llbzow 的摸鱼日记 (づ￣ 3￣)づ

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abstract class GnssDataLink {
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  Stream<Uint8List> get dataStream;
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  Future<void> connect(String deviceId);
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  Future<void> write(Uint8List bytes);
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  Future<void> disconnect();
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}

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class BleGnssLink implements GnssDataLink {
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  final BluetoothDevice device;
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  final Set<String> approvedSerialUuids;
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  BluetoothCharacteristic? _rxCharacteristic; // 接收数据特征值
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  BluetoothCharacteristic? _txCharacteristic; // 发送差分数据特征值
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  final _controller = StreamController<Uint8List>.broadcast();
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  BleGnssLink(this.device, this.approvedSerialUuids);
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  @override
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  Stream<Uint8List> get dataStream => _controller.stream;
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  @override
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  Future<void> connect(String deviceId) async {
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    await device.connect();
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    // 1. 协商最大 MTU（部分 Android 设备支持协商到 512 字节）
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    if (Platform.isAndroid) {
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      await device.requestMtu(512);
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    }
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    // 2. 发现服务并定位特征值
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    List<BluetoothService> services = await device.discoverServices();
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    for (var service in services) {
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      for (var char in service.characteristics) {
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        // 串口服务 UUID 由设备适配配置注入
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        if (approvedSerialUuids.contains(char.uuid.toString())) {
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          _rxCharacteristic = char;
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          _txCharacteristic = char;
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          break;
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        }
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      }
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    }
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    if (_rxCharacteristic != null) {
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      // 3. 启用特征值通知
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      await _rxCharacteristic!.setNotifyValue(true);
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      _rxCharacteristic!.lastValueStream.listen((value) {
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        _controller.add(Uint8List.fromList(value));
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      });
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    }
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  }
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  @override
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  Future<void> write(Uint8List bytes) async {
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    if (_txCharacteristic == null) return;
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    // BLE 写入需要注意分包，每次写入大小不能超过 (MTU - 3) 字节
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    int mtu = device.mtuNow;
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    int chunkSize = mtu - 3;
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    for (int i = 0; i < bytes.length; i += chunkSize) {
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      int end = (i + chunkSize < bytes.length) ? i + chunkSize : bytes.length;
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      await _txCharacteristic!.write(
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        bytes.sublist(i, end),
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        withoutResponse: true, // 提升吞吐率，使用 Write Without Response
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      );
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    }
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  }
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  @override
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  Future<void> disconnect() async {
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    await device.disconnect();
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    await _controller.close();
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  }
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}

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class NmeaFrameDecoder {
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  final List<int> _buffer = [];
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  final _sentenceController = StreamController<String>.broadcast();
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  Stream<String> get sentenceStream => _sentenceController.stream;
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  void appendRawData(Uint8List chunk) {
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    _buffer.addAll(chunk);
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    _parseBuffer();
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  }
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  void _parseBuffer() {
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    while (_buffer.length >= 2) {
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      int rnIndex = -1;
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      // 在缓冲区中寻找 \r\n
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      for (int i = 0; i < _buffer.length - 1; i++) {
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        if (_buffer[i] == 0x0D && _buffer[i + 1] == 0x0A) {
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          rnIndex = i;
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          break;
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        }
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      }
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      if (rnIndex != -1) {
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        // 提取一整行语句
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        final frameBytes = _buffer.sublist(0, rnIndex);
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        final sentence = utf8.decode(frameBytes, allowMalformed: true);
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        // 派发语句
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        if (sentence.startsWith(r'$')) {
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          _sentenceController.add(sentence);
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        }
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        // 清理已解析的缓冲区（包括 \r\n）
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        _buffer.removeRange(0, rnIndex + 2);
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      } else {
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        // 没有找到完整的 \r\n，等待下一次数据分包到达
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        break;
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      }
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    }
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    // 防止非标脏数据导致缓冲区无限膨胀，设定安全上限
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    if (_buffer.length > 2048) {
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      _buffer.clear();
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    }
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  }
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  void dispose() {
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    _sentenceController.close();
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  }
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}