import 'dart:async';

import 'package:flutter/material.dart';
import 'package:firebase_database/firebase_database.dart';

import '../models/notification_model.dart';
import '../services/firebase_service.dart';
import '../services/notification_service.dart';

class NotificationProvider extends ChangeNotifier {
  List<NotificationModel> _notifications = [];
  List<NotificationModel> get notifications => _notifications;

  /// Track how many notifications existed on the previous update so we can
  /// detect newly added entries and fire an OS push for them.
  int _previousCount = 0;

  StreamSubscription<DatabaseEvent>? subscription;

  void startListening() {
    subscription?.cancel();

    subscription = FirebaseService.notificationRef.onValue.listen((event) {
      final prev = _previousCount;

      _notifications = [];

      if (event.snapshot.value == null) {
        _previousCount = 0;
        notifyListeners();
        return;
      }

      final data = Map<dynamic, dynamic>.from(event.snapshot.value as Map);

      data.forEach((key, value) {
        _notifications.add(
          NotificationModel.fromMap(Map<dynamic, dynamic>.from(value)),
        );
      });

      _notifications = _notifications.reversed.toList();
      _previousCount = _notifications.length;

      // If new entries appeared, fire an OS notification for the latest one
      if (_notifications.isNotEmpty && _notifications.length > prev) {
        final latest = _notifications.first;
        NotificationService.showNotification(
          title: latest.title,
          body: latest.message,
          id: DateTime.now().millisecondsSinceEpoch ~/ 1000,
        );
      }

      notifyListeners();
    });
  }

  @override
  void dispose() {
    subscription?.cancel();
    super.dispose();
  }
}