refuse to add existing subscribtion

app/src/main/java/sh/sar/gridflow/ui/subscriptions/SubscriptionsFragment.kt

@@ -75,6 +75,12 @@ class SubscriptionsFragment : Fragment() {
                 val billNumber = binding.editBillNumber.text.toString().trim()
                 
                 if (alias.isNotEmpty()) {
+                    // Check if subscription number already exists
+                    if (isSubscriptionNumberExists(subscriptionNumber)) {
+                        Toast.makeText(requireContext(), "Subscription number already added", Toast.LENGTH_SHORT).show()
+                        return@setOnClickListener
+                    }
+                    
                     subscriptionsViewModel.addSubscription(
                         name = alias,
                         subscriptionNumber = subscriptionNumber,
@@ -390,6 +396,12 @@ class SubscriptionsFragment : Fragment() {
         }
     }
     
+    private fun isSubscriptionNumberExists(subscriptionNumber: String): Boolean {
+        return subscriptionsViewModel.subscriptions.value?.any { 
+            it.subscription.subscriptionNumber == subscriptionNumber 
+        } ?: false
+    }
+
     override fun onDestroyView() {
         super.onDestroyView()
         _binding = null