Add comprehensive unit tests for Security, UserModel, and Validation utilities

- Implemented SecurityTest to validate token generation, CSRF protection, input sanitization, and rate limiting.
- Created UserModelTest to ensure correct database operations for user management, including creation, updating, banning, and fetching active users.
- Developed ValidationTest to verify input validation and sanitization for user IDs, nicknames, messages, and API requests.
- Introduced Security and Validation utility classes with methods for secure token generation, input sanitization, and comprehensive validation rules.

assets/js/chat.js

@@ -65,8 +65,8 @@
                     UIControls.DOMUtils.addEvent(sendButton, 'click', sendMessage);
                 }
 
-                // Start polling for messages
-                startMessagePolling();
+                // Start real-time SSE connection for chat
+                startSSEConnection();
 
                 // Send initial heartbeat
                 API.sendHeartbeat();
@@ -306,8 +306,132 @@
             });
     }
 
-    // Message polling system
+    // SSE (Server-Sent Events) for real-time communication
+    let eventSource = null;
+    let sseReconnectAttempts = 0;
+    const maxSSEReconnectAttempts = 5;
+
+    function startSSEConnection() {
+        if (typeof(EventSource) === 'undefined') {
+            // Fallback to polling if SSE not supported
+            AppLogger.warn('EventSource not supported, falling back to polling');
+            startMessagePolling();
+            return;
+        }
+
+        if (eventSource) {
+            eventSource.close();
+        }
+
+        const userId = AppState.userId;
+        const csrfToken = document.querySelector('meta[name="csrf-token"]')?.getAttribute('content') || '';
+
+        // Build SSE URL with CSRF protection and last message ID
+        const sseUrl = `?sse=1&user_id=${encodeURIComponent(userId)}&csrf=${encodeURIComponent(csrfToken)}&last_id=${encodeURIComponent(AppState.lastMessageId)}`;
+
+        eventSource = new EventSource(sseUrl);
+
+        // Connection established
+        eventSource.addEventListener('connection', function(event) {
+            const data = JSON.parse(event.data);
+            AppLogger.log('SSE connected:', data);
+            sseReconnectAttempts = 0;
+
+            updateConnectionStatus(true);
+            ScreenReader.connectionStatus('connected');
+        });
+
+        // New messages arrived
+        eventSource.addEventListener('new_messages', function(event) {
+            const messageData = JSON.parse(event.data);
+            const newMessages = messageData.data.messages;
+
+            if (newMessages && newMessages.length > 0) {
+                // Process each new message
+                newMessages.forEach(msg => {
+                    // Skip if it's our own message (might be received via SSE faster than AJAX response)
+                    if (msg.user_id === AppState.userId) {
+                        return;
+                    }
+
+                    appendMessage(msg);
+                    AppState.allMessages.push(msg);
+
+                    // Show notification if chat is collapsed
+                    if (AppState.chatCollapsed) {
+                        AppState.unreadCount++;
+                        UIControls.updateNotificationBadge();
+                        playNotificationSound();
+                    }
+                });
+
+                // Update last message ID
+                const lastMessage = newMessages[newMessages.length - 1];
+                if (lastMessage && lastMessage.id) {
+                    AppState.lastMessageId = lastMessage.id;
+                }
+
+                // Announce new messages for screen readers
+                if (newMessages.length === 1) {
+                    ScreenReader.messageReceived('New message received');
+                } else {
+                    ScreenReader.messageGroup(newMessages.map(msg => ({
+                        nickname: msg.nickname,
+                        message: msg.message
+                    })), 'added');
+                }
+            }
+        });
+
+        // Viewer count updates
+        eventSource.addEventListener('viewer_count_update', function(event) {
+            const viewerData = JSON.parse(event.data);
+            const count = viewerData.data.count;
+
+            updateViewerCount(count);
+            ScreenReader.viewerCount(count);
+        });
+
+        // Heartbeat for connection monitoring
+        eventSource.addEventListener('heartbeat', function(event) {
+            const heartbeatData = JSON.parse(event.data);
+            // Connection is alive, no action needed
+        });
+
+        // Connection errors
+        eventSource.addEventListener('error', function(event) {
+            AppLogger.warn('SSE connection error:', event);
+
+            updateConnectionStatus(false);
+            ScreenReader.connectionStatus('error', 'Connection lost, attempting to reconnect');
+
+            // Auto-reconnect with backoff
+            if (sseReconnectAttempts < maxSSEReconnectAttempts) {
+                sseReconnectAttempts++;
+                const delay = Math.min(1000 * Math.pow(2, sseReconnectAttempts), 30000);
+
+                setTimeout(() => {
+                    AppLogger.log(`Attempting SSE reconnection (${sseReconnectAttempts}/${maxSSEReconnectAttempts})`);
+                    startSSEConnection();
+                }, delay);
+            } else {
+                // Fall back to polling after max attempts
+                AppLogger.error('SSE maximum reconnection attempts reached, falling back to polling');
+                startMessagePolling();
+            }
+        });
+
+        // Connection closed
+        eventSource.addEventListener('disconnect', function(event) {
+            const disconnectData = JSON.parse(event.data);
+            AppLogger.log('SSE disconnected:', disconnectData.data.reason);
+        });
+    }
+
+    // Traditional polling system (fallback)
     function startMessagePolling() {
+        AppLogger.log('Starting message polling (fallback)');
+
         // Poll for new messages
         setInterval(fetchMessages, AppConfig.api.chatPollInterval);
 
@@ -515,6 +639,29 @@
         AppState.lastMessageId = '';
     }
 
+    // Update connection status functions (from UI controls)
+    function updateConnectionStatus(online) {
+        const statusDot = document.getElementById('statusDot');
+        const statusText = document.getElementById('statusText');
+
+        if (statusDot && statusText) {
+            if (online) {
+                statusDot.classList.remove('offline');
+                statusText.textContent = 'Connected';
+            } else {
+                statusDot.classList.add('offline');
+                statusText.textContent = 'Reconnecting...';
+            }
+        }
+    }
+
+    function updateViewerCount(count) {
+        const viewerElement = document.getElementById('viewerCount');
+        if (viewerElement) {
+            viewerElement.textContent = count + (count === 1 ? ' viewer' : ' viewers');
+        }
+    }
+
     // Utility function for HTML escaping
     function escapeHtml(text) {
         const div = document.createElement('div');