/// Echo-one 面对面 BLE 协议的纯函数编解码。
///
/// 字节布局以 `docs/face_to_face_ble_protocol.md` v0.2 为准，
/// 由 `test/devices/bes_f2f_protocol_test.dart` 钉死。原生组包必须与这里一致。
library;

class BesF2f {
  BesF2f._();

  static const int protoVer = 0x02;
  static const int capG722 = 0x01;
  static const int codecG722 = 0x01;

  static const int earLeft = 0x01;
  static const int earRight = 0x02;

  static const int magic0 = 0xF2;
  static const int magic1 = 0xF2;

  /// 控制与音频分开的四个特征。UUID 按协议占位，固件已按此实现。
  static const String serviceUuid = 'AEAF5F32-0001-4C4B-A100-000000000001';
  static const String ctrlTxUuid = 'AEAF5F32-0002-4C4B-A100-000000000001';
  static const String ctrlRxUuid = 'AEAF5F32-0003-4C4B-A100-000000000001';
  static const String audioUpUuid = 'AEAF5F32-0004-4C4B-A100-000000000001';
  static const String audioDownUuid = 'AEAF5F32-0005-4C4B-A100-000000000001';

  static const int opHello = 0x01;
  static const int opSessionCfg = 0x02;
  static const int opStartStream = 0x03;
  static const int opStopStream = 0x04;
  static const int opKeepalive = 0x05;
  static const int opExit = 0x06;
  static const int opAudioUp = 0x90;
  static const int opAudioDown = 0x91;
  static const int opEvent = 0x87;
  static const int opPace = 0x88;

  static const int roleApp = 0x01;
  static const int vadAlways = 0x00;
  static const int triggerContinuous = 0x00;
  static const int defaultGain = 80;

  static const int flagVad = 0x10;
  static const int flagSegBegin = 0x20;
  static const int flagSegEnd = 0x40;
  static const int flagOwnVoice = 0x80;
  static const int flagPlayBegin = 0x10;
  static const int flagPlayEnd = 0x20;
  static const int flagFlush = 0x40;

  static const int evtButton = 0x01;
  static const int evtWear = 0x02;
  static const int evtBattery = 0x03;
  static const int evtStats = 0x04;
  static const int evtFault = 0x05;
  static const int evtExitRequest = 0x06;

  static const int exitUser = 0x01;
  static const int exitBattery = 0x02;
  static const int exitIncomingCall = 0x03;
  static const int exitPeerLost = 0x04;

  static const int ok = 0x00;
  static const int errUnsupported = 0x01;
  static const int errBusy = 0x02;
  static const int errEarUnavailable = 0x03;
  static const int errToken = 0x04;
  static const int errBleResource = 0x05;
  static const int errCodec = 0x06;
  static const int errTimeout = 0x07;
  static const int errEarMismatch = 0x08;
  static const int errOverflow = 0x09;
  static const int errInternal = 0x0A;
  static const int errTwsSplit = 0x0B;

  /// `AA 6B 06 <ver> <cap> <token 4>`
  static List<int> enterFrame(List<int> token) {
    if (token.length != 4) {
      throw ArgumentError('token must be 4 bytes');
    }
    return <int>[
      0xAA, 0x6B, 0x06, protoVer, capG722,
      token[0] & 0xFF, token[1] & 0xFF, token[2] & 0xFF, token[3] & 0xFF,
    ];
  }

  static List<int> exitFrame() => const <int>[0xAA, 0x6C];

  /// 解析 `BB EB`。长度不够返回 null。
  static BesF2fEnterAck? parseEnterAck(List<int> frame) {
    if (frame.length < 10) return null;
    if ((frame[0] & 0xFF) != 0xBB || (frame[1] & 0xFF) != 0xEB) return null;
    return BesF2fEnterAck(
      result: frame[3] & 0xFF,
      earMask: frame[4] & 0xFF,
      protoVer: frame[5] & 0xFF,
      codec: frame[6] & 0xFF,
      frameMs: frame[7] & 0xFF,
      fwMinor: frame[8] & 0xFF,
      classicKeep: (frame[9] & 0xFF) == 0x01,
    );
  }

  static bool isExitAckOk(List<int> frame) {
    if (frame.length < 4) return false;
    return (frame[0] & 0xFF) == 0xBB &&
        (frame[1] & 0xFF) == 0xEC &&
        (frame[3] & 0xFF) == ok;
  }

  /// 广播里 Manufacturer Data 去掉 Company ID 之后的 9 字节。
  static BesF2fAdvert? parseAdvertPayload(List<int> afterCompanyId) {
    if (afterCompanyId.length < 9) return null;
    if ((afterCompanyId[0] & 0xFF) != magic0 ||
        (afterCompanyId[1] & 0xFF) != magic1) {
      return null;
    }
    final ear = afterCompanyId[3] & 0xFF;
    if (ear != earLeft && ear != earRight) return null;
    return BesF2fAdvert(
      version: afterCompanyId[2] & 0xFF,
      ear: ear,
      token: List<int>.unmodifiable(afterCompanyId.sublist(4, 8)),
      battery: afterCompanyId[8] & 0x7F,
      charging: (afterCompanyId[8] & 0x80) != 0,
    );
  }

  static List<int> hello(List<int> token) => <int>[
        0xAA, opHello, 0x06, protoVer,
        token[0] & 0xFF, token[1] & 0xFF, token[2] & 0xFF, token[3] & 0xFF,
        roleApp,
      ];

  static List<int> sessionCfg() => <int>[
        0xAA, opSessionCfg, 0x03, vadAlways, defaultGain, triggerContinuous,
      ];

  static List<int> startStream() => <int>[0xAA, opStartStream, 0x00];

  static List<int> stopStream() => <int>[0xAA, opStopStream, 0x00];

  static List<int> keepalive(int seq) =>
      <int>[0xAA, opKeepalive, 0x01, seq & 0xFF];

  static List<int> exitEar() => <int>[0xAA, opExit, 0x00];

  /// `AA 91` 下行音频。payload = flags(含耳位) + seq16le + g722。
  static List<int> audioDown({
    required int ear,
    required int flags,
    required int seq,
    required List<int> g722,
  }) {
    final head = (ear & 0x0F) | (flags & 0xF0);
    final body = <int>[head, seq & 0xFF, (seq >> 8) & 0xFF, ...g722];
    return <int>[0xAA, opAudioDown, body.length & 0xFF, ...body];
  }

  /// 解析一条 BLE 通知帧。不是本协议返回 null。
  static BesF2fBleFrame? parseBle(List<int> frame) {
    if (frame.length < 3) return null;
    final sof = frame[0] & 0xFF;
    if (sof != 0xAA && sof != 0xBB) return null;
    final op = frame[1] & 0xFF;
    final len = frame[2] & 0xFF;
    if (frame.length < 3 + len) return null;
    return BesF2fBleFrame(op: op, payload: frame.sublist(3, 3 + len));
  }

  static BesF2fAudio? parseAudioUp(BesF2fBleFrame frame) {
    if (frame.op != opAudioUp || frame.payload.length < 3) return null;
    final b = frame.payload[0] & 0xFF;
    return BesF2fAudio(
      ear: b & 0x0F,
      flags: b & 0xF0,
      seq: (frame.payload[1] & 0xFF) | ((frame.payload[2] & 0xFF) << 8),
      g722: List<int>.unmodifiable(frame.payload.sublist(3)),
    );
  }

  /// 用户能看懂的失败文案键。未知码用超时。
  static String messageKey(int code) {
    switch (code) {
      case errUnsupported:
        return 'f2fFirmwareUpgrade';
      case errBusy:
        return 'f2fEndOtherFeature';
      case errEarUnavailable:
        return 'f2fWearBothEars';
      case errTwsSplit:
        return 'f2fPutBackInCase';
      default:
        return 'f2fEarNotReady';
    }
  }
}

class BesF2fEnterAck {
  const BesF2fEnterAck({
    required this.result,
    required this.earMask,
    required this.protoVer,
    required this.codec,
    required this.frameMs,
    required this.fwMinor,
    required this.classicKeep,
  });

  final int result;
  final int earMask;
  final int protoVer;
  final int codec;
  final int frameMs;
  final int fwMinor;
  final bool classicKeep;

  bool get bothEars => (earMask & 0x03) == 0x03;
}

class BesF2fAdvert {
  const BesF2fAdvert({
    required this.version,
    required this.ear,
    required this.token,
    required this.battery,
    required this.charging,
  });

  final int version;
  final int ear;
  final List<int> token;
  final int battery;
  final bool charging;

  bool tokenEquals(List<int> expected) {
    if (token.length != expected.length) return false;
    for (var i = 0; i < token.length; i++) {
      if ((token[i] & 0xFF) != (expected[i] & 0xFF)) return false;
    }
    return true;
  }
}

class BesF2fBleFrame {
  const BesF2fBleFrame({required this.op, required this.payload});
  final int op;
  final List<int> payload;

  int get result => payload.isEmpty ? 0xFF : payload[0] & 0xFF;
}

class BesF2fAudio {
  const BesF2fAudio({
    required this.ear,
    required this.flags,
    required this.seq,
    required this.g722,
  });

  final int ear;
  final int flags;
  final int seq;
  final List<int> g722;

  bool get ownVoice => (flags & BesF2f.flagOwnVoice) != 0;
}