import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:go_router/go_router.dart';

import 'core/auth/auth_notifier.dart';
import 'core/auth/auth_state.dart';
import 'core/theme/app_theme.dart';
import 'core/widgets/error_view.dart';
import 'shared/providers/permissions_provider.dart';

import 'features/auth/splash_screen.dart';
import 'features/auth/login_screen.dart';
import 'features/dashboard/dashboard_screen.dart';
import 'features/tasks/task_list_screen.dart';
import 'features/tasks/task_detail_screen.dart';
import 'features/tasks/task_form_screen.dart';
import 'features/tasks/subtask_detail_screen.dart';
import 'features/surat/surat_list_screen.dart';
import 'features/surat/surat_detail_screen.dart';
import 'features/surat/surat_form_screen.dart';
import 'features/contracts/contract_list_screen.dart';
import 'features/contracts/contract_detail_screen.dart';
import 'features/contracts/contract_upload_screen.dart';
import 'features/contracts/contract_form_screen.dart';
import 'features/notifications/notification_screen.dart';
import 'features/profile/profile_screen.dart';
import 'features/profile/change_password_screen.dart';
import 'features/leave/leave_list_screen.dart';

final _rootNavKey = GlobalKey<NavigatorState>(debugLabel: 'root');
final _shellNavKey = GlobalKey<NavigatorState>(debugLabel: 'shell');

// Saves the deep link URL that arrived before the user was logged in
final _pendingDeepLinkProvider = StateProvider<String?>((ref) => null);

// ChangeNotifier that triggers GoRouter refresh when auth/permissions change
class _RouterNotifier extends ChangeNotifier {
  _RouterNotifier(Ref ref) {
    ref.listen(authProvider,        (_, __) => notifyListeners());
    ref.listen(permissionsProvider, (_, __) => notifyListeners());
  }
}

final routerProvider = Provider<GoRouter>((ref) {
  final notifier = _RouterNotifier(ref);
  ref.onDispose(notifier.dispose);

  return GoRouter(
    navigatorKey: _rootNavKey,
    initialLocation: '/splash',
    refreshListenable: notifier,
    redirect: (context, state) {
      final authState  = ref.read(authProvider);
      final permissions = ref.read(permissionsProvider).valueOrNull;
      final loc = state.matchedLocation;

      if (authState is AuthLoading) return '/splash';

      if (authState is AuthUnauthenticated && loc != '/login') {
        // Save the intended destination so we can redirect after login
        final fullPath = state.uri.toString();
        if (fullPath != '/splash' && fullPath != '/login') {
          ref.read(_pendingDeepLinkProvider.notifier).state = fullPath;
        }
        return '/login';
      }

      if (authState is AuthAuthenticated && (loc == '/login' || loc == '/splash')) {
        // If a deep link was pending, navigate there instead of /home
        final pending = ref.read(_pendingDeepLinkProvider);
        if (pending != null && pending != '/login' && pending != '/splash') {
          ref.read(_pendingDeepLinkProvider.notifier).state = null;
          return pending;
        }
        return '/home';
      }

      if (permissions != null && authState is AuthAuthenticated) {
        if (loc.startsWith('/surat')     && !permissions.contains('letters'))   return '/home';
        if (loc.startsWith('/contracts') && !permissions.contains('contracts')) return '/home';
      }
      return null;
    },
    routes: [
      GoRoute(path: '/splash', builder: (_, __) => const SplashScreen()),
      GoRoute(path: '/login',  builder: (_, __) => const LoginScreen()),

      ShellRoute(
        navigatorKey: _shellNavKey,
        builder: (context, state, child) => MainShell(child: child, location: state.matchedLocation),
        routes: [
          GoRoute(path: '/home', builder: (_, __) => const DashboardScreen()),

          // Tasks
          GoRoute(path: '/tasks', builder: (_, __) => const TaskListScreen()),
          GoRoute(path: '/tasks/create', builder: (_, __) => const TaskFormScreen()),
          GoRoute(path: '/tasks/:id', builder: (_, s) => TaskDetailScreen(id: int.parse(s.pathParameters['id']!))),
          GoRoute(path: '/tasks/:id/edit', builder: (_, s) => TaskFormScreen(editId: int.parse(s.pathParameters['id']!))),
          GoRoute(path: '/tasks/:id/subtasks/:sid', builder: (_, s) => SubtaskDetailScreen(
            taskId: int.parse(s.pathParameters['id']!),
            subtaskId: int.parse(s.pathParameters['sid']!),
          )),

          // Letters (web uses /letters, mobile uses /surat — both supported)
          GoRoute(path: '/surat', builder: (_, __) => const SuratListScreen()),
          GoRoute(path: '/surat/create', builder: (_, s) => SuratFormScreen(prefillTaskId: int.tryParse(s.uri.queryParameters['task_id'] ?? ''))),
          GoRoute(path: '/surat/:id', builder: (_, s) => SuratDetailScreen(id: int.parse(s.pathParameters['id']!))),
          GoRoute(path: '/surat/:id/edit', builder: (_, s) => SuratFormScreen(editId: int.parse(s.pathParameters['id']!))),
          // Web URL aliases
          GoRoute(path: '/letters', builder: (_, __) => const SuratListScreen()),
          GoRoute(path: '/letters/:id', builder: (_, s) => SuratDetailScreen(id: int.parse(s.pathParameters['id']!))),

          // Contracts
          GoRoute(path: '/contracts', builder: (_, __) => const ContractListScreen()),
          GoRoute(path: '/contracts/upload', builder: (_, __) => const ContractUploadScreen()),
          GoRoute(path: '/contracts/:id', builder: (_, s) => ContractDetailScreen(id: int.parse(s.pathParameters['id']!))),
          GoRoute(path: '/contracts/:id/edit', builder: (_, s) => ContractFormScreen(editId: int.parse(s.pathParameters['id']!))),

          // Leave Requests
          GoRoute(path: '/leave', builder: (_, __) => const LeaveListScreen()),

          // Utils
          GoRoute(path: '/notifications', builder: (_, __) => const NotificationScreen()),
          GoRoute(path: '/profile', builder: (_, __) => const ProfileScreen()),
          GoRoute(path: '/profile/password', builder: (_, __) => const ChangePasswordScreen()),
        ],
      ),
    ],
    errorBuilder: (_, state) => Scaffold(
      body: ErrorView(message: 'Page not found: ${state.error}'),
    ),
  );
});

// ── Bottom nav shell ─────────────────────────────────────────────────────────

class MainShell extends ConsumerWidget {
  final Widget child;
  final String location;

  const MainShell({super.key, required this.child, required this.location});

  @override
  Widget build(BuildContext context, WidgetRef ref) {
    final permissionsAsync = ref.watch(permissionsProvider);
    final permissions = permissionsAsync.valueOrNull;

    final canLetters   = permissions?.contains('letters')   ?? true;
    final canContracts = permissions?.contains('contracts') ?? true;

    // Build dynamic tab list
    final tabs = <_NavTab>[
      const _NavTab(path: '/home',      label: 'Home',      icon: Icons.dashboard_outlined,    activeIcon: Icons.dashboard),
      const _NavTab(path: '/tasks',     label: 'Tasks',     icon: Icons.check_box_outlined,    activeIcon: Icons.check_box),
      if (canLetters)
        const _NavTab(path: '/surat',     label: 'Letters',   icon: Icons.mail_outline,          activeIcon: Icons.mail),
      if (canContracts)
        const _NavTab(path: '/contracts', label: 'Contracts', icon: Icons.description_outlined,  activeIcon: Icons.description),
      const _NavTab(path: '/leave', label: 'Leave Request', icon: Icons.event_busy_outlined, activeIcon: Icons.event_busy),
    ];

    final currentIndex = tabs.indexWhere((t) => location.startsWith(t.path));
    final tabIndex = currentIndex < 0 ? 0 : currentIndex;

    // Hide bottom nav on form/detail screens
    final hideNav = location.contains('/create') ||
        location.contains('/edit') ||
        location.contains('/upload') ||
        (location.startsWith('/tasks/') && !location.endsWith('/tasks/')) ||
        (location.startsWith('/surat/') && !location.endsWith('/surat/')) ||
        (location.startsWith('/contracts/') && !location.endsWith('/contracts/')) ||
        (location.startsWith('/leave/') && !location.endsWith('/leave/')) ||
        location == '/notifications' ||
        location == '/profile' ||
        location == '/profile/password';

    return Scaffold(
      body: child,
      bottomNavigationBar: hideNav ? null : BottomNavigationBar(
        currentIndex: tabIndex,
        onTap: (i) => context.go(tabs[i].path),
        type: BottomNavigationBarType.fixed,
        selectedItemColor: AppColors.primary,
        unselectedItemColor: AppColors.textSub,
        backgroundColor: AppColors.surface,
        elevation: 8,
        selectedFontSize: 11,
        unselectedFontSize: 11,
        items: tabs.map((t) => BottomNavigationBarItem(
          icon: Icon(t.icon),
          activeIcon: Icon(t.activeIcon),
          label: t.label,
        )).toList(),
      ),
    );
  }
}

class _NavTab {
  final String path;
  final String label;
  final IconData icon;
  final IconData activeIcon;
  const _NavTab({required this.path, required this.label, required this.icon, required this.activeIcon});
}