import 'dart:typed_data';

class RawPacket {
  final int command; // 第三位指令位
  final Uint8List payload; // 数据位
  RawPacket({required this.command, required this.payload});
}

class ProtocolDecoder {
  static const head = [0xAB, 0xAA];
  static const tail = [0xAA, 0xAB];
  final List<int> _buffer = [];

  List<RawPacket> decode(List<int> newData) {
    _buffer.addAll(newData);
    List<RawPacket> packets = [];

    while (_buffer.length >= 5) {
      // 最小包长度：头2+指令1+尾2 = 5，加1位数据=6，但是心跳包是AB AA FF AA AB
      // 1. 找头
      int headIdx = -1;
      for (int i = 0; i < _buffer.length - 1; i++) {
        if (_buffer[i] == head[0] && _buffer[i + 1] == head[1]) {
          headIdx = i;
          break;
        }
      }

      if (headIdx == -1) {
        _buffer.clear(); // 没头，全是垃圾数据
        break;
      }

      // 2. 找尾
      int tailIdx = -1;
      for (int i = headIdx + 2; i < _buffer.length - 1; i++) {
        if (_buffer[i] == tail[0] && _buffer[i + 1] == tail[1]) {
          tailIdx = i;
          break;
        }
      }

      if (tailIdx != -1) {
        // 3. 提取
        int cmd = _buffer[headIdx + 2];
        Uint8List payload = Uint8List.fromList(
          _buffer.sublist(headIdx + 3, tailIdx),
        );
        packets.add(RawPacket(command: cmd, payload: payload));

        // 4. 移除已处理部分
        _buffer.removeRange(0, tailIdx + 2);
      } else {
        break; // 还没传完
      }
    }
    return packets;
  }
}