PKHeX/PKHeX.Core/Legality/Evolutions/EvolutionSets/EvolutionSet1.cs

using System;
using System.Collections.Generic;

namespace PKHeX.Core;

/// <summary>
/// Generation 1 Evolution Branch Entries
/// </summary>
public static class EvolutionSet1
{
    private static EvolutionMethod GetMethod(ReadOnlySpan<byte> data)
    {
        var method = data[0];
        var species = data[1];
        var arg = data[2];

        return method == 1
            ? new EvolutionMethod(EvolutionType.LevelUp, species, Level: arg, LevelUp: 1)
            : new EvolutionMethod((EvolutionType)method, species, Argument: arg);
    }

    public static IReadOnlyList<EvolutionMethod[]> GetArray(ReadOnlySpan<byte> data, int maxSpecies)
    {
        var evos = new EvolutionMethod[maxSpecies + 1][];
        int ofs = 0;
        const int bpe = 3;
        for (int i = 0; i < evos.Length; i++)
        {
            int count = data[ofs];
            ofs++;
            if (count == 0)
            {
                evos[i] = Array.Empty<EvolutionMethod>();
                continue;
            }
            var m = new EvolutionMethod[count];
            for (int j = 0; j < m.Length; j++)
            {
                m[j] = GetMethod(data.Slice(ofs, bpe));
                ofs += bpe;
            }
            evos[i] = m;
        }
        return evos;
    }
}