<?php
/**
 * Real-time Chat Service using Server-Sent Events (SSE)
 * Provides efficient real-time communication without polling
 */

class ChatServer
{
    private $userModel;
    private $chatMessageModel;
    private $activeViewerModel;

    public function __construct()
    {
        $this->userModel = new UserModel();
        $this->chatMessageModel = new ChatMessageModel();
        $this->activeViewerModel = new ActiveViewerModel();
    }

    /**
     * Handle SSE connection for real-time chat updates
     */
    public function handleSSE($userId)
    {
        // Validate user ID
        if (!$this->validateSSEConnection($userId)) {
            http_response_code(403);
            die("Invalid connection");
        }

        // Set headers for SSE
        header('Content-Type: text/event-stream');
        header('Cache-Control: no-cache');
        header('Access-Control-Allow-Origin: *');
        header('Access-Control-Allow-Methods: GET');
        header('Connection: keep-alive');

        // Disable output buffering
        if (function_exists('apache_setenv')) {
            apache_setenv('no-gzip', '1');
        }
        ini_set('zlib.output_compression', '0');
        ini_set('output_buffering', '0');
        ob_implicit_flush(1);

        // Clear any existing output
        while (ob_get_level()) {
            ob_end_clean();
        }

        // Send initial connection event
        $this->sendEvent('connection', [
            'status' => 'connected',
            'user_id' => $userId,
            'timestamp' => time()
        ]);

        // Get last message ID for incremental updates
        $lastMessageId = $this->getLastMessageIdForUser($userId);

        // Store connection info for heartbeat
        $_SESSION['sse_connected'] = true;
        $_SESSION['sse_user_id'] = $userId;
        $_SESSION['sse_start_time'] = time();

        Security::logSecurityEvent('sse_connection_opened', ['user_id' => $userId]);

        try {
            // Update user's last seen
            if ($userId) {
                $this->userModel->updateLastSeen($userId);
            }

            // Send heartbeat every 30 seconds to keep connection alive
            $heartbeatInterval = 30;
            $lastHeartbeat = time();
            $lastCheck = time();
            $checkInterval = 2; // Check for new messages every 2 seconds

            $connected = true;
            while ($connected && !connection_aborted()) {
                $currentTime = time();

                // Send heartbeat
                if ($currentTime - $lastHeartbeat >= $heartbeatInterval) {
                    $this->sendEvent('heartbeat', [
                        'timestamp' => $currentTime,
                        'uptime' => $currentTime - $_SESSION['sse_start_time']
                    ]);
                    $lastHeartbeat = $currentTime;

                    // Update user's active status during heartbeat
                    if ($userId) {
                        $this->userModel->updateLastSeen($userId);
                    }
                }

                // Check for new messages
                if ($currentTime - $lastCheck >= $checkInterval) {
                    $newMessages = $this->chatMessageModel->getMessagesAfterId($lastMessageId);

                    if (!empty($newMessages)) {
                        // Send new messages
                        $this->sendEvent('new_messages', [
                            'messages' => $newMessages,
                            'count' => count($newMessages)
                        ]);

                        // Update last message ID from the most recent message
                        $lastMessage = end($newMessages);
                        $lastMessageId = $lastMessage['id'];
                    }

                    // Send viewer count updates periodically
                    $viewerCount = $this->activeViewerModel->getActiveCount();
                    $this->sendEvent('viewer_count_update', [
                        'count' => $viewerCount
                    ]);

                    $lastCheck = $currentTime;
                }

                // Clean up old viewers (run this every few heartbeat cycles)
                static $cleanupCounter = 0;
                if (++$cleanupCounter % 5 === 0) { // Every 5 heartbeats = every 150 seconds
                    $this->activeViewerModel->cleanupInactive();
                }

                // Check for PHP timeouts or memory issues
                if ($this->shouldTerminateConnection()) {
                    $connected = false;
                    break;
                }

                // Sleep to avoid consuming too much CPU
                usleep(500000); // 0.5 seconds
            }

        } catch (Exception $e) {
            Security::logSecurityEvent('sse_connection_error', [
                'user_id' => $userId,
                'error' => $e->getMessage()
            ]);

            $this->sendEvent('error', [
                'message' => 'Connection error occurred',
                'code' => 'CONNECTION_ERROR'
            ]);
        }

        // Send disconnect event
        $this->sendEvent('disconnect', [
            'reason' => 'connection_closed',
            'timestamp' => time()
        ]);

        // Clean up connection state
        unset($_SESSION['sse_connected'], $_SESSION['sse_user_id'], $_SESSION['sse_start_time']);

        Security::logSecurityEvent('sse_connection_closed', ['user_id' => $userId, 'duration' => $currentTime - $_SESSION['sse_start_time']]);
    }

    /**
     * Send a server-sent event
     */
    private function sendEvent($eventType, $data)
    {
        $eventData = json_encode([
            'event' => $eventType,
            'data' => $data,
            'timestamp' => time()
        ]);

        echo "event: {$eventType}\n";
        echo "data: {$eventData}\n\n";

        // Force output
        if (ob_get_level()) {
            ob_flush();
        }
        flush();
    }

    /**
     * Validate SSE connection request
     */
    private function validateSSEConnection($userId)
    {
        // Check if user ID is valid format
        if (!Validation::validateUserId($userId)['valid']) {
            return false;
        }

        // Verify CSRF token if provided in URL
        $csrfToken = $_GET['csrf'] ?? '';
        if (!empty($csrfToken) && !Security::validateCSRFToken($csrfToken)) {
            return false;
        }

        // Check rate limiting for SSE connections
        if (!Security::checkRateLimit(Security::getClientIP(), 'sse_connection', 5, 60)) {
            return false;
        }

        return true;
    }

    /**
     * Get the last message ID that a user has seen
     */
    private function getLastMessageIdForUser($userId)
    {
        // Get from GET parameter, session, or database preference
        $lastId = $_GET['last_id'] ?? $_SESSION['sse_last_message_id'] ?? null;

        if (!$lastId) {
            // If no last ID, start from last 50 messages
            $recentMessages = $this->chatMessageModel->getRecent(1);
            $lastId = !empty($recentMessages) ? $recentMessages[0]['id'] : 0;
        }

        $_SESSION['sse_last_message_id'] = $lastId;
        return $lastId;
    }

    /**
     * Check if connection should be terminated
     */
    private function shouldTerminateConnection()
    {
        // Check memory usage (terminate if > 32MB)
        $memoryUsage = memory_get_usage(true);
        if ($memoryUsage > 32 * 1024 * 1024) {
            return true;
        }

        // Check execution time (terminate after 10 minutes)
        $executionTime = time() - $_SESSION['sse_start_time'];
        if ($executionTime > 600) {
            return true;
        }

        // Check if user is still authenticated (if admin)
        if (Security::isAdminAuthenticated()) {
            $timeout = Config::get('admin.session_timeout', 3600);
            $loginTime = $_SESSION['admin_login_time'] ?? 0;
            if (time() - $loginTime > $timeout) {
                return true;
            }
        }

        return false;
    }

    /**
     * Handle broadcasting a new message to any registered listeners
     * (This would be used in a more advanced implementation with process communication)
     */
    public function broadcastMessage($messageData)
    {
        // Store message in database
        $messageId = $this->chatMessageModel->create($messageData);

        if ($messageId) {
            // Log message creation
            Security::logSecurityEvent('message_broadcast', [
                'message_id' => $messageId,
                'user_id' => $messageData['user_id']
            ]);

            return $messageId;
        }

        return false;
    }
}