using System;
using System.Linq;
using static System.Buffers.Binary.BinaryPrimitives;

namespace PKHeX.Core
{
    public abstract class EggMoves
    {
        public readonly int[] Moves;
        protected EggMoves(int[] moves) => Moves = moves;
        public bool GetHasEggMove(int move) => Moves.Contains(move);
    }

    public sealed class EggMoves2 : EggMoves
    {
        private EggMoves2(int[] moves) : base(moves) { }

        public static EggMoves2[] GetArray(ReadOnlySpan<byte> data, int count)
        {
            var entries = new EggMoves2[count + 1];
            var empty = entries[0] = new EggMoves2(Array.Empty<int>());

            int baseOffset = ReadInt16LittleEndian(data) - (count * 2);
            for (int i = 1; i < entries.Length; i++)
            {
                int start = ReadInt16LittleEndian(data[((i - 1) * 2)..]) - baseOffset;
                var slice = data[start..];
                int moveCount = slice.IndexOf((byte)0xFF);
                if (moveCount == 0)
                {
                    entries[i] = empty;
                    continue;
                }

                int[] moves = new int[moveCount];
                for (int m = 0; m < moves.Length; m++)
                    moves[m] = slice[m];

                entries[i] = new EggMoves2(moves);
            }

            return entries;
        }
    }

    public sealed class EggMoves6 : EggMoves
    {
        private EggMoves6(int[] moves) : base(moves) { }

        public static EggMoves6[] GetArray(BinLinkerAccessor entries)
        {
            var result = new EggMoves6[entries.Length];
            var empty = result[0] = new EggMoves6(Array.Empty<int>());
            for (int i = 1; i < result.Length; i++)
            {
                var data = entries[i];
                int count = ReadInt16LittleEndian(data);
                if (count == 0)
                {
                    result[i] = empty;
                    continue;
                }

                var moves = new int[count];
                var span = data[2..];
                for (int j = 0; j < moves.Length; j++)
                    moves[j] = ReadInt16LittleEndian(span[(j * 2)..]);
                result[i] = new EggMoves6(moves);
            }
            return result;
        }
    }

    public sealed class EggMoves7 : EggMoves
    {
        public readonly int FormTableIndex;

        private EggMoves7(int[] moves, int formIndex = 0) : base(moves) => FormTableIndex = formIndex;

        public static EggMoves7[] GetArray(BinLinkerAccessor entries)
        {
            var result = new EggMoves7[entries.Length];
            var empty = result[0] = new EggMoves7(Array.Empty<int>());
            for (int i = 1; i < result.Length; i++)
            {
                var data = entries[i];
                int count = ReadInt16LittleEndian(data[2..]);
                int formIndex = ReadInt16LittleEndian(data);
                if (count == 0)
                {
                    // Might need to keep track of the Form Index for unavailable forms pointing to valid forms.
                    if (formIndex != 0)
                        result[i] = new EggMoves7(Array.Empty<int>(), formIndex);
                    else
                        result[i] = empty;
                    continue;
                }

                var moves = new int[count];
                var span = data[4..];
                for (int j = 0; j < moves.Length; j++)
                    moves[j] = ReadInt16LittleEndian(span[(j * 2)..]);
                result[i] = new EggMoves7(moves, formIndex);
            }
            return result;
        }
    }
}