import 'dart:async';
import 'dart:io';
import 'dart:ui';

import 'package:flutter/foundation.dart';
import 'package:flutter_background_service/flutter_background_service.dart';
import 'package:flutter_local_notifications/flutter_local_notifications.dart';

const _notificationChannelId = 'worldhopper_downloads';
const _notificationId = 888;
const _completeNotificationId = 889;

/// Plugin instance for showing rich notifications from the main isolate.
FlutterLocalNotificationsPlugin? _flnPlugin;

/// Timestamp of the last progress notification update (for throttling).
DateTime _lastProgressUpdate = DateTime(0);

/// Initializes the background service configuration.
/// Must be called once at app startup.
Future<void> initializeBackgroundService() async {
  final service = FlutterBackgroundService();

  if (Platform.isAndroid) {
    final plugin = FlutterLocalNotificationsPlugin();

    const channel = AndroidNotificationChannel(
      _notificationChannelId,
      'Downloads',
      description: 'Worldhopper download progress',
      importance: Importance.low,
    );

    await plugin
        .resolvePlatformSpecificImplementation<
            AndroidFlutterLocalNotificationsPlugin>()
        ?.createNotificationChannel(channel);

    const initSettings = AndroidInitializationSettings('@mipmap/ic_launcher');
    await plugin.initialize(
      const InitializationSettings(android: initSettings),
    );

    _flnPlugin = plugin;
  }

  await service.configure(
    androidConfiguration: AndroidConfiguration(
      onStart: _onStart,
      autoStart: false,
      isForegroundMode: true,
      notificationChannelId: _notificationChannelId,
      initialNotificationTitle: 'Worldhopper',
      initialNotificationContent: 'Downloading...',
      foregroundServiceNotificationId: _notificationId,
      foregroundServiceTypes: [AndroidForegroundType.dataSync],
    ),
    iosConfiguration: IosConfiguration(
      autoStart: false,
      onForeground: _onStart,
      onBackground: _onIosBackground,
    ),
  );
}

@pragma('vm:entry-point')
Future<bool> _onIosBackground(ServiceInstance service) async {
  DartPluginRegistrant.ensureInitialized();
  return true;
}

/// Background isolate entry point.
/// This isolate does NO work itself — it only keeps the Android foreground
/// service (and its notification) alive.  The main isolate sends
/// `stopService` events.  Notification updates are handled directly
/// via flutter_local_notifications from the main isolate.
@pragma('vm:entry-point')
void _onStart(ServiceInstance service) async {
  DartPluginRegistrant.ensureInitialized();

  // Main isolate tells us to stop when all downloads finish
  service.on('stopService').listen((_) {
    service.stopSelf();
  });
}

// ---------------------------------------------------------------------------
// Public helpers called from the main isolate
// ---------------------------------------------------------------------------

/// Start the foreground service so Android keeps the process alive.
Future<void> startForegroundService() async {
  if (!Platform.isAndroid) return;
  try {
    final service = FlutterBackgroundService();
    final running = await service.isRunning();
    if (!running) {
      await service.startService();
    }
  } catch (e) {
    debugPrint('Could not start foreground service: $e');
  }
}

/// Update the foreground notification from the main isolate.
///
/// When [progress] and [maxProgress] are provided, shows a native progress
/// bar. Updates are throttled to at most once per 500ms unless [force] is true.
void updateDownloadNotification({
  required String title,
  required String content,
  int? progress,
  int? maxProgress,
  bool force = false,
}) {
  if (!Platform.isAndroid) return;

  // Throttle: skip if <500ms since last update (unless forced)
  final now = DateTime.now();
  if (!force && now.difference(_lastProgressUpdate).inMilliseconds < 500) {
    return;
  }
  _lastProgressUpdate = now;

  // Try rich notification via flutter_local_notifications
  if (_flnPlugin != null && progress != null && maxProgress != null) {
    final details = AndroidNotificationDetails(
      _notificationChannelId,
      'Downloads',
      channelDescription: 'Worldhopper download progress',
      importance: Importance.low,
      priority: Priority.low,
      showProgress: true,
      maxProgress: maxProgress,
      progress: progress,
      ongoing: true,
      onlyAlertOnce: true,
      icon: '@mipmap/ic_launcher',
    );
    _flnPlugin!
        .show(
          _notificationId,
          title,
          content,
          NotificationDetails(android: details),
        )
        .catchError(
          (e) => debugPrint('Failed to show notification: $e'),
        );
    return;
  }

  // Fallback: text-only via background service
  try {
    final service = FlutterBackgroundService();
    service.invoke('updateNotification', {
      'title': title,
      'content': content,
    });
  } catch (e) {
    debugPrint('Notification fallback failed: $e');
  }
}

/// Dismiss the progress notification (e.g. when download finishes).
void dismissDownloadNotification() {
  if (!Platform.isAndroid) return;
  _flnPlugin?.cancel(_notificationId);
}

/// Show a brief "download complete" notification that auto-dismisses on tap.
void showDownloadCompleteNotification({
  required String title,
  required String body,
}) {
  if (!Platform.isAndroid || _flnPlugin == null) return;

  const details = AndroidNotificationDetails(
    _notificationChannelId,
    'Downloads',
    channelDescription: 'Worldhopper download progress',
    importance: Importance.defaultImportance,
    priority: Priority.defaultPriority,
    autoCancel: true,
    icon: '@mipmap/ic_launcher',
  );
  _flnPlugin!
      .show(
        _completeNotificationId,
        title,
        body,
        const NotificationDetails(android: details),
      )
      .catchError(
        (e) => debugPrint('Failed to show completion notification: $e'),
      );
}

/// Stop the foreground service (e.g. when all downloads finish).
Future<void> stopForegroundService() async {
  if (!Platform.isAndroid) return;
  try {
    final service = FlutterBackgroundService();
    final running = await service.isRunning();
    if (running) {
      service.invoke('stopService');
    }
  } catch (e) {
    debugPrint('Could not stop foreground service: $e');
  }
}