import 'dart:async';
import 'dart:developer' as developer;
import 'package:flutter/widgets.dart';
import 'package:geolocator/geolocator.dart';
import '../../core/constants/gps_constants.dart';
import '../../services/logger.dart';
import '../models/location_data.dart';
import '../services/gps_service.dart';

/// Repository that wraps GpsService and applies GPS business logic.
///
/// Single source of truth for location data. Handles:
/// - GPS stream management (start/stop/restart)
/// - Data processing (staleness, precision switching, validation)
/// - Lifecycle management (app foreground/background, wake lock)
class LocationRepository extends ChangeNotifier with WidgetsBindingObserver {
  StreamSubscription<Position>? _gpsSubscription;
  final StreamController<LocationData> _dataController =
      StreamController<LocationData>.broadcast();

  // Use late to defer DateTime.now() — const constructors can't call methods
  late LocationData _currentData = LocationData(
    speed: 0.0,
    heading: -1.0,
    displaySpeed: '--',
    displayHeading: 'N/A',
    isSpeedValid: false,
    isHeadingValid: false,
    timestamp: DateTime.now(),
  );

  Timer? _staleDataTimer;
  Timer? _backgroundGracePeriodTimer;
  bool _isDisposed = false;

  // Lifecycle and precision state
  LocationAccuracy _currentAccuracy = LocationAccuracy.high;
  bool _hasFirstFix = false;
  DateTime? _firstFixTime;
  bool _isAppInForeground = true;
  bool _isGpsActive = false;

  // Public stream for UI components to subscribe to
  Stream<LocationData> get locationStream => _dataController.stream;

  // Get current data synchronously
  LocationData get currentData => _currentData;

  bool get isInitialized => _isInitialized;
  bool get isGpsActive => _isGpsActive;

  bool _isInitialized = false;

  /// Initialize GPS: check permissions, get first fix, start stream.
  Future<void> initialize() async {
    if (_isInitialized) {
      Logger.warn('Already initialized, skipping...', 'LocationRepository');
      return;
    }

    Logger.info('Starting location repository initialization...', 'LocationRepository');
    WidgetsBinding.instance.addObserver(this);

    // Check GPS permissions and services first
    final serviceEnabled = await GpsService.isLocationServiceEnabled();
    Logger.debug('Location service enabled: $serviceEnabled', 'LocationRepository');
    if (!serviceEnabled) {
      Logger.error('GPS service disabled', 'LocationRepository');
      _updateData(_currentData.copyWith(
        displaySpeed: 'GPS OFF',
        displayHeading: 'GPS OFF',
      ));
      _isInitialized = true;
      return;
    }

    final permissionGranted = await GpsService.requestPermissions();
    Logger.debug('GPS permission granted: $permissionGranted', 'LocationRepository');
    if (!permissionGranted) {
      Logger.error('GPS permission denied', 'LocationRepository');
      _updateData(_currentData.copyWith(
        displaySpeed: 'NO PERM',
        displayHeading: 'NO PERM',
      ));
      _isInitialized = true;
      return;
    }

    try {
      // Get initial position with long timeout for cold start
      final initialPosition = await GpsService.getCurrentPosition(
        accuracy: LocationAccuracy.bestForNavigation,
        timeLimit: GpsConfig.INITIAL_FIX_TIMEOUT,
      );

      if (initialPosition == null) {
        Logger.error('Initial GPS fix failed — null position', 'LocationRepository');
        _updateData(_currentData.copyWith(
          displaySpeed: 'GPS ERR',
          displayHeading: 'GPS ERR',
        ));
        _isInitialized = true;
        return;
      }

      Logger.info('Initial GPS fix obtained', 'LocationRepository');
      _hasFirstFix = true;
      _firstFixTime = DateTime.now();
      _onPositionUpdate(initialPosition);

      // Start position stream
      Logger.debug('Starting GPS stream with accuracy: $_currentAccuracy', 'LocationRepository');
      _startPositionStream(_currentAccuracy);

      _isGpsActive = true;
      await GpsService.setWakeLock(true);
      _isInitialized = true;
    } catch (e, stackTrace) {
      developer.log('GPS subscription creation failed: $e',
          error: e, stackTrace: stackTrace, name: 'LocationRepository');
      _updateData(_currentData.copyWith(
        displaySpeed: 'GPS ERR',
        displayHeading: 'GPS ERR',
      ));
      _isInitialized = true;
    }

    Logger.info('Location repository initialized successfully', 'LocationRepository');
  }

  void _startPositionStream(LocationAccuracy accuracy) {
    _gpsSubscription = GpsService.createPositionStream(accuracy: accuracy).listen(
      (Position position) {
        Logger.debug('GPS callback triggered', 'LocationRepository');
        _onPositionUpdate(position);
      },
      onError: (error) {
        Logger.error('GPS stream error callback: $error', 'LocationRepository');
        _onGpsError(error);
      },
      onDone: () {
        Logger.warn('GPS stream done callback - stream ended', 'LocationRepository');
      },
      cancelOnError: false,
    );
  }

  void _onPositionUpdate(Position position) {
    Logger.debug('Raw GPS update: speed=${position.speed.toStringAsFixed(2)} m/s, heading=${position.heading.toStringAsFixed(1)}°', 'LocationRepository');

    _scheduleStaleDataTimer();

    // Validate speed
    final rawSpeed = position.speed;
    final bool speedValid = rawSpeed.isFinite && rawSpeed >= 0;
    final double speed = speedValid ? rawSpeed : 0.0;

    // Validate heading
    final rawHeading = position.heading;
    final bool headingValid = rawHeading.isFinite &&
        rawHeading >= GpsConfig.VALID_HEADING_MIN &&
        rawHeading < GpsConfig.VALID_HEADING_MAX;
    final double heading = headingValid ? rawHeading : _currentData.heading;

    // Format display
    final displaySpeed = speed.toStringAsFixed(1);
    final displayHeading = headingValid
        ? GpsService.formatHeading(heading)
        : _currentData.displayHeading;

    Logger.debug('Processed: displaySpeed="$displaySpeed", displayHeading="$displayHeading"', 'LocationRepository');

    final locationData = LocationData(
      speed: speed,
      heading: heading,
      displaySpeed: displaySpeed,
      displayHeading: displayHeading,
      isSpeedValid: speedValid,
      isHeadingValid: headingValid,
      timestamp: DateTime.now(),
    );

    _updateData(locationData);

    // Check precision switching after first-fix gate
    if (_hasFirstFix && _firstFixTime != null) {
      final timeSinceFirstFix = DateTime.now().difference(_firstFixTime!);
      if (timeSinceFirstFix >= GpsConfig.PRECISION_SWITCH_FIRST_FIX_DELAY) {
        _checkPrecisionSwitch(position.speed);
      }
    }
  }

  void _onGpsError(dynamic error) {
    if (_isDisposed) return;
    final errorString = error.toString().toLowerCase();
    if (!errorString.contains('timeout') && !errorString.contains('temporarily')) {
      _updateData(_currentData.copyWith(
        displaySpeed: 'GPS ERR',
        displayHeading: 'GPS ERR',
        isSpeedValid: false,
        isHeadingValid: false,
      ));
    }
  }

  void _scheduleStaleDataTimer() {
    _staleDataTimer?.cancel();
    _staleDataTimer = Timer(GpsConfig.STALE_DATA_THRESHOLD, _handleStaleDataTimeout);
  }

  void _handleStaleDataTimeout() {
    if (_isDisposed) return;
    final displayText = _currentData.displaySpeed;
    if (displayText == '--' || displayText.startsWith('GPS') || displayText == 'NO PERM') {
      return;
    }

    final headingStillValid = _currentData.isHeadingValid &&
        _currentData.heading >= GpsConfig.VALID_HEADING_MIN &&
        _currentData.heading < GpsConfig.VALID_HEADING_MAX;
    final displayHeading = headingStillValid ? _currentData.displayHeading : '--';

    Logger.warn('No GPS updates within ${GpsConfig.STALE_DATA_THRESHOLD.inSeconds}s - marking data as stale', 'LocationRepository');

    final staleData = _currentData.copyWith(
      displaySpeed: '--',
      displayHeading: displayHeading,
      isSpeedValid: false,
      isHeadingValid: headingStillValid,
    );

    _staleDataTimer = null;
    _updateData(staleData);
  }

  void _updateData(LocationData newData) {
    if (_isDisposed) return;
    _currentData = newData;
    _dataController.add(newData);
    notifyListeners();
    Logger.debug('Broadcasting data: ${newData.displaySpeed} ${newData.displayHeading}', 'LocationRepository');
  }

  /// Check if GPS precision should be switched based on speed.
  void _checkPrecisionSwitch(double speedMps) {
    if (_currentAccuracy == LocationAccuracy.high) {
      if (speedMps < GpsConfig.PRECISION_DOWN_THRESHOLD_MPS) {
        _switchPrecision(LocationAccuracy.medium);
      }
    } else if (_currentAccuracy == LocationAccuracy.medium) {
      if (speedMps > GpsConfig.PRECISION_UP_THRESHOLD_MPS) {
        _switchPrecision(LocationAccuracy.high);
      }
    }
  }

  /// Switch GPS precision and restart stream with new accuracy.
  void _switchPrecision(LocationAccuracy newAccuracy) {
    if (_currentAccuracy == newAccuracy) return;

    final speedKmh = _currentData.speed * 3.6;
    Logger.debug('Precision switched to $newAccuracy at ${speedKmh.toStringAsFixed(1)} km/h', 'LocationRepository');

    _currentAccuracy = newAccuracy;
    _gpsSubscription?.cancel();
    _startPositionStream(newAccuracy);
  }

  /// Handle app lifecycle state changes.
  @override
  void didChangeAppLifecycleState(AppLifecycleState state) {
    if (state == AppLifecycleState.paused) {
      _isAppInForeground = false;
      // No overlay logic here — overlay is deferred
      _updateWakeLock();
    } else if (state == AppLifecycleState.resumed) {
      _isAppInForeground = true;
      _backgroundGracePeriodTimer?.cancel();
      _backgroundGracePeriodTimer = null;

      // Restart GPS if it was stopped
      if (_gpsSubscription == null && _isInitialized) {
        restartGps();
      }

      _updateWakeLock();
    }
  }

  /// Stop GPS tracking.
  void stopGps() {
    _gpsSubscription?.cancel();
    _gpsSubscription = null;
    _isGpsActive = false;
    _staleDataTimer?.cancel();
    _updateWakeLock();
    Logger.info('GPS stopped', 'LocationRepository');
  }

  /// Restart GPS tracking.
  void restartGps() {
    Logger.info('Restarting GPS', 'LocationRepository');
    _startPositionStream(_currentAccuracy);
    _isGpsActive = true;
    _updateWakeLock();
  }

  /// Update wake lock based on GPS state and app visibility.
  Future<void> _updateWakeLock() async {
    final shouldKeepAwake = _isGpsActive && _isAppInForeground;
    await GpsService.setWakeLock(shouldKeepAwake);
    Logger.debug(
      'Wake lock ${shouldKeepAwake ? "enabled" : "disabled"} (GPS: $_isGpsActive, foreground: $_isAppInForeground)',
      'LocationRepository',
    );
  }

  @override
  void dispose() {
    super.dispose();
    _isDisposed = true;
    Logger.info('Disposing location repository...', 'LocationRepository');
    WidgetsBinding.instance.removeObserver(this);
    _backgroundGracePeriodTimer?.cancel();
    _backgroundGracePeriodTimer = null;
    _gpsSubscription?.cancel();
    _gpsSubscription = null;
    _staleDataTimer?.cancel();
    _staleDataTimer = null;
    _dataController.close();
    GpsService.setWakeLock(false);
    Logger.info('Location repository disposed', 'LocationRepository');
  }
}