PKHeX/PKHeX.Core/Saves/Substructures/Battle Videos/BV3.cs

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

namespace PKHeX.Core;

public sealed class BV3 : BattleVideo
{
    internal const int SIZE = 0xF80;
    public override int Generation => 3;

    public override IReadOnlyList<PK3> BattlePKMs => PlayerTeams.SelectMany(z => z).ToArray();

    public readonly byte[] Data;

    internal new static bool IsValid(ReadOnlySpan<byte> data)
    {
        if (data.Length != SIZE)
            return false;
        var chkSpan = data[^4..];
        var chk = ReadUInt32LittleEndian(chkSpan);
        if (chk > 0xF7080)
            return false; // max if all are FF

        var chkRegion = data[..^4];
        var expect = GetByteSum(chkRegion);
        return chk == expect;
    }

    public BV3(byte[] data) => Data = (byte[])data.Clone();
    public BV3() : this(new byte[SIZE]) { }

    public IReadOnlyList<PK3[]> PlayerTeams
    {
        get => new[]
        {
            GetTeam(0),
            GetTeam(1),
        };
        set
        {
            SetTeam(value[0], 0);
            SetTeam(value[1], 1);
        }
    }

    public PK3[] GetTeam(int teamIndex)
    {
        if ((uint)teamIndex > 2)
            throw new ArgumentOutOfRangeException(nameof(teamIndex));

        var ofs = 6 * PokeCrypto.SIZE_3PARTY * teamIndex;
        var team = new PK3[6];
        for (int p = 0; p < 6; p++)
        {
            int offset = ofs + (PokeCrypto.SIZE_3PARTY * p);
            team[p] = new PK3(Data.Slice(offset, PokeCrypto.SIZE_3PARTY));
        }

        return team;
    }

    public void SetTeam(IReadOnlyList<PK3> team, int teamIndex)
    {
        var ofs = 6 * PokeCrypto.SIZE_3PARTY * teamIndex;
        for (int p = 0; p < 6; p++)
        {
            int offset = ofs + (PokeCrypto.SIZE_3PARTY * p);
            team[p].EncryptedPartyData.CopyTo(Data, offset);
        }
    }

    // 0x4B0 - string3[4][8] Trainer Names
    // 0x4D0 - u8[4] Trainer Genders
    // 0x4D4 - u32[4] Trainer IDs
    // 0x4E4 - u8[4] Trainer Languages

    public uint Seed
    {
        get => ReadUInt32LittleEndian(Data.AsSpan(0x4E8));
        set => WriteUInt32LittleEndian(Data.AsSpan(0x4E8), value);
    }

    public uint Mode
    {
        get => ReadUInt32LittleEndian(Data.AsSpan(0x4EC));
        set => WriteUInt32LittleEndian(Data.AsSpan(0x4EC), value);
    }

    // ...

    public uint Checksum
    {
        get => ReadUInt32LittleEndian(Data.AsSpan(SIZE - 4));
        set => WriteUInt32LittleEndian(Data.AsSpan(SIZE - 4), value);
    }

    public bool IsChecksumValid() => Checksum == GetByteSum(Data.AsSpan()[..^4]);

    public static uint GetByteSum(ReadOnlySpan<byte> data)
    {
        uint result = 0;
        foreach (byte b in data)
            result += b;
        return result;
    }
}