account = migrationsHelper.account
+
+        account.inboxFolderId = getFolderId(account.legacyInboxFolder)
+        account.outboxFolderId = getFolderId("K9MAIL_INTERNAL_OUTBOX")
+        account.draftsFolderId = getFolderId(account.importedDraftsFolder)
+        account.sentFolderId = getFolderId(account.importedSentFolder)
+        account.trashFolderId = getFolderId(account.importedTrashFolder)
+        account.archiveFolderId = getFolderId(account.importedArchiveFolder)
+        account.spamFolderId = getFolderId(account.importedSpamFolder)
+        account.autoExpandFolderId = getFolderId(account.importedAutoExpandFolder)
+
+        account.importedDraftsFolder = null
+        account.importedSentFolder = null
+        account.importedTrashFolder = null
+        account.importedArchiveFolder = null
+        account.importedSpamFolder = null
+        account.importedAutoExpandFolder = null
+
+        migrationsHelper.saveAccount()
+    }
+
+    private fun getFolderId(serverId: String?): Long? {
+        if (serverId == null) return null
+
+        return db.query("folders", arrayOf("id"), "server_id = ?", arrayOf(serverId), null, null, null).use { cursor ->
+            if (cursor.moveToFirst() && !cursor.isNull(0)) cursor.getLong(0) else null
+        }
+    }
+}

app/storage/src/main/java/com/fsck/k9/storage/migrations/MigrationTo76.kt

@@ -0,0 +1,131 @@
+package com.fsck.k9.storage.migrations
+
+import android.content.ContentValues
+import android.database.sqlite.SQLiteDatabase
+import app.k9mail.core.android.common.database.map
+import com.fsck.k9.Account
+import com.fsck.k9.mailstore.MigrationsHelper
+import com.fsck.k9.preferences.Protocols
+import timber.log.Timber
+
+/**
+ * Clean up special local folders
+ *
+ * In the past local special folders were not always created. For example, when importing settings or when setting up
+ * an account, but checking the server settings didn't succeed and the user decided to continue anyway.
+ *
+ * Clicking "Next" in the incoming server settings screen would check the server settings and, in the case of success,
+ * create new special local folders even if they already existed. So it's also possible existing installations have
+ * multiple special local folders of one type.
+ *
+ * Here, we clean up local special folders to have exactly one of each type. Messages in additional folders will be
+ * moved to the folder we keep and then the other folders will be deleted. An exception are messages in old Outbox
+ * folders. They will be deleted and not be moved to the new/current Outbox folder because this would cause potentially
+ * very old messages to be sent. The right thing would be to move them to the Drafts folder. But this is much more
+ * complicated. They'd have to be uploaded if the Drafts folder is not a local folder. It's also not clear what should
+ * happen if there is no Drafts folder configured.
+ */
+internal class MigrationTo76(private val db: SQLiteDatabase, private val migrationsHelper: MigrationsHelper) {
+    fun cleanUpSpecialLocalFolders() {
+        val account = migrationsHelper.account
+
+        Timber.v("Cleaning up Outbox folder")
+        val outboxFolderId = account.outboxFolderId ?: createFolder("Outbox", "K9MAIL_INTERNAL_OUTBOX", OUTBOX_FOLDER_TYPE)
+        deleteOtherOutboxFolders(outboxFolderId)
+        account.outboxFolderId = outboxFolderId
+
+        if (account.isPop3()) {
+            Timber.v("Cleaning up Drafts folder")
+            val draftsFolderId = account.draftsFolderId ?: createFolder("Drafts", "Drafts", DRAFTS_FOLDER_TYPE)
+            moveMessages(DRAFTS_FOLDER_TYPE, draftsFolderId)
+            account.draftsFolderId = draftsFolderId
+
+            Timber.v("Cleaning up Sent folder")
+            val sentFolderId = account.sentFolderId ?: createFolder("Sent", "Sent", SENT_FOLDER_TYPE)
+            moveMessages(SENT_FOLDER_TYPE, sentFolderId)
+            account.sentFolderId = sentFolderId
+
+            Timber.v("Cleaning up Trash folder")
+            val trashFolderId = account.trashFolderId ?: createFolder("Trash", "Trash", TRASH_FOLDER_TYPE)
+            moveMessages(TRASH_FOLDER_TYPE, trashFolderId)
+            account.trashFolderId = trashFolderId
+        }
+
+        migrationsHelper.saveAccount()
+    }
+
+    private fun createFolder(name: String, serverId: String, type: String): Long {
+        Timber.v("  Creating new local folder (name=$name, serverId=$serverId, type=$type)…")
+        val values = ContentValues().apply {
+            put("name", name)
+            put("visible_limit", 25)
+            put("integrate", 0)
+            put("top_group", 0)
+            put("poll_class", "NO_CLASS")
+            put("push_class", "SECOND_CLASS")
+            put("display_class", "NO_CLASS")
+            put("server_id", serverId)
+            put("local_only", 1)
+            put("type", type)
+        }
+
+        val folderId = db.insert("folders", null, values)
+        Timber.v("    Created folder with ID $folderId")
+
+        return folderId
+    }
+
+    private fun deleteOtherOutboxFolders(outboxFolderId: Long) {
+        val otherFolderIds = getOtherFolders(OUTBOX_FOLDER_TYPE, outboxFolderId)
+        for (folderId in otherFolderIds) {
+            deleteFolder(folderId)
+        }
+    }
+
+    private fun getOtherFolders(folderType: String, excludeFolderId: Long): List<Long> {
+        return db.query(
+            "folders",
+            arrayOf("id"),
+            "local_only = 1 AND type = ? AND id != ?",
+            arrayOf(folderType, excludeFolderId.toString()),
+            null,
+            null,
+            null
+        ).use { cursor ->
+            cursor.map { cursor.getLong(0) }
+        }
+    }
+
+    private fun moveMessages(folderType: String, destinationFolderId: Long) {
+        val sourceFolderIds = getOtherFolders(folderType, destinationFolderId)
+        for (sourceFolderId in sourceFolderIds) {
+            moveMessages(sourceFolderId, destinationFolderId)
+            deleteFolder(sourceFolderId)
+        }
+    }
+
+    private fun moveMessages(sourceFolderId: Long, destinationFolderId: Long) {
+        Timber.v("  Moving messages from folder [$sourceFolderId] to folder [$destinationFolderId]…")
+
+        val values = ContentValues().apply {
+            put("folder_id", destinationFolderId)
+        }
+        val rows = db.update("messages", values, "folder_id = ?", arrayOf(sourceFolderId.toString()))
+
+        Timber.v("    $rows messages moved.")
+    }
+
+    private fun deleteFolder(folderId: Long) {
+        Timber.v("  Deleting folder [$folderId]")
+        db.delete("folders", "id = ?", arrayOf(folderId.toString()))
+    }
+
+    private fun Account.isPop3() = incomingServerSettings.type == Protocols.POP3
+
+    companion object {
+        private const val OUTBOX_FOLDER_TYPE = "outbox"
+        private const val DRAFTS_FOLDER_TYPE = "drafts"
+        private const val SENT_FOLDER_TYPE = "sent"
+        private const val TRASH_FOLDER_TYPE = "trash"
+    }
+}

app/storage/src/main/java/com/fsck/k9/storage/migrations/MigrationTo78.kt

@@ -0,0 +1,12 @@
+package com.fsck.k9.storage.migrations
+
+import android.database.sqlite.SQLiteDatabase
+
+/**
+ * Set 'server_id' value to NULL for local folders
+ */
+internal class MigrationTo78(private val db: SQLiteDatabase) {
+    fun removeServerIdFromLocalFolders() {
+        db.execSQL("UPDATE folders SET server_id = NULL WHERE local_only = 1")
+    }
+}

app/storage/src/main/java/com/fsck/k9/storage/migrations/MigrationTo79.kt

@@ -0,0 +1,21 @@
+package com.fsck.k9.storage.migrations
+
+import android.database.sqlite.SQLiteDatabase
+
+/**
+ * Add 'threads' table to 'delete_message' trigger
+ */
+internal class MigrationTo79(private val db: SQLiteDatabase) {
+    fun updateDeleteMessageTrigger() {
+        db.execSQL("DROP TRIGGER IF EXISTS delete_message")
+        db.execSQL(
+            "CREATE TRIGGER delete_message " +
+                "BEFORE DELETE ON messages " +
+                "BEGIN " +
+                "DELETE FROM message_parts WHERE root = OLD.message_part_id; " +
+                "DELETE FROM messages_fulltext WHERE docid = OLD.id; " +
+                "DELETE FROM threads WHERE message_id = OLD.id; " +
+                "END"
+        )
+    }
+}

app/storage/src/main/java/com/fsck/k9/storage/migrations/MigrationTo80.kt

@@ -0,0 +1,12 @@
+package com.fsck.k9.storage.migrations
+
+import android.database.sqlite.SQLiteDatabase
+
+/**
+ * Rewrite 'last_update' column to NULL when the value is 0
+ */
+internal class MigrationTo80(private val db: SQLiteDatabase) {
+    fun rewriteLastUpdatedColumn() {
+        db.execSQL("UPDATE folders SET last_updated = NULL WHERE last_updated = 0")
+    }
+}

app/storage/src/main/java/com/fsck/k9/storage/migrations/MigrationTo81.kt

@@ -0,0 +1,22 @@
+package com.fsck.k9.storage.migrations
+
+import android.database.sqlite.SQLiteDatabase
+
+/**
+ * Add 'notifications' table to keep track of notifications.
+ */
+internal class MigrationTo81(private val db: SQLiteDatabase) {
+    fun addNotificationsTable() {
+        db.execSQL("DROP TABLE IF EXISTS notifications")
+        db.execSQL(
+            "CREATE TABLE notifications (" +
+                "message_id INTEGER PRIMARY KEY NOT NULL REFERENCES messages(id) ON DELETE CASCADE," +
+                "notification_id INTEGER UNIQUE," +
+                "timestamp INTEGER NOT NULL" +
+                ")"
+        )
+
+        db.execSQL("DROP INDEX IF EXISTS notifications_timestamp")
+        db.execSQL("CREATE INDEX IF NOT EXISTS notifications_timestamp ON notifications(timestamp)")
+    }
+}

app/storage/src/main/java/com/fsck/k9/storage/migrations/MigrationTo82.kt

@@ -0,0 +1,27 @@
+package com.fsck.k9.storage.migrations
+
+import android.database.sqlite.SQLiteDatabase
+
+/**
+ * Add 'new_message' column to 'messages' table.
+ */
+internal class MigrationTo82(private val db: SQLiteDatabase) {
+    fun addNewMessageColumn() {
+        db.execSQL("ALTER TABLE messages ADD new_message INTEGER DEFAULT 0")
+
+        db.execSQL("DROP INDEX IF EXISTS new_messages")
+        db.execSQL("CREATE INDEX IF NOT EXISTS new_messages ON messages(new_message)")
+
+        db.execSQL(
+            "CREATE TRIGGER new_message_reset " +
+                "AFTER UPDATE OF read ON messages " +
+                "FOR EACH ROW WHEN NEW.read = 1 AND NEW.new_message = 1 " +
+                "BEGIN " +
+                "UPDATE messages SET new_message = 0 WHERE ROWID = NEW.ROWID; " +
+                "END"
+        )
+
+        // Mark messages with existing notifications as "new"
+        db.execSQL("UPDATE messages SET new_message = 1 WHERE id in (SELECT message_id FROM notifications)")
+    }
+}

app/storage/src/main/java/com/fsck/k9/storage/migrations/MigrationTo83.kt

@@ -0,0 +1,42 @@
+package com.fsck.k9.storage.migrations
+
+import android.content.ContentValues
+import android.database.sqlite.SQLiteDatabase
+import androidx.core.database.getLongOrNull
+import app.k9mail.core.android.common.database.map
+import com.fsck.k9.mailstore.MigrationsHelper
+
+private const val EXTRA_HIGHEST_KNOWN_UID = "imapHighestKnownUid"
+
+/**
+ * Write the highest known IMAP message UID to the 'folder_extra_values' table.
+ */
+internal class MigrationTo83(private val db: SQLiteDatabase, private val migrationsHelper: MigrationsHelper) {
+    fun rewriteHighestKnownUid() {
+        if (migrationsHelper.account.incomingServerSettings.type != "imap") return
+
+        val highestKnownUids = db.rawQuery(
+            "SELECT folder_id, MAX(CAST(uid AS INTEGER)) FROM messages GROUP BY folder_id",
+            null
+        ).use { cursor ->
+            cursor.map {
+                it.getLong(0) to it.getLongOrNull(1)
+            }.toMap()
+        }
+
+        for ((folderId, highestKnownUid) in highestKnownUids) {
+            if (highestKnownUid != null && highestKnownUid > 0L) {
+                rewriteHighestKnownUid(folderId, highestKnownUid)
+            }
+        }
+    }
+
+    private fun rewriteHighestKnownUid(folderId: Long, highestKnownUid: Long) {
+        val contentValues = ContentValues().apply {
+            put("folder_id", folderId)
+            put("name", EXTRA_HIGHEST_KNOWN_UID)
+            put("value_integer", highestKnownUid)
+        }
+        db.insertWithOnConflict("folder_extra_values", null, contentValues, SQLiteDatabase.CONFLICT_REPLACE)
+    }
+}

app/storage/src/main/java/com/fsck/k9/storage/migrations/MigrationTo84.kt

@@ -0,0 +1,59 @@
+package com.fsck.k9.storage.migrations
+
+import android.content.ContentValues
+import android.database.sqlite.SQLiteDatabase
+import androidx.core.database.getStringOrNull
+import app.k9mail.core.android.common.database.map
+
+/**
+ * Write the address fields to use ASCII 1 instead of ASCII 0 as separator.
+ * Separator was previously ASCII 0 but this caused problems with LIKE and searching.
+ */
+internal class MigrationTo84(private val db: SQLiteDatabase) {
+
+    fun rewriteAddresses() {
+        val addressSets = db.rawQuery(
+            "SELECT id, to_list, cc_list, bcc_list, reply_to_list, sender_list FROM messages WHERE empty = 0 AND deleted = 0",
+            null
+        ).use { cursor ->
+            cursor.map {
+                val messageId = it.getLong(0)
+
+                messageId to AddressSet(
+                    toList = it.getStringOrNull(1),
+                    ccList = it.getStringOrNull(2),
+                    bccList = it.getStringOrNull(3),
+                    replyToList = it.getStringOrNull(4),
+                    senderList = it.getStringOrNull(5)
+                )
+            }.toMap()
+        }
+
+        for ((messageId, addressSet) in addressSets) {
+            rewriteAddresses(messageId, addressSet)
+        }
+    }
+
+    private fun rewriteAddress(inAddress: String?): String? {
+        return inAddress?.replace(oldChar = '\u0000', newChar = '\u0001')
+    }
+
+    private fun rewriteAddresses(messageId: Long, addressSet: AddressSet) {
+        val cv = ContentValues().apply {
+            put("to_list", rewriteAddress(addressSet.toList))
+            put("cc_list", rewriteAddress(addressSet.ccList))
+            put("bcc_list", rewriteAddress(addressSet.bccList))
+            put("reply_to_list", rewriteAddress(addressSet.replyToList))
+            put("sender_list", rewriteAddress(addressSet.senderList))
+        }
+        db.update("messages", cv, "id = ?", arrayOf(messageId.toString()))
+    }
+}
+
+private data class AddressSet(
+    val toList: String?,
+    val ccList: String?,
+    val bccList: String?,
+    val replyToList: String?,
+    val senderList: String?
+)

app/storage/src/main/java/com/fsck/k9/storage/migrations/Migrations.kt

@@ -0,0 +1,34 @@
+package com.fsck.k9.storage.migrations
+
+import android.database.sqlite.SQLiteDatabase
+import com.fsck.k9.mailstore.MigrationsHelper
+
+object Migrations {
+    @JvmStatic
+    fun upgradeDatabase(db: SQLiteDatabase, migrationsHelper: MigrationsHelper) {
+        val oldVersion = db.version
+
+        if (oldVersion < 62) MigrationTo62.addServerIdColumnToFoldersTable(db)
+        if (oldVersion < 64) MigrationTo64.addExtraValuesTables(db)
+        if (oldVersion < 65) MigrationTo65.addLocalOnlyColumnToFoldersTable(db, migrationsHelper)
+        if (oldVersion < 66) MigrationTo66.addEncryptionTypeColumnToMessagesTable(db)
+        if (oldVersion < 67) MigrationTo67.addTypeColumnToFoldersTable(db, migrationsHelper)
+        if (oldVersion < 68) MigrationTo68.addOutboxStateTable(db)
+        if (oldVersion < 69) MigrationTo69(db).createPendingDelete()
+        if (oldVersion < 70) MigrationTo70(db).removePushState()
+        if (oldVersion < 71) MigrationTo71(db).cleanUpFolderClass()
+        if (oldVersion < 72) MigrationTo72(db).createMessagePartsRootIndex()
+        if (oldVersion < 73) MigrationTo73(db).rewritePendingCommandsToUseFolderIds()
+        if (oldVersion < 74) MigrationTo74(db, migrationsHelper.account).removeDeletedMessages()
+        if (oldVersion < 75) MigrationTo75(db, migrationsHelper).updateAccountWithSpecialFolderIds()
+        if (oldVersion < 76) MigrationTo76(db, migrationsHelper).cleanUpSpecialLocalFolders()
+        // 77: No longer necessary
+        if (oldVersion < 78) MigrationTo78(db).removeServerIdFromLocalFolders()
+        if (oldVersion < 79) MigrationTo79(db).updateDeleteMessageTrigger()
+        if (oldVersion < 80) MigrationTo80(db).rewriteLastUpdatedColumn()
+        if (oldVersion < 81) MigrationTo81(db).addNotificationsTable()
+        if (oldVersion < 82) MigrationTo82(db).addNewMessageColumn()
+        if (oldVersion < 83) MigrationTo83(db, migrationsHelper).rewriteHighestKnownUid()
+        if (oldVersion < 84) MigrationTo84(db).rewriteAddresses()
+    }
+}

app/storage/src/main/java/com/fsck/k9/storage/notifications/K9NotificationStore.kt

@@ -0,0 +1,72 @@
+package com.fsck.k9.storage.notifications
+
+import android.database.sqlite.SQLiteDatabase
+import com.fsck.k9.controller.MessageReference
+import com.fsck.k9.mailstore.LockableDatabase
+import com.fsck.k9.notification.NotificationStore
+import com.fsck.k9.notification.NotificationStoreOperation
+
+class K9NotificationStore(private val lockableDatabase: LockableDatabase) : NotificationStore {
+    override fun persistNotificationChanges(operations: List<NotificationStoreOperation>) {
+        lockableDatabase.execute(true) { db ->
+            for (operation in operations) {
+                when (operation) {
+                    is NotificationStoreOperation.Add -> {
+                        addNotification(db, operation.messageReference, operation.notificationId, operation.timestamp)
+                    }
+                    is NotificationStoreOperation.ChangeToActive -> {
+                        setNotificationId(db, operation.messageReference, operation.notificationId)
+                    }
+                    is NotificationStoreOperation.ChangeToInactive -> {
+                        clearNotificationId(db, operation.messageReference)
+                    }
+                    is NotificationStoreOperation.Remove -> {
+                        removeNotification(db, operation.messageReference)
+                    }
+                }
+            }
+        }
+    }
+
+    override fun clearNotifications() {
+        lockableDatabase.execute(false) { db ->
+            db.delete("notifications", null, null)
+        }
+    }
+
+    private fun addNotification(
+        database: SQLiteDatabase,
+        messageReference: MessageReference,
+        notificationId: Int,
+        timestamp: Long
+    ) {
+        database.execSQL(
+            "INSERT INTO notifications(message_id, notification_id, timestamp) " +
+                "SELECT id, ?, ? FROM messages WHERE folder_id = ? AND uid = ?",
+            arrayOf(notificationId, timestamp, messageReference.folderId, messageReference.uid)
+        )
+    }
+
+    private fun setNotificationId(database: SQLiteDatabase, messageReference: MessageReference, notificationId: Int) {
+        database.execSQL(
+            "UPDATE notifications SET notification_id = ? WHERE message_id IN " +
+                "(SELECT id FROM messages WHERE folder_id = ? AND uid = ?)",
+            arrayOf(notificationId, messageReference.folderId, messageReference.uid)
+        )
+    }
+
+    private fun clearNotificationId(database: SQLiteDatabase, messageReference: MessageReference) {
+        database.execSQL(
+            "UPDATE notifications SET notification_id = NULL WHERE message_id IN " +
+                "(SELECT id FROM messages WHERE folder_id = ? AND uid = ?)",
+            arrayOf(messageReference.folderId, messageReference.uid)
+        )
+    }
+
+    private fun removeNotification(database: SQLiteDatabase, messageReference: MessageReference) {
+        database.execSQL(
+            "DELETE FROM notifications WHERE message_id IN (SELECT id FROM messages WHERE folder_id = ? AND uid = ?)",
+            arrayOf(messageReference.folderId, messageReference.uid)
+        )
+    }
+}

app/storage/src/main/java/com/fsck/k9/storage/notifications/K9NotificationStoreProvider.kt

@@ -0,0 +1,13 @@
+package com.fsck.k9.storage.notifications
+
+import com.fsck.k9.Account
+import com.fsck.k9.mailstore.LocalStoreProvider
+import com.fsck.k9.notification.NotificationStore
+import com.fsck.k9.notification.NotificationStoreProvider
+
+class K9NotificationStoreProvider(private val localStoreProvider: LocalStoreProvider) : NotificationStoreProvider {
+    override fun getNotificationStore(account: Account): NotificationStore {
+        val localStore = localStoreProvider.getInstance(account)
+        return K9NotificationStore(lockableDatabase = localStore.database)
+    }
+}

app/storage/src/test/java/com/fsck/k9/preferences/StorageEditorTest.kt

@@ -0,0 +1,207 @@
+package com.fsck.k9.preferences
+
+import assertk.assertThat
+import assertk.assertions.isEmpty
+import assertk.assertions.isEqualTo
+import assertk.assertions.isFalse
+import assertk.assertions.isTrue
+import com.fsck.k9.preferences.K9StoragePersister.StoragePersistOperationCallback
+import com.fsck.k9.preferences.K9StoragePersister.StoragePersistOperations
+import com.fsck.k9.storage.K9RobolectricTest
+import org.junit.Test
+import org.mockito.ArgumentMatchers.any
+import org.mockito.kotlin.doAnswer
+import org.mockito.kotlin.doThrow
+import org.mockito.kotlin.mock
+import org.mockito.kotlin.stubbing
+import org.mockito.kotlin.verify
+import org.mockito.kotlin.verifyNoMoreInteractions
+
+class StorageEditorTest : K9RobolectricTest() {
+    private val storage: Storage = Storage(mapOf("storage-key" to "storage-value"))
+    private val storageUpdater = TestStorageUpdater(storage)
+    private val storagePersister = mock<K9StoragePersister>()
+    private val storagePersisterOps = mock<StoragePersistOperations>()
+    private val editor = K9StorageEditor(storageUpdater, storagePersister)
+
+    private val workingMap = mutableMapOf<String, String>()
+
+    private val newValues: Map<String, String>
+        get() = storageUpdater.newStorage!!.all
+
+    @Test
+    fun commit_exception() {
+        stubbing(storagePersister) {
+            on { doInTransaction(any()) } doThrow RuntimeException()
+        }
+
+        val success = editor.commit()
+
+        assertThat(success).isFalse()
+    }
+
+    @Test
+    fun commit_trivial() {
+        prepareStoragePersisterMock()
+
+        val success = editor.commit()
+
+        assertThat(success).isTrue()
+        assertThat(newValues).isEqualTo(storage.all)
+
+        verifyNoMoreInteractions(storagePersisterOps)
+    }
+
+    @Test
+    fun putBoolean() {
+        prepareStoragePersisterMock()
+
+        editor.putBoolean("x", true)
+        val success = editor.commit()
+
+        assertThat(success).isTrue()
+        assertThat(newValues).isEqualTo(mapOf("storage-key" to "storage-value", "x" to "true"))
+        verify(storagePersisterOps).put("x", "true")
+        verifyNoMoreInteractions(storagePersisterOps)
+    }
+
+    @Test
+    fun putInt() {
+        prepareStoragePersisterMock()
+
+        editor.putInt("x", 123)
+        val success = editor.commit()
+
+        assertThat(success).isTrue()
+        assertThat(newValues).isEqualTo(mapOf("storage-key" to "storage-value", "x" to "123"))
+        verify(storagePersisterOps).put("x", "123")
+        verifyNoMoreInteractions(storagePersisterOps)
+    }
+
+    @Test
+    fun putLong() {
+        prepareStoragePersisterMock()
+
+        editor.putLong("x", 1234)
+        val success = editor.commit()
+
+        assertThat(success).isTrue()
+        assertThat(newValues).isEqualTo(mapOf("storage-key" to "storage-value", "x" to "1234"))
+        verify(storagePersisterOps).put("x", "1234")
+        verifyNoMoreInteractions(storagePersisterOps)
+    }
+
+    @Test
+    fun putString() {
+        prepareStoragePersisterMock()
+
+        editor.putString("x", "y")
+        val success = editor.commit()
+
+        assertThat(success).isTrue()
+        assertThat(newValues).isEqualTo(mapOf("storage-key" to "storage-value", "x" to "y"))
+        verify(storagePersisterOps).put("x", "y")
+        verifyNoMoreInteractions(storagePersisterOps)
+    }
+
+    @Test
+    fun putString_duplicateSame() {
+        prepareStoragePersisterMock()
+
+        editor.putString("storage-key", "storage-value")
+        val success = editor.commit()
+
+        assertThat(success).isTrue()
+        assertThat(newValues).isEqualTo(mapOf("storage-key" to "storage-value"))
+        verifyNoMoreInteractions(storagePersisterOps)
+    }
+
+    @Test
+    fun putString_duplicateOther() {
+        prepareStoragePersisterMock()
+
+        editor.putString("storage-key", "other-value")
+        val success = editor.commit()
+
+        assertThat(success).isTrue()
+        assertThat(newValues).isEqualTo(mapOf("storage-key" to "other-value"))
+        verify(storagePersisterOps).put("storage-key", "other-value")
+        verifyNoMoreInteractions(storagePersisterOps)
+    }
+
+    @Test
+    fun putString_removedDuplicate() {
+        prepareStoragePersisterMock()
+
+        editor.remove("storage-key")
+        editor.putString("storage-key", "storage-value")
+        val success = editor.commit()
+
+        assertThat(success).isTrue()
+        assertThat(newValues).isEqualTo(mapOf("storage-key" to "storage-value"))
+        verify(storagePersisterOps).remove("storage-key")
+        verify(storagePersisterOps).put("storage-key", "storage-value")
+        verifyNoMoreInteractions(storagePersisterOps)
+    }
+
+    @Test
+    fun `remove key that doesn't exist`() {
+        prepareStoragePersisterMock()
+
+        editor.remove("x")
+        val success = editor.commit()
+
+        assertThat(success).isTrue()
+        assertThat(newValues).isEqualTo(mapOf("storage-key" to "storage-value"))
+        verify(storagePersisterOps).remove("x")
+        verifyNoMoreInteractions(storagePersisterOps)
+    }
+
+    @Test
+    fun remove() {
+        prepareStoragePersisterMock()
+
+        editor.remove("storage-key")
+        val success = editor.commit()
+
+        assertThat(success).isTrue()
+        assertThat(newValues).isEmpty()
+        verify(storagePersisterOps).remove("storage-key")
+        verifyNoMoreInteractions(storagePersisterOps)
+    }
+
+    private fun prepareStoragePersisterMock() {
+        stubbing(storagePersisterOps) {
+            on { put(any(), any()) } doAnswer {
+                val key = it.getArgument<String>(0)
+                val value = it.getArgument<String>(1)
+                workingMap[key] = value
+            }
+
+            on { remove(any()) } doAnswer {
+                val key = it.getArgument<String>(0)
+                workingMap.remove(key)
+
+                Unit
+            }
+        }
+
+        stubbing(storagePersister) {
+            on { doInTransaction(any()) } doAnswer {
+                val operationCallback = it.getArgument<StoragePersistOperationCallback>(0)
+
+                operationCallback.beforePersistTransaction(workingMap)
+                operationCallback.persist(storagePersisterOps)
+                operationCallback.onPersistTransactionSuccess(workingMap)
+            }
+        }
+    }
+}
+
+class TestStorageUpdater(private val currentStorage: Storage) : StorageUpdater {
+    var newStorage: Storage? = null
+
+    override fun updateStorage(updater: (currentStorage: Storage) -> Storage) {
+        newStorage = updater(currentStorage)
+    }
+}

app/storage/src/test/java/com/fsck/k9/preferences/StoragePersisterTest.kt

@@ -0,0 +1,120 @@
+package com.fsck.k9.preferences
+
+import android.content.Context
+import com.fsck.k9.preferences.K9StoragePersister.StoragePersistOperationCallback
+import com.fsck.k9.preferences.K9StoragePersister.StoragePersistOperations
+import com.fsck.k9.storage.K9RobolectricTest
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertSame
+import org.junit.Assert.assertTrue
+import org.junit.Assert.fail
+import org.junit.Test
+import org.mockito.kotlin.any
+import org.mockito.kotlin.inOrder
+import org.mockito.kotlin.never
+import org.mockito.kotlin.spy
+import org.mockito.kotlin.verify
+import org.mockito.kotlin.verifyNoMoreInteractions
+import org.robolectric.RuntimeEnvironment
+
+class StoragePersisterTest : K9RobolectricTest() {
+    private var context: Context = RuntimeEnvironment.getApplication()
+    private var storagePersister = K9StoragePersister(context)
+
+    @Test
+    fun doInTransaction_order() {
+        val operationCallback = prepareCallback()
+        storagePersister.doInTransaction(operationCallback)
+
+        inOrder(operationCallback) {
+            verify(operationCallback).beforePersistTransaction(any())
+            verify(operationCallback).persist(any())
+            verify(operationCallback).onPersistTransactionSuccess(any())
+        }
+        verifyNoMoreInteractions(operationCallback)
+    }
+
+    @Test
+    fun doInTransaction_put() {
+        val operationCallback = prepareCallback(
+            persistOp = { ops -> ops.put("x", "y") },
+            onSuccess = { map ->
+                assertEquals(1, map.size)
+                assertEquals("y", map["x"])
+            }
+        )
+
+        storagePersister.doInTransaction(operationCallback)
+
+        val values = storagePersister.loadValues().all
+        assertEquals(1, values.size)
+        assertEquals("y", values["x"])
+    }
+
+    @Test
+    fun doInTransaction_putAndThrow() {
+        val exception = Exception("boom")
+        val operationCallback = prepareCallback(
+            persistOp = { ops ->
+                ops.put("x", "y")
+                throw exception
+            }
+        )
+
+        try {
+            storagePersister.doInTransaction(operationCallback)
+            fail("expected exception")
+        } catch (e: Exception) {
+            assertSame(exception, e)
+        }
+
+        val values = storagePersister.loadValues()
+        assertTrue(values.isEmpty())
+        verify(operationCallback, never()).onPersistTransactionSuccess(any())
+    }
+
+    @Test
+    fun doInTransaction_remove() {
+        val operationCallback = prepareCallback(
+            before = { map -> map["x"] = "y" },
+            persistOp = { ops -> ops.remove("x") },
+            onSuccess = { map -> assertTrue(map.isEmpty()) }
+        )
+
+        storagePersister.doInTransaction(operationCallback)
+
+        val values = storagePersister.loadValues()
+        assertTrue(values.isEmpty())
+    }
+
+    @Test
+    fun doInTransaction_before_preserveButNotPersist() {
+        val operationCallback = prepareCallback(
+            before = { map -> map["x"] = "y" },
+            onSuccess = { map -> assertEquals("y", map["x"]) }
+        )
+
+        storagePersister.doInTransaction(operationCallback)
+
+        val values = storagePersister.loadValues()
+        assertTrue(values.isEmpty())
+    }
+
+    private fun prepareCallback(
+        persistOp: ((StoragePersistOperations) -> Unit)? = null,
+        before: ((MutableMap<String, String>) -> Unit)? = null,
+        onSuccess: ((Map<String, String>) -> Unit)? = null
+    ): StoragePersistOperationCallback = spy(object : StoragePersistOperationCallback {
+        override fun beforePersistTransaction(workingStorage: MutableMap<String, String>) {
+            before?.invoke(workingStorage)
+        }
+
+        override fun persist(ops: StoragePersistOperations) {
+            persistOp?.invoke(ops)
+        }
+
+        override fun onPersistTransactionSuccess(workingStorage: Map<String, String>) {
+            onSuccess?.invoke(workingStorage)
+        }
+    })
+}

app/storage/src/test/java/com/fsck/k9/storage/K9RobolectricTest.kt

@@ -0,0 +1,16 @@
+package com.fsck.k9.storage
+
+import android.app.Application
+import org.junit.runner.RunWith
+import org.koin.test.AutoCloseKoinTest
+import org.robolectric.RobolectricTestRunner
+import org.robolectric.annotation.Config
+
+/**
+ * A Robolectric test that creates an instance of our [Application] test class [TestApp].
+ *
+ * See also [RobolectricTest].
+ */
+@RunWith(RobolectricTestRunner::class)
+@Config(application = TestApp::class)
+abstract class K9RobolectricTest : AutoCloseKoinTest()

app/storage/src/test/java/com/fsck/k9/storage/RobolectricTest.kt

@@ -0,0 +1,15 @@
+package com.fsck.k9.storage
+
+import android.app.Application
+import org.junit.runner.RunWith
+import org.robolectric.RobolectricTestRunner
+import org.robolectric.annotation.Config
+
+/**
+ * A Robolectric test that does not create an instance of our [Application] class.
+ */
+@RunWith(RobolectricTestRunner::class)
+@Config(application = EmptyApplication::class)
+abstract class RobolectricTest
+
+class EmptyApplication : Application()

app/storage/src/test/java/com/fsck/k9/storage/StoreSchemaDefinitionTest.java

@@ -0,0 +1,424 @@
+package com.fsck.k9.storage;
+
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+
+import android.app.Application;
+import android.content.ContentValues;
+import android.database.Cursor;
+import android.database.sqlite.SQLiteDatabase;
+import android.text.TextUtils;
+
+import com.fsck.k9.Account;
+import com.fsck.k9.core.BuildConfig;
+import com.fsck.k9.mail.AuthType;
+import com.fsck.k9.mail.ConnectionSecurity;
+import com.fsck.k9.mail.MessagingException;
+import com.fsck.k9.mail.ServerSettings;
+import com.fsck.k9.mailstore.LocalStore;
+import com.fsck.k9.mailstore.LockableDatabase;
+import com.fsck.k9.mailstore.MigrationsHelper;
+import com.fsck.k9.mailstore.StorageManager;
+import org.junit.Before;
+import org.junit.Test;
+import org.robolectric.RuntimeEnvironment;
+import org.robolectric.shadows.ShadowLog;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotEquals;
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.anyBoolean;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+
+public class StoreSchemaDefinitionTest extends K9RobolectricTest {
+    private StoreSchemaDefinition storeSchemaDefinition;
+
+
+    @Before
+    public void setUp() throws MessagingException {
+        ShadowLog.stream = System.out;
+
+        Application application = RuntimeEnvironment.getApplication();
+        StorageManager.getInstance(application);
+
+        storeSchemaDefinition = createStoreSchemaDefinition();
+    }
+
+    @Test
+    public void getVersion_shouldReturnCurrentDatabaseVersion() {
+        int version = storeSchemaDefinition.getVersion();
+
+        assertEquals(StoreSchemaDefinition.DB_VERSION, version);
+    }
+
+    @Test
+    public void doDbUpgrade_withEmptyDatabase_shouldSetsDatabaseVersion() {
+        SQLiteDatabase database = SQLiteDatabase.create(null);
+
+        storeSchemaDefinition.doDbUpgrade(database);
+
+        assertEquals(StoreSchemaDefinition.DB_VERSION, database.getVersion());
+    }
+
+    @Test
+    public void doDbUpgrade_withBadDatabase_shouldThrowInDebugBuild() {
+        if (BuildConfig.DEBUG) {
+            SQLiteDatabase database = SQLiteDatabase.create(null);
+            database.setVersion(61);
+
+            try {
+                storeSchemaDefinition.doDbUpgrade(database);
+                fail("Expected Error");
+            } catch (Error e) {
+                assertEquals("Exception while upgrading database", e.getMessage());
+            }
+        }
+    }
+
+    @Test
+    public void doDbUpgrade_withV61_shouldUpgradeDatabaseToLatestVersion() {
+        SQLiteDatabase database = createV61Database();
+
+        storeSchemaDefinition.doDbUpgrade(database);
+
+        assertEquals(StoreSchemaDefinition.DB_VERSION, database.getVersion());
+    }
+
+    @Test
+    public void doDbUpgrade_withV61() {
+        SQLiteDatabase database = createV61Database();
+        insertMessageWithSubject(database, "Test Email");
+
+        storeSchemaDefinition.doDbUpgrade(database);
+
+        assertMessageWithSubjectExists(database, "Test Email");
+    }
+
+    @Test
+    public void doDbUpgrade_fromV61_shouldResultInSameTables() {
+        SQLiteDatabase newDatabase = createNewDatabase();
+        SQLiteDatabase upgradedDatabase = createV61Database();
+
+        storeSchemaDefinition.doDbUpgrade(upgradedDatabase);
+
+        assertDatabaseTablesEquals(newDatabase, upgradedDatabase);
+    }
+
+    @Test
+    public void doDbUpgrade_fromV61_shouldResultInSameTriggers() {
+        SQLiteDatabase newDatabase = createNewDatabase();
+        SQLiteDatabase upgradedDatabase = createV61Database();
+
+        storeSchemaDefinition.doDbUpgrade(upgradedDatabase);
+
+        assertDatabaseTriggersEquals(newDatabase, upgradedDatabase);
+    }
+
+    @Test
+    public void doDbUpgrade_fromV61_shouldResultInSameIndexes() {
+        SQLiteDatabase newDatabase = createNewDatabase();
+        SQLiteDatabase upgradedDatabase = createV61Database();
+
+        storeSchemaDefinition.doDbUpgrade(upgradedDatabase);
+
+        assertDatabaseIndexesEquals(newDatabase, upgradedDatabase);
+    }
+
+
+    private SQLiteDatabase createV61Database() {
+        SQLiteDatabase database = SQLiteDatabase.create(null);
+        initV61Database(database);
+        return database;
+    }
+
+    private void initV61Database(SQLiteDatabase db) {
+
+        db.beginTransaction();
+
+        db.execSQL("DROP TABLE IF EXISTS folders");
+        db.execSQL("CREATE TABLE folders (" +
+                "id INTEGER PRIMARY KEY," +
+                "name TEXT, " +
+                "last_updated INTEGER, " +
+                "unread_count INTEGER, " +
+                "visible_limit INTEGER, " +
+                "status TEXT, " +
+                "push_state TEXT, " +
+                "last_pushed INTEGER, " +
+                "flagged_count INTEGER default 0, " +
+                "integrate INTEGER, " +
+                "top_group INTEGER, " +
+                "poll_class TEXT, " +
+                "push_class TEXT, " +
+                "display_class TEXT, " +
+                "notify_class TEXT default 'INHERITED', " +
+                "more_messages TEXT default \"unknown\"" +
+                ")");
+
+        db.execSQL("CREATE INDEX IF NOT EXISTS folder_name ON folders (name)");
+        db.execSQL("DROP TABLE IF EXISTS messages");
+        db.execSQL("CREATE TABLE messages (" +
+                "id INTEGER PRIMARY KEY, " +
+                "deleted INTEGER default 0, " +
+                "folder_id INTEGER, " +
+                "uid TEXT, " +
+                "subject TEXT, " +
+                "date INTEGER, " +
+                "flags TEXT, " +
+                "sender_list TEXT, " +
+                "to_list TEXT, " +
+                "cc_list TEXT, " +
+                "bcc_list TEXT, " +
+                "reply_to_list TEXT, " +
+                "attachment_count INTEGER, " +
+                "internal_date INTEGER, " +
+                "message_id TEXT, " +
+                "preview_type TEXT default \"none\", " +
+                "preview TEXT, " +
+                "mime_type TEXT, "+
+                "normalized_subject_hash INTEGER, " +
+                "empty INTEGER default 0, " +
+                "read INTEGER default 0, " +
+                "flagged INTEGER default 0, " +
+                "answered INTEGER default 0, " +
+                "forwarded INTEGER default 0, " +
+                "message_part_id INTEGER" +
+                ")");
+
+        db.execSQL("DROP TABLE IF EXISTS message_parts");
+        db.execSQL("CREATE TABLE message_parts (" +
+                "id INTEGER PRIMARY KEY, " +
+                "type INTEGER NOT NULL, " +
+                "root INTEGER, " +
+                "parent INTEGER NOT NULL, " +
+                "seq INTEGER NOT NULL, " +
+                "mime_type TEXT, " +
+                "decoded_body_size INTEGER, " +
+                "display_name TEXT, " +
+                "header TEXT, " +
+                "encoding TEXT, " +
+                "charset TEXT, " +
+                "data_location INTEGER NOT NULL, " +
+                "data BLOB, " +
+                "preamble TEXT, " +
+                "epilogue TEXT, " +
+                "boundary TEXT, " +
+                "content_id TEXT, " +
+                "server_extra TEXT" +
+                ")");
+
+        db.execSQL("CREATE TRIGGER set_message_part_root " +
+                "AFTER INSERT ON message_parts " +
+                "BEGIN " +
+                "UPDATE message_parts SET root=id WHERE root IS NULL AND ROWID = NEW.ROWID; " +
+                "END");
+
+        db.execSQL("CREATE INDEX IF NOT EXISTS msg_uid ON messages (uid, folder_id)");
+        db.execSQL("DROP INDEX IF EXISTS msg_folder_id");
+        db.execSQL("DROP INDEX IF EXISTS msg_folder_id_date");
+        db.execSQL("CREATE INDEX IF NOT EXISTS msg_folder_id_deleted_date ON messages (folder_id,deleted,internal_date)");
+
+        db.execSQL("DROP INDEX IF EXISTS msg_empty");
+        db.execSQL("CREATE INDEX IF NOT EXISTS msg_empty ON messages (empty)");
+
+        db.execSQL("DROP INDEX IF EXISTS msg_read");
+        db.execSQL("CREATE INDEX IF NOT EXISTS msg_read ON messages (read)");
+
+        db.execSQL("DROP INDEX IF EXISTS msg_flagged");
+        db.execSQL("CREATE INDEX IF NOT EXISTS msg_flagged ON messages (flagged)");
+
+        db.execSQL("DROP INDEX IF EXISTS msg_composite");
+        db.execSQL("CREATE INDEX IF NOT EXISTS msg_composite ON messages (deleted, empty,folder_id,flagged,read)");
+
+
+        db.execSQL("DROP TABLE IF EXISTS threads");
+        db.execSQL("CREATE TABLE threads (" +
+                "id INTEGER PRIMARY KEY, " +
+                "message_id INTEGER, " +
+                "root INTEGER, " +
+                "parent INTEGER" +
+                ")");
+
+        db.execSQL("DROP INDEX IF EXISTS threads_message_id");
+        db.execSQL("CREATE INDEX IF NOT EXISTS threads_message_id ON threads (message_id)");
+
+        db.execSQL("DROP INDEX IF EXISTS threads_root");
+        db.execSQL("CREATE INDEX IF NOT EXISTS threads_root ON threads (root)");
+
+        db.execSQL("DROP INDEX IF EXISTS threads_parent");
+        db.execSQL("CREATE INDEX IF NOT EXISTS threads_parent ON threads (parent)");
+
+        db.execSQL("DROP TRIGGER IF EXISTS set_thread_root");
+        db.execSQL("CREATE TRIGGER set_thread_root " +
+                "AFTER INSERT ON threads " +
+                "BEGIN " +
+                "UPDATE threads SET root=id WHERE root IS NULL AND ROWID = NEW.ROWID; " +
+                "END");
+
+        db.execSQL("DROP TABLE IF EXISTS pending_commands");
+        db.execSQL("CREATE TABLE pending_commands " +
+                "(id INTEGER PRIMARY KEY, command TEXT, data TEXT)");
+
+        db.execSQL("DROP TRIGGER IF EXISTS delete_folder");
+        db.execSQL("CREATE TRIGGER delete_folder BEFORE DELETE ON folders BEGIN DELETE FROM messages WHERE old.id = folder_id; END;");
+
+        db.execSQL("DROP TRIGGER IF EXISTS delete_message");
+        db.execSQL("CREATE TRIGGER delete_message " +
+                "BEFORE DELETE ON messages " +
+                "BEGIN " +
+                "DELETE FROM message_parts WHERE root = OLD.message_part_id; " +
+                "DELETE FROM messages_fulltext WHERE docid = OLD.id; " +
+                "END");
+
+        db.execSQL("DROP TABLE IF EXISTS messages_fulltext");
+        db.execSQL("CREATE VIRTUAL TABLE messages_fulltext USING fts4 (fulltext)");
+
+        db.setVersion(61);
+
+        db.setTransactionSuccessful();
+        db.endTransaction();
+    }
+
+    private void assertMessageWithSubjectExists(SQLiteDatabase database, String subject) {
+        Cursor cursor = database.query("messages", new String[] { "subject" }, null, null, null, null, null);
+        try {
+            assertTrue(cursor.moveToFirst());
+            assertEquals(subject, cursor.getString(0));
+        } finally {
+            cursor.close();
+        }
+    }
+
+    private void assertDatabaseTablesEquals(SQLiteDatabase expected, SQLiteDatabase actual) {
+        List<String> tablesInNewDatabase = tablesInDatabase(expected);
+        Collections.sort(tablesInNewDatabase);
+
+        List<String> tablesInUpgradedDatabase = tablesInDatabase(actual);
+        Collections.sort(tablesInUpgradedDatabase);
+
+        assertEquals(tablesInNewDatabase, tablesInUpgradedDatabase);
+    }
+
+    private void assertDatabaseTriggersEquals(SQLiteDatabase expected, SQLiteDatabase actual) {
+        List<String> triggersInNewDatabase = triggersInDatabase(expected);
+        Collections.sort(triggersInNewDatabase);
+
+        List<String> triggersInUpgradedDatabase = triggersInDatabase(actual);
+        Collections.sort(triggersInUpgradedDatabase);
+
+        assertEquals(triggersInNewDatabase, triggersInUpgradedDatabase);
+    }
+
+    private void assertDatabaseIndexesEquals(SQLiteDatabase expected, SQLiteDatabase actual) {
+        List<String> indexesInNewDatabase = indexesInDatabase(expected);
+        Collections.sort(indexesInNewDatabase);
+
+        List<String> indexesInUpgradedDatabase = indexesInDatabase(actual);
+        Collections.sort(indexesInUpgradedDatabase);
+
+        assertEquals(indexesInNewDatabase, indexesInUpgradedDatabase);
+    }
+
+    private List<String> tablesInDatabase(SQLiteDatabase db) {
+        return objectsInDatabase(db, "table");
+    }
+
+    private List<String> triggersInDatabase(SQLiteDatabase db) {
+        return objectsInDatabase(db, "trigger");
+    }
+
+    private List<String> indexesInDatabase(SQLiteDatabase db) {
+        return objectsInDatabase(db, "index");
+    }
+
+    private List<String> objectsInDatabase(SQLiteDatabase db, String type) {
+        List<String> databaseObjects = new ArrayList<>();
+        Cursor cursor = db.rawQuery("SELECT sql FROM sqlite_master WHERE type = ? AND sql IS NOT NULL",
+                new String[] { type });
+        try {
+            while (cursor.moveToNext()) {
+                String sql = cursor.getString(cursor.getColumnIndex("sql"));
+                String resortedSql = "table".equals(type) ? sortTableColumns(sql) : sql;
+                databaseObjects.add(resortedSql);
+            }
+        } finally {
+            cursor.close();
+        }
+
+        return databaseObjects;
+    }
+
+    private String sortTableColumns(String sql) {
+        int positionOfColumnDefinitions = sql.indexOf('(');
+        String columnDefinitionsSql = sql.substring(positionOfColumnDefinitions + 1, sql.length() - 1);
+        String[] columnDefinitions = columnDefinitionsSql.split(" *, *(?![^(]*\\))");
+        Arrays.sort(columnDefinitions);
+
+        String sqlPrefix = sql.substring(0, positionOfColumnDefinitions + 1);
+        String sortedColumnDefinitionsSql = TextUtils.join(", ", columnDefinitions);
+        return sqlPrefix + sortedColumnDefinitionsSql + ")";
+    }
+
+    private void insertMessageWithSubject(SQLiteDatabase database, String subject) {
+        ContentValues data = new ContentValues();
+        data.put("subject", subject);
+        long rowId = database.insert("messages", null, data);
+        assertNotEquals(-1, rowId);
+    }
+
+    private StoreSchemaDefinition createStoreSchemaDefinition() throws MessagingException {
+        final Account account = createAccount();
+        final LockableDatabase lockableDatabase = createLockableDatabase();
+        final LocalStore localStore = mock(LocalStore.class);
+        when(localStore.getDatabase()).thenReturn(lockableDatabase);
+
+        MigrationsHelper migrationsHelper = new MigrationsHelper() {
+            @Override
+            public Account getAccount() {
+                return account;
+            }
+
+            @Override
+            public void saveAccount() {
+                // Do nothing
+            }
+        };
+
+        return new StoreSchemaDefinition(migrationsHelper);
+    }
+
+    private LockableDatabase createLockableDatabase() throws MessagingException {
+        LockableDatabase lockableDatabase = mock(LockableDatabase.class);
+        when(lockableDatabase.execute(anyBoolean(), any(LockableDatabase.DbCallback.class))).thenReturn(false);
+        return lockableDatabase;
+    }
+
+    private Account createAccount() {
+        Account account = mock(Account.class);
+        when(account.getLegacyInboxFolder()).thenReturn("Inbox");
+        when(account.getImportedTrashFolder()).thenReturn("Trash");
+        when(account.getImportedDraftsFolder()).thenReturn("Drafts");
+        when(account.getImportedSpamFolder()).thenReturn("Spam");
+        when(account.getImportedSentFolder()).thenReturn("Sent");
+        when(account.getImportedArchiveFolder()).thenReturn(null);
+        when(account.getLocalStorageProviderId()).thenReturn(StorageManager.InternalStorageProvider.ID);
+
+        ServerSettings incomingServerSettings = new ServerSettings("dummy", "", -1, ConnectionSecurity.NONE,
+                AuthType.AUTOMATIC, "", "", null);
+        when(account.getIncomingServerSettings()).thenReturn(incomingServerSettings);
+        return account;
+    }
+
+    private SQLiteDatabase createNewDatabase() {
+        SQLiteDatabase database = SQLiteDatabase.create(null);
+        storeSchemaDefinition.doDbUpgrade(database);
+        return database;
+    }
+}

app/storage/src/test/java/com/fsck/k9/storage/TestApp.kt

@@ -0,0 +1,35 @@
+package com.fsck.k9.storage
+
+import android.app.Application
+import com.fsck.k9.AppConfig
+import com.fsck.k9.Core
+import com.fsck.k9.CoreResourceProvider
+import com.fsck.k9.DI
+import com.fsck.k9.K9
+import com.fsck.k9.backend.BackendManager
+import com.fsck.k9.coreModules
+import com.fsck.k9.crypto.EncryptionExtractor
+import com.fsck.k9.preferences.K9StoragePersister
+import com.fsck.k9.preferences.StoragePersister
+import org.koin.dsl.module
+import org.mockito.kotlin.mock
+
+class TestApp : Application() {
+    override fun onCreate() {
+        Core.earlyInit()
+
+        super.onCreate()
+        DI.start(this, coreModules + storageModule + testModule)
+
+        K9.init(this)
+        Core.init(this)
+    }
+}
+
+val testModule = module {
+    single { AppConfig(emptyList()) }
+    single { mock<CoreResourceProvider>() }
+    single { mock<EncryptionExtractor>() }
+    single<StoragePersister> { K9StoragePersister(get()) }
+    single { mock<BackendManager>() }
+}

app/storage/src/test/java/com/fsck/k9/storage/messages/CheckFolderOperationsTest.kt

@@ -0,0 +1,65 @@
+package com.fsck.k9.storage.messages
+
+import assertk.assertThat
+import assertk.assertions.isFalse
+import assertk.assertions.isTrue
+import com.fsck.k9.storage.RobolectricTest
+import org.junit.Test
+
+class CheckFolderOperationsTest : RobolectricTest() {
+    private val sqliteDatabase = createDatabase()
+    private val lockableDatabase = createLockableDatabaseMock(sqliteDatabase)
+    private val checkFolderOperations = CheckFolderOperations(lockableDatabase)
+
+    @Test
+    fun `single folder not included in Unified Inbox`() {
+        val folderIds = listOf(sqliteDatabase.createFolder(integrate = false))
+
+        val result = checkFolderOperations.areAllIncludedInUnifiedInbox(folderIds)
+
+        assertThat(result).isFalse()
+    }
+
+    @Test
+    fun `single folder included in Unified Inbox`() {
+        val folderIds = listOf(sqliteDatabase.createFolder(integrate = true))
+
+        val result = checkFolderOperations.areAllIncludedInUnifiedInbox(folderIds)
+
+        assertThat(result).isTrue()
+    }
+
+    @Test
+    fun `not all folders included in Unified Inbox`() {
+        val folderIds = listOf(
+            sqliteDatabase.createFolder(integrate = true),
+            sqliteDatabase.createFolder(integrate = false)
+        )
+
+        val result = checkFolderOperations.areAllIncludedInUnifiedInbox(folderIds)
+
+        assertThat(result).isFalse()
+    }
+
+    @Test
+    fun `1000 folders included in Unified Inbox`() {
+        val folderIds = List(1000) {
+            sqliteDatabase.createFolder(integrate = true)
+        }
+
+        val result = checkFolderOperations.areAllIncludedInUnifiedInbox(folderIds)
+
+        assertThat(result).isTrue()
+    }
+
+    @Test
+    fun `999 of 1000 folders included in Unified Inbox`() {
+        val folderIds = List(999) {
+            sqliteDatabase.createFolder(integrate = true)
+        } + sqliteDatabase.createFolder(integrate = false)
+
+        val result = checkFolderOperations.areAllIncludedInUnifiedInbox(folderIds)
+
+        assertThat(result).isFalse()
+    }
+}

app/storage/src/test/java/com/fsck/k9/storage/messages/ChunkedDatabaseOperationsTest.kt

@@ -0,0 +1,114 @@
+package com.fsck.k9.storage.messages
+
+import assertk.assertThat
+import assertk.assertions.hasSize
+import assertk.assertions.isEqualTo
+import org.junit.Assert.fail
+import org.junit.Test
+
+class ChunkedDatabaseOperationsTest {
+    @Test(expected = IllegalArgumentException::class)
+    fun `empty list`() {
+        performChunkedOperation(
+            arguments = emptyList(),
+            argumentTransformation = Int::toString,
+            operation = ::failCallback
+        )
+    }
+
+    @Test(expected = IllegalArgumentException::class)
+    fun `chunkSize = 0`() {
+        performChunkedOperation(
+            arguments = listOf(1),
+            argumentTransformation = Int::toString,
+            chunkSize = 0,
+            operation = ::failCallback
+        )
+    }
+
+    @Test(expected = IllegalArgumentException::class)
+    fun `chunkSize = 1001`() {
+        performChunkedOperation(
+            arguments = listOf(1),
+            argumentTransformation = Int::toString,
+            chunkSize = 1001,
+            operation = ::failCallback
+        )
+    }
+
+    @Test
+    fun `single item`() {
+        val chunks = mutableListOf<Pair<String, Array<String>>>()
+
+        performChunkedOperation(
+            arguments = listOf(1),
+            argumentTransformation = Int::toString
+        ) { selectionSet, selectionArguments ->
+            chunks.add(selectionSet to selectionArguments)
+            Unit
+        }
+
+        assertThat(chunks).hasSize(1)
+        with(chunks.first()) {
+            assertThat(first).isEqualTo("IN (?)")
+            assertThat(second).isEqualTo(arrayOf("1"))
+        }
+    }
+
+    @Test
+    fun `2 items with chunk size of 1`() {
+        val chunks = mutableListOf<Pair<String, Array<String>>>()
+
+        performChunkedOperation(
+            arguments = listOf(1, 2),
+            argumentTransformation = Int::toString,
+            chunkSize = 1
+        ) { selectionSet, selectionArguments ->
+            chunks.add(selectionSet to selectionArguments)
+            Unit
+        }
+
+        assertThat(chunks).hasSize(2)
+        with(chunks[0]) {
+            assertThat(first).isEqualTo("IN (?)")
+            assertThat(second).isEqualTo(arrayOf("1"))
+        }
+        with(chunks[1]) {
+            assertThat(first).isEqualTo("IN (?)")
+            assertThat(second).isEqualTo(arrayOf("2"))
+        }
+    }
+
+    @Test
+    fun `14 items with chunk size of 5`() {
+        val chunks = mutableListOf<Pair<String, Array<String>>>()
+
+        performChunkedOperation(
+            arguments = (1..14).toList(),
+            argumentTransformation = Int::toString,
+            chunkSize = 5
+        ) { selectionSet, selectionArguments ->
+            chunks.add(selectionSet to selectionArguments)
+            Unit
+        }
+
+        assertThat(chunks).hasSize(3)
+        with(chunks[0]) {
+            assertThat(first).isEqualTo("IN (?,?,?,?,?)")
+            assertThat(second).isEqualTo(arrayOf("1", "2", "3", "4", "5"))
+        }
+        with(chunks[1]) {
+            assertThat(first).isEqualTo("IN (?,?,?,?,?)")
+            assertThat(second).isEqualTo(arrayOf("6", "7", "8", "9", "10"))
+        }
+        with(chunks[2]) {
+            assertThat(first).isEqualTo("IN (?,?,?,?)")
+            assertThat(second).isEqualTo(arrayOf("11", "12", "13", "14"))
+        }
+    }
+
+    @Suppress("UNUSED_PARAMETER")
+    private fun failCallback(selectionSet: String, selectionArguments: Array<String>) {
+        fail("'operation' callback called when it shouldn't")
+    }
+}

app/storage/src/test/java/com/fsck/k9/storage/messages/CopyMessageOperationsTest.kt

@@ -0,0 +1,252 @@
+package com.fsck.k9.storage.messages
+
+import assertk.assertThat
+import assertk.assertions.hasSize
+import assertk.assertions.isEqualTo
+import assertk.assertions.isNotIn
+import assertk.assertions.isNull
+import com.fsck.k9.mail.crlf
+import com.fsck.k9.mailstore.StorageManager
+import com.fsck.k9.storage.RobolectricTest
+import okio.buffer
+import okio.sink
+import okio.source
+import org.junit.After
+import org.junit.Test
+import org.mockito.kotlin.anyOrNull
+import org.mockito.kotlin.doReturn
+import org.mockito.kotlin.eq
+import org.mockito.kotlin.mock
+
+private const val ACCOUNT_UUID = "00000000-0000-4000-0000-000000000000"
+
+class CopyMessageOperationsTest : RobolectricTest() {
+    private val messagePartDirectory = createRandomTempDirectory()
+    private val sqliteDatabase = createDatabase()
+    private val storageManager = mock<StorageManager> {
+        on { getAttachmentDirectory(eq(ACCOUNT_UUID), anyOrNull()) } doReturn messagePartDirectory
+    }
+    private val lockableDatabase = createLockableDatabaseMock(sqliteDatabase)
+    private val attachmentFileManager = AttachmentFileManager(storageManager, ACCOUNT_UUID)
+    private val threadMessageOperations = ThreadMessageOperations()
+    private val copyMessageOperations = CopyMessageOperations(
+        lockableDatabase,
+        attachmentFileManager,
+        threadMessageOperations
+    )
+
+    @After
+    fun tearDown() {
+        messagePartDirectory.deleteRecursively()
+    }
+
+    @Test
+    fun `copy message that is part of a thread`() {
+        val sourceMessagePartId1 = sqliteDatabase.createMessagePart(
+            seq = 0,
+            dataLocation = DataLocation.CHILD_PART_CONTAINS_DATA,
+            mimeType = "multipart/mixed",
+            boundary = "--boundary",
+            header = "Message-ID: <msg0002@domain.example>\nIn-Reply-To: <msg0001@domain.example>\n".crlf()
+        )
+        val sourceMessagePartId2 = sqliteDatabase.createMessagePart(
+            seq = 1,
+            root = sourceMessagePartId1,
+            parent = sourceMessagePartId1,
+            mimeType = "text/plain",
+            dataLocation = DataLocation.IN_DATABASE,
+            data = "Text part".toByteArray()
+        )
+        val sourceMessagePartId3 = sqliteDatabase.createMessagePart(
+            seq = 2,
+            root = sourceMessagePartId1,
+            parent = sourceMessagePartId1,
+            mimeType = "application/octet-stream",
+            dataLocation = DataLocation.ON_DISK
+        )
+        attachmentFileManager.getAttachmentFile(sourceMessagePartId3).sink().buffer().use { sink ->
+            sink.writeUtf8("Part contents")
+        }
+
+        val messageId1 = sqliteDatabase.createMessage(
+            folderId = 1,
+            empty = true,
+            messageIdHeader = "<msg0001@domain.example>"
+        )
+        val messageId2 = sqliteDatabase.createMessage(
+            folderId = 1,
+            empty = false,
+            messageIdHeader = "<msg0002@domain.example>",
+            messagePartId = sourceMessagePartId1
+        )
+        val messageId3 = sqliteDatabase.createMessage(
+            folderId = 1,
+            empty = false,
+            messageIdHeader = "<msg0003@domain.example>"
+        )
+        val threadId1 = sqliteDatabase.createThread(messageId1)
+        val threadId2 = sqliteDatabase.createThread(messageId2, root = threadId1, parent = threadId1)
+        val threadId3 = sqliteDatabase.createThread(messageId3, root = threadId1, parent = threadId2)
+
+        val destinationMessageId = copyMessageOperations.copyMessage(messageId = messageId2, destinationFolderId = 2)
+
+        assertThat(destinationMessageId).isNotIn(setOf(messageId1, messageId2, messageId3))
+
+        val threads = sqliteDatabase.readThreads()
+        assertThat(threads).hasSize(3 + 2)
+
+        val destinationMessageThread = threads.first { it.messageId == destinationMessageId }
+        assertThat(destinationMessageThread.id).isNotIn(setOf(threadId1, threadId2, threadId3))
+        assertThat(destinationMessageThread.parent).isEqualTo(destinationMessageThread.root)
+
+        val destinationRootThread = threads.first { it.id == destinationMessageThread.root }
+        assertThat(destinationRootThread.messageId).isNotIn(setOf(messageId1, messageId2, messageId3))
+        assertThat(destinationRootThread.root).isEqualTo(destinationRootThread.id)
+        assertThat(destinationRootThread.parent).isNull()
+
+        val messages = sqliteDatabase.readMessages()
+        val destinationRootThreadMessage = messages.first { it.id == destinationRootThread.messageId }
+        assertThat(destinationRootThreadMessage.empty).isEqualTo(1)
+        assertThat(destinationRootThreadMessage.folderId).isEqualTo(2)
+        assertThat(destinationRootThreadMessage.messageId).isEqualTo("<msg0001@domain.example>")
+
+        val destinationMessage = messages.first { it.id == destinationMessageThread.messageId }
+        val sourceMessage = messages.first { it.id == messageId2 }
+        assertThat(destinationMessage).isEqualTo(
+            sourceMessage.copy(
+                id = destinationMessageId,
+                uid = destinationMessage.uid,
+                folderId = 2,
+                messagePartId = destinationMessage.messagePartId
+            )
+        )
+
+        val messageParts = sqliteDatabase.readMessageParts()
+        assertThat(messageParts).hasSize(3 + 3)
+
+        val sourceMessagePart1 = messageParts.first { it.id == sourceMessagePartId1 }
+        val sourceMessagePart2 = messageParts.first { it.id == sourceMessagePartId2 }
+        val sourceMessagePart3 = messageParts.first { it.id == sourceMessagePartId3 }
+        val destinationMessagePart1 = messageParts.first { it.id == destinationMessage.messagePartId }
+        val destinationMessagePart2 = messageParts.first { it.root == destinationMessage.messagePartId && it.seq == 1 }
+        val destinationMessagePart3 = messageParts.first { it.root == destinationMessage.messagePartId && it.seq == 2 }
+        assertThat(destinationMessagePart1).isNotIn(setOf(sourceMessagePart1, sourceMessagePart2, sourceMessagePart3))
+        assertThat(destinationMessagePart1).isEqualTo(
+            sourceMessagePart1.copy(
+                id = destinationMessagePart1.id,
+                root = destinationMessagePart1.id,
+                parent = -1
+            )
+        )
+        assertThat(destinationMessagePart2).isNotIn(setOf(sourceMessagePart1, sourceMessagePart2, sourceMessagePart3))
+        assertThat(destinationMessagePart2).isEqualTo(
+            sourceMessagePart2.copy(
+                id = destinationMessagePart2.id,
+                root = destinationMessagePart1.id,
+                parent = destinationMessagePart1.id
+            )
+        )
+        assertThat(destinationMessagePart3).isNotIn(setOf(sourceMessagePart1, sourceMessagePart2, sourceMessagePart3))
+        assertThat(destinationMessagePart3).isEqualTo(
+            sourceMessagePart3.copy(
+                id = destinationMessagePart3.id,
+                root = destinationMessagePart1.id,
+                parent = destinationMessagePart1.id
+            )
+        )
+
+        val files = messagePartDirectory.list()?.toList() ?: emptyList()
+        assertThat(files).hasSize(2)
+
+        attachmentFileManager.getAttachmentFile(destinationMessagePart3.id!!).source().buffer().use { source ->
+            assertThat(source.readUtf8()).isEqualTo("Part contents")
+        }
+    }
+
+    @Test
+    fun `copy message into an existing thread`() {
+        val sourceMessagePartId = sqliteDatabase.createMessagePart(
+            header = "Message-ID: <msg0002@domain.example>\nIn-Reply-To: <msg0001@domain.example>\n".crlf(),
+            mimeType = "text/plain",
+            dataLocation = DataLocation.IN_DATABASE,
+            data = "Text part".toByteArray()
+        )
+        attachmentFileManager.getAttachmentFile(sourceMessagePartId).sink().buffer().use { sink ->
+            sink.writeUtf8("Part contents")
+        }
+
+        val sourceMessageId = sqliteDatabase.createMessage(
+            folderId = 1,
+            empty = false,
+            messageIdHeader = "<msg0002@domain.example>",
+            messagePartId = sourceMessagePartId
+        )
+        val destinationMessageId = sqliteDatabase.createMessage(
+            folderId = 2,
+            empty = true,
+            messageIdHeader = "<msg0002@domain.example>"
+        )
+        val otherDestinationMessageId = sqliteDatabase.createMessage(
+            folderId = 2,
+            empty = false,
+            messageIdHeader = "<msg0003@domain.example>"
+        )
+        val destinationThreadId = sqliteDatabase.createThread(destinationMessageId)
+        val otherDestinationThreadId = sqliteDatabase.createThread(
+            otherDestinationMessageId,
+            root = destinationThreadId,
+            parent = destinationThreadId
+        )
+
+        val resultMessageId = copyMessageOperations.copyMessage(messageId = sourceMessageId, destinationFolderId = 2)
+
+        assertThat(resultMessageId).isEqualTo(destinationMessageId)
+
+        val threads = sqliteDatabase.readThreads()
+        assertThat(threads).hasSize(2 + 1)
+
+        val destinationThread = threads.first { it.messageId == destinationMessageId }
+        assertThat(destinationThread.id).isEqualTo(destinationThreadId)
+        assertThat(destinationThread.parent).isEqualTo(destinationThread.root)
+
+        val destinationRootThread = threads.first { it.id == destinationThread.root }
+        assertThat(destinationRootThread.root).isEqualTo(destinationRootThread.id)
+        assertThat(destinationRootThread.parent).isNull()
+
+        val otherDestinationThread = threads.first { it.id == otherDestinationThreadId }
+        assertThat(otherDestinationThread.root).isEqualTo(destinationRootThread.id)
+        assertThat(otherDestinationThread.parent).isEqualTo(destinationThread.id)
+
+        val messages = sqliteDatabase.readMessages()
+        assertThat(messages).hasSize(3 + 1)
+
+        val destinationRootThreadMessage = messages.first { it.id == destinationRootThread.messageId }
+        assertThat(destinationRootThreadMessage.empty).isEqualTo(1)
+        assertThat(destinationRootThreadMessage.folderId).isEqualTo(2)
+        assertThat(destinationRootThreadMessage.messageId).isEqualTo("<msg0001@domain.example>")
+
+        val destinationMessage = messages.first { it.id == destinationMessageId }
+        val sourceMessage = messages.first { it.id == sourceMessageId }
+        assertThat(destinationMessage).isEqualTo(
+            sourceMessage.copy(
+                id = destinationMessageId,
+                uid = destinationMessage.uid,
+                folderId = 2,
+                messagePartId = destinationMessage.messagePartId
+            )
+        )
+
+        val messageParts = sqliteDatabase.readMessageParts()
+        assertThat(messageParts).hasSize(1 + 1)
+
+        val sourceMessagePart = messageParts.first { it.id == sourceMessagePartId }
+        val destinationMessagePart = messageParts.first { it.id == destinationMessage.messagePartId }
+        assertThat(destinationMessagePart).isEqualTo(
+            sourceMessagePart.copy(
+                id = destinationMessagePart.id,
+                root = destinationMessagePart.id,
+                parent = -1
+            )
+        )
+    }
+}

app/storage/src/test/java/com/fsck/k9/storage/messages/CreateFolderOperationsTest.kt

@@ -0,0 +1,91 @@
+package com.fsck.k9.storage.messages
+
+import assertk.assertThat
+import assertk.assertions.hasSize
+import assertk.assertions.isEqualTo
+import com.fsck.k9.mail.FolderClass
+import com.fsck.k9.mail.FolderType
+import com.fsck.k9.mailstore.CreateFolderInfo
+import com.fsck.k9.mailstore.FolderSettings
+import com.fsck.k9.storage.RobolectricTest
+import org.junit.Test
+
+class CreateFolderOperationsTest : RobolectricTest() {
+    private val sqliteDatabase = createDatabase()
+    private val lockableDatabase = createLockableDatabaseMock(sqliteDatabase)
+    private val createFolderOperations = CreateFolderOperations(lockableDatabase)
+
+    @Test
+    fun `create single folder`() {
+        createFolderOperations.createFolders(
+            listOf(
+                CreateFolderInfo(
+                    serverId = "archived_messages",
+                    name = "Archive",
+                    type = FolderType.ARCHIVE,
+                    settings = FolderSettings(
+                        visibleLimit = 10,
+                        displayClass = FolderClass.FIRST_CLASS,
+                        syncClass = FolderClass.SECOND_CLASS,
+                        notifyClass = FolderClass.NO_CLASS,
+                        pushClass = FolderClass.NO_CLASS,
+                        inTopGroup = true,
+                        integrate = false
+                    )
+                )
+            )
+        )
+
+        val folders = sqliteDatabase.readFolders()
+        assertThat(folders).hasSize(1)
+        val folder = folders.first()
+        assertThat(folder.serverId).isEqualTo("archived_messages")
+        assertThat(folder.name).isEqualTo("Archive")
+        assertThat(folder.type).isEqualTo("archive")
+        assertThat(folder.visibleLimit).isEqualTo(10)
+        assertThat(folder.displayClass).isEqualTo("FIRST_CLASS")
+        assertThat(folder.syncClass).isEqualTo("SECOND_CLASS")
+        assertThat(folder.notifyClass).isEqualTo("NO_CLASS")
+        assertThat(folder.pushClass).isEqualTo("NO_CLASS")
+        assertThat(folder.inTopGroup).isEqualTo(1)
+        assertThat(folder.integrate).isEqualTo(0)
+    }
+
+    @Test
+    fun `create multiple folders`() {
+        createFolderOperations.createFolders(
+            listOf(
+                createCreateFolderInfo(serverId = "folder1", name = "Inbox"),
+                createCreateFolderInfo(serverId = "folder2", name = "Sent"),
+                createCreateFolderInfo(serverId = "folder3", name = "Trash")
+            )
+        )
+
+        val folders = sqliteDatabase.readFolders()
+        assertThat(folders).hasSize(3)
+        assertThat(folders.map { it.serverId to it.name }.toSet()).isEqualTo(
+            setOf(
+                "folder1" to "Inbox",
+                "folder2" to "Sent",
+                "folder3" to "Trash"
+            )
+        )
+    }
+
+    fun createCreateFolderInfo(serverId: String, name: String): CreateFolderInfo {
+        return CreateFolderInfo(
+            serverId = serverId,
+            name = name,
+            type = FolderType.REGULAR,
+            settings = FolderSettings(
+                visibleLimit = 25,
+                displayClass = FolderClass.NO_CLASS,
+                syncClass = FolderClass.INHERITED,
+                notifyClass = FolderClass.INHERITED,
+                pushClass = FolderClass.NO_CLASS,
+                inTopGroup = false,
+                integrate = false
+            )
+        )
+    }
+}

app/storage/src/test/java/com/fsck/k9/storage/messages/DeleteFolderOperationsTest.kt

@@ -0,0 +1,62 @@
+package com.fsck.k9.storage.messages
+
+import assertk.assertThat
+import assertk.assertions.containsExactly
+import assertk.assertions.extracting
+import assertk.assertions.hasSize
+import assertk.assertions.isEqualTo
+import assertk.assertions.isNotNull
+import com.fsck.k9.mailstore.StorageManager
+import com.fsck.k9.storage.RobolectricTest
+import org.junit.After
+import org.junit.Test
+import org.mockito.kotlin.anyOrNull
+import org.mockito.kotlin.doReturn
+import org.mockito.kotlin.eq
+import org.mockito.kotlin.mock
+
+private const val ACCOUNT_UUID = "00000000-0000-4000-0000-000000000000"
+
+class DeleteFolderOperationsTest : RobolectricTest() {
+    private val messagePartDirectory = createRandomTempDirectory()
+    private val sqliteDatabase = createDatabase()
+    private val storageManager = mock<StorageManager> {
+        on { getAttachmentDirectory(eq(ACCOUNT_UUID), anyOrNull()) } doReturn messagePartDirectory
+    }
+    private val lockableDatabase = createLockableDatabaseMock(sqliteDatabase)
+    private val attachmentFileManager = AttachmentFileManager(storageManager, ACCOUNT_UUID)
+    private val deleteFolderOperations = DeleteFolderOperations(lockableDatabase, attachmentFileManager)
+
+    @After
+    fun tearDown() {
+        messagePartDirectory.deleteRecursively()
+    }
+
+    @Test
+    fun `delete folder should remove message part files`() {
+        createFolderWithMessage("delete", "message1")
+        val messagePartId = createFolderWithMessage("retain", "message2")
+
+        deleteFolderOperations.deleteFolders(listOf("delete"))
+
+        val folders = sqliteDatabase.readFolders()
+        assertThat(folders).hasSize(1)
+        assertThat(folders.first().serverId).isEqualTo("retain")
+
+        val messages = sqliteDatabase.readMessages()
+        assertThat(messages).hasSize(1)
+        assertThat(messages.first().uid).isEqualTo("message2")
+
+        val messagePartFiles = messagePartDirectory.listFiles()
+        assertThat(messagePartFiles).isNotNull()
+            .extracting { it.name }.containsExactly(messagePartId.toString())
+    }
+
+    private fun createFolderWithMessage(folderServerId: String, messageServerId: String): Long {
+        val folderId = sqliteDatabase.createFolder(serverId = folderServerId)
+        val messagePartId = sqliteDatabase.createMessagePart(dataLocation = 2, directory = messagePartDirectory)
+        sqliteDatabase.createMessage(folderId = folderId, uid = messageServerId, messagePartId = messagePartId)
+
+        return messagePartId
+    }
+}

app/storage/src/test/java/com/fsck/k9/storage/messages/DeleteMessageOperationsTest.kt

@@ -0,0 +1,196 @@
+package com.fsck.k9.storage.messages
+
+import assertk.assertThat
+import assertk.assertions.containsExactlyInAnyOrder
+import assertk.assertions.extracting
+import assertk.assertions.hasSize
+import assertk.assertions.isEmpty
+import assertk.assertions.isEqualTo
+import assertk.assertions.isNotNull
+import assertk.assertions.isNull
+import com.fsck.k9.mailstore.StorageManager
+import com.fsck.k9.storage.RobolectricTest
+import org.junit.After
+import org.junit.Test
+import org.mockito.kotlin.anyOrNull
+import org.mockito.kotlin.doReturn
+import org.mockito.kotlin.eq
+import org.mockito.kotlin.mock
+
+private const val ACCOUNT_UUID = "00000000-0000-4000-0000-000000000000"
+
+class DeleteMessageOperationsTest : RobolectricTest() {
+    private val messagePartDirectory = createRandomTempDirectory()
+    private val sqliteDatabase = createDatabase()
+    private val storageManager = mock<StorageManager> {
+        on { getAttachmentDirectory(eq(ACCOUNT_UUID), anyOrNull()) } doReturn messagePartDirectory
+    }
+    private val lockableDatabase = createLockableDatabaseMock(sqliteDatabase)
+    private val attachmentFileManager = AttachmentFileManager(storageManager, ACCOUNT_UUID)
+    private val deleteMessageOperations = DeleteMessageOperations(lockableDatabase, attachmentFileManager)
+
+    @After
+    fun tearDown() {
+        messagePartDirectory.deleteRecursively()
+    }
+
+    @Test
+    fun `destroy message with empty parent messages`() {
+        val folderId = sqliteDatabase.createFolder()
+        val messageId1 = sqliteDatabase.createMessage(
+            folderId = folderId,
+            uid = "empty1",
+            empty = true,
+            messageIdHeader = "msg001@domain.example"
+        )
+        val messageId2 = sqliteDatabase.createMessage(
+            folderId = folderId,
+            uid = "empty2",
+            empty = true,
+            messageIdHeader = "msg002@domain.example"
+        )
+        val messageId3 = sqliteDatabase.createMessage(
+            folderId = folderId,
+            uid = "delete",
+            empty = false,
+            messageIdHeader = "msg003@domain.example"
+        )
+        val threadId1 = sqliteDatabase.createThread(messageId = messageId1)
+        val threadId2 = sqliteDatabase.createThread(messageId = messageId2, root = threadId1, parent = threadId1)
+        sqliteDatabase.createThread(messageId = messageId3, root = threadId1, parent = threadId2)
+
+        deleteMessageOperations.destroyMessages(folderId = folderId, messageServerIds = listOf("delete"))
+
+        assertThat(sqliteDatabase.readMessages()).isEmpty()
+        assertThat(sqliteDatabase.readThreads()).isEmpty()
+    }
+
+    @Test
+    fun `destroy message with empty parent message that has another child`() {
+        val folderId = sqliteDatabase.createFolder()
+        val messageId1 = sqliteDatabase.createMessage(
+            folderId = folderId,
+            uid = "empty",
+            empty = true,
+            messageIdHeader = "msg001@domain.example"
+        )
+        val messageId2 = sqliteDatabase.createMessage(
+            folderId = folderId,
+            uid = "child1",
+            empty = false,
+            messageIdHeader = "msg002@domain.example"
+        )
+        val messageId3 = sqliteDatabase.createMessage(
+            folderId = folderId,
+            uid = "delete",
+            empty = false,
+            messageIdHeader = "msg003@domain.example"
+        )
+        val threadId1 = sqliteDatabase.createThread(messageId = messageId1)
+        val threadId2 = sqliteDatabase.createThread(messageId = messageId2, root = threadId1, parent = threadId1)
+        sqliteDatabase.createThread(messageId = messageId3, root = threadId1, parent = threadId1)
+
+        deleteMessageOperations.destroyMessages(folderId = folderId, messageServerIds = listOf("delete"))
+
+        val messages = sqliteDatabase.readMessages()
+        assertThat(messages).hasSize(2)
+        assertThat(messages.map { it.id }.toSet()).isEqualTo(setOf(messageId1, messageId2))
+
+        val threads = sqliteDatabase.readThreads()
+        assertThat(threads).hasSize(2)
+        assertThat(threads.map { it.id }.toSet()).isEqualTo(setOf(threadId1, threadId2))
+    }
+
+    @Test
+    fun `destroy message with non-empty parent message`() {
+        val folderId = sqliteDatabase.createFolder()
+        val messageId1 = sqliteDatabase.createMessage(
+            folderId = folderId,
+            uid = "parent",
+            empty = false,
+            messageIdHeader = "msg001@domain.example"
+        )
+        val messageId2 = sqliteDatabase.createMessage(
+            folderId = folderId,
+            uid = "delete",
+            empty = false,
+            messageIdHeader = "msg002@domain.example"
+        )
+        val threadId1 = sqliteDatabase.createThread(messageId = messageId1)
+        sqliteDatabase.createThread(messageId = messageId2, root = threadId1, parent = threadId1)
+
+        deleteMessageOperations.destroyMessages(folderId = folderId, messageServerIds = listOf("delete"))
+
+        val messages = sqliteDatabase.readMessages()
+        assertThat(messages).hasSize(1)
+        assertThat(messages.first().id).isEqualTo(messageId1)
+
+        val threads = sqliteDatabase.readThreads()
+        assertThat(threads).hasSize(1)
+        assertThat(threads.first().id).isEqualTo(threadId1)
+    }
+
+    @Test
+    fun `destroy message without parent message`() {
+        val folderId = sqliteDatabase.createFolder()
+        val messageId1 = sqliteDatabase.createMessage(
+            folderId = folderId,
+            uid = "delete",
+            empty = false,
+            messageIdHeader = "msg001@domain.example"
+        )
+        sqliteDatabase.createThread(messageId = messageId1)
+
+        deleteMessageOperations.destroyMessages(folderId = folderId, messageServerIds = listOf("delete"))
+
+        assertThat(sqliteDatabase.readMessages()).isEmpty()
+        assertThat(sqliteDatabase.readThreads()).isEmpty()
+    }
+
+    @Test
+    fun `destroy message with child message should convert to empty message`() {
+        val folderId = sqliteDatabase.createFolder()
+        val messageId1 = sqliteDatabase.createMessage(
+            folderId = folderId,
+            uid = "delete",
+            empty = false,
+            messageIdHeader = "msg001@domain.example"
+        )
+        val messageId2 = sqliteDatabase.createMessage(
+            folderId = folderId,
+            uid = "child",
+            empty = false,
+            messageIdHeader = "msg002@domain.example"
+        )
+        val threadId1 = sqliteDatabase.createThread(messageId = messageId1)
+        val threadId2 = sqliteDatabase.createThread(messageId = messageId2, root = threadId1, parent = threadId1)
+
+        deleteMessageOperations.destroyMessages(folderId = folderId, messageServerIds = listOf("delete"))
+
+        val messages = sqliteDatabase.readMessages()
+        assertThat(messages).hasSize(2)
+        val message1 = messages.first { it.id == messageId1 }
+        assertThat(message1.empty).isEqualTo(1)
+        assertThat(message1.subject).isNull()
+        assertThat(message1.date).isNull()
+        assertThat(message1.flags).isNull()
+        assertThat(message1.senderList).isNull()
+        assertThat(message1.toList).isNull()
+        assertThat(message1.ccList).isNull()
+        assertThat(message1.bccList).isNull()
+        assertThat(message1.replyToList).isNull()
+        assertThat(message1.attachmentCount).isNull()
+        assertThat(message1.internalDate).isNull()
+        assertThat(message1.previewType).isEqualTo("none")
+        assertThat(message1.preview).isNull()
+        assertThat(message1.mimeType).isNull()
+        assertThat(message1.normalizedSubjectHash).isNull()
+        assertThat(message1.messagePartId).isNull()
+        assertThat(message1.encryptionType).isNull()
+        assertThat(messages.firstOrNull { it.id == messageId2 }).isNotNull()
+
+        val threads = sqliteDatabase.readThreads()
+        assertThat(threads).hasSize(2)
+        assertThat(threads).extracting { it.id }.containsExactlyInAnyOrder(threadId1, threadId2)
+    }
+}

app/storage/src/test/java/com/fsck/k9/storage/messages/FileHelpers.kt

@@ -0,0 +1,10 @@
+package com.fsck.k9.storage.messages
+
+import java.io.File
+import java.util.UUID
+
+@Suppress("NULLABILITY_MISMATCH_BASED_ON_JAVA_ANNOTATIONS")
+fun createRandomTempDirectory(): File {
+    val tempDirectory = File(System.getProperty("java.io.tmpdir", "."))
+    return File(tempDirectory, UUID.randomUUID().toString()).also { it.mkdir() }
+}

app/storage/src/test/java/com/fsck/k9/storage/messages/FlagMessageOperationsTest.kt

@@ -0,0 +1,100 @@
+package com.fsck.k9.storage.messages
+
+import assertk.assertThat
+import assertk.assertions.hasSize
+import assertk.assertions.isEqualTo
+import assertk.assertions.isTrue
+import com.fsck.k9.mail.Flag
+import com.fsck.k9.storage.RobolectricTest
+import org.junit.Test
+
+class FlagMessageOperationsTest : RobolectricTest() {
+    private val sqliteDatabase = createDatabase()
+    private val lockableDatabase = createLockableDatabaseMock(sqliteDatabase)
+    private val flagMessageOperations = FlagMessageOperations(lockableDatabase)
+
+    @Test(expected = IllegalArgumentException::class)
+    fun `empty messageIds list`() {
+        flagMessageOperations.setFlag(emptyList(), Flag.SEEN, true)
+    }
+
+    @Test
+    fun `mark one message as answered`() {
+        val messageId = sqliteDatabase.createMessage(folderId = 1, uid = "uid1", answered = false)
+        sqliteDatabase.createMessage(folderId = 1, uid = "uid2", answered = false)
+        val messageIds = listOf(messageId)
+
+        flagMessageOperations.setFlag(messageIds, Flag.ANSWERED, true)
+
+        val messages = sqliteDatabase.readMessages()
+
+        val message = messages.find { it.id == messageId } ?: error("Original message not found")
+        assertThat(message.answered).isEqualTo(1)
+
+        val otherMessages = messages.filterNot { it.id == messageId }
+        assertThat(otherMessages).hasSize(1)
+        assertThat(otherMessages.all { it.answered == 0 }).isTrue()
+    }
+
+    @Test
+    fun `mark multiple messages as read`() {
+        val messageId1 = sqliteDatabase.createMessage(folderId = 1, uid = "uid1", read = false)
+        val messageId2 = sqliteDatabase.createMessage(folderId = 1, uid = "uid2", read = false)
+        val messageId3 = sqliteDatabase.createMessage(folderId = 1, uid = "uid3", read = false)
+        sqliteDatabase.createMessage(folderId = 1, uid = "uidx", read = false)
+        val messageIds = listOf(messageId1, messageId2, messageId3)
+
+        flagMessageOperations.setFlag(messageIds, Flag.SEEN, true)
+
+        val messages = sqliteDatabase.readMessages()
+
+        val affectedMessages = messages.filter { it.id in messageIds }
+        assertThat(affectedMessages).hasSize(3)
+        assertThat(affectedMessages.all { it.read == 1 }).isTrue()
+
+        val otherMessages = messages.filterNot { it.id in messageIds }
+        assertThat(otherMessages).hasSize(1)
+        assertThat(otherMessages.all { it.read == 0 }).isTrue()
+    }
+
+    @Test
+    fun `mark message as read`() {
+        sqliteDatabase.createMessage(folderId = 1, uid = "uid1", read = false)
+
+        flagMessageOperations.setMessageFlag(folderId = 1, messageServerId = "uid1", Flag.SEEN, true)
+
+        val message = sqliteDatabase.readMessages().first()
+        assertThat(message.read).isEqualTo(1)
+    }
+
+    @Test
+    fun `mark message as unread`() {
+        sqliteDatabase.createMessage(folderId = 1, uid = "uid1", read = true)
+
+        flagMessageOperations.setMessageFlag(folderId = 1, messageServerId = "uid1", Flag.SEEN, false)
+
+        val message = sqliteDatabase.readMessages().first()
+        assertThat(message.read).isEqualTo(0)
+    }
+
+    @Test
+    fun `mark message as X_DOWNLOADED_FULL`() {
+        sqliteDatabase.createMessage(folderId = 1, uid = "uid1", flags = "X_SUBJECT_DECRYPTED")
+
+        flagMessageOperations.setMessageFlag(folderId = 1, messageServerId = "uid1", Flag.X_DOWNLOADED_FULL, true)
+
+        val message = sqliteDatabase.readMessages().first()
+        val readFlags = message.flags!!.split(',').toSet()
+        assertThat(readFlags).isEqualTo(setOf("X_SUBJECT_DECRYPTED", "X_DOWNLOADED_FULL"))
+    }
+
+    @Test
+    fun `remove X_DOWNLOADED_FULL flag`() {
+        sqliteDatabase.createMessage(folderId = 1, uid = "uid1", flags = "X_DOWNLOADED_FULL")
+
+        flagMessageOperations.setMessageFlag(folderId = 1, messageServerId = "uid1", Flag.X_DOWNLOADED_FULL, false)
+
+        val message = sqliteDatabase.readMessages().first()
+        assertThat(message.flags).isEqualTo("")
+    }
+}

app/storage/src/test/java/com/fsck/k9/storage/messages/FolderHelpers.kt

@@ -0,0 +1,95 @@
+package com.fsck.k9.storage.messages
+
+import android.content.ContentValues
+import android.database.sqlite.SQLiteDatabase
+import app.k9mail.core.android.common.database.getIntOrNull
+import app.k9mail.core.android.common.database.getLongOrNull
+import app.k9mail.core.android.common.database.getStringOrNull
+import app.k9mail.core.android.common.database.map
+
+fun SQLiteDatabase.createFolder(
+    name: String = "irrelevant",
+    type: String = "regular",
+    serverId: String? = null,
+    isLocalOnly: Boolean = true,
+    integrate: Boolean = false,
+    inTopGroup: Boolean = false,
+    displayClass: String = "NO_CLASS",
+    syncClass: String? = "INHERITED",
+    notifyClass: String? = "INHERITED",
+    pushClass: String? = "SECOND_CLASS",
+    lastUpdated: Long = 0L,
+    unreadCount: Int = 0,
+    visibleLimit: Int = 25,
+    status: String? = null,
+    flaggedCount: Int = 0,
+    moreMessages: String = "unknown"
+): Long {
+    val values = ContentValues().apply {
+        put("name", name)
+        put("type", type)
+        put("server_id", serverId)
+        put("local_only", isLocalOnly)
+        put("integrate", integrate)
+        put("top_group", inTopGroup)
+        put("display_class", displayClass)
+        put("poll_class", syncClass)
+        put("notify_class", notifyClass)
+        put("push_class", pushClass)
+        put("last_updated", lastUpdated)
+        put("unread_count", unreadCount)
+        put("visible_limit", visibleLimit)
+        put("status", status)
+        put("flagged_count", flaggedCount)
+        put("more_messages", moreMessages)
+    }
+
+    return insert("folders", null, values)
+}
+
+fun SQLiteDatabase.readFolders(): List<FolderEntry> {
+    val cursor = rawQuery("SELECT * FROM folders", null)
+    return cursor.use {
+        cursor.map {
+            FolderEntry(
+                id = cursor.getLongOrNull("id"),
+                name = cursor.getStringOrNull("name"),
+                type = cursor.getStringOrNull("type"),
+                serverId = cursor.getStringOrNull("server_id"),
+                isLocalOnly = cursor.getIntOrNull("local_only"),
+                integrate = cursor.getIntOrNull("integrate"),
+                inTopGroup = cursor.getIntOrNull("top_group"),
+                displayClass = cursor.getStringOrNull("display_class"),
+                syncClass = cursor.getStringOrNull("poll_class"),
+                notifyClass = cursor.getStringOrNull("notify_class"),
+                pushClass = cursor.getStringOrNull("push_class"),
+                lastUpdated = cursor.getLongOrNull("last_updated"),
+                unreadCount = cursor.getIntOrNull("unread_count"),
+                visibleLimit = cursor.getIntOrNull("visible_limit"),
+                status = cursor.getStringOrNull("status"),
+                flaggedCount = cursor.getIntOrNull("flagged_count"),
+                moreMessages = cursor.getStringOrNull("more_messages")
+            )
+        }
+    }
+}
+
+data class FolderEntry(
+    val id: Long?,
+    val name: String?,
+    val type: String?,
+    val serverId: String?,
+    val isLocalOnly: Int?,
+    val integrate: Int?,
+    val inTopGroup: Int?,
+    val displayClass: String?,
+    val syncClass: String?,
+    val notifyClass: String?,
+    val pushClass: String?,
+    val lastUpdated: Long?,
+    val unreadCount: Int?,
+    val visibleLimit: Int?,
+    val status: String?,
+    val flaggedCount: Int?,
+    val moreMessages: String?
+)

app/storage/src/test/java/com/fsck/k9/storage/messages/KeyValueHelpers.kt

@@ -0,0 +1,77 @@
+package com.fsck.k9.storage.messages
+
+import android.content.ContentValues
+import android.database.sqlite.SQLiteDatabase
+import app.k9mail.core.android.common.database.getLongOrNull
+import app.k9mail.core.android.common.database.getStringOrNull
+import app.k9mail.core.android.common.database.map
+
+fun SQLiteDatabase.createExtraValue(
+    name: String = "irrelevant",
+    text: String? = null,
+    number: Long? = null
+): Long {
+    val values = ContentValues().apply {
+        put("name", name)
+        put("value_text", text)
+        put("value_integer", number)
+    }
+
+    return insert("account_extra_values", null, values)
+}
+
+fun SQLiteDatabase.readExtraValues(): List<ExtraValueEntry> {
+    val cursor = rawQuery("SELECT * FROM account_extra_values", null)
+    return cursor.use {
+        cursor.map {
+            ExtraValueEntry(
+                name = cursor.getStringOrNull("name"),
+                text = cursor.getStringOrNull("value_text"),
+                number = cursor.getLongOrNull("value_integer")
+            )
+        }
+    }
+}
+
+data class ExtraValueEntry(
+    val name: String?,
+    val text: String?,
+    val number: Long?
+)
+
+fun SQLiteDatabase.createFolderExtraValue(
+    folderId: Long,
+    name: String = "irrelevant",
+    text: String? = null,
+    number: Long? = null
+): Long {
+    val values = ContentValues().apply {
+        put("folder_id", folderId)
+        put("name", name)
+        put("value_text", text)
+        put("value_integer", number)
+    }
+
+    return insert("folder_extra_values", null, values)
+}
+
+fun SQLiteDatabase.readFolderExtraValues(): List<FolderExtraValueEntry> {
+    val cursor = rawQuery("SELECT * FROM folder_extra_values", null)
+    return cursor.use {
+        cursor.map {
+            FolderExtraValueEntry(
+                folderId = cursor.getLongOrNull("folder_id"),
+                name = cursor.getStringOrNull("name"),
+                text = cursor.getStringOrNull("value_text"),
+                number = cursor.getLongOrNull("value_integer")
+            )
+        }
+    }
+}
+
+data class FolderExtraValueEntry(
+    val folderId: Long?,
+    val name: String?,
+    val text: String?,
+    val number: Long?
+)

app/storage/src/test/java/com/fsck/k9/storage/messages/KeyValueStoreOperationsTest.kt

@@ -0,0 +1,210 @@
+package com.fsck.k9.storage.messages
+
+import assertk.assertThat
+import assertk.assertions.hasSize
+import assertk.assertions.isEqualTo
+import assertk.assertions.isNull
+import com.fsck.k9.storage.RobolectricTest
+import org.junit.Test
+
+class KeyValueStoreOperationsTest : RobolectricTest() {
+    private val sqliteDatabase = createDatabase()
+    private val lockableDatabase = createLockableDatabaseMock(sqliteDatabase)
+    private val keyValueStoreOperations = KeyValueStoreOperations(lockableDatabase)
+
+    @Test
+    fun `get extra string`() {
+        sqliteDatabase.createExtraValue(name = "test", text = "Wurstsalat")
+
+        val result = keyValueStoreOperations.getExtraString("test")
+
+        assertThat(result).isEqualTo("Wurstsalat")
+    }
+
+    @Test
+    fun `get non-existent extra string`() {
+        val result = keyValueStoreOperations.getExtraString("test")
+
+        assertThat(result).isNull()
+    }
+
+    @Test
+    fun `create extra string`() {
+        keyValueStoreOperations.setExtraString("jmapState", "ABC42")
+
+        val extraValues = sqliteDatabase.readExtraValues()
+        assertThat(extraValues).hasSize(1)
+        assertThat(extraValues.first()).isEqualTo(
+            ExtraValueEntry(
+                name = "jmapState",
+                text = "ABC42",
+                number = null
+            )
+        )
+    }
+
+    @Test
+    fun `update extra string`() {
+        sqliteDatabase.createExtraValue(name = "jmapState", text = "XYZ23")
+
+        keyValueStoreOperations.setExtraString("jmapState", "ABC42")
+
+        val extraValues = sqliteDatabase.readExtraValues()
+        assertThat(extraValues).hasSize(1)
+        assertThat(extraValues.first()).isEqualTo(
+            ExtraValueEntry(
+                name = "jmapState",
+                text = "ABC42",
+                number = null
+            )
+        )
+    }
+
+    @Test
+    fun `get extra number`() {
+        sqliteDatabase.createExtraValue(name = "test", number = 23)
+
+        val result = keyValueStoreOperations.getExtraNumber("test")
+
+        assertThat(result).isEqualTo(23)
+    }
+
+    @Test
+    fun `get non-existent extra number`() {
+        val result = keyValueStoreOperations.getExtraNumber("test")
+
+        assertThat(result).isNull()
+    }
+
+    @Test
+    fun `create extra number`() {
+        keyValueStoreOperations.setExtraNumber("lastChanged", 123L)
+
+        val extraValues = sqliteDatabase.readExtraValues()
+        assertThat(extraValues).hasSize(1)
+        assertThat(extraValues.first()).isEqualTo(
+            ExtraValueEntry(
+                name = "lastChanged",
+                text = null,
+                number = 123L
+            )
+        )
+    }
+
+    @Test
+    fun `update extra number`() {
+        sqliteDatabase.createExtraValue(name = "lastChanged", number = 0L)
+
+        keyValueStoreOperations.setExtraNumber("lastChanged", 42L)
+
+        val extraValues = sqliteDatabase.readExtraValues()
+        assertThat(extraValues).hasSize(1)
+        assertThat(extraValues.first()).isEqualTo(
+            ExtraValueEntry(
+                name = "lastChanged",
+                text = null,
+                number = 42
+            )
+        )
+    }
+
+    @Test
+    fun `get extra folder string`() {
+        sqliteDatabase.createFolderExtraValue(folderId = 1, name = "test", text = "Wurstsalat")
+
+        val result = keyValueStoreOperations.getFolderExtraString(folderId = 1, name = "test")
+
+        assertThat(result).isEqualTo("Wurstsalat")
+    }
+
+    @Test
+    fun `get non-existent extra folder string`() {
+        val result = keyValueStoreOperations.getFolderExtraString(folderId = 1, name = "test")
+
+        assertThat(result).isNull()
+    }
+
+    @Test
+    fun `create extra folder string`() {
+        keyValueStoreOperations.setFolderExtraString(folderId = 1, name = "imapUidValidity", value = "1")
+
+        val folderExtraValues = sqliteDatabase.readFolderExtraValues()
+        assertThat(folderExtraValues).hasSize(1)
+        assertThat(folderExtraValues.first()).isEqualTo(
+            FolderExtraValueEntry(
+                folderId = 1,
+                name = "imapUidValidity",
+                text = "1",
+                number = null
+            )
+        )
+    }
+
+    @Test
+    fun `update extra folder string`() {
+        sqliteDatabase.createFolderExtraValue(folderId = 1, name = "imapUidValidity", text = "23")
+
+        keyValueStoreOperations.setFolderExtraString(folderId = 1, name = "imapUidValidity", value = "42")
+
+        val folderExtraValues = sqliteDatabase.readFolderExtraValues()
+        assertThat(folderExtraValues).hasSize(1)
+        assertThat(folderExtraValues.first()).isEqualTo(
+            FolderExtraValueEntry(
+                folderId = 1,
+                name = "imapUidValidity",
+                text = "42",
+                number = null
+            )
+        )
+    }
+
+    @Test
+    fun `get extra folder number`() {
+        sqliteDatabase.createFolderExtraValue(folderId = 1, name = "test", number = 23)
+
+        val result = keyValueStoreOperations.getFolderExtraNumber(folderId = 1, name = "test")
+
+        assertThat(result).isEqualTo(23)
+    }
+
+    @Test
+    fun `get non-existent extra folder number`() {
+        val result = keyValueStoreOperations.getFolderExtraNumber(folderId = 1, name = "test")
+
+        assertThat(result).isNull()
+    }
+
+    @Test
+    fun `create extra folder number`() {
+        keyValueStoreOperations.setFolderExtraNumber(folderId = 1, name = "lastChanged", value = 123L)
+
+        val folderExtraValues = sqliteDatabase.readFolderExtraValues()
+        assertThat(folderExtraValues).hasSize(1)
+        assertThat(folderExtraValues.first()).isEqualTo(
+            FolderExtraValueEntry(
+                folderId = 1,
+                name = "lastChanged",
+                text = null,
+                number = 123L
+            )
+        )
+    }
+
+    @Test
+    fun `update extra folder number`() {
+        sqliteDatabase.createFolderExtraValue(folderId = 1, name = "lastChanged", number = 0L)
+
+        keyValueStoreOperations.setFolderExtraNumber(folderId = 1, name = "lastChanged", value = 42L)
+
+        val folderExtraValues = sqliteDatabase.readFolderExtraValues()
+        assertThat(folderExtraValues).hasSize(1)
+        assertThat(folderExtraValues.first()).isEqualTo(
+            FolderExtraValueEntry(
+                folderId = 1,
+                name = "lastChanged",
+                text = null,
+                number = 42
+            )
+        )
+    }
+}

app/storage/src/test/java/com/fsck/k9/storage/messages/MessageDatabaseHelpers.kt

@@ -0,0 +1,213 @@
+package com.fsck.k9.storage.messages
+
+import android.content.ContentValues
+import android.database.sqlite.SQLiteDatabase
+import app.k9mail.core.android.common.database.getIntOrNull
+import app.k9mail.core.android.common.database.getLongOrNull
+import app.k9mail.core.android.common.database.getStringOrNull
+import app.k9mail.core.android.common.database.map
+import com.fsck.k9.mailstore.DatabasePreviewType
+import com.fsck.k9.mailstore.LockableDatabase
+import com.fsck.k9.mailstore.MigrationsHelper
+import com.fsck.k9.storage.K9SchemaDefinitionFactory
+import java.io.File
+import org.mockito.ArgumentMatchers
+import org.mockito.kotlin.any
+import org.mockito.kotlin.doAnswer
+import org.mockito.kotlin.mock
+
+fun createLockableDatabaseMock(sqliteDatabase: SQLiteDatabase): LockableDatabase {
+    return mock {
+        on { execute(ArgumentMatchers.anyBoolean(), any<LockableDatabase.DbCallback<Any>>()) } doAnswer { stubbing ->
+            val callback: LockableDatabase.DbCallback<Any> = stubbing.getArgument(1)
+            callback.doDbWork(sqliteDatabase)
+        }
+    }
+}
+
+fun createDatabase(): SQLiteDatabase {
+    val migrationsHelper = mock<MigrationsHelper>()
+
+    val sqliteDatabase = SQLiteDatabase.create(null)
+    val schemaDefinitionFactory = K9SchemaDefinitionFactory()
+    val schemaDefinition = schemaDefinitionFactory.createSchemaDefinition(migrationsHelper)
+
+    schemaDefinition.doDbUpgrade(sqliteDatabase)
+
+    return sqliteDatabase
+}
+
+fun SQLiteDatabase.createMessage(
+    folderId: Long,
+    deleted: Boolean = false,
+    uid: String? = null,
+    subject: String = "",
+    date: Long = 0L,
+    flags: String = "",
+    senderList: String = "",
+    toList: String = "",
+    ccList: String = "",
+    bccList: String = "",
+    replyToList: String = "",
+    attachmentCount: Int = 0,
+    internalDate: Long = 0L,
+    messageIdHeader: String? = null,
+    previewType: DatabasePreviewType = DatabasePreviewType.NONE,
+    preview: String = "",
+    mimeType: String = "text/plain",
+    normalizedSubjectHash: Long = 0L,
+    empty: Boolean = false,
+    read: Boolean = false,
+    flagged: Boolean = false,
+    answered: Boolean = false,
+    forwarded: Boolean = false,
+    messagePartId: Long = 0L,
+    encryptionType: String? = null,
+    newMessage: Boolean = false
+): Long {
+    val values = ContentValues().apply {
+        put("deleted", if (deleted) 1 else 0)
+        put("folder_id", folderId)
+        put("uid", uid)
+        put("subject", subject)
+        put("date", date)
+        put("flags", flags)
+        put("sender_list", senderList)
+        put("to_list", toList)
+        put("cc_list", ccList)
+        put("bcc_list", bccList)
+        put("reply_to_list", replyToList)
+        put("attachment_count", attachmentCount)
+        put("internal_date", internalDate)
+        put("message_id", messageIdHeader)
+        put("preview_type", previewType.databaseValue)
+        put("preview", preview)
+        put("mime_type", mimeType)
+        put("normalized_subject_hash", normalizedSubjectHash)
+        put("empty", if (empty) 1 else 0)
+        put("read", if (read) 1 else 0)
+        put("flagged", if (flagged) 1 else 0)
+        put("answered", if (answered) 1 else 0)
+        put("forwarded", if (forwarded) 1 else 0)
+        put("message_part_id", messagePartId)
+        put("encryption_type", encryptionType)
+        put("new_message", if (newMessage) 1 else 0)
+    }
+
+    return insert("messages", null, values)
+}
+
+fun SQLiteDatabase.readMessages(): List<MessageEntry> {
+    val cursor = rawQuery("SELECT * FROM messages", null)
+    return cursor.use {
+        cursor.map {
+            MessageEntry(
+                id = cursor.getLongOrNull("id"),
+                deleted = cursor.getIntOrNull("deleted"),
+                folderId = cursor.getLongOrNull("folder_id"),
+                uid = cursor.getStringOrNull("uid"),
+                subject = cursor.getStringOrNull("subject"),
+                date = cursor.getLongOrNull("date"),
+                flags = cursor.getStringOrNull("flags"),
+                senderList = cursor.getStringOrNull("sender_list"),
+                toList = cursor.getStringOrNull("to_list"),
+                ccList = cursor.getStringOrNull("cc_list"),
+                bccList = cursor.getStringOrNull("bcc_list"),
+                replyToList = cursor.getStringOrNull("reply_to_list"),
+                attachmentCount = cursor.getIntOrNull("attachment_count"),
+                internalDate = cursor.getLongOrNull("internal_date"),
+                messageId = cursor.getStringOrNull("message_id"),
+                previewType = cursor.getStringOrNull("preview_type"),
+                preview = cursor.getStringOrNull("preview"),
+                mimeType = cursor.getStringOrNull("mime_type"),
+                normalizedSubjectHash = cursor.getLongOrNull("normalized_subject_hash"),
+                empty = cursor.getIntOrNull("empty"),
+                read = cursor.getIntOrNull("read"),
+                flagged = cursor.getIntOrNull("flagged"),
+                answered = cursor.getIntOrNull("answered"),
+                forwarded = cursor.getIntOrNull("forwarded"),
+                messagePartId = cursor.getLongOrNull("message_part_id"),
+                encryptionType = cursor.getStringOrNull("encryption_type"),
+                newMessage = cursor.getIntOrNull("new_message")
+            )
+        }
+    }
+}
+
+data class MessageEntry(
+    val id: Long?,
+    val deleted: Int?,
+    val folderId: Long?,
+    val uid: String?,
+    val subject: String?,
+    val date: Long?,
+    val flags: String?,
+    val senderList: String?,
+    val toList: String?,
+    val ccList: String?,
+    val bccList: String?,
+    val replyToList: String?,
+    val attachmentCount: Int?,
+    val internalDate: Long?,
+    val messageId: String?,
+    val previewType: String?,
+    val preview: String?,
+    val mimeType: String?,
+    val normalizedSubjectHash: Long?,
+    val empty: Int?,
+    val read: Int?,
+    val flagged: Int?,
+    val answered: Int?,
+    val forwarded: Int?,
+    val messagePartId: Long?,
+    val encryptionType: String?,
+    val newMessage: Int?
+)
+
+fun SQLiteDatabase.createMessagePart(
+    type: Int = 0,
+    root: Int? = null,
+    parent: Int = -1,
+    seq: Int = 0,
+    mimeType: String = "text/plain",
+    decodedBodySize: Int = 0,
+    displayName: String? = null,
+    header: String? = null,
+    encoding: String = "7bit",
+    charset: String? = null,
+    dataLocation: Int = 0,
+    data: ByteArray? = null,
+    preamble: String? = null,
+    epilogue: String? = null,
+    boundary: String? = null,
+    contentId: String? = null,
+    serverExtra: String? = null,
+    directory: File? = null
+): Long {
+    val values = ContentValues().apply {
+        put("type", type)
+        put("root", root)
+        put("parent", parent)
+        put("seq", seq)
+        put("mime_type", mimeType)
+        put("decoded_body_size", decodedBodySize)
+        put("display_name", displayName)
+        put("header", header?.toByteArray())
+        put("encoding", encoding)
+        put("charset", charset)
+        put("data_location", dataLocation)
+        put("data", data)
+        put("preamble", preamble)
+        put("epilogue", epilogue)
+        put("boundary", boundary)
+        put("content_id", contentId)
+        put("server_extra", serverExtra)
+    }
+
+    return insert("message_parts", null, values).also { messagePartId ->
+        if (dataLocation == DATA_LOCATION_ON_DISK) {
+            requireNotNull(directory) { "Argument 'directory' can't be null when 'dataLocation = 2'" }
+            File(directory, messagePartId.toString()).createNewFile()
+        }
+    }
+}

app/storage/src/test/java/com/fsck/k9/storage/messages/MessagePartDatabaseHelpers.kt

@@ -0,0 +1,182 @@
+package com.fsck.k9.storage.messages
+
+import android.content.ContentValues
+import android.database.Cursor
+import android.database.sqlite.SQLiteDatabase
+import app.k9mail.core.android.common.database.getIntOrNull
+import app.k9mail.core.android.common.database.getLongOrNull
+import app.k9mail.core.android.common.database.getStringOrNull
+import app.k9mail.core.android.common.database.map
+
+fun SQLiteDatabase.createMessagePart(
+    type: Int = MessagePartType.UNKNOWN,
+    root: Long? = null,
+    parent: Long = -1,
+    seq: Int = 0,
+    mimeType: String? = null,
+    decodedBodySize: Int? = null,
+    displayName: String? = null,
+    header: String? = null,
+    encoding: String? = null,
+    charset: String? = null,
+    dataLocation: Int = DataLocation.MISSING,
+    data: ByteArray? = null,
+    preamble: String? = null,
+    epilogue: String? = null,
+    boundary: String? = null,
+    contentId: String? = null,
+    serverExtra: String? = null
+): Long {
+    val values = ContentValues().apply {
+        put("type", type)
+        put("root", root)
+        put("parent", parent)
+        put("seq", seq)
+        put("mime_type", mimeType)
+        put("decoded_body_size", decodedBodySize)
+        put("display_name", displayName)
+        put("header", header?.toByteArray())
+        put("encoding", encoding)
+        put("charset", charset)
+        put("data_location", dataLocation)
+        put("data", data)
+        put("preamble", preamble)
+        put("epilogue", epilogue)
+        put("boundary", boundary)
+        put("content_id", contentId)
+        put("server_extra", serverExtra)
+    }
+
+    return insert("message_parts", null, values)
+}
+
+fun SQLiteDatabase.readMessageParts(): List<MessagePartEntry> {
+    return rawQuery("SELECT * FROM message_parts", null).use { cursor ->
+        cursor.map {
+            MessagePartEntry(
+                id = cursor.getLongOrNull("id"),
+                type = cursor.getIntOrNull("type"),
+                root = cursor.getLongOrNull("root"),
+                parent = cursor.getLongOrNull("parent"),
+                seq = cursor.getIntOrNull("seq"),
+                mimeType = cursor.getStringOrNull("mime_type"),
+                decodedBodySize = cursor.getIntOrNull("decoded_body_size"),
+                displayName = cursor.getStringOrNull("display_name"),
+                header = cursor.getBlobOrNull("header"),
+                encoding = cursor.getStringOrNull("encoding"),
+                charset = cursor.getStringOrNull("charset"),
+                dataLocation = cursor.getIntOrNull("data_location"),
+                data = cursor.getBlobOrNull("data"),
+                preamble = cursor.getStringOrNull("preamble"),
+                epilogue = cursor.getStringOrNull("epilogue"),
+                boundary = cursor.getStringOrNull("boundary"),
+                contentId = cursor.getStringOrNull("content_id"),
+                serverExtra = cursor.getStringOrNull("server_extra")
+            )
+        }
+    }
+}
+
+data class MessagePartEntry(
+    val id: Long?,
+    val type: Int?,
+    val root: Long?,
+    val parent: Long?,
+    val seq: Int?,
+    val mimeType: String?,
+    val decodedBodySize: Int?,
+    val displayName: String?,
+    val header: ByteArray?,
+    val encoding: String?,
+    val charset: String?,
+    val dataLocation: Int?,
+    val data: ByteArray?,
+    val preamble: String?,
+    val epilogue: String?,
+    val boundary: String?,
+    val contentId: String?,
+    val serverExtra: String?
+) {
+    override fun equals(other: Any?): Boolean {
+        if (this === other) return true
+        if (javaClass != other?.javaClass) return false
+
+        other as MessagePartEntry
+
+        if (id != other.id) return false
+        if (type != other.type) return false
+        if (root != other.root) return false
+        if (parent != other.parent) return false
+        if (seq != other.seq) return false
+        if (mimeType != other.mimeType) return false
+        if (decodedBodySize != other.decodedBodySize) return false
+        if (displayName != other.displayName) return false
+        if (header != null) {
+            if (other.header == null) return false
+            if (!header.contentEquals(other.header)) return false
+        } else if (other.header != null) return false
+        if (encoding != other.encoding) return false
+        if (charset != other.charset) return false
+        if (dataLocation != other.dataLocation) return false
+        if (data != null) {
+            if (other.data == null) return false
+            if (!data.contentEquals(other.data)) return false
+        } else if (other.data != null) return false
+        if (preamble != other.preamble) return false
+        if (epilogue != other.epilogue) return false
+        if (boundary != other.boundary) return false
+        if (contentId != other.contentId) return false
+        if (serverExtra != other.serverExtra) return false
+
+        return true
+    }
+
+    override fun hashCode(): Int {
+        var result = id?.hashCode() ?: 0
+        result = 31 * result + (type ?: 0)
+        result = 31 * result + (root?.hashCode() ?: 0)
+        result = 31 * result + (parent?.hashCode() ?: 0)
+        result = 31 * result + (seq ?: 0)
+        result = 31 * result + (mimeType?.hashCode() ?: 0)
+        result = 31 * result + (decodedBodySize ?: 0)
+        result = 31 * result + (displayName?.hashCode() ?: 0)
+        result = 31 * result + (header?.contentHashCode() ?: 0)
+        result = 31 * result + (encoding?.hashCode() ?: 0)
+        result = 31 * result + (charset?.hashCode() ?: 0)
+        result = 31 * result + (dataLocation ?: 0)
+        result = 31 * result + (data?.contentHashCode() ?: 0)
+        result = 31 * result + (preamble?.hashCode() ?: 0)
+        result = 31 * result + (epilogue?.hashCode() ?: 0)
+        result = 31 * result + (boundary?.hashCode() ?: 0)
+        result = 31 * result + (contentId?.hashCode() ?: 0)
+        result = 31 * result + (serverExtra?.hashCode() ?: 0)
+        return result
+    }
+
+    override fun toString(): String {
+        return "MessagePartEntry(" +
+            "id=$id, " +
+            "type=$type, " +
+            "root=$root, " +
+            "parent=$parent, " +
+            "seq=$seq, " +
+            "mimeType=$mimeType, " +
+            "decodedBodySize=$decodedBodySize, " +
+            "displayName=$displayName, " +
+            "header=${header?.decodeToString()}, " +
+            "encoding=$encoding, " +
+            "charset=$charset, " +
+            "dataLocation=$dataLocation, " +
+            "data=${data?.decodeToString()}, " +
+            "preamble=$preamble, " +
+            "epilogue=$epilogue, " +
+            "boundary=$boundary, " +
+            "contentId=$contentId, " +
+            "serverExtra=$serverExtra)"
+    }
+}
+
+private fun Cursor.getBlobOrNull(columnName: String): ByteArray? {
+    val columnIndex = getColumnIndex(columnName)
+    return if (isNull(columnIndex)) null else getBlob(columnIndex)
+}