using System;
using System.Collections.Generic;
using static System.Buffers.Binary.BinaryPrimitives;

namespace PKHeX.Core;

/// <summary>
/// Generation 6 Evolution Branch Entries
/// </summary>
public static class EvolutionSet6
{
    internal static readonly HashSet<int> EvosWithArg = new() {6, 8, 16, 17, 18, 19, 20, 21, 22, 29};
    private const int SIZE = 6;

    private static EvolutionMethod[] GetMethods(ReadOnlySpan<byte> data)
    {
        var evos = new EvolutionMethod[data.Length / SIZE];
        for (int i = 0; i < data.Length; i += SIZE)
        {
            var entry = data.Slice(i, SIZE);
            evos[i/SIZE] = GetMethod(entry);
        }
        return evos;
    }

    private static EvolutionMethod GetMethod(ReadOnlySpan<byte> entry)
    {
        var method = ReadUInt16LittleEndian(entry);
        var arg = ReadUInt16LittleEndian(entry[2..]);
        var species = ReadUInt16LittleEndian(entry[4..]);

        // Argument is used by both Level argument and Item/Move/etc. Clear if appropriate.
        var lvl = EvosWithArg.Contains(method) ? 0 : arg;

        return new EvolutionMethod(method, species, argument: arg, level: (byte)lvl);
    }

    public static IReadOnlyList<EvolutionMethod[]> GetArray(BinLinkerAccessor data)
    {
        var evos = new EvolutionMethod[data.Length][];
        for (int i = 0; i < evos.Length; i++)
            evos[i] = GetMethods(data[i]);
        return evos;
    }
}