FS functions

private static readonly ReferenceTable<WrappingStream> Files = new ReferenceTable<WrappingStream>();

private static RESULT FSUserSeek(IntPtr handle, uint pos, IntPtr userdata)
{
    WrappingStream? stream = Files.TryGet(handle);
    if (stream == null)
        return RESULT.ERR_FILE_BAD;

    if (!stream.Underlying.CanSeek)
    {
        stream.Underlying = new MemoryStream(Content.LoadBytes(stream.ContentPath));
    }

    stream.Position = pos;
    return RESULT.OK;
}

private static unsafe RESULT FSUserRead(IntPtr handle, IntPtr buffer, uint sizebytes, ref uint bytesread, IntPtr userdata)
{
    WrappingStream? stream = Files.TryGet(handle);
    if (stream == null)
        return RESULT.ERR_FILE_BAD;

    Span<byte> readSpan = new ((byte*)buffer, (int)sizebytes);
    bytesread = (uint)stream.Read(readSpan);
    return bytesread < sizebytes ? RESULT.ERR_FILE_EOF : RESULT.OK;
}

private static RESULT FSUserClose(IntPtr handle, IntPtr userdata)
{
    WrappingStream? stream = Files.TryGet(handle);
    if (stream == null)
        return RESULT.ERR_FILE_BAD;

    stream.Close();
    Files.Free(handle);
    return RESULT.OK;
}

private static RESULT FSUserOpen(IntPtr name, ref uint filesize, ref IntPtr handle, IntPtr userdata)
{
    ContentLump? lump = Content.Load(name.GetString());

    if (lump == null)
        return RESULT.ERR_FILE_NOTFOUND;

    WrappingStream stream = new WrappingStream(Content.LoadStream(lump));
    stream.ContentPath = name.GetString();
    handle = Files.Create(stream);
    return RESULT.OK;
}