update: add inventory limit

app/Services/OrderService.php

@@ -249,6 +249,11 @@ class OrderService
                 return false;
             }
         }
+        $planService = new PlanService($order->plan_id);
+        if (!$planService->incrementInventory()) {
+            DB::rollBack();
+            return false;
+        }
         DB::commit();
         return true;
     }

app/Services/PlanService.php

@@ -0,0 +1,29 @@
+<?php
+
+namespace App\Services;
+
+use App\Models\Plan;
+
+class PlanService
+{
+    public $plan;
+
+    public function __construct(int $planId)
+    {
+        $this->plan = Plan::lockForUpdate()->find($planId);
+    }
+
+    public function incrementInventory()
+    {
+        if ($this->plan->inventory_limit !== NULL) {
+            return $this->plan->increment('inventory_limit');
+        }
+    }
+
+    public function decrementInventory()
+    {
+        if ($this->plan->inventory_limit !== NULL) {
+            return $this->plan->decrement('inventory_limit');
+        }
+    }
+}