import 'dart:async';

/// GPS 定位服务
/// 提供获取当前位置、权限请求等功能
class LocationService {
  static LocationService? _instance;

  LocationService._internal();

  factory LocationService() {
    _instance ??= LocationService._internal();
    return _instance!;
  }

  /// 请求位置权限
  Future<bool> requestPermission() async {
    // TODO: 使用 geolocator 请求权限
    // final permission = await Geolocator.requestPermission();
    // return permission == LocationPermission.always || permission == LocationPermission.whileInUse;
    print('[LocationService] 请求位置权限（模拟）');
    return true;
  }

  /// 检查位置权限状态
  Future<bool> hasPermission() async {
    // TODO: 使用 geolocator 检查权限
    return true;
  }

  /// 检查 GPS 是否开启
  Future<bool> isGpsEnabled() async {
    // TODO: 使用 geolocator 检查 GPS 状态
    // return await Geolocator.isLocationServiceEnabled();
    return true;
  }

  /// 获取当前位置
  Future<LocationData?> getCurrentLocation() async {
    try {
      final hasPermission = await requestPermission();
      if (!hasPermission) return null;

      // TODO: 使用 geolocator 获取位置
      // final position = await Geolocator.getCurrentPosition(
      //   desiredAccuracy: LocationAccuracy.high,
      // );
      // return LocationData(
      //   latitude: position.latitude,
      //   longitude: position.longitude,
      //   accuracy: position.accuracy,
      // );

      // 模拟位置数据（杭州市中心）
      return LocationData(
        latitude: 30.2741,
        longitude: 120.1551,
        accuracy: 10.0,
        altitude: 15.0,
        timestamp: DateTime.now(),
      );
    } catch (e) {
      print('[LocationService] 获取位置失败: $e');
      return null;
    }
  }

  /// 持续监听位置变化
  Stream<LocationData> watchLocation() async* {
    // TODO: 使用 geolocator 的位置流
    // final positionStream = Geolocator.getPositionStream(
    //   locationSettings: LocationSettings(accuracy: LocationAccuracy.high),
    // );
    // await for (final position in positionStream) {
    //   yield LocationData.fromPosition(position);
    // }

    // 模拟位置流
    while (true) {
      await Future.delayed(const Duration(seconds: 5));
      yield LocationData(
        latitude: 30.2741 + (DateTime.now().millisecondsSinceEpoch % 100) / 10000,
        longitude: 120.1551 + (DateTime.now().millisecondsSinceEpoch % 100) / 10000,
        accuracy: 10.0,
        timestamp: DateTime.now(),
      );
    }
  }

  /// 计算两点之间的距离（米）
  double distanceBetween(
    double startLatitude,
    double startLongitude,
    double endLatitude,
    double endLongitude,
  ) {
    // TODO: 使用 geolocator 计算距离
    // return Geolocator.distanceBetween(startLatitude, startLongitude, endLatitude, endLongitude);
    // 简单估算
    const earthRadius = 6371000.0;
    final dLat = (endLatitude - startLatitude) * 3.14159 / 180;
    final dLon = (endLongitude - startLongitude) * 3.14159 / 180;
    final a = dLat * dLat + dLon * dLon * 0.25;
    return earthRadius * 2 * a * 1000;
  }
}

/// 位置数据模型
class LocationData {
  final double latitude;
  final double longitude;
  final double accuracy;
  final double? altitude;
  final DateTime timestamp;

  LocationData({
    required this.latitude,
    required this.longitude,
    required this.accuracy,
    this.altitude,
    required this.timestamp,
  });

  @override
  String toString() => 'LocationData(lat: $latitude, lng: $longitude, accuracy: $accuracy)';
}