import 'package:firebase_messaging/firebase_messaging.dart';
import 'package:flutter/foundation.dart';

class NotificationService {
  static final NotificationService _instance = NotificationService._internal();
  factory NotificationService() => _instance;
  NotificationService._internal();

  FirebaseMessaging? _messaging;
  
  static const String vapidKey = 'BKrFSFm2cb2DNtEpTNmEy3acpi2ziRA5DhzKSyjshqAWANaoydztUTa0Cn3jwh1v7KN6pHUQfsODFXUWrKG6aSU';
  
  static const List<String> topics = [
    'all',
    'newposts',
    'newinvites',
    'invitesfollowup',
    'appnews',
  ];

  Future<void> initialize() async {
    try {
      if (!kIsWeb) {
        print('Notifications are only supported on web platform');
        return;
      }

      if (!_isNotificationSupported()) {
        print('Notifications are not supported in this browser');
        return;
      }

      _messaging = FirebaseMessaging.instance;
      
      await _requestPermission();
      await _subscribeToTopics();
      await _setupMessageHandlers();
    } catch (e) {
      print('Error initializing notifications: $e');
    }
  }

  bool _isNotificationSupported() {
    if (!kIsWeb) return false;
    
    // Check if the browser supports notifications
    try {
      // This will throw an error if notifications are not supported
      return true; // Firebase already handles browser support checks
    } catch (e) {
      return false;
    }
  }

  Future<void> _requestPermission() async {
    if (_messaging == null) return;

    try {
      NotificationSettings settings = await _messaging!.requestPermission(
        alert: true,
        announcement: false,
        badge: true,
        carPlay: false,
        criticalAlert: false,
        provisional: false,
        sound: true,
      );

      print('User granted permission: ${settings.authorizationStatus}');
      
      if (settings.authorizationStatus == AuthorizationStatus.authorized) {
        print('User granted permission for notifications');
      } else if (settings.authorizationStatus == AuthorizationStatus.provisional) {
        print('User granted provisional permission for notifications');
      } else {
        print('User declined or has not accepted permission for notifications');
      }
    } catch (e) {
      print('Error requesting notification permission: $e');
    }
  }

  Future<void> _subscribeToTopics() async {
    if (_messaging == null) return;

    for (String topic in topics) {
      try {
        await _messaging!.subscribeToTopic(topic);
        print('Subscribed to topic: $topic');
      } catch (e) {
        print('Error subscribing to topic $topic: $e');
      }
    }
  }

  Future<void> _setupMessageHandlers() async {
    if (_messaging == null) return;

    // Handle foreground messages
    FirebaseMessaging.onMessage.listen((RemoteMessage message) {
      print('Got a message whilst in the foreground!');
      print('Message data: ${message.data}');

      if (message.notification != null) {
        print('Message also contained a notification: ${message.notification}');
        _showNotification(message.notification!);
      }
    });

    // Handle background messages
    FirebaseMessaging.onBackgroundMessage(_firebaseMessagingBackgroundHandler);

    // Handle notification taps
    FirebaseMessaging.onMessageOpenedApp.listen((RemoteMessage message) {
      print('A new onMessageOpenedApp event was published!');
      print('Message data: ${message.data}');
      _handleNotificationTap(message);
    });

    // Get the initial message if the app was opened from a notification
    RemoteMessage? initialMessage = await _messaging!.getInitialMessage();
    if (initialMessage != null) {
      print('App opened from notification: ${initialMessage.data}');
      _handleNotificationTap(initialMessage);
    }

    // Get the FCM token for this device
    String? token = await _messaging!.getToken(vapidKey: vapidKey);
    print('FCM Token: $token');
  }

  void _showNotification(RemoteNotification notification) {
    // For web, we rely on the service worker to show notifications
    // This is mainly for logging and debugging
    print('Notification Title: ${notification.title}');
    print('Notification Body: ${notification.body}');
  }

  void _handleNotificationTap(RemoteMessage message) {
    // Handle notification tap actions here
    print('Notification tapped: ${message.data}');
    
    // You can navigate to specific screens based on the notification data
    // For example:
    // if (message.data['type'] == 'newpost') {
    //   // Navigate to posts screen
    // } else if (message.data['type'] == 'newinvite') {
    //   // Navigate to invitations screen
    // }
  }

  Future<void> unsubscribeFromTopic(String topic) async {
    if (_messaging == null) return;
    
    try {
      await _messaging!.unsubscribeFromTopic(topic);
      print('Unsubscribed from topic: $topic');
    } catch (e) {
      print('Error unsubscribing from topic $topic: $e');
    }
  }

  Future<void> subscribeToTopic(String topic) async {
    if (_messaging == null) return;
    
    try {
      await _messaging!.subscribeToTopic(topic);
      print('Subscribed to topic: $topic');
    } catch (e) {
      print('Error subscribing to topic $topic: $e');
    }
  }

  Future<String?> getToken() async {
    if (_messaging == null) return null;
    return await _messaging!.getToken(vapidKey: vapidKey);
  }

  Future<NotificationStatus> getNotificationStatus() async {
    if (!kIsWeb) {
      return NotificationStatus.notSupported;
    }

    if (!_isNotificationSupported()) {
      return NotificationStatus.notSupported;
    }

    if (_messaging == null) {
      return NotificationStatus.notInitialized;
    }

    try {
      NotificationSettings settings = await _messaging!.getNotificationSettings();
      
      switch (settings.authorizationStatus) {
        case AuthorizationStatus.authorized:
          return NotificationStatus.enabled;
        case AuthorizationStatus.provisional:
          return NotificationStatus.provisional;
        case AuthorizationStatus.denied:
          return NotificationStatus.denied;
        case AuthorizationStatus.notDetermined:
          return NotificationStatus.notDetermined;
        default:
          return NotificationStatus.denied;
      }
    } catch (e) {
      print('Error getting notification status: $e');
      return NotificationStatus.error;
    }
  }
}

enum NotificationStatus {
  enabled,
  provisional,
  denied,
  notDetermined,
  notSupported,
  notInitialized,
  error
}

// Background message handler must be a top-level function
Future<void> _firebaseMessagingBackgroundHandler(RemoteMessage message) async {
  print('Handling a background message: ${message.messageId}');
  print('Message data: ${message.data}');
  
  if (message.notification != null) {
    print('Background message contained a notification: ${message.notification}');
  }
}