// Author: Orlys
// Github: https://github.com/Orlys

namespace Yuuna.Contracts.Optimization
{
    using System;
    using System.Collections.Generic;
    using System.Collections.Immutable;
    using System.Diagnostics.CodeAnalysis;
    using System.Runtime.CompilerServices;

    using Yuuna.Contracts.Patterns;
    using Yuuna.Contracts.Modules;
    using Yuuna.Contracts.Semantics;
    using System.Linq;

    public enum Status
    {
        /// <summary>
        /// 無有效解。
        /// </summary>
        Invalid,
        /// <summary>
        /// 最佳解。表示與模式(Pattern)完全符合。
        /// </summary>
        Optimal,
        /// <summary>
        /// 近似解。表示缺少一個群組(Group)。
        /// </summary>
        Closest,
        /// <summary>
        /// 命題。表示具有兩個近似解(<see cref="Closest"/>)。
        /// </summary>
        Proposition,
        /// <summary>
        /// 悖論。表示具有多個最佳解(<see cref="Optimal"/>)，這實際上屬於模組設計上的問題。
        /// </summary>
        Paradox,

        /// <summary>
        /// 沒有已安裝的模組。
        /// </summary>
        NoModuleInstalled = -1,
    }

    public class Alternative
    {
        public Status Status { get; }
        public IImmutableList<Match> Matches { get; }

        public Alternative(IImmutableList<Match> matches)
        {
            var count = matches?.Count ?? 0;
            if (count.Equals(1))
            {
                var single = matches[0].Missing.Count;
                if (single.Equals(0))
                {
                    this.Status = Status.Optimal;  // 最佳解

                }
                else if (single.Equals(1))
                {
                    this.Status = Status.Closest;// 近似解(缺一組條件，詢問使用者) 
                }
            }
            else if (count.Equals(2))
            {
                if (matches.All(x => x.Missing.Count == 0))
                {
                    this.Status = Status.Paradox;// 內部錯誤(多個意圖重複)
                }
                else if (matches.All(x => x.Missing.Count == 1))
                {
                    this.Status = Status.Proposition;// 兩個近似解，詢問使用者(二選一 + 離開情境)
                }
            } 
            else if (count.Equals(0))
            {
                // 無有效模組
                this.Status = Status.NoModuleInstalled;
            }
            else
            {
                // 不採用
                this.Status = Status.Invalid;
            }

            this.Matches = matches;
        }
         
    }

    public class DefaultStrategy : IStrategy
    {
        public DefaultStrategy()
        {

        }

        public Alternative FindBest(IEnumerable<IPatternSet> patternSetCollection, IImmutableList<string> feed)
        {
            var list = ImmutableArray.CreateBuilder<Match>();
            foreach (var pattern in patternSetCollection)
            {
                foreach (var p in pattern.ToImmutable())
                {
                    var match = this.CountPatternMatch(p, feed);  
                    list.Add(match);
                }
            }

            var e = this.SelectBestMatch(list.ToImmutable());
            return e;
        }

        /// <summary>
        /// 
        /// </summary>
        /// <param name="matches"></param>
        /// <returns></returns>
        protected virtual Alternative SelectBestMatch(IImmutableList<Match> matches)
        { 
           //if(matches is null || matches.Count == 0)
           //     return //沒有安裝任何模組

            var sta = new SortedList<int, List<Match>>();
            foreach (var match in matches)
            {
                var key = match.SequentialMatches.Count;
                if (!sta.ContainsKey(key))
                { 
                    sta.Add(key, new List<Match> { match }); 
                }
                else
                {
                    sta[key].Add(match);
                }
            }


            var weight = double.MinValue;
            var bestSelect = default(List<Match>);
            foreach (var s in sta)
            {
                var y = -( Math.Tanh(Math.Pow(Math.E, (s.Value.Count) / (double)-(matches.Count * s.Key))));
                if (y > weight)
                {
                    weight = y;
                    bestSelect = s.Value;
                }
            }


            return new Alternative(bestSelect?.ToImmutableArray());



            //var tuple = new List<Tuple<Match, double>>();
            //foreach (var s in sta)
            //{
            //    var x = (s.Value) / (double)-(matches.Count * s.Key.SequentialMatches.Count);
            //    var y = Math.Tanh(Math.Pow(Math.E, x));
            //    tuple.Add(Tuple.Create(s.Key, y));
            //}
            //var bestSelect = tuple.OrderByDescending(x => x.Item2).FirstOrDefault();
            //return bestSelect?.Item1;


            //var hold = double.MinValue;
            //var bestSelect = default(Match);
            //foreach (var s in sta)
            //{
            //    var y = Math.Tanh(Math.Pow(Math.E, (s.Value) / (double)-(matches.Count * s.Key.Pattern.Count))); 
            //    if (y > hold)
            //    {
            //        hold = y;
            //        bestSelect = s.Key;
            //    }
            //}

            //if (bestSelect.SequentialMatches.Count == 0)
            //    return null;

            //return bestSelect;
        }

        /// <summary>
        /// 評估 <paramref name="pattern"/> 與 <paramref name="feed"/> 的符合程度並返回一個 <see cref="Match"/> 物件。
        /// </summary>
        /// <param name="pattern"></param>
        /// <param name="feed"></param>
        /// <returns></returns>
        protected virtual Match CountPatternMatch(IPattern pattern, IImmutableList<string> feed)
        {
            var matches = ImmutableArray.CreateBuilder<ISynonym>();

            using (var iterator = pattern.ToImmutable().GetEnumerator())
            {
                iterator.MoveNext();
                foreach (var word in feed)
                {
                    if (iterator.Current.TryGetSynonym(word, out var s))
                    {
                        matches.Add(s);
                        if (!iterator.MoveNext())
                            break;
                    }
                }
            }

            return new Match(pattern, matches.ToImmutable());
        }
    }
}