import 'dart:typed_data';



/**
 * 
 *    需要按照格式严格封装  
 * 
 * 
 *    4个字节  放全部信息长度 头+body
 *    2字节  header长度
 *    2字节  默认填1 
 *    4字节  登录1，消息5
 *    4字节  默认填1 
 *    不限制长度body  但是不要超过2048-16 
 *    需要严格控制每条消息发送不超过 2048  
 */ 


class Proto {
  static const int HEADER_LENGTH = 16; // 假设头部长度为16字节
  static const int VERSION = 1;

  int operation;
  int seqId;
  Uint8List body;

  Proto(this.operation, this.seqId, this.body);

  Uint8List toBytes() {
    final buffer = BytesBuilder();
    buffer.add(_intToBytes(HEADER_LENGTH + body.length, 4));
    buffer.add(_shortToBytes(HEADER_LENGTH, 2));
    buffer.add(_shortToBytes(VERSION, 2));
    buffer.add(_intToBytes(operation, 4));
    buffer.add(_intToBytes(seqId, 4));
    buffer.add(body);
    return buffer.toBytes();
  }


  static Proto fromBytes(Uint8List data) {
    final buffer = ByteData.sublistView(data);
    int offset = 0;

    int packetLen = buffer.getInt32(offset, Endian.big);
    offset += 4;
    int headerLen = buffer.getInt16(offset, Endian.big);
    offset += 2;
    int version = buffer.getInt16(offset, Endian.big);
    offset += 2;
    int operation = buffer.getInt32(offset, Endian.big);
    offset += 4;
    int seqId = buffer.getInt32(offset, Endian.big);
    offset += 4;
    Uint8List body = data.sublist(offset);

    return Proto(operation, seqId, body);
  }

  List<int> _intToBytes(int value, int length) {
    final bytes = ByteData(length);
    bytes.setInt32(0, value, Endian.big);
    return bytes.buffer.asUint8List();
  }

  List<int> _shortToBytes(int value, int length) {
    final bytes = ByteData(length);
    bytes.setInt16(0, value, Endian.big);
    return bytes.buffer.asUint8List();
  }
}