namespace LobbyServerDto
{
    /// <summary>
    /// Used to read the message identifer from a received object
    /// </summary>
    public static class LobbyMessageIdentifier
    {
        /// <summary>
        /// Read the message identifiere from the stream
        /// </summary>
        /// <param name="buffer"></param>
        /// <returns>The message identifier or -1 if invalid</returns>
        public static int ReadLobbyMessageIdentifier(ReadOnlySpan<byte> buffer)
        {
            if(buffer.Length == 0)
                return -1;   

            int typeId = 0;
            int shift = 0;
            int offset = 0;
            byte currentByte;
            do
            {
                if (offset < buffer.Length)
                {
                    // Check for a corrupted stream.  Read a max of 5 bytes.
                    // In a future version, add a DataFormatException.
                    if (shift == 5 * 7)  // 5 bytes max per Int32, shift += 7
                        return -1;

                    // ReadByte handles end of stream cases for us.
                    currentByte = buffer[offset++];
                    typeId |= (currentByte & 0x7F) << shift;
                    shift += 7;
                }
                else
                    return -1;

            } while ((currentByte & 0x80) != 0);

            return typeId;
        }
    }
}