import 'dart:typed_data';

class BlePacket {
  final int command;
  final Uint8List payload;
  const BlePacket({required this.command, required this.payload});
}

/// 有状态的 BLE 协议解析器
/// 支持分片接收：多次调用 [append] 累积数据，[parse] 提取完整帧
class ProtocolParser {
  static const int _header1 = 0xAB;
  static const int _header2 = 0xAA;
  static const int _tail1 = 0xAA;
  static const int _tail2 = 0xAB;

  final List<int> _buffer = [];

  /// 清空缓冲区
  void clear() {
    _buffer.clear();
  }

  /// 获取缓冲区长度
  int get bufferLength => _buffer.length;

  /// 打包命令为字节帧（用于发送）
  /// CRC16 覆盖 command + payload 确保整帧完整性
  static Uint8List pack(int command, List<int> payload) {
    final dataToCheck = [command, ...payload];
    final crc = _crc16(dataToCheck);
    final builder = BytesBuilder()
      ..addByte(_header1)
      ..addByte(_header2)
      ..addByte(command)
      ..add(payload)
      ..addByte(crc & 0xFF)
      ..addByte((crc >> 8) & 0xFF)
      ..addByte(_tail1)
      ..addByte(_tail2);
    return builder.takeBytes();
  }

  /// 追加新接收的数据到缓冲区
  void append(List<int> data) {
    _buffer.addAll(data);
  }

  /// 从缓冲区解析所有完整的数据包
  /// 未完成的帧保留在缓冲区等待后续数据
  List<BlePacket> parse() {
    final List<BlePacket> packets = [];

    while (_buffer.length >= 6) {
      // 1. 查找帧头
      int headIdx = -1;
      for (int i = 0; i < _buffer.length - 1; i++) {
        if (_buffer[i] == _header1 && _buffer[i + 1] == _header2) {
          headIdx = i;
          break;
        }
      }

      if (headIdx == -1) {
        // 无有效帧头，清空缓冲区
        _buffer.clear();
        break;
      }

      // 移除帧头前的垃圾数据
      if (headIdx > 0) _buffer.removeRange(0, headIdx);

      // 2. 查找帧尾
      int tailIdx = -1;
      for (int i = 2; i < _buffer.length - 1; i++) {
        if (_buffer[i] == _tail1 && _buffer[i + 1] == _tail2) {
          tailIdx = i;
          break;
        }
      }

      if (tailIdx == -1) {
        // 帧尾未找到，可能是分片数据，等待更多数据
        break;
      }

      // 3. 提取数据包
      if (_buffer.length >= 5) {
        final cmd = _buffer[2];
        final payload = Uint8List.fromList(_buffer.sublist(3, tailIdx));
        packets.add(BlePacket(command: cmd, payload: payload));
      }

      // 4. 移除已处理的帧
      _buffer.removeRange(0, tailIdx + 2);
    }

    return packets;
  }

  /// 便捷方法：追加数据并立即解析
  List<BlePacket> appendAndParse(List<int> data) {
    append(data);
    return parse();
  }

  /// CRC16-Modbus: polynomial=0x8005, init=0xFFFF, refIn/refOut=true
  static int _crc16(List<int> data) {
    int crc = 0xFFFF;
    for (final b in data) {
      crc ^= b;
      for (int j = 0; j < 8; j++) {
        if ((crc & 0x0001) != 0) {
          crc = (crc >> 1) ^ 0xA001;
        } else {
          crc >>= 1;
        }
      }
    }
    return crc;
  }
}