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

namespace PKHeX.Core;

public sealed class LinkBlock6 : SaveBlock<SAV6>
{
    public LinkBlock6(SAV6XY sav, int offset) : base(sav) => Offset = offset;
    public LinkBlock6(SAV6AO sav, int offset) : base(sav) => Offset = offset;

    public byte[] GetLinkInfoData() => Data.Slice(Offset + 0x1FF, PL6.Size);
    public PL6 GetLinkInfo() => new(GetLinkInfoData());

    public void SetLinkInfoData(ReadOnlySpan<byte> data)
    {
        data.CopyTo(Data.AsSpan(Offset));
        Checksum = GetCalculatedChecksum(); // [app,chk)
    }

    public void SetLinkInfo(PL6 pl6)
    {
        pl6.Data.CopyTo(Data, Offset + 0x1FF);
        Checksum = GetCalculatedChecksum(); // [app,chk)
    }

    private ushort GetCalculatedChecksum() => Checksums.CRC16_CCITT(new ReadOnlySpan<byte>(Data, Offset + 0x200, 0xC48 - 4 - 0x200)); // [app,chk)

    private int GetChecksumOffset() => Offset + 0xC48 - 4;

    public ushort Checksum
    {
        get => ReadUInt16LittleEndian(Data.AsSpan(GetChecksumOffset()));
        set => WriteUInt16LittleEndian(Data.AsSpan(GetChecksumOffset()), value);
    }
}