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using Implab;
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using System;
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using System.Collections.Generic;
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using System.Diagnostics;
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using System.Linq;
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namespace Implab.Automaton.RegularExpressions {
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/// <summary>
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/// Используется для построения ДКА по регулярному выражению, сначала обходит
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/// регулярное выражение и вычисляет followpos, затем используется метод
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/// <see cref="BuildDFA(IDFADefinition)"/> для построения автомата.
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/// </summary>
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public class RegularExpressionVisitor : IVisitor {
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int m_idx;
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Token m_root;
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HashSet<int> m_firstpos;
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HashSet<int> m_lastpos;
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readonly Dictionary<int, HashSet<int>> m_followpos = new Dictionary<int, HashSet<int>>();
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readonly Dictionary<int, int> m_indexes = new Dictionary<int, int>();
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readonly HashSet<int> m_ends = new HashSet<int>();
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readonly IDFATableBuilder m_builder;
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readonly IAlphabetBuilder<HashSet<int>> m_states = new MapAlphabet<HashSet<int>>(
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false,
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new CustomEqualityComparer<HashSet<int>>(
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(x, y) => x.SetEquals(y),
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x => x.Sum(n => n.GetHashCode())
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)
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);
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public RegularExpressionVisitor(IDFATableBuilder builder) {
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Safe.ArgumentNotNull(builder, "builder");
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m_builder = builder;
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}
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HashSet<int> Followpos(int pos) {
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HashSet<int> set;
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return m_followpos.TryGetValue(pos, out set) ? set : m_followpos[pos] = new HashSet<int>();
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}
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bool Nullable(object n) {
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if (n is EmptyToken || n is StarToken)
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return true;
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var altToken = n as AltToken;
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if (altToken != null)
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return Nullable(altToken.Left) || Nullable(altToken.Right);
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var catToken = n as CatToken;
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if (catToken != null)
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return Nullable(catToken.Left) && Nullable(catToken.Right);
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return false;
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}
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protected int Index {
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get { return m_idx; }
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}
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public void Visit(AltToken token) {
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if (m_root == null)
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m_root = token;
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var firtspos = new HashSet<int>();
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var lastpos = new HashSet<int>();
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token.Left.Accept(this);
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firtspos.UnionWith(m_firstpos);
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lastpos.UnionWith(m_lastpos);
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token.Right.Accept(this);
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firtspos.UnionWith(m_firstpos);
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lastpos.UnionWith(m_lastpos);
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m_firstpos = firtspos;
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m_lastpos = lastpos;
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}
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public void Visit(StarToken token) {
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if (m_root == null)
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m_root = token;
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token.Token.Accept(this);
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foreach (var i in m_lastpos)
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Followpos(i).UnionWith(m_firstpos);
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}
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public void Visit(CatToken token) {
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if (m_root == null)
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m_root = token;
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var firtspos = new HashSet<int>();
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var lastpos = new HashSet<int>();
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token.Left.Accept(this);
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firtspos.UnionWith(m_firstpos);
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var leftLastpos = m_lastpos;
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token.Right.Accept(this);
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lastpos.UnionWith(m_lastpos);
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var rightFirstpos = m_firstpos;
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if (Nullable(token.Left))
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firtspos.UnionWith(rightFirstpos);
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if (Nullable(token.Right))
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lastpos.UnionWith(leftLastpos);
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m_firstpos = firtspos;
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m_lastpos = lastpos;
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foreach (var i in leftLastpos)
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Followpos(i).UnionWith(rightFirstpos);
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}
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public void Visit(EmptyToken token) {
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if (m_root == null)
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m_root = token;
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}
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public void Visit(SymbolToken token) {
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if (m_root == null)
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m_root = token;
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m_idx++;
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m_indexes[m_idx] = token.Value;
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m_firstpos = new HashSet<int>(new[] { m_idx });
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m_lastpos = new HashSet<int>(new[] { m_idx });
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}
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public virtual void Visit(EndToken token) {
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if (m_root == null)
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m_root = token;
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m_idx++;
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m_indexes[m_idx] = AutomatonConst.UnclassifiedInput;
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m_firstpos = new HashSet<int>(new[] { m_idx });
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m_lastpos = new HashSet<int>(new[] { m_idx });
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Followpos(m_idx);
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m_ends.Add(m_idx);
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}
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public void BuildDFA() {
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AddState(m_firstpos);
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SetInitialState(m_firstpos);
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if(IsFinal(m_firstpos))
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MarkFinalState(m_firstpos);
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var inputMax = m_indexes.Values.Max();
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var queue = new Queue<HashSet<int>>();
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queue.Enqueue(m_firstpos);
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while (queue.Count > 0) {
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var s1 = queue.Dequeue();
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for (int a = 0; a <= inputMax; a++) {
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var s2 = new HashSet<int>();
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foreach (var p in s1) {
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if (m_indexes[p] == a) {
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s2.UnionWith(Followpos(p));
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}
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}
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if (s2.Count > 0) {
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if (!HasState(s2)) {
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AddState(s2);
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if (IsFinal(s2))
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MarkFinalState(s2);
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queue.Enqueue(s2);
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}
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DefineTransition(s1, s2, a);
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}
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}
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}
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}
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protected bool HasState(HashSet<int> state) {
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return m_states.Contains(state);
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}
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protected void AddState(HashSet<int> state) {
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Debug.Assert(!HasState(state));
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m_states.DefineSymbol(state);
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}
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protected int Translate(HashSet<int> state) {
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Debug.Assert(HasState(state));
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return m_states.Translate(state);
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}
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protected virtual void SetInitialState(HashSet<int> state) {
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m_builder.SetInitialState(Translate(state));
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}
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protected virtual void MarkFinalState(HashSet<int> state) {
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m_builder.MarkFinalState(Translate(state));
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}
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protected virtual void DefineTransition(HashSet<int> s1, HashSet<int> s2, int ch) {
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m_builder.Add(new AutomatonTransition(Translate(s1), Translate(s2), ch));
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}
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bool IsFinal(IEnumerable<int> state) {
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Debug.Assert(state != null);
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return state.Any(m_ends.Contains);
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}
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}
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}
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