feat: implement multi-line session failover with round-robin strategy and session readiness validation for OTP delivery.

backend/app/Models/WhatsAppSession.php

@@ -49,26 +49,25 @@ class WhatsAppSession extends BaseModel
     }
 
     /**
-     * Get next connected session using Round-Robin strategy via Redis
+     * Get and increment Round-Robin index with Redis and file-based fallback
      */
-    public static function getRoundRobinSession(int $companyId): ?array
+    public static function getNextRoundRobinIndex(int $companyId, int $count): int
     {
-        $connectedSessions = static::getConnectedSessionsForCompany($companyId);
-
-        if (empty($connectedSessions)) {
-            // Fallback to legacy single session if no connected sessions are found
-            return static::findByCompany($companyId, false);
-        }
-
-        $count = count($connectedSessions);
-        if ($count === 1) {
-            return $connectedSessions[0];
+        if ($count <= 1) {
+            return 0;
         }
 
         $rrKey = "rr_index:company_{$companyId}";
         $currentIndex = Cache::get($rrKey);
+
         if ($currentIndex === null || !is_numeric($currentIndex)) {
-            $currentIndex = 0;
+            // File-based persistent fallback if Redis is unavailable
+            $tempFile = sys_get_temp_dir() . "/nabeh_rr_company_{$companyId}.txt";
+            if (file_exists($tempFile)) {
+                $currentIndex = (int)@file_get_contents($tempFile);
+            } else {
+                $currentIndex = 0;
+            }
         } else {
             $currentIndex = (int)$currentIndex;
         }
@@ -77,8 +76,52 @@ class WhatsAppSession extends BaseModel
         $nextIndex = ($selectedIndex + 1) % $count;
 
         Cache::set($rrKey, $nextIndex, 86400);
+        
+        $tempFile = sys_get_temp_dir() . "/nabeh_rr_company_{$companyId}.txt";
+        @file_put_contents($tempFile, (string)$nextIndex, LOCK_EX);
 
-        return $connectedSessions[$selectedIndex];
+        return $selectedIndex;
+    }
+
+    /**
+     * Get all active connected sessions ordered by Round-Robin index for seamless failover
+     */
+    public static function getRoundRobinSessionsList(int $companyId): array
+    {
+        $connectedSessions = static::getConnectedSessionsForCompany($companyId);
+        $count = count($connectedSessions);
+
+        if ($count === 0) {
+            return [];
+        }
+
+        if ($count === 1) {
+            return $connectedSessions;
+        }
+
+        $startIndex = static::getNextRoundRobinIndex($companyId, $count);
+
+        // Reorder list starting from $startIndex: [start..end, 0..start-1]
+        $ordered = [];
+        for ($i = 0; $i < $count; $i++) {
+            $ordered[] = $connectedSessions[($startIndex + $i) % $count];
+        }
+
+        return $ordered;
+    }
+
+    /**
+     * Get next connected session using Round-Robin strategy via Redis
+     */
+    public static function getRoundRobinSession(int $companyId): ?array
+    {
+        $list = static::getRoundRobinSessionsList($companyId);
+        if (!empty($list)) {
+            return $list[0];
+        }
+
+        // Fallback to legacy single session if no connected sessions are found
+        return static::findByCompany($companyId, false);
     }
 
     /**