using Implab;
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;

namespace Implab.Automaton.RegularExpressions {
    /// <summary>
    /// Используется для построения ДКА по регулярному выражению, сначала обходит
    /// регулярное выражение и вычисляет followpos, затем используется метод
    /// <see cref="BuildDFA(IDFADefinition)"/> для построения автомата.
    /// </summary>
    public class DFABuilder<TTag> : IVisitor<TTag> {
        int m_idx = 0;
        Token<TTag> m_root;
        HashSet<int> m_firstpos;
        HashSet<int> m_lastpos;

        readonly Dictionary<int, HashSet<int>> m_followpos = new Dictionary<int, HashSet<int>>();
        readonly Dictionary<int, int> m_indexes = new Dictionary<int, int>();
        readonly Dictionary<int, TTag> m_ends = new Dictionary<int, TTag>();

        public Dictionary<int, HashSet<int>> FollowposMap {
            get { return m_followpos; }
        }

        public HashSet<int> Followpos(int pos) {
            HashSet<int> set;
            if (m_followpos.TryGetValue(pos, out set))
                return set;
            return m_followpos[pos] = new HashSet<int>();
        }

        bool Nullable(object n) {
            if (n is EmptyToken<TTag> || n is StarToken<TTag>)
                return true;
            if (n is AltToken<TTag>)
                return Nullable(((AltToken<TTag>)n).Left) || Nullable(((AltToken<TTag>)n).Right);
            if (n is CatToken<TTag>)
                return Nullable(((CatToken<TTag>)n).Left) && Nullable(((CatToken<TTag>)n).Right);
            return false;
        }


        public void Visit(AltToken<TTag> token) {
            if (m_root == null)
                m_root = token;
            var firtspos = new HashSet<int>();
            var lastpos = new HashSet<int>();

            token.Left.Accept(this);
            firtspos.UnionWith(m_firstpos);
            lastpos.UnionWith(m_lastpos);

            token.Right.Accept(this);
            firtspos.UnionWith(m_firstpos);
            lastpos.UnionWith(m_lastpos);

            m_firstpos = firtspos;
            m_lastpos = lastpos;
        }

        public void Visit(StarToken<TTag> token) {
            if (m_root == null)
                m_root = token;
            token.Token.Accept(this);

            foreach (var i in m_lastpos)
                Followpos(i).UnionWith(m_firstpos);
        }

        public void Visit(CatToken<TTag> token) {
            if (m_root == null)
                m_root = token;

            var firtspos = new HashSet<int>();
            var lastpos = new HashSet<int>();
            token.Left.Accept(this);
            firtspos.UnionWith(m_firstpos);
            var leftLastpos = m_lastpos;

            token.Right.Accept(this);
            lastpos.UnionWith(m_lastpos);
            var rightFirstpos = m_firstpos;

            if (Nullable(token.Left))
                firtspos.UnionWith(rightFirstpos);

            if (Nullable(token.Right))
                lastpos.UnionWith(leftLastpos);

            m_firstpos = firtspos;
            m_lastpos = lastpos;

            foreach (var i in leftLastpos)
                Followpos(i).UnionWith(rightFirstpos);

        }

        public void Visit(EmptyToken<TTag> token) {
            if (m_root == null)
                m_root = token;
        }

        public void Visit(SymbolToken<TTag> token) {
            if (m_root == null)
                m_root = token;
            m_idx++;
            m_indexes[m_idx] = token.Value;
            m_firstpos = new HashSet<int>(new[] { m_idx });
            m_lastpos = new HashSet<int>(new[] { m_idx });
        }

        public void Visit(EndToken<TTag> token) {
            if (m_root == null)
                m_root = token;
            m_idx++;
            m_indexes[m_idx] = DFAConst.UNCLASSIFIED_INPUT;
            m_firstpos = new HashSet<int>(new[] { m_idx });
            m_lastpos = new HashSet<int>(new[] { m_idx });
            Followpos(m_idx);
            m_ends.Add(m_idx, token.Tag);
        }

        public void BuildDFA(IDFADefinitionBuilder<TTag> dfa, IAlphabetBuilder<int> states) {
            Safe.ArgumentNotNull(dfa,"dfa");
            
            var stateMap = new Dictionary<HashSet<int>, int>(new CustomEqualityComparer<HashSet<int>>(
                (x, y) => x.SetEquals(y),
                x => x.Sum(n => n.GetHashCode())
            ));

            int nextState = 0;
            
            int initialState = states.DefineSymbol(nextState++);
            stateMap[m_firstpos] = initialState;

            var tags = GetStateTags(m_firstpos);
            if (tags != null && tags.Length > 0)
                dfa.MarkFinalState(initialState, tags);

            var inputMax = m_indexes.Values.Max();
            var queue = new Queue<HashSet<int>>();

            queue.Enqueue(m_firstpos);

            while (queue.Count > 0) {
                var state = queue.Dequeue();
                var s1 = stateMap[state];

                for (int a = 0; a <= inputMax; a++) {
                    var next = new HashSet<int>();
                    foreach (var p in state) {
                        if (m_indexes[p] == a) {
                            next.UnionWith(Followpos(p));
                        }
                    }
                    if (next.Count > 0) {
                        int s2;
                        if (!stateMap.TryGetValue(next, out s2)) {
                            s2 = states.DefineSymbol(nextState++);
                            stateMap[next] = s2;
                            tags = GetStateTags(next);
                            if (tags != null && tags.Length > 0)
                                dfa.MarkFinalState(s2, tags);
                            
                            queue.Enqueue(next);
                        }
                        dfa.DefineTransition(s1, s2, a);
                    }
                }
            }
        }

        TTag[] GetStateTags(IEnumerable<int> state) {
            Debug.Assert(state != null);
            return state.Where(m_ends.ContainsKey).Select(pos => m_ends[pos]).ToArray();
        }

    }
}