Add performance, security, and reliability improvements

- Consolidate all 20 API files to use centralized Database helper
- Add optimistic locking to ticket updates to prevent concurrent conflicts
- Add caching to StatsModel (60s TTL) for dashboard performance
- Add health check endpoint (api/health.php) for monitoring
- Improve rate limit cleanup with cron script and efficient DirectoryIterator
- Enable rate limit response headers (X-RateLimit-*)
- Add audit logging for workflow transitions
- Log Discord webhook failures instead of silencing
- Fix visibility check on export_tickets.php
- Add database migration system with performance indexes
- Fix cron recurring tickets to use assignTicket method

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

models/StatsModel.php

@@ -2,20 +2,29 @@
 /**
  * StatsModel - Dashboard statistics and metrics
  *
- * Provides various ticket statistics for dashboard widgets
+ * Provides various ticket statistics for dashboard widgets.
+ * Uses caching to reduce database load for frequently accessed stats.
  */
 
-class StatsModel {
-    private $conn;
+require_once dirname(__DIR__) . '/helpers/CacheHelper.php';
 
-    public function __construct($conn) {
+class StatsModel {
+    private mysqli $conn;
+
+    /** Cache TTL for dashboard stats in seconds */
+    private const STATS_CACHE_TTL = 60;
+
+    /** Cache prefix for stats */
+    private const CACHE_PREFIX = 'stats';
+
+    public function __construct(mysqli $conn) {
         $this->conn = $conn;
     }
 
     /**
      * Get count of open tickets
      */
-    public function getOpenTicketCount() {
+    public function getOpenTicketCount(): int {
         $sql = "SELECT COUNT(*) as count FROM tickets WHERE status IN ('Open', 'Pending', 'In Progress')";
         $result = $this->conn->query($sql);
         $row = $result->fetch_assoc();
@@ -25,7 +34,7 @@ class StatsModel {
     /**
      * Get count of closed tickets
      */
-    public function getClosedTicketCount() {
+    public function getClosedTicketCount(): int {
         $sql = "SELECT COUNT(*) as count FROM tickets WHERE status = 'Closed'";
         $result = $this->conn->query($sql);
         $row = $result->fetch_assoc();
@@ -35,7 +44,7 @@ class StatsModel {
     /**
      * Get tickets grouped by priority
      */
-    public function getTicketsByPriority() {
+    public function getTicketsByPriority(): array {
         $sql = "SELECT priority, COUNT(*) as count FROM tickets WHERE status != 'Closed' GROUP BY priority ORDER BY priority";
         $result = $this->conn->query($sql);
         $data = [];
@@ -48,7 +57,7 @@ class StatsModel {
     /**
      * Get tickets grouped by status
      */
-    public function getTicketsByStatus() {
+    public function getTicketsByStatus(): array {
         $sql = "SELECT status, COUNT(*) as count FROM tickets GROUP BY status ORDER BY FIELD(status, 'Open', 'Pending', 'In Progress', 'Closed')";
         $result = $this->conn->query($sql);
         $data = [];
@@ -61,7 +70,7 @@ class StatsModel {
     /**
      * Get tickets grouped by category
      */
-    public function getTicketsByCategory() {
+    public function getTicketsByCategory(): array {
         $sql = "SELECT category, COUNT(*) as count FROM tickets WHERE status != 'Closed' GROUP BY category ORDER BY count DESC";
         $result = $this->conn->query($sql);
         $data = [];
@@ -74,7 +83,7 @@ class StatsModel {
     /**
      * Get average resolution time in hours
      */
-    public function getAverageResolutionTime() {
+    public function getAverageResolutionTime(): float {
         $sql = "SELECT AVG(TIMESTAMPDIFF(HOUR, created_at, updated_at)) as avg_hours
                 FROM tickets
                 WHERE status = 'Closed'
@@ -89,7 +98,7 @@ class StatsModel {
     /**
      * Get count of tickets created today
      */
-    public function getTicketsCreatedToday() {
+    public function getTicketsCreatedToday(): int {
         $sql = "SELECT COUNT(*) as count FROM tickets WHERE DATE(created_at) = CURDATE()";
         $result = $this->conn->query($sql);
         $row = $result->fetch_assoc();
@@ -99,7 +108,7 @@ class StatsModel {
     /**
      * Get count of tickets created this week
      */
-    public function getTicketsCreatedThisWeek() {
+    public function getTicketsCreatedThisWeek(): int {
         $sql = "SELECT COUNT(*) as count FROM tickets WHERE YEARWEEK(created_at, 1) = YEARWEEK(CURDATE(), 1)";
         $result = $this->conn->query($sql);
         $row = $result->fetch_assoc();
@@ -109,7 +118,7 @@ class StatsModel {
     /**
      * Get count of tickets closed today
      */
-    public function getTicketsClosedToday() {
+    public function getTicketsClosedToday(): int {
         $sql = "SELECT COUNT(*) as count FROM tickets WHERE status = 'Closed' AND DATE(updated_at) = CURDATE()";
         $result = $this->conn->query($sql);
         $row = $result->fetch_assoc();
@@ -119,7 +128,7 @@ class StatsModel {
     /**
      * Get tickets by assignee (top 5)
      */
-    public function getTicketsByAssignee($limit = 5) {
+    public function getTicketsByAssignee(int $limit = 5): array {
         $sql = "SELECT
                     u.display_name,
                     u.username,
@@ -146,7 +155,7 @@ class StatsModel {
     /**
      * Get unassigned ticket count
      */
-    public function getUnassignedTicketCount() {
+    public function getUnassignedTicketCount(): int {
         $sql = "SELECT COUNT(*) as count FROM tickets WHERE assigned_to IS NULL AND status != 'Closed'";
         $result = $this->conn->query($sql);
         $row = $result->fetch_assoc();
@@ -156,7 +165,7 @@ class StatsModel {
     /**
      * Get critical (P1) ticket count
      */
-    public function getCriticalTicketCount() {
+    public function getCriticalTicketCount(): int {
         $sql = "SELECT COUNT(*) as count FROM tickets WHERE priority = 1 AND status != 'Closed'";
         $result = $this->conn->query($sql);
         $row = $result->fetch_assoc();
@@ -165,8 +174,35 @@ class StatsModel {
 
     /**
      * Get all stats as a single array
+     *
+     * Uses caching to reduce database load. Stats are cached for STATS_CACHE_TTL seconds.
+     *
+     * @param bool $forceRefresh Force a cache refresh
+     * @return array All dashboard statistics
      */
-    public function getAllStats() {
+    public function getAllStats(bool $forceRefresh = false): array {
+        $cacheKey = 'dashboard_all';
+
+        if ($forceRefresh) {
+            CacheHelper::delete(self::CACHE_PREFIX, $cacheKey);
+        }
+
+        return CacheHelper::remember(
+            self::CACHE_PREFIX,
+            $cacheKey,
+            function() {
+                return $this->fetchAllStats();
+            },
+            self::STATS_CACHE_TTL
+        );
+    }
+
+    /**
+     * Fetch all stats from database (uncached)
+     *
+     * @return array All dashboard statistics
+     */
+    private function fetchAllStats(): array {
         return [
             'open_tickets' => $this->getOpenTicketCount(),
             'closed_tickets' => $this->getClosedTicketCount(),
@@ -182,5 +218,13 @@ class StatsModel {
             'by_assignee' => $this->getTicketsByAssignee()
         ];
     }
+
+    /**
+     * Invalidate cached stats
+     *
+     * Call this method when ticket data changes to ensure fresh stats.
+     */
+    public function invalidateCache(): void {
+        CacheHelper::delete(self::CACHE_PREFIX, null);
+    }
 }
-?>