import 'package:flutter/foundation.dart';
import 'package:flutter_local_notifications/flutter_local_notifications.dart';
import 'package:relationship_saver/features/local/local_models.dart';
import 'package:relationship_saver/features/reminders/scheduling/reminder_scheduler.dart';
import 'package:timezone/timezone.dart' as tz;

const String _channelId = 'relationship_saver_reminders';
const String _channelName = 'Relationship Reminders';
const String _channelDescription =
    'Reminders for relationship plans and follow-ups';

/// Schedules reminders with local notifications where platform support exists.
class LocalNotificationsReminderScheduler implements ReminderScheduler {
  LocalNotificationsReminderScheduler({
    ReminderNotificationsDriver? driver,
    DateTime Function()? now,
  }) : _driver = driver ?? FlutterReminderNotificationsDriver(),
       _now = now ?? DateTime.now;

  final ReminderNotificationsDriver _driver;
  final DateTime Function() _now;

  @override
  Future<void> clearAll() async {
    if (!_supportsSchedulingPlatform()) {
      return;
    }
    await _driver.ensureInitialized();
    await _driver.cancelAll();
  }

  @override
  Future<void> reconcile(List<ReminderRule> reminders) async {
    if (!_supportsSchedulingPlatform()) {
      return;
    }
    await _driver.ensureInitialized();
    await _driver.cancelAll();

    final DateTime now = _now();
    final List<ReminderRule> enabled = reminders
        .where((ReminderRule reminder) => reminder.enabled)
        .toList(growable: false);

    for (final ReminderRule reminder in enabled) {
      final DateTimeComponents? repeating = _repeatComponents(reminder.cadence);
      if (repeating == null && reminder.nextAt.isBefore(now)) {
        continue;
      }

      await _driver.schedule(
        id: _notificationId(reminder.id),
        title: reminder.title,
        body: _buildBody(reminder),
        scheduledAt: reminder.nextAt,
        repeatComponents: repeating,
        payload: reminder.id,
      );
    }
  }

  DateTimeComponents? _repeatComponents(ReminderCadence cadence) {
    return switch (cadence) {
      ReminderCadence.daily => DateTimeComponents.time,
      ReminderCadence.weekly => DateTimeComponents.dayOfWeekAndTime,
      ReminderCadence.monthly => DateTimeComponents.dayOfMonthAndTime,
    };
  }

  String _buildBody(ReminderRule reminder) {
    final String frequency = switch (reminder.cadence) {
      ReminderCadence.daily => 'daily',
      ReminderCadence.weekly => 'weekly',
      ReminderCadence.monthly => 'monthly',
    };
    return 'Your $frequency reminder is due now.';
  }

  bool _supportsSchedulingPlatform() {
    if (kIsWeb) {
      return false;
    }

    return defaultTargetPlatform != TargetPlatform.linux;
  }

  int _notificationId(String raw) {
    int hash = 0;
    for (final int unit in raw.codeUnits) {
      hash = ((hash * 31) + unit) & 0x7fffffff;
    }
    return hash;
  }
}

/// Driver wrapper around the notification plugin for easier testing.
abstract class ReminderNotificationsDriver {
  Future<void> ensureInitialized();

  Future<void> cancelAll();

  Future<void> schedule({
    required int id,
    required String title,
    required String body,
    required DateTime scheduledAt,
    required DateTimeComponents? repeatComponents,
    required String payload,
  });
}

class FlutterReminderNotificationsDriver
    implements ReminderNotificationsDriver {
  FlutterReminderNotificationsDriver({FlutterLocalNotificationsPlugin? plugin})
    : _plugin = plugin ?? FlutterLocalNotificationsPlugin();

  final FlutterLocalNotificationsPlugin _plugin;
  Future<void>? _initializeFuture;

  @override
  Future<void> ensureInitialized() {
    return _initializeFuture ??= _initialize();
  }

  @override
  Future<void> cancelAll() async {
    await _plugin.cancelAll();
  }

  @override
  Future<void> schedule({
    required int id,
    required String title,
    required String body,
    required DateTime scheduledAt,
    required DateTimeComponents? repeatComponents,
    required String payload,
  }) async {
    await _plugin.zonedSchedule(
      id: id,
      title: title,
      body: body,
      scheduledDate: tz.TZDateTime.from(scheduledAt.toUtc(), tz.UTC),
      notificationDetails: _notificationDetails,
      androidScheduleMode: AndroidScheduleMode.inexactAllowWhileIdle,
      matchDateTimeComponents: repeatComponents,
      payload: payload,
    );
  }

  Future<void> _initialize() async {
    await _plugin.initialize(
      settings: const InitializationSettings(
        android: AndroidInitializationSettings('@mipmap/ic_launcher'),
        iOS: DarwinInitializationSettings(),
        macOS: DarwinInitializationSettings(),
        linux: LinuxInitializationSettings(defaultActionName: 'Open reminders'),
        windows: WindowsInitializationSettings(
          appName: 'Relationship Saver',
          appUserModelId: 'com.relationshipsaver.app',
          guid: 'ee23c0af-5898-4d96-b599-cf2d7d0d37d7',
        ),
      ),
    );
  }

  NotificationDetails get _notificationDetails {
    return const NotificationDetails(
      android: AndroidNotificationDetails(
        _channelId,
        _channelName,
        channelDescription: _channelDescription,
        importance: Importance.high,
        priority: Priority.high,
      ),
      iOS: DarwinNotificationDetails(),
      macOS: DarwinNotificationDetails(),
      linux: LinuxNotificationDetails(),
      windows: WindowsNotificationDetails(),
    );
  }
}