PKHeX/PKHeX.Core/Saves/Substructures/Gen6/LinkBlock6.cs

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);
        }
    }
}