feat: add rows count (broken), fix: bug with low stock items

lib/viewmodels/bar_screen_view_model.dart

@@ -6,6 +6,7 @@ import '../models/bar_tab.dart';
 import '../models/product.dart';
 import '../models/tab_item.dart';
 import '../services/bar_tab_service.dart';
+import '../services/product_service.dart';
 import 'inventory_view_model.dart';
 
 class BarScreenViewModel extends ChangeNotifier {
@@ -95,9 +96,7 @@ class BarScreenViewModel extends ChangeNotifier {
     if (tab == null) return;
 
     if (product.stockQuantity <= 0) {
-      _errorMessage = 'Product is out of stock.';
-      notifyListeners();
-      return;
+      throw const InsufficientStockException();
     }
 
     try {
@@ -109,6 +108,8 @@ class BarScreenViewModel extends ChangeNotifier {
 
       await _reloadTabs();
     } catch (e, stack) {
+      if (e is InsufficientStockException) rethrow;
+
       debugPrint('BarScreenViewModel: addProductToSelectedTab error: $e');
       _errorMessage = 'Could not add product to tab.';
       notifyListeners();
@@ -120,6 +121,20 @@ class BarScreenViewModel extends ChangeNotifier {
   Future<void> changeItemQuantity(TabItem item, int quantity) async {
     final difference = quantity - item.quantity;
 
+    if (difference > 0) {
+      Product? product;
+      for (final candidate in inventory.products) {
+        if (candidate.id == item.productId) {
+          product = candidate;
+          break;
+        }
+      }
+
+      if (product != null && product.stockQuantity < difference) {
+        throw const InsufficientStockException();
+      }
+    }
+
     try {
       await barTabService.updateTabItemQuantity(
         tabItemId: item.id,
@@ -135,6 +150,8 @@ class BarScreenViewModel extends ChangeNotifier {
 
       await _reloadTabs();
     } catch (e, stack) {
+      if (e is InsufficientStockException) rethrow;
+
       debugPrint('BarScreenViewModel: changeItemQuantity error: $e');
       _errorMessage = 'Could not update item quantity.';
       notifyListeners();