import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart' show TimeOfDay;
import 'package:flutter_local_notifications/flutter_local_notifications.dart';
import 'package:timezone/timezone.dart' as tz;

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

  final _plugin = FlutterLocalNotificationsPlugin();

  Future<void> initialize() async {
    const android = AndroidInitializationSettings('@mipmap/ic_launcher');
    const settings = InitializationSettings(android: android);
    await _plugin.initialize(
      settings,
      onDidReceiveNotificationResponse: _onTap,
    );
  }

  Future<bool> requestPermission() async {
    final android = _plugin
        .resolvePlatformSpecificImplementation<
            AndroidFlutterLocalNotificationsPlugin>();
    return await android?.requestNotificationsPermission() ?? false;
  }

  Future<void> scheduleDailyNotification({
    required TimeOfDay time,
    required String title,
    required String body,
  }) async {
    await _plugin.cancelAll();
    final scheduledDate = _nextInstanceOf(time);
    const details = NotificationDetails(
      android: AndroidNotificationDetails(
        'daily_summary',
        'Tägliche Zusammenfassung',
        channelDescription: 'Tägliche Aufgaben-Erinnerung',
        importance: Importance.defaultImportance,
        priority: Priority.defaultPriority,
      ),
    );
    await _plugin.zonedSchedule(
      0,
      title: title,
      body: body,
      scheduledDate: scheduledDate,
      details,
      androidScheduleMode: AndroidScheduleMode.inexactAllowWhileIdle,
      matchDateTimeComponents: DateTimeComponents.time,
    );
  }

  Future<void> cancelAll() => _plugin.cancelAll();

  /// Computes the next occurrence of [time] as a [tz.TZDateTime].
  /// Returns today if [time] is still in the future, tomorrow otherwise.
  @visibleForTesting
  tz.TZDateTime nextInstanceOf(TimeOfDay time) {
    final now = tz.TZDateTime.now(tz.local);
    var scheduled = tz.TZDateTime(
      tz.local,
      now.year,
      now.month,
      now.day,
      time.hour,
      time.minute,
    );
    if (scheduled.isBefore(now)) {
      scheduled = scheduled.add(const Duration(days: 1));
    }
    return scheduled;
  }

  static void _onTap(NotificationResponse response) {
    // Navigation to Home tab — wired in Plan 02 via global navigator key
  }
}