using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Linq;
using System.Threading.Tasks;

namespace GameOfLife.Entities
{
    public class Pattern : ReadOnlyCollection<Cell>
    {
        public Pattern(IEnumerable<Cell> pattern) : base(pattern.OrderBy(c => c.Item2).ThenBy(c => c.Item1).ToList())
        {
            // https://stackoverflow.com/a/263416/99492
            unchecked
            {
                _hashCodeCache = 
                    this //.OrderBy(c => c)
                        .Aggregate(23, (hash, c) 
                            => hash * 37 + c.GetHashCode());
            }
        }

        public Cell GetBoundaryMin() =>
            new Cell(
                this.Min(c => c.Item1) - 1,
                this.Min(c => c.Item2) - 1);

        public Cell GetBoundaryMax() =>
            new Cell(
                this.Max(c => c.Item1) + 1,
                this.Max(c => c.Item2) + 1);

        public Cell GetFirstRowFirstCell() =>
            this.OrderBy(c => c.Item2).ThenBy(c => c.Item1).First();

        public bool ContainsAll(IEnumerable<Cell> cells) => cells.All(Contains);
        public bool ContainsNone(IEnumerable<Cell> cells) => cells.All(c => !Contains(c));

        public short GetMinY() =>
            this.Min(c => c.Item2);

        // All neighboring cells
        public Pattern GetBoundary =>
            this.SelectMany(cell => cell.NeighborCells).Distinct().ToPattern() - this;

        public Pattern Rotate() =>
            /*  Rotate 90deg clockwise
             *  .....    .....    .oo..     ...o.
             *  ..o.. -> .oo.. -> ..o..  -> ..oo.
             *  ..oo.    .o...    .....     .....
             *  .....    .....    .....     .....
             *  [0,0]    [0,0]    [0,0]     [0,0]
             *  [0,1]    [-1,0]   [0,-1]    [1,0]
             *  [1,1]    [-1,1]   [-1,-1]   [1,-1]
             */
            this
                .Select(cell
                    => new Cell(-cell.Item2, cell.Item1))
                .ToPattern();

        public Pattern Rotate(int count)
        {
            var p = new Pattern(this);
            for (var i = 0; i < count; i++)
                p = p.Rotate();
            return p.ToPattern();
        }

        public Pattern ReflectX() =>
            /*  .....   .....   ..oo.  
             *  ..o..   ..o..   ..o..  
             *  ..oo.   .oo..   .....  
             *  .....   .....   .....  
             *  [0,0]   [0,0]   [0,0]  
             *  [0,1]   [0,1]   [0,-1] 
             *  [1,1]   [-1,1]  [1,-1]
             */
            this
                .Select(cell
                    => new Cell((short)-cell.Item1, cell.Item2))
                .ToPattern();

        public Pattern ReflectY() =>
            this
                .Select(cell
                    => new Cell((short)cell.Item1, (short)-cell.Item2))
                .ToPattern();

        // move pattern to deterministic position
        public Pattern Normalize() =>
            this.Select(c => c - GetFirstRowFirstCell()).ToPattern();

        public Pattern Offset(Cell offsetCell) =>
            this.Select(c => c + offsetCell).ToPattern();

        // Subtract cells from another pattern
        public static Pattern operator -(Pattern p1, Pattern p2) 
            => p1.Where(c => !p2.Contains(c)).ToPattern();

        // Adds cells from another pattern
        public static Pattern operator +(Pattern p1, Pattern p2)
            => p1.Concat(p2).Distinct().ToPattern();

        /// <summary>
        /// Extracts coordinates from text encoded pattern, treating 'char c' as cells
        /// </summary>
        public static Pattern Extract(string text, char c = 'o')
            => Extract(text.SplitByLine(), c);

        public static Pattern Extract(IEnumerable<string> text, char c = 'o')
            => ExtractCells(text, c).ToPattern();

        private static IEnumerable<Cell> ExtractCells(IEnumerable<string> text, char c = 'o')
        {
            short y = 0;
            foreach (var line in text)
            {
                for (short x = 0; x < line.Length; x++)
                    if (line[x] == c)
                        yield return new Cell(x, y);
                y++;
            }
        }

        public IEnumerable<string> ToGrid(char live = 'O', char dead = '.')
        {
            var boundaryMin = GetBoundaryMin();
            var boundaryMax = GetBoundaryMax();

            for (var y = boundaryMin.Item2; y < boundaryMax.Item2; y++)
            {
                var s = "";
                for (var x = boundaryMin.Item1; x < boundaryMax.Item1; x++)
                    s += (Contains(new Cell(x, y)) ? live : dead) + " ";
                yield return s;
            }
        }

        public override bool Equals(object obj)
        {
            if (!(obj is Pattern pattern))
                return false;
            
            return this.All(pattern.Contains) && pattern.All(this.Contains);
        }

        public override int GetHashCode() => _hashCodeCache;

        private readonly int _hashCodeCache;

        public IEnumerable<Pattern> FindPatterns(Projections projections)
        {
            var livingCells = new ConcurrentBag<Cell>(this);
            var foundPatterns = new ConcurrentBag<Pattern>();

            Parallel.ForEach(projections,
                projection =>
                {
                    foreach (var livingCell in livingCells)
                    {
                        var patternProjection
                            = projection.Select(c => livingCell + c).ToArray();
                        var patternMatch = ContainsAll(patternProjection);
                        if (!patternMatch)
                            continue;

                        // check if surrounding cells are not alive
                        var boundaryProjection
                            = projections.BoundaryCells[projection].Select(c => livingCell + c).ToArray();
                        var boundaryMatch = ContainsNone(boundaryProjection);

                        if (boundaryMatch)
                            foundPatterns.Add(patternProjection.ToPattern());

                        // shorten search time by removing these cells
                        // from examination for other patterns
                        foreach (var foundsCell in patternProjection)
                        {
                            // ReSharper disable once NotAccessedVariable
                            var cell = new Cell(foundsCell.Item1, foundsCell.Item2);
                            livingCells.TryTake(out cell);
                        }
                    }
                });

            return foundPatterns;
        }

        public IEnumerable<Pattern> FindPatterns_Serial(Projections projections)
        {
            var cells = new List<Cell>(this);
            var foundPatterns = new ConcurrentBag<Pattern>();

            foreach (var projection in projections)
            {
                foreach (var livingCell in cells)
                {
                    var patternProjection
                        = projection.Select(c => livingCell + c).ToArray();
                    var patternMatch = ContainsAll(patternProjection);
                    if (!patternMatch)
                        continue;

                    // check if surrounding cells are dead
                    var boundaryProjection
                        = projections.BoundaryCells[projection].Select(c => livingCell + c).ToArray();
                    var boundaryMatch = ContainsNone(boundaryProjection);

                    if (boundaryMatch)
                        foundPatterns.Add(patternProjection.ToPattern());

                    // shorten search time by removing these cells
                    // from examination for other patterns
                    //foreach (var foundsCell in patternProjection)
                    //{
                    //    // ReSharper disable once NotAccessedVariable
                    //    //var cell = new Cell(foundsCell.Item1, foundsCell.Item2);
                    //    cells.Remove(foundsCell);
                    //}
                }
            }

            return foundPatterns;
        }

        public IEnumerable<Pattern> FindPattern(Pattern pattern)
        {
            return FindPatterns(new Projections(pattern));
        }

        public override string ToString()
        {
            return string.Join(", ", this);
        }
    }
}