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

namespace Implab.Parsing {
    /// <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 : IVisitor {
        int m_idx = 0;
        Token m_root;
        HashSet<int> m_firstpos;
        HashSet<int> m_lastpos;

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

        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 || n is StarToken)
                return true;
            if (n is AltToken)
                return Nullable(((AltToken)n).Left) || Nullable(((AltToken)n).Right);
            if (n is CatToken)
                return Nullable(((CatToken)n).Left) && Nullable(((CatToken)n).Right);
            return false;
        }


        public void Visit(AltToken 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 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 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 token) {
            if (m_root == null)
                m_root = token;
            ;
        }

        public void Visit(SymbolToken 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 token) {
            if (m_root == null)
                m_root = token;
            m_idx++;
            m_indexes[m_idx] = IndexedAlphabetBase<char>.UNCLASSIFIED;
            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(IDFADefinition dfa) {
            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())
            ));
            
            stateMap[m_firstpos] = DefineState( dfa, m_firstpos);
            Debug.Assert(stateMap[m_firstpos] == DFADefinition.INITIAL_STATE);

            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 < dfa.AlphabetSize; 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)) {
                            stateMap[next] = s2 = DefineState(dfa, next);
                            queue.Enqueue(next);
                        }
                        dfa.DefineTransition(s1, s2, a);
                    }
                }

            }
        }

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

        int DefineState(IDFADefinition automa, HashSet<int> state) {
            Debug.Assert(automa != null);
            Debug.Assert(state != null);

            var tags = GetStateTags(state);
         
            return tags.Length > 0 ? automa.AddState(tags) : automa.AddState();
        }

    }
}