Refactor code structure for improved readability and maintainability

Co-authored-by: Copilot <copilot@github.com>

flutter/lib/core/api/api_client.dart

@@ -24,7 +24,7 @@ class ApiClient {
         if (token != null) 'Authorization': 'Bearer $token',
       };
 
-  Future<Map<String, dynamic>> getJson(String path, {String? token}) async {
+  Future<dynamic> getJson(String path, {String? token}) async {
     final response = await _client.get(
       Uri.parse('$baseUrl$path'),
       headers: _headers(token: token),

flutter/lib/core/api/api_paths.dart

@@ -28,6 +28,15 @@ class PantryApiPaths {
   static String remove(int id) => '/pantry/$id';
 }
 
+class UserApiPaths {
+  static const me = '/users/me';
+  static const list = '/users';
+  static String setRole(int id) => '/users/$id/role';
+  static String setPremium(int id) => '/users/$id/premium';
+  static String delete(int id) => '/users/$id';
+  static String resetPassword(int id) => '/users/$id/reset-password';
+}
+
 class MealPlanApiPaths {
   static const list = '/meal-plan';
 

flutter/lib/core/auth/jwt_decoder.dart

@@ -0,0 +1,26 @@
+import 'dart:convert';
+
+/// Decodes a JWT token payload without verifying signature.
+/// Returns the decoded claims or an empty map on failure.
+Map<String, dynamic> decodeJwtPayload(String token) {
+  try {
+    final parts = token.split('.');
+    if (parts.length != 3) return {};
+    // Normalize base64url to standard base64.
+    final payload = base64Url.normalize(parts[1]);
+    final decoded = utf8.decode(base64Url.decode(payload));
+    return json.decode(decoded) as Map<String, dynamic>;
+  } catch (_) {
+    return {};
+  }
+}
+
+/// Returns the role claim from a JWT token. Defaults to 'user'.
+String jwtRole(String? token) {
+  if (token == null || token.isEmpty) return 'user';
+  final claims = decodeJwtPayload(token);
+  return claims['role'] as String? ?? 'user';
+}
+
+/// Returns true if the JWT token contains role == 'admin'.
+bool jwtIsAdmin(String? token) => jwtRole(token) == 'admin';

flutter/lib/core/router/app_router.dart

@@ -5,6 +5,7 @@ import 'package:go_router/go_router.dart';
 import '../ui/app_shell.dart';
 import '../ui/async_state_views.dart';
 import '../../features/auth/data/auth_providers.dart';
+import '../../core/auth/jwt_decoder.dart';
 import '../../features/auth/presentation/login_screen.dart';
 import '../../features/profile/presentation/profile_screen.dart';
 import '../../features/recipes/presentation/create_recipe_screen.dart';
@@ -20,6 +21,7 @@ import '../../features/inventory/presentation/consumption_history_screen.dart';
 import '../../features/meal_plan/presentation/meal_plan_screen.dart';
 import '../../features/pantry/presentation/pantry_screen.dart';
 import '../../features/import/presentation/import_screen.dart';
+import '../../features/admin/presentation/admin_screen.dart';
 
 final appRouterProvider = Provider<GoRouter>((ref) {
   final authState = ref.watch(authStateProvider);
@@ -28,7 +30,7 @@ final appRouterProvider = Provider<GoRouter>((ref) {
     initialLocation: '/',
     redirect: (context, state) {
       final isLoading = authState.isLoading;
-      final token = authState.valueOrNull;
+      final token = authState.maybeWhen(data: (t) => t, orElse: () => null);
       final isLoggedIn = token != null && token.isNotEmpty;
       final location = state.matchedLocation;
       final isSplash = location == '/';
@@ -194,6 +196,14 @@ final appRouterProvider = Provider<GoRouter>((ref) {
             path: '/profile',
             builder: (context, state) => const ProfileScreen(),
           ),
+          GoRoute(
+            path: '/admin',
+            redirect: (context, state) {
+              final token = ref.read(authStateProvider).maybeWhen(data: (t) => t, orElse: () => null);
+              return jwtIsAdmin(token) ? null : '/recipes';
+            },
+            builder: (context, state) => const AdminScreen(),
+          ),
         ],
       ),
     ],

flutter/lib/core/ui/app_shell.dart

@@ -4,6 +4,13 @@ import 'package:go_router/go_router.dart';
 
 import '../../features/auth/data/auth_providers.dart';
 
+const _adminDestination = _AppDestination(
+  path: '/admin',
+  title: 'Admin',
+  icon: Icons.admin_panel_settings_outlined,
+  label: 'Admin',
+);
+
 class AppShell extends ConsumerWidget {
   final String location;
   final Widget child;
@@ -14,7 +21,7 @@ class AppShell extends ConsumerWidget {
     required this.child,
   });
 
-  static const _destinations = [
+  static const _baseDestinations = [
     _AppDestination(
       path: '/recipes',
       title: 'Recept',
@@ -53,8 +60,13 @@ class AppShell extends ConsumerWidget {
     ),
   ];
 
-  int _selectedIndex() {
-    final index = _destinations.indexWhere(
+  List<_AppDestination> _destinations(bool isAdmin) => [
+        ..._baseDestinations,
+        if (isAdmin) _adminDestination,
+      ];
+
+  int _selectedIndex(List<_AppDestination> destinations) {
+    final index = destinations.indexWhere(
       (destination) => location.startsWith(destination.path),
     );
     return index < 0 ? 0 : index;
@@ -62,8 +74,10 @@ class AppShell extends ConsumerWidget {
 
   @override
   Widget build(BuildContext context, WidgetRef ref) {
-    final selectedIndex = _selectedIndex();
-    final selectedDestination = _destinations[selectedIndex];
+    final isAdmin = ref.watch(isAdminProvider);
+    final dests = _destinations(isAdmin);
+    final selectedIndex = _selectedIndex(dests);
+    final selectedDestination = dests[selectedIndex];
     final isWide = MediaQuery.of(context).size.width >= 900;
 
     Future<void> logout() async {
@@ -74,7 +88,7 @@ class AppShell extends ConsumerWidget {
     }
 
     void navigateTo(int index) {
-      final target = _destinations[index].path;
+      final target = dests[index].path;
       if (target != location && context.mounted) {
         context.go(target);
       }
@@ -98,7 +112,7 @@ class AppShell extends ConsumerWidget {
                   selectedIndex: selectedIndex,
                   onDestinationSelected: navigateTo,
                   labelType: NavigationRailLabelType.all,
-                  destinations: _destinations
+                  destinations: dests
                       .map(
                         (destination) => NavigationRailDestination(
                           icon: Icon(destination.icon),
@@ -117,7 +131,7 @@ class AppShell extends ConsumerWidget {
           : NavigationBar(
               selectedIndex: selectedIndex,
               onDestinationSelected: navigateTo,
-              destinations: _destinations
+              destinations: dests
                   .map(
                     (destination) => NavigationDestination(
                       icon: Icon(destination.icon),