Repo created

libs/base/dfa_helpers.hpp

@@ -0,0 +1,102 @@
+#pragma once
+
+#include "base/string_utils.hpp"
+
+#include <cstddef>
+#include <string>
+
+namespace strings
+{
+template <typename DFA>
+class PrefixDFAModifier
+{
+public:
+  class Iterator
+  {
+  public:
+    Iterator & Move(UniChar c)
+    {
+      if (Rejects())
+        return *this;
+
+      if (Accepts())
+      {
+        auto currentIt = m_it;
+        currentIt.Move(c);
+
+        // While moving m_it, errors number decreases while matching unmatched symbols:
+        // source:  a b c d e f
+        // query:   a b c d e f
+        // errors:  5 4 3 2 1 0
+        //
+        // After a misprinted symbol errors number remains the same:
+        // source:  a b c d e f
+        // query:   a b z d e f
+        // errors:  5 4 3 3 2 1
+        //
+        // source:  a b c d e f
+        // query:   a b d c e f
+        // errors:  5 4 3 3 2 1
+        //
+        // source:  a b c d e f
+        // query:   a b d e f
+        // errors:  5 4 3 3 2
+        //
+        // source:  a b c d e f
+        // query:   a b c z d e f
+        // errors:  5 4 3 3 3 2 1
+        //
+        // Errors number cannot decrease after it has increased once.
+
+        if (currentIt.ErrorsMade() > ErrorsMade())
+          return *this;
+      }
+
+      m_it.Move(c);
+      if (m_it.Accepts())
+        m_accepts = true;
+
+      return *this;
+    }
+
+    bool Accepts() const { return m_accepts; }
+    bool Rejects() const { return !Accepts() && m_it.Rejects(); }
+    size_t ErrorsMade() const { return m_it.ErrorsMade(); }
+    size_t PrefixErrorsMade() const { return m_it.PrefixErrorsMade(); }
+
+  private:
+    friend class PrefixDFAModifier;
+
+    Iterator(typename DFA::Iterator it) : m_it(it), m_accepts(m_it.Accepts()) {}
+
+    typename DFA::Iterator m_it;
+    bool m_accepts;
+  };
+
+  explicit PrefixDFAModifier(DFA && dfa) : m_dfa(std::move(dfa)) {}
+
+  Iterator Begin() const { return Iterator(m_dfa.Begin()); }
+
+private:
+  DFA m_dfa;
+};
+
+template <typename DFAIt, typename It>
+void DFAMove(DFAIt & it, It begin, It end)
+{
+  for (; begin != end; ++begin)
+    it.Move(*begin);
+}
+
+template <typename DFAIt>
+void DFAMove(DFAIt & it, UniString const & s)
+{
+  DFAMove(it, s.begin(), s.end());
+}
+
+template <typename DFAIt>
+void DFAMove(DFAIt & it, std::string const & s)
+{
+  DFAMove(it, MakeUniString(s));
+}
+}  // namespace strings