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

import 'package:firebase_core/firebase_core.dart';
import 'package:firebase_messaging/firebase_messaging.dart';
import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';
import 'package:flutter/scheduler.dart' show timeDilation;
import 'package:flutter/services.dart';
import 'package:flutter_bloc/flutter_bloc.dart';
import 'package:flutter_localizations/flutter_localizations.dart';
import 'package:jiffy/jiffy.dart';
import 'package:loader_overlay/loader_overlay.dart';
import 'package:path_provider/path_provider.dart';
import 'package:persistent_bottom_nav_bar_v2/persistent_bottom_nav_bar_v2.dart';

import 'api/marianumcloud/webdav/queries/list_files/list_files_cache.dart';
import 'api/marianumconnect/auth/session_validator.dart';
import 'api/marianumconnect/marianumconnect_endpoint.dart';
import 'api/marianumconnect/queries/get_breakers/get_breakers_response.dart';
import 'api/marianumconnect/queries/report_client_error/client_error_reporter.dart';
import 'api/marianumconnect/queries/telemetry_heartbeat/telemetry_heartbeat.dart';
import 'app.dart';
import 'background/widget_background_task.dart';
import 'firebase_options.dart';
import 'model/session_wipe.dart';
import 'notification/notification_service.dart';
import 'push/push_message_handler.dart';
import 'push/push_registration.dart';
import 'push/push_registration_store.dart';
import 'push/push_renderer.dart';
import 'routing/app_routes.dart';
import 'session/account_codec.dart';
import 'session/session_lifecycle.dart';
import 'session/session_manager.dart';
import 'share_intent/share_intent_listener.dart';
import 'state/app/modules/account/account_scope.dart';
import 'state/app/modules/account/bloc/account_bloc.dart';
import 'state/app/modules/account/bloc/account_state.dart';
import 'state/app/modules/app_modules.dart';
import 'state/app/modules/capabilities/bloc/capabilities_cubit.dart';
import 'state/app/modules/chat_list/bloc/chat_list_bloc.dart';
import 'state/app/modules/nextcloud_capabilities/bloc/nextcloud_capabilities_cubit.dart';
import 'state/app/modules/settings/bloc/settings_cubit.dart';
import 'state/app/modules/timetable/bloc/timetable_bloc.dart';
import 'storage/account_storage.dart';
import 'storage/settings.dart';
import 'theming/dark_app_theme.dart';
import 'theming/light_app_theme.dart';
import 'utils/app_paths.dart';
import 'utils/downloads/download_manager.dart';
import 'view/login/account_loading_screen.dart';
import 'view/login/login.dart';
import 'view/login/post_login_splash.dart';
import 'widget/avatar_disk_cache.dart';
import 'widget/breaker/breaker.dart';
import 'widget/debug/debug_stats_overlay.dart';
import 'widget/downloads/download_tray.dart';
import 'widget/emergency/emergency_notice_gate.dart';
import 'widget/info_dialog.dart';
import 'widget_data/widget_sync.dart';

/// Runs one startup step with a time limit. Anything that throws or hangs
/// before `runApp` would otherwise leave the native launch screen up for
/// good, so failures are logged and reported and the app starts degraded.
Future<void> _startupStep(
  String name,
  Future<void> Function() step, {
  Duration? timeout = const Duration(seconds: 10),
  bool report = true,
}) async {
  try {
    final future = step();
    await (timeout == null ? future : future.timeout(timeout));
  } catch (e, s) {
    log('Startup step "$name" failed: $e', stackTrace: s);
    if (report) {
      ClientErrorReporter.reportPlatformError('Startup step "$name": $e', s);
    }
  }
}

void _installErrorHandlers() {
  if (kReleaseMode) {
    ErrorWidget.builder = (error) => Material(
      color: Colors.white,
      child: Center(
        child: Padding(
          padding: const EdgeInsets.all(24),
          child: Column(
            mainAxisSize: MainAxisSize.min,
            children: [
              const Icon(Icons.phonelink_erase_rounded, size: 40),
              const SizedBox(height: 12),
              Text(error.toStringShort(), textAlign: TextAlign.center),
            ],
          ),
        ),
      ),
    );
  }

  FlutterError.onError = (details) {
    log(
      'Uncaught Flutter error: ${details.exception}',
      stackTrace: details.stack,
    );
    ClientErrorReporter.reportFlutterError(details);
    FlutterError.presentError(details);
  };
  PlatformDispatcher.instance.onError = (error, stack) {
    log('Uncaught platform error: $error', stackTrace: stack);
    ClientErrorReporter.reportPlatformError(error, stack);
    return true;
  };
}

Future<void> main() async {
  log('MarianumMobile started');
  WidgetsFlutterBinding.ensureInitialized();
  SessionManager().markUiEngine();
  // Before any initialisation so startup failures reach the backend too.
  _installErrorHandlers();

  Future<void> trustCertificate(String asset) => PlatformAssetBundle()
      .load(asset)
      .then(
        (certificate) => SecurityContext.defaultContext
            .setTrustedCertificatesBytes(certificate.buffer.asUint8List()),
      );

  final initialisationTasks = [
    _startupStep(
      'firebase',
      () => Firebase.initializeApp(
        options: DefaultFirebaseOptions.currentPlatform,
      ),
    ),
    _startupStep(
      'ca certificates',
      () => Future.wait([
        trustCertificate('assets/ca/lets-encrypt-r3.pem'),
        trustCertificate('assets/ca/lets-encrypt-r10.pem'),
        trustCertificate('assets/ca/lets-encrypt-r13.pem'),
      ]),
    ),
    _startupStep('hydrated storage', () async {
      await AccountStorage.init((await getTemporaryDirectory()).path);
    }, timeout: null),
    _startupStep('documents dir', () async {
      AppPaths.documentsDir = (await getApplicationDocumentsDirectory()).path;
    }),
    // The keychain may still be locked right after device unlock; the session
    // keeps retrying, so on timeout the app starts on the loading screen and
    // flips to the real state once the session is readable (see _MainState).
    _startupStep(
      'account data',
      SessionManager().waitForLoad,
      timeout: const Duration(seconds: 5),
      // Expected on every background wake of a locked device; not an error.
      report: false,
    ),
    _startupStep('share intent', ShareIntentListener.instance.initialize),
  ];

  log('starting app initialisation...');
  await Future.wait(initialisationTasks);
  // Snapshot: the session may still finish loading later (see _MainState),
  // the bloc and the storage must agree on the account they start with.
  final initialAccount = SessionManager().isLoaded
      ? SessionManager().activeAccount
      : null;
  await _startupStep(
    'account storage',
    () => AccountStorage.activate(initialAccount),
    timeout: null,
  );
  log('app initialisation done!');

  // Independent of the notification setup below, so it runs alongside it.
  final widgetSyncInit = _startupStep(
    'widget sync',
    WidgetSync.ensureInitialized,
  );

  // Local notifications: init the plugin (with tap/action callbacks) and the
  // Android channels, then register the FCM background isolate handler that
  // decrypts and renders Nextcloud pushes while the app is not in foreground.
  await _startupStep(
    'notifications',
    NotificationService().initializeNotifications,
  );
  await _startupStep('notification channels', PushRenderer.ensureChannels);
  FirebaseMessaging.onBackgroundMessage(pushOnBackgroundMessage);

  // Wire up the native background downloader (progress notifications + tap
  // handling) before the UI so a completion notification tapped during cold
  // start is captured and opened once the downloads tray mounts.
  unawaited(
    DownloadManager.instance.initialize().onError(
      (e, _) => log('DownloadManager init failed: $e'),
    ),
  );

  // The home-screen widget bridge must be ready before runApp so any widget
  // render triggered during startup hits initialised native storage.
  await widgetSyncInit;
  unawaited(
    WidgetBackgroundTask.initialize().onError(
      (e, _) => log('Workmanager init failed: $e'),
    ),
  );

  // Diagnostic log only. getToken() can fail transiently during cold start
  // (Android: "IOException: FCM Registration failed!" from Play Services,
  // iOS: apns-token-not-set until APNS registration completes), so tolerate
  // the failure instead of letting it surface as an uncaught async error that
  // gets reported to the telemetry backend as noise.
  unawaited(
    FirebaseMessaging.instance
        .getToken()
        .then(
          (token) =>
              log('Firebase token: ${token ?? "Error: no Firebase token!"}'),
        )
        .onError((e, _) => log('Firebase token unavailable: $e')),
  );

  // Warm up the Nextcloud root listing in the background while the user is
  // still on the launch screen / other modules — the root endpoint is slow
  // on our instance, so kicking it off early means the Files page already
  // has data ready by the time the user navigates to it. No-op when a
  // cached payload is already present, so this does not undo the day-long
  // root cache TTL.
  if (SessionManager().hasNextcloud) {
    unawaited(
      ListFilesCache.prefetchRootListing().onError(
        (e, _) => log('Files root prefetch failed: $e'),
      ),
    );
  }

  // Resolve the avatar cache directory ahead of the first avatar render so the
  // synchronous disk read hits and cold-start avatars appear without a blank
  // placeholder flash.
  AvatarDiskCache.instance.warmUp();

  // Created eagerly so the endpoint is configured before anything below can
  // issue a request (the timetable bloc loads on creation).
  final settingsCubit = SettingsCubit(storage: AccountStorage.global);
  _syncMarianumConnectEndpoint(settingsCubit.state);
  settingsCubit.stream.listen(_syncMarianumConnectEndpoint);

  log('running app...');
  runApp(
    MultiBlocProvider(
      providers: [
        BlocProvider<SettingsCubit>.value(value: settingsCubit),
        BlocProvider<AccountBloc>(
          create: (_) => AccountBloc(
            initialStatus: _initialAccountStatus(initialAccount),
            accountId: initialAccount?.id,
          ),
        ),
      ],
      child: const Main(),
    ),
  );
}

String? _syncedMcBaseUrl;

/// Keeps the MC dio singleton aligned with the selected endpoint (live /
/// beta / custom), mirrored into WidgetSync so the background isolate
/// refreshes against the same endpoint. Settings emit on every toggle; only
/// an actual URL change is applied.
void _syncMarianumConnectEndpoint(Settings settings) {
  final url = settings.devToolsSettings.resolveMarianumConnectBaseUrl();
  if (url == _syncedMcBaseUrl) return;
  _syncedMcBaseUrl = url;
  MarianumConnectEndpoint.update(url);
  unawaited(WidgetSync.setMarianumConnectBaseUrl(url));
}

AccountStatus _initialAccountStatus(AccountEntry? account) {
  if (account != null) return AccountStatus.loggedIn;
  return SessionManager().isLoaded
      ? AccountStatus.loggedOut
      : AccountStatus.undefined;
}

class Main extends StatefulWidget {
  const Main({super.key});

  static PersistentTabController bottomNavigator = PersistentTabController(
    initialIndex: 0,
  );

  @override
  State<Main> createState() => _MainState();
}

class _MainState extends State<Main> {
  final List<NavigatorObserver> _navigatorObservers = [
    AppRoutes.chatRouteObserver,
    DownloadRouteObserver(),
  ];
  bool _showPostLoginSplash = false;
  bool _appMounted = true;
  late AccountStatus _lastStatus;

  @override
  void initState() {
    super.initState();
    Jiffy.setLocale('de');
    _lastStatus = context.read<AccountBloc>().state.status;

    SessionManager().waitForLoad().then((session) async {
      if (!mounted) return;
      final accountBloc = context.read<AccountBloc>();
      if (session == null) {
        accountBloc.setStatus(AccountStatus.loggedOut);
        return;
      }
      // Covers a session that finished loading after the startup snapshot;
      // otherwise the id is unchanged and nothing remounts.
      final account = SessionManager().activeAccount;
      await AccountStorage.activate(account);
      if (!mounted) return;
      accountBloc.activated(account?.id);
      _scheduleSessionValidation(accountBloc);
    });
  }

  /// Runs whenever the account-scoped tree mounts for a signed-in account:
  /// pulls the capability flags, then registers push for this account.
  void _onSessionActive(BuildContext scopeContext) {
    final settingsCubit = scopeContext.read<SettingsCubit>();
    final capabilitiesCubit = scopeContext.read<CapabilitiesCubit>();
    unawaited(
      capabilitiesCubit.load().then((_) {
        // Closed: the account was switched away from while loading.
        if (!mounted || capabilitiesCubit.isClosed) return;
        _syncPush(settingsCubit, capabilitiesCubit);
        _applyRoleDefaults(settingsCubit, capabilitiesCubit);
      }),
    );
    unawaited(scopeContext.read<NextcloudCapabilitiesCubit>().load());
    unawaited(SessionLifecycle.refreshDisplayName());
    _prefetchBaseData(scopeContext);
    WidgetsBinding.instance.addPostFrameCallback((_) => _showTakeoverNotice());
  }

  /// A forced sign-out that handed over to another account never reaches the
  /// login screen, which normally explains it.
  void _showTakeoverNotice() {
    final notice = SessionLifecycle.signOutNotice.value;
    final overlayContext = AppRoutes.overlayContext;
    if (notice == null || overlayContext == null) return;
    SessionLifecycle.signOutNotice.value = null;
    InfoDialog.show(overlayContext, notice, title: 'Abgemeldet');
  }

  /// Warms the core caches (timetable, chat list, files root) in the
  /// background so the first screen render hits populated data.
  void _prefetchBaseData(BuildContext context) {
    context.read<TimetableBloc>().refresh();
    unawaited(context.read<ChatListBloc>().refresh(silent: true));
    if (SessionManager().hasNextcloud) {
      unawaited(ListFilesCache.prefetchRootListing());
    }
  }

  /// Registers/self-heals the push subscription whenever the backend advertises
  /// the capability — independent of the notification toggle, so a user with
  /// notifications off stays registered for silent sync pushes. Fire-and-forget.
  void _syncPush(SettingsCubit settings, CapabilitiesCubit capabilities) {
    final enabled = settings.val().notificationSettings.enabled;
    unawaited(
      PushRegistration.syncSubscription(
        capable: capabilities.canReceivePushNotifications,
      ).then((registered) {
        // The app-start heartbeat runs before this async registration
        // finishes, so it reports the pre-registration state. Re-emit once
        // the identifier is persisted so the new push status shows up this
        // session instead of only after the next launch.
        if (registered) {
          TelemetryHeartbeat.report(notificationsEnabled: enabled);
        }
      }),
    );
  }

  /// userType is only known once capabilities are loaded.
  void _applyRoleDefaults(
    SettingsCubit settings,
    CapabilitiesCubit capabilities,
  ) {
    if (AppModule.applyTeacherDefaults(
      settings.val().modulesSettings,
      isTeacher: capabilities.isTeacher,
    )) {
      settings.val(write: true);
    }
  }

  /// Background credential check: a 401 means the password was rotated
  /// server-side, so the validator signs the account out and the app moves
  /// on to another stored account or the login screen.
  void _scheduleSessionValidation(AccountBloc accountBloc) {
    unawaited(
      SessionValidator.probeStored(
        onInvalidated: (nextAccountId) async {
          if (!mounted) return;
          accountBloc.activated(nextAccountId);
        },
      ),
    );
  }

  void _onAccountChanged(BuildContext context, AccountState accountState) {
    if (accountState.status == AccountStatus.loggedIn &&
        accountState.freshLogin) {
      _showPostLoginSplash = true;
      _appMounted = false;
      WidgetsBinding.instance.addPostFrameCallback((_) {
        if (mounted) setState(() => _appMounted = true);
      });
    }
    final wasLoggedIn = _lastStatus == AccountStatus.loggedIn;
    _lastStatus = accountState.status;
    // A cold start that merely resolves as signed out has nothing to wipe,
    // and a share waiting for the login must survive it.
    if (accountState.status != AccountStatus.loggedOut || !wasLoggedIn) return;
    // Deferred until the account-scoped tree is torn down.
    WidgetsBinding.instance.addPostFrameCallback(
      (_) => unawaited(SessionWipe.deviceLeft()),
    );
  }

  /// The account-scoped tree only lives while its account is the one in use:
  /// adding another account parks it, so its blocs go as well.
  static Object _scopeOf(AccountState state) => (
    state.accountId,
    state.status == AccountStatus.addingAccount,
  );

  Object? _scope;

  @override
  Widget build(BuildContext context) => Directionality(
    textDirection: TextDirection.ltr,
    // Selects only what the root uses: Settings is mutated in place and
    // re-emitted as a fresh instance on every write, so a plain BlocBuilder
    // would rebuild MaterialApp (and every route) for unrelated settings.
    child: BlocSelector<SettingsCubit, Settings, _RootSettings>(
      selector: (settings) => (
        appTheme: settings.appTheme,
        notificationsEnabled: settings.notificationSettings.enabled,
        showPerformanceOverlay:
            settings.devToolsSettings.showPerformanceOverlay,
        showSemanticsDebugger: settings.devToolsSettings.showSemanticsDebugger,
        showFrameStats: settings.devToolsSettings.showFrameStats,
        showMemoryStats: settings.devToolsSettings.showMemoryStats,
        slowAnimations: settings.devToolsSettings.slowAnimations,
        textScaleOverride: settings.devToolsSettings.textScaleOverride,
      ),
      builder: (context, root) {
        // Mirror the notification toggle into group-scoped storage so the FCM
        // background isolate and the iOS NSE can suppress rendering when off.
        unawaited(
          const PushRegistrationStore().setNotificationsEnabled(
            root.notificationsEnabled,
          ),
        );
        timeDilation = root.slowAnimations ? 5.0 : 1.0;
        return BlocConsumer<AccountBloc, AccountState>(
          listenWhen: (previous, current) =>
              previous.status != current.status ||
              previous.accountId != current.accountId,
          listener: _onAccountChanged,
          buildWhen: (previous, current) =>
              _scopeOf(previous) != _scopeOf(current),
          builder: (context, account) {
            final scope = _scopeOf(account);
            if (scope != _scope) {
              _scope = scope;
              // The old navigator (and every route on it) goes with the old
              // account; a shared GlobalKey would carry it over instead.
              AppRoutes.rootNavigatorKey = GlobalKey<NavigatorState>();
            }
            return AccountScope(
              key: ValueKey(scope),
              onActive: _onSessionActive,
              child: _buildApp(root),
            );
          },
        );
      },
    ),
  );

  Widget _buildApp(_RootSettings root) => MaterialApp(
    showPerformanceOverlay: root.showPerformanceOverlay,
    showSemanticsDebugger: root.showSemanticsDebugger,
    debugShowCheckedModeBanner: false,
    navigatorKey: AppRoutes.rootNavigatorKey,
    // Used by ChatView.didPopNext to reclaim the global ChatBloc.
    // DownloadRouteObserver tracks full-page navigations so the downloads
    // chip only surfaces once the user leaves the screen they started on.
    navigatorObservers: _navigatorObservers,
    localizationsDelegates: const [
      ...GlobalMaterialLocalizations.delegates,
      GlobalWidgetsLocalizations.delegate,
    ],
    supportedLocales: const [Locale('de'), Locale('en')],
    locale: const Locale('de'),
    title: 'Marianum Fulda',
    themeMode: root.appTheme,
    theme: LightAppTheme.theme,
    darkTheme: DarkAppTheme.theme,
    // Brand-colored backdrop behind every route. During the logout
    // home-swap and route pop animations the framework can briefly
    // expose the layer below the topmost Scaffold; without this
    // the dark Material default shows through and the user sees a
    // black flash.
    builder: (context, child) {
      Widget app = ColoredBox(
        color: LightAppTheme.marianumRed,
        // Downloads tray mounted ABOVE the navigator so its chip floats
        // over every route (folder views, chat, viewer are full-page
        // pushes that would otherwise cover it).
        child: DownloadTrayHost(child: child ?? const SizedBox.shrink()),
      );
      final scale = root.textScaleOverride;
      if (scale > 0) {
        app = MediaQuery.withClampedTextScaling(
          minScaleFactor: scale,
          maxScaleFactor: scale,
          child: app,
        );
      }
      return DebugStatsOverlay(
        showFrameStats: root.showFrameStats,
        showMemoryStats: root.showMemoryStats,
        child: app,
      );
    },
    home: EmergencyNoticeGate(
      child: LoaderOverlay(
        child: Breaker(
          breaker: BreakerArea.global,
          child: BlocBuilder<AccountBloc, AccountState>(
            buildWhen: (previous, current) => previous.status != current.status,
            builder: (context, accountState) {
              switch (accountState.status) {
                case AccountStatus.loggedIn:
                  return Stack(
                    fit: StackFit.expand,
                    children: [
                      if (_appMounted) const App(key: ValueKey('app-shell')),
                      if (_showPostLoginSplash)
                        PostLoginSplash(
                          key: const ValueKey('post-login-splash'),
                          onComplete: () =>
                              setState(() => _showPostLoginSplash = false),
                        ),
                    ],
                  );
                case AccountStatus.loggedOut:
                  return const Login();
                case AccountStatus.addingAccount:
                  return const Login(addingAccount: true);
                case AccountStatus.undefined:
                  return const AccountLoadingScreen();
              }
            },
          ),
        ),
      ),
    ),
  );
}

typedef _RootSettings = ({
  ThemeMode appTheme,
  bool notificationsEnabled,
  bool showPerformanceOverlay,
  bool showSemanticsDebugger,
  bool showFrameStats,
  bool showMemoryStats,
  bool slowAnimations,
  double textScaleOverride,
});