add logic example

Frontend-user/lib/basket.dart

@@ -20,7 +20,7 @@ class ShowBasket extends StatelessWidget {
           return Card(
             child: ListTile(
               leading: const Icon(Icons.abc),
-              title: Text(SampleData().basket.purchases[index].product.name),
+              title: Text(SampleData().basket.purchases.keys.elementAt(index).name),
               //trailing: Text(),
             ),
           );

Frontend-user/lib/sample_data.dart

@@ -40,9 +40,22 @@ class Purchase {
 }
 
 class Basket {
-  List<Purchase> purchases;
-  int price;
+  Map<Product, int> purchases;
+  double price;
+
   Basket(this.purchases, this.price);
+
+  void addItem(Product product, int quantity) {
+    if (purchases.containsKey(product)) {
+      purchases.update(product, (existingQuantity) => existingQuantity + quantity);
+    } else {
+      purchases[product] = quantity;
+    }
+  }
+
+  void removeItem(Product product) {
+    purchases.remove(product);
+  }
 }
 
 //sample data
@@ -90,13 +103,13 @@ class SampleData {
     Product('Schokolade', Unit.menge, 0.23, 7, Category.suessesUndKnabbereien)
   ];
 
-  Basket basket = Basket([
-    Purchase(products[0], 20),
-    Purchase(products[1], 2200),
-    Purchase(products[2], 2),
-    Purchase(products[3], 1),
-    Purchase(products[4], 1),
-    Purchase(products[5], 2),
-    Purchase(products[6], 202)
-  ], 304);
+  Basket basket = Basket({
+    products[0]: 20,
+    products[1]: 2200,
+    products[2]: 2,
+    products[3]: 1,
+    products[4]: 1,
+    products[5]: 2,
+    products[6]: 202
+  }, 304);
 }