import 'dart:async';
import 'dart:io' show Directory, File, Platform;
import 'dart:isolate';
import 'dart:ui' as ui;
import 'dart:ui' show PlatformDispatcher;

import 'package:background_downloader/background_downloader.dart' hide Request;
import 'package:flutter/foundation.dart' show FlutterError, kDebugMode;
import 'package:flutter_local_notifications/flutter_local_notifications.dart';
import 'package:flutter/widgets.dart';
import 'package:permission_handler/permission_handler.dart';
import 'package:go_router/go_router.dart';
import 'package:hooks_riverpod/hooks_riverpod.dart';
import 'package:models/models.dart';
import 'package:path/path.dart' as path;
import 'package:path_provider/path_provider.dart';
import 'package:purplebase/purplebase.dart';
import 'package:workmanager/workmanager.dart';
import 'package:zapstore/router.dart';
import 'package:zapstore/services/log_service.dart';
import 'package:zapstore/services/package_manager/background_package_manager.dart';
import 'package:zapstore/services/package_manager/dummy_package_manager.dart';
import 'package:zapstore/services/package_manager/package_manager.dart';
import 'package:zapstore/services/catalog_fetcher.dart';
import 'package:zapstore/services/settings_service.dart';
import 'package:zapstore/utils/extensions.dart';

/// Unique task name for background update checking
const kBackgroundUpdateTaskName = 'dev.zapstore.backgroundUpdateCheck';

/// Unique task name for weekly cleanup
const kWeeklyCleanupTaskName = 'dev.zapstore.weeklyCleanup';

/// Unique task identifier
const kBackgroundUpdateTaskId = 'backgroundUpdateCheck';

/// Unique task identifier for weekly cleanup
const kWeeklyCleanupTaskId = 'weeklyCleanup';

/// Notification channel for update notifications
const kUpdateNotificationChannelId = 'zapstore_updates';
const kUpdateNotificationChannelName = 'App Updates';
const kUpdateNotificationChannelDescription =
    'Notifications for available app updates';

/// Stale download threshold for cleanup
const _staleDownloadThreshold = Duration(days: 7);

/// How long user must be inactive before showing background notification
const _inactivityThreshold = Duration(hours: 24);

/// Notification payload for deep linking to updates screen
const _kNotificationPayload = 'updates';

/// Input data key for AppCatalog relay URLs
const kAppCatalogRelaysKey = 'appCatalogRelays';

/// Holds the isolate error port for the workmanager background
/// isolate. Top-level so the GC cannot collect the port while the
/// task is running.
// ignore: unused_element
RawReceivePort? _workmanagerErrorPort;

/// The entry point for WorkManager background tasks.
/// This MUST be a top-level function (not a class method).
@pragma('vm:entry-point')
void callbackDispatcher() {
  WidgetsFlutterBinding.ensureInitialized();
  ui.DartPluginRegistrant.ensureInitialized();

  // Wire all four error sinks for this background isolate.
  // LogService.init is fire-and-forget — pre-init writes go to the
  // ring buffer and are flushed once disk is ready.
  unawaited(LogService.I.init(isolateName: 'workmanager'));

  FlutterError.onError = (details) {
    FlutterError.presentError(details);
    LogService.I.fatal(
      'uncaught error',
      tag: 'crash',
      fields: const {'source': 'flutter'},
      err: details.exception,
      stack: details.stack,
    );
    LogService.I.flushSync();
  };

  PlatformDispatcher.instance.onError = (error, stack) {
    LogService.I.fatal(
      'uncaught error',
      tag: 'crash',
      fields: const {'source': 'platform_dispatcher'},
      err: error,
      stack: stack,
    );
    LogService.I.flushSync();
    return true;
  };

  final port = RawReceivePort((dynamic pair) {
    if (pair is List && pair.length == 2) {
      final err = pair[0]?.toString() ?? 'unknown';
      final stack = pair[1] == null
          ? null
          : StackTrace.fromString(pair[1].toString());
      LogService.I.fatal(
        'uncaught error',
        tag: 'crash',
        fields: const {'source': 'isolate'},
        err: err,
        stack: stack,
      );
      LogService.I.flushSync();
    }
  });
  Isolate.current.addErrorListener(port.sendPort);
  _workmanagerErrorPort = port;

  runZonedGuarded(() {
    Workmanager().executeTask((task, inputData) async {
      try {
        switch (task) {
          case kBackgroundUpdateTaskName:
            final relayUrls =
                (inputData?[kAppCatalogRelaysKey] as List<dynamic>?)
                    ?.cast<String>()
                    .toSet();
            return await _checkForUpdatesInBackground(relayUrls);
          case kWeeklyCleanupTaskName:
            return await _performWeeklyCleanup();
          default:
            return false;
        }
      } catch (e, st) {
        LogService.I.error(
          'background task failed',
          tag: 'workmanager',
          fields: {'task': task},
          err: e,
          stack: st,
        );
        return false;
      } finally {
        // Ensure entries from this task hit disk before the isolate
        // tears down.
        await LogService.I.flush();
      }
    });
  }, (error, stack) {
    LogService.I.fatal(
      'uncaught error',
      tag: 'crash',
      fields: const {'source': 'zone'},
      err: error,
      stack: stack,
    );
    LogService.I.flushSync();
  });
}

/// Perform weekly cleanup of stale downloads
Future<bool> _performWeeklyCleanup() async {
  try {
    final downloader = FileDownloader();

    // Get all tracked records from background_downloader's database
    final trackedRecords = await downloader.database.allRecords(
      group: FileDownloader.defaultGroup,
    );

    for (final record in trackedRecords) {
      final task = record.task;
      if (task is! DownloadTask) continue;

      final taskAge = DateTime.now().difference(record.task.creationTime);
      if (taskAge > _staleDownloadThreshold) {
        try {
          // Cancel if active
          await downloader.cancelTaskWithId(task.taskId);
        } catch (_) {}

        try {
          // Delete the file if it exists
          final filePath = await task.filePath();
          final file = File(filePath);
          if (await file.exists()) {
            await file.delete();
          }
        } catch (_) {}

        try {
          // Remove from database
          await downloader.database.deleteRecordWithId(task.taskId);
        } catch (_) {}
      }
    }

    // Also clean up orphaned APK files in download directory
    try {
      final cacheDir = await getApplicationCacheDirectory();
      final downloadDir = Directory(
        path.join(cacheDir.path, 'flutter_background_downloader'),
      );

      if (await downloadDir.exists()) {
        final entities = downloadDir.listSync();
        final cutoff = DateTime.now().subtract(_staleDownloadThreshold);

        for (final entity in entities) {
          if (entity is File) {
            final stat = await entity.stat();
            if (stat.modified.isBefore(cutoff)) {
              await entity.delete();
            }
          }
        }
      }
    } catch (_) {
      // Ignore cleanup failures for orphaned files
    }

    return true;
  } catch (e) {
    // Cleanup failed - return false for retry
    return false;
  }
}

/// Background update check logic - runs in a separate isolate via WorkManager.
///
/// [appCatalogRelays] - Relay URLs resolved from main isolate. Falls back to
/// default relay if not provided.
Future<bool> _checkForUpdatesInBackground(Set<String>? appCatalogRelays) async {
  try {
    final relays = appCatalogRelays ?? {'wss://relay.zapstore.dev'};

    final container = ProviderContainer(
      overrides: [
        storageNotifierProvider.overrideWith(PurplebaseStorageNotifier.new),
        packageManagerProvider.overrideWith(
          (ref) => Platform.isAndroid
              ? BackgroundPackageManager(ref)
              : DummyPackageManager(ref),
        ),
      ],
    );

    try {
      final dir = await getApplicationSupportDirectory();
      final dbPath = path.join(dir.path, 'zapstore.db');

      await container.read(
        initializationProvider(
          StorageConfiguration(
            databasePath: dbPath,
            defaultRelays: {'AppCatalog': relays},
          ),
        ).future,
      );

      final packageManager = container.read(packageManagerProvider.notifier);
      await packageManager.syncInstalledPackages();

      final pmState = container.read(packageManagerProvider);
      if (pmState.installed.isEmpty) {
        return true;
      }

      final storage = container.read(storageNotifierProvider.notifier);
      final catalog = await fetchCatalog(
        storage: storage,
        installedIds: pmState.installed.keys.toSet(),
        platform: packageManager.platform,
        subscriptionPrefix: 'app-bg',
      );

      final updatableInstallables = <String, Installable>{};
      for (final entry in catalog.installableByApp.entries) {
        if (packageManager.hasUpdate(entry.key, entry.value)) {
          updatableInstallables[entry.key] = entry.value;
        }
      }

      if (updatableInstallables.isNotEmpty) {
        final updatableApps = await storage.query(
          RequestFilter<App>(
            tags: {
              '#d': updatableInstallables.keys.toSet(),
              '#f': {packageManager.platform},
            },
          ).toRequest(),
          source: const LocalSource(),
        );
        await _showUpdateNotificationIfNeeded(
          updatableApps,
          updatableInstallables,
        );
      }

      return true;
    } finally {
      container.dispose();
    }
  } catch (e) {
    return false;
  }
}

/// Show a local notification for available updates.
/// Only notifies if:
/// 1. User hasn't opened app in 24+ hours
/// 2. There are updates with installable.createdAt > seenUntil AND > lastOpened
///    (new since both last notification AND last time user saw the app)
///
/// [installables] maps app identifier → the installable (SoftwareAsset or
/// FileMetadata) that represents the available update. Its `createdAt` is used
/// for freshness checks instead of `app.latestRelease.value` which is not
/// populated in the background isolate context.
Future<void> _showUpdateNotificationIfNeeded(
  List<App> updates,
  Map<String, Installable> installables,
) async {
  final settingsService = SettingsService();
  final settings = await settingsService.load();

  // Skip if user recently opened the app
  if (settings.lastAppOpened != null &&
      DateTime.now().difference(settings.lastAppOpened!) < _inactivityThreshold) {
    return;
  }

  // Get the "seen until" timestamp - updates with createdAt > this are new
  final seenUntil = settings.seenUntil;

  // Filter to only updates that are genuinely new:
  // - installable.createdAt > seenUntil (not already notified via background)
  // - installable.createdAt > lastOpened (not already seen when user opened app)
  // This prevents nagging about updates user saw in the app but chose to ignore
  final newUpdates = updates.where((app) {
    final installable = installables[app.identifier];
    if (installable == null) return false;
    final releaseTime = installable.createdAt;

    // Must be newer than last notification (if any)
    if (seenUntil != null && !releaseTime.isAfter(seenUntil)) {
      return false;
    }

    // Must be newer than last app open (if any) - user may have seen it in UI
    if (settings.lastAppOpened != null && !releaseTime.isAfter(settings.lastAppOpened!)) {
      return false;
    }

    return true;
  }).toList();

  if (newUpdates.isEmpty) {
    return; // No new updates to notify about
  }

  // Show the notification
  final plugin = FlutterLocalNotificationsPlugin();
  const initSettings = InitializationSettings(
    android: AndroidInitializationSettings('@drawable/ic_notification'),
  );
  await plugin.initialize(initSettings);
  await _ensureUpdateNotificationChannel(plugin);

  final appNames = newUpdates.map((a) => a.name ?? a.identifier).toList();
  final title = newUpdates.length == 1
      ? '1 app update available'
      : '${newUpdates.length} app updates available';
  final body = appNames.length <= 3
      ? appNames.join(', ')
      : '${appNames.take(3).join(', ')} and ${appNames.length - 3} more';

  await plugin.show(
    0,
    title,
    body,
    const NotificationDetails(
      android: AndroidNotificationDetails(
        kUpdateNotificationChannelId,
        kUpdateNotificationChannelName,
        channelDescription: kUpdateNotificationChannelDescription,
        importance: Importance.defaultImportance,
        priority: Priority.defaultPriority,
        showWhen: true,
        autoCancel: true,
      ),
    ),
    payload: _kNotificationPayload,
  );

  // Update seenUntil to now - future checks will only notify about releases after this
  await settingsService.update((s) => s.copyWith(seenUntil: DateTime.now()));
}

/// Service for managing background update checks
class BackgroundUpdateService {
  BackgroundUpdateService(this.ref);

  final Ref ref;

  /// Initialize WorkManager and register periodic task
  Future<void> initialize() async {
    if (!Platform.isAndroid) {
      // WorkManager only works on Android/iOS, skip on other platforms
      return;
    }

    // Initialize WorkManager
    await Workmanager().initialize(callbackDispatcher);

    // Initialize local notifications
    await _initializeNotifications();

    // Resolve AppCatalog relays from main isolate to pass to background task
    final appCatalogRelays = await ref
        .read(storageNotifierProvider.notifier)
        .resolveRelays('AppCatalog');

    // Register periodic task (minimum 15 minutes on Android)
    // We use 24 hours to match the inactivity threshold for notifications.
    // More frequent checks would be wasted since we only notify users
    // who haven't opened the app in 24+ hours.
    await Workmanager().registerPeriodicTask(
      kBackgroundUpdateTaskId,
      kBackgroundUpdateTaskName,
      frequency: const Duration(hours: 24),
      constraints: Constraints(
        networkType: NetworkType.connected,
        requiresBatteryNotLow: true,
      ),
      existingWorkPolicy: ExistingPeriodicWorkPolicy.keep,
      backoffPolicy: BackoffPolicy.exponential,
      initialDelay: const Duration(hours: 1),
      inputData: {kAppCatalogRelaysKey: appCatalogRelays.toList()},
    );

    // Register weekly cleanup task
    await Workmanager().registerPeriodicTask(
      kWeeklyCleanupTaskId,
      kWeeklyCleanupTaskName,
      frequency: const Duration(days: 7),
      constraints: Constraints(
        requiresBatteryNotLow: true,
        requiresCharging: true, // Only run when charging for cleanup
      ),
      existingWorkPolicy: ExistingPeriodicWorkPolicy.keep,
      backoffPolicy: BackoffPolicy.exponential,
      initialDelay: const Duration(hours: 24), // Start first cleanup after 24h
    );
  }

  /// Initialize local notifications plugin and request permission (release/profile only).
  Future<void> _initializeNotifications() async {
    // Request notification permission on Android 13+ (API 33+); skip in debug / dev runs.
    if (Platform.isAndroid && !kDebugMode) {
      final status = await Permission.notification.status;
      if (!status.isGranted) {
        await Permission.notification.request();
      }
    }

    final flutterLocalNotificationsPlugin = FlutterLocalNotificationsPlugin();

    const initializationSettingsAndroid = AndroidInitializationSettings(
      '@drawable/ic_notification',
    );
    const initializationSettings = InitializationSettings(
      android: initializationSettingsAndroid,
    );

    await flutterLocalNotificationsPlugin.initialize(
      initializationSettings,
      onDidReceiveNotificationResponse: _handleNotificationTap,
    );

    // Check if app was launched from a notification (terminated state)
    final launchDetails = await flutterLocalNotificationsPlugin
        .getNotificationAppLaunchDetails();
    if (launchDetails?.didNotificationLaunchApp == true &&
        launchDetails?.notificationResponse?.payload == _kNotificationPayload) {
      _navigateToUpdates();
    }

    await _ensureUpdateNotificationChannel(flutterLocalNotificationsPlugin);
  }

  /// Handle notification tap - navigate to updates screen
  static void _handleNotificationTap(NotificationResponse response) {
    if (response.payload == _kNotificationPayload) {
      _navigateToUpdates();
    }
  }

  /// Navigate to the updates screen
  static void _navigateToUpdates() {
    // Use the root navigator key to navigate
    final context = rootNavigatorKey.currentContext;
    if (context != null) {
      GoRouter.of(context).go('/updates');
    }
  }

  /// Cancel background update checks
  Future<void> cancelBackgroundChecks() async {
    await Workmanager().cancelByUniqueName(kBackgroundUpdateTaskId);
  }
}

Future<void> _ensureUpdateNotificationChannel(
  FlutterLocalNotificationsPlugin plugin,
) async {
  final androidPlugin = plugin
      .resolvePlatformSpecificImplementation<
        AndroidFlutterLocalNotificationsPlugin
      >();

  if (androidPlugin != null) {
    await androidPlugin.createNotificationChannel(
      const AndroidNotificationChannel(
        kUpdateNotificationChannelId,
        kUpdateNotificationChannelName,
        description: kUpdateNotificationChannelDescription,
        importance: Importance.defaultImportance,
      ),
    );
  }
}

/// Provider for the background update service
final backgroundUpdateServiceProvider = Provider<BackgroundUpdateService>(
  BackgroundUpdateService.new,
);