Multiple improvements in authentication functionality

frontend/lib/app_menu.dart

@@ -1,5 +1,8 @@
 import 'package:flutter/material.dart';
+import 'package:flutter_secure_storage/flutter_secure_storage.dart';
 import 'chat_list_screen.dart';
+import 'user_checker.dart';
+import 'backend.dart';
 
 class AppMenu extends StatelessWidget {
   const AppMenu({super.key});
@@ -21,6 +24,22 @@ class AppMenu extends StatelessWidget {
               );
             },
           ),
+          ListTile(
+            title: const Text('Logout'),
+            onTap: () async {
+              final storage = const FlutterSecureStorage();
+              await storage.delete(key: 'username');
+              await storage.delete(key: 'password');
+              Backend.disconnect();
+
+              Navigator.push(
+                context,
+                MaterialPageRoute(
+                  builder: (context) => UserChecker(),
+                ),
+              );
+            },
+          ),
           // Add other settings options here
         ],
       ),

frontend/lib/backend.dart

@@ -6,26 +6,46 @@ import 'dart:async'; // Import for handling Completers
 class Backend {
   static WebSocket? _socket;
   static String? _url;
-  static String? _username;
   static Map<int, Completer> _pendingActions = {};
   static Map<int, StreamController<Map<String, dynamic>>> _chatControllers = {};
   static int _nextNonce = 0; // Tracking nonce for each action
   static StreamController<Map<String, dynamic>> _packetStreamController = StreamController.broadcast();
+  
+  // Authentication
+  static ({String username, String password})? _credentials;
+  static Completer? _loginCompleter;
+  static Completer? _credentialsCompleter;
 
   static void setup(String url) {
     _url = url;
     connect();
   }
 
-  static void auth(String username, String password) {
+  static Future<void> auth(String username, String password) {
     _socket!.send(json.encode({'username': username, 'password': password}));
-    _username = username;
+    _credentials = (username: username, password: password);
+    if (_credentialsCompleter != null) {
+      _credentialsCompleter!.complete(_credentials);
+      _credentialsCompleter = null;
+    }
+    _loginCompleter = Completer();
+    return _loginCompleter!.future;
   }
 
   static void connect() {
     _socket = WebSocket(_url!);
     _socket!.onOpen.listen((event) {
       print('Connected to the WebSocket server');
+      print('Logging in...');
+      if (_credentials != null) {
+        _socket!.send(json.encode({'username': _credentials!.username, 'password': _credentials!.password}));
+      } else {
+        _credentialsCompleter = Completer();
+        _credentialsCompleter!.future.then((credentials) {
+          _socket!.send(json.encode({'username': credentials.username, 'password': credentials.password}));
+        });
+      }
+      _loginCompleter?.complete();
     });
     _socket!.onError.listen((event) {
       print('Error: $event');
@@ -40,6 +60,11 @@ class Backend {
     });
   }
 
+  static void disconnect() {
+    _socket?.close();
+    _loginCompleter = null;
+  }
+
   static void _reconnect() {
     Future.delayed(Duration(seconds: 5), () {
       connect();

frontend/lib/login_screen.dart

@@ -8,6 +8,13 @@ class LoginScreen extends StatelessWidget {
   final TextEditingController usernameController = TextEditingController();
   final TextEditingController passwordController = TextEditingController();
 
+  final FocusNode usernameFocusNode = FocusNode();
+  final FocusNode passwordFocusNode = FocusNode();
+
+  void _handleLogin() {
+    onLogin(usernameController.text, passwordController.text);
+  }
+
   @override
   Widget build(BuildContext context) {
     return Scaffold(
@@ -18,18 +25,29 @@ class LoginScreen extends StatelessWidget {
           child: Column(
             mainAxisAlignment: MainAxisAlignment.center,
             children: [
-              TextField(controller: usernameController, decoration: InputDecoration(labelText: 'Username')),
+              TextField(
+                controller: usernameController,
+                focusNode: usernameFocusNode,
+                decoration: InputDecoration(labelText: 'Username'),
+                textInputAction: TextInputAction.next,
+                onSubmitted: (_) {
+                  FocusScope.of(context).requestFocus(passwordFocusNode);
+                },
+              ),
               SizedBox(height: 20),
               TextField(
                 controller: passwordController,
+                focusNode: passwordFocusNode,
                 decoration: InputDecoration(labelText: 'Password'),
-                obscureText: true, // Hide password characters
+                obscureText: true,
+                textInputAction: TextInputAction.done,
+                onSubmitted: (_) {
+                  _handleLogin();
+                },
               ),
               SizedBox(height: 20),
               ElevatedButton(
-                onPressed: () {
-                  onLogin(usernameController.text, passwordController.text);
-                },
+                onPressed: _handleLogin,
                 child: Text('Login'),
               ),
             ],

frontend/lib/user_checker.dart

@@ -1,4 +1,5 @@
 import 'package:flutter/material.dart';
+import 'package:flutter_secure_storage/flutter_secure_storage.dart';
 import 'backend.dart';
 import 'login_screen.dart';
 import 'chat_screen.dart';
@@ -11,12 +12,26 @@ class UserChecker extends StatefulWidget {
 
 class _UserCheckerState extends State<UserChecker> {
   String? username;
-  bool isLoading = false;
+  bool isLoading = true;
+  final _storage = const FlutterSecureStorage();
 
   @override
   void initState() {
     super.initState();
-    username = null;
+    _checkSavedCredentials();
+  }
+
+  Future<void> _checkSavedCredentials() async {
+    final savedUsername = await _storage.read(key: 'username');
+    final savedPassword = await _storage.read(key: 'password');
+
+    if (savedUsername != null && savedPassword != null) {
+      _handleLogin(savedUsername, savedPassword);
+    } else {
+      setState(() {
+        isLoading = false;
+      });
+    }
   }
 
   static void fetchChats(Function(List<int>) onSuccess) {
@@ -28,13 +43,15 @@ class _UserCheckerState extends State<UserChecker> {
     });
   }
 
-  void _handleLogin(String user, String password) {
-    Backend.auth(user, password);
-  
+  void _handleLogin(String user, String password) async {
     setState(() {
       username = user;
-      isLoading = true; // Show loading spinner
+      isLoading = true;
     });
+  
+    await Backend.auth(user, password);
+    await _storage.write(key: 'username', value: user);
+    await _storage.write(key: 'password', value: password);
 
     fetchChats((chatIds) {
       if (chatIds.isEmpty) {
@@ -49,14 +66,13 @@ class _UserCheckerState extends State<UserChecker> {
         );
       }
     });
-
   }
 
   @override
   Widget build(BuildContext context) {
     print("Build UserChecker: $username $isLoading");
     if (isLoading) {
-      return Center(child: CircularProgressIndicator()); // Loading state UI
+      return Center(child: CircularProgressIndicator());
     }
 
     return LoginScreen(onLogin: _handleLogin);