Implement cart store

lib/app.dart

@@ -3,6 +3,7 @@ import 'package:thesis_shop/route_key.dart';
 import 'package:thesis_shop/screens/cart/cart_screen.dart';
 import 'package:thesis_shop/screens/product_list/product_list_screen.dart';
 import 'package:thesis_shop/service/product_service.dart';
+import 'package:thesis_shop/stores/cart_store.dart';
 import 'package:thesis_shop/stores/product_store.dart';
 import 'package:thesis_shop/stores/user_store.dart';
 import 'package:thesis_shop/utils/map_keys_extension.dart';
@@ -16,7 +17,9 @@ class ThesisShopApp extends StatelessWidget {
     return UserStoreImplementation(
       child: ProductStoreImplementation(
         productService: productService,
-        child: child,
+        child: CartStoreImplementation(
+          child: child,
+        ),
       ),
     );
   }

lib/screens/product_list/cart_button.dart

@@ -1,17 +1,19 @@
 import 'package:flutter/material.dart';
 import 'package:thesis_shop/benchmark_counter.dart';
 import 'package:thesis_shop/route_key.dart';
+import 'package:thesis_shop/stores/cart_store.dart';
 
 class CartButton extends StatelessWidget {
   const CartButton() : super(key: const Key('cart_button'));
 
   @override
   Widget build(BuildContext context) {
+    final cartStore = CartStore.of(context);
     BenchmarkCounters.cartButton++;
     return ElevatedButton.icon(
       onPressed: () => Navigator.of(context).pushRouteKey(RouteKey.cart),
       icon: const Icon(Icons.shopping_basket),
-      label: const Text('Warenkorb (3 Produkte)'),
+      label: Text('Warenkorb (${cartStore.cartItems.length} Produkte)'),
     );
   }
 }

lib/screens/product_list/product_item.dart

@@ -1,5 +1,6 @@
 import 'package:flutter/material.dart';
 import 'package:thesis_shop/models/product.dart';
+import 'package:thesis_shop/stores/cart_store.dart';
 import 'package:thesis_shop/widgets/number_picker.dart';
 
 class ProductItem extends StatelessWidget {
@@ -8,9 +9,14 @@ class ProductItem extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
+    final cartStore = CartStore.of(context);
     return ListTile(
       title: Text('${product.title} (${product.priceAsString}€/Stück)'),
-      trailing: NumberPicker(value: 5, onUp: () {}, onDown: () {}),
+      trailing: NumberPicker(
+        value: cartStore.amountOfProduct(product),
+        onUp: () => cartStore.increaseAmount(product),
+        onDown: () => cartStore.decreaseAmount(product),
+      ),
     );
   }
 }

lib/stores/cart_store.dart

@@ -0,0 +1,82 @@
+import 'package:flutter/material.dart';
+import 'package:thesis_shop/models/cart_item.dart';
+import 'package:thesis_shop/models/product.dart';
+import 'package:thesis_shop/stores/product_store.dart';
+
+class CartStoreImplementation extends StatefulWidget {
+  final Widget child;
+  const CartStoreImplementation({Key? key, required this.child})
+      : super(key: key);
+
+  @override
+  _CartStoreImplementationState createState() =>
+      _CartStoreImplementationState();
+}
+
+class _CartStoreImplementationState extends State<CartStoreImplementation> {
+  Map<ProductTitle, int> productAmounts = {};
+  void increaseAmount(Product product) => setState(() {
+        final currentAmount =
+            productAmounts.putIfAbsent(product.title, () => 0);
+        productAmounts[product.title] = currentAmount + 1;
+      });
+  void decreaseAmount(Product product) => setState(() {
+        final currentAmount =
+            productAmounts.putIfAbsent(product.title, () => 0);
+        productAmounts[product.title] =
+            currentAmount <= 0 ? 0 : currentAmount - 1;
+      });
+  @override
+  Widget build(BuildContext context) {
+    final products = ProductStore.of(context).productsOrNull ?? const [];
+    final productsByTitle = {
+      for (var product in products) product.title: product
+    };
+    final cartItems = productAmounts
+        .map((key, value) => MapEntry(productsByTitle[key], value))
+        .entries
+        .where((entry) => entry.key != null && entry.value > 0)
+        .map((entry) => CartItem(product: entry.key!, amount: entry.value))
+        .toList();
+    return CartStore(
+      cartItems: cartItems,
+      increaseAmount: increaseAmount,
+      decreaseAmount: decreaseAmount,
+      child: widget.child,
+    );
+  }
+}
+
+class CartStore extends InheritedWidget {
+  const CartStore({
+    Key? key,
+    required this.cartItems,
+    required this.increaseAmount,
+    required this.decreaseAmount,
+    required Widget child,
+  }) : super(key: key, child: child);
+
+  final List<CartItem> cartItems;
+
+  final Function(Product) increaseAmount;
+  final Function(Product) decreaseAmount;
+
+  int amountOfProduct(Product product) {
+    final amounts = {
+      for (final item in cartItems) item.product: item.amount,
+    };
+    return amounts.putIfAbsent(product, () => 0);
+  }
+
+  static CartStore of(BuildContext context) {
+    final CartStore? result =
+        context.dependOnInheritedWidgetOfExactType<CartStore>();
+    assert(result != null, 'No CartStore found in context');
+    return result!;
+  }
+
+  @override
+  bool updateShouldNotify(CartStore oldWidget) {
+    return cartItems != oldWidget.cartItems;
+  }
+}

lib/stores/product_selection_store.dart

@@ -1,31 +0,0 @@
-import 'package:flutter/material.dart';
-import 'package:thesis_shop/models/product.dart';
-
-class ProductSelectionStore extends InheritedWidget {
-  const ProductSelectionStore({
-    Key? key,
-    required this.products,
-    required this.productAmounts,
-    required this.increaseAmount,
-    required this.decreaseAmount,
-    required Widget child,
-  }) : super(key: key, child: child);
-
-  final List<Product> products;
-  final Map<ProductTitle, int> productAmounts;
-
-  final Function(Product) increaseAmount;
-  final Function(Product) decreaseAmount;
-
-  static ProductSelectionStore of(BuildContext context) {
-    final ProductSelectionStore? result =
-        context.dependOnInheritedWidgetOfExactType<ProductSelectionStore>();
-    assert(result != null, 'No ProductSelectionStore found in context');
-    return result!;
-  }
-
-  @override
-  bool updateShouldNotify(ProductSelectionStore oldWidget) {
-    return productAmounts != oldWidget.productAmounts;
-  }
-}

lib/stores/product_store.dart

@@ -55,6 +55,12 @@ class ProductStore extends InheritedWidget {
 
   final RemoteResource<List<Product>> products;
   List<Product> get mustProducts => products.asFinished().value;
+  List<Product>? get productsOrNull {
+    if (products is FinishedRemoteResource) {
+      return mustProducts;
+    }
+    return null;
+  }
 
   static ProductStore of(BuildContext context) {
     final ProductStore? result =