Add cart store

lib/app.dart

@@ -8,6 +8,7 @@ import 'package:thesis_shop/store/product_store.dart';
 import 'package:thesis_shop/store/user_store.dart';
 import 'package:thesis_shop/utils/map_keys_extension.dart';
 
+import 'store/cart_store.dart';
 import 'store/product_loading_store.dart';
 
 class ThesisShopApp extends StatelessWidget {
@@ -22,6 +23,7 @@ class ThesisShopApp extends StatelessWidget {
         ChangeNotifierProvider(create: (context) => UserStore()),
         ProductLoadingStoreProvider(productService: productService),
         ProductStoreProvider(),
+        CartStoreProvider(),
       ],
       child: MaterialApp(
         title: 'Thesis Shop',

lib/screens/cart/cart_screen.dart

@@ -1,7 +1,9 @@
 import 'package:flutter/material.dart';
+import 'package:provider/provider.dart';
 import 'package:thesis_shop/models/cart_item.dart';
 import 'package:thesis_shop/models/product.dart';
 import 'package:thesis_shop/screens/cart/total_price_text.dart';
+import 'package:thesis_shop/store/cart_store.dart';
 import 'package:thesis_shop/widgets/user_switch.dart';
 
 import 'cart_item_list.dart';
@@ -17,6 +19,7 @@ class CartScreen extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
+    final items = context.watch<CartStore>().cart;
     return Scaffold(
       appBar: AppBar(
         title: const Text('Warenkorb'),
@@ -24,9 +27,9 @@ class CartScreen extends StatelessWidget {
       ),
       body: Column(
         mainAxisSize: MainAxisSize.max,
-        children: const [
-          Expanded(child: CartItemList(items: _placeHolderItems)),
-          TotalPriceText(),
+        children: [
+          Expanded(child: CartItemList(items: items)),
+          const TotalPriceText(),
         ],
       ),
     );

lib/screens/cart/total_price_text.dart

@@ -1,15 +1,20 @@
 import 'package:flutter/material.dart';
+import 'package:provider/provider.dart';
+import 'package:thesis_shop/store/cart_store.dart';
 
 class TotalPriceText extends StatelessWidget {
   const TotalPriceText({Key? key}) : super(key: key);
 
   @override
   Widget build(BuildContext context) {
+    final totalPrice = context
+        .select<CartStore, double>((store) => store.totalPrice)
+        .toStringAsFixed(2);
     return SafeArea(
       child: Padding(
         padding: const EdgeInsets.all(8.0),
         child: Text(
-          'Gesamtpreis: 27€',
+          'Gesamtpreis: $totalPrice',
           style: Theme.of(context).textTheme.labelLarge?.copyWith(fontSize: 24),
         ),
       ),

lib/screens/product_list/cart_button.dart

@@ -1,17 +1,21 @@
 import 'package:flutter/material.dart';
+import 'package:provider/provider.dart';
 import 'package:thesis_shop/benchmark_counter.dart';
 import 'package:thesis_shop/route_key.dart';
+import 'package:thesis_shop/store/cart_store.dart';
 
 class CartButton extends StatelessWidget {
   const CartButton() : super(key: const Key('cart_button'));
 
   @override
   Widget build(BuildContext context) {
+    final numberOfProducts =
+        context.select<CartStore, int>((store) => store.numberOfProducts);
     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 ($numberOfProducts Produkte)'),
     );
   }
 }

lib/screens/product_list/product_item.dart

@@ -1,5 +1,7 @@
 import 'package:flutter/material.dart';
+import 'package:provider/provider.dart';
 import 'package:thesis_shop/models/product.dart';
+import 'package:thesis_shop/store/cart_store.dart';
 import 'package:thesis_shop/widgets/number_picker.dart';
 
 class ProductItem extends StatelessWidget {
@@ -8,9 +10,16 @@ class ProductItem extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
+    final numberOfProduct = context
+        .select<CartStore, int>((store) => store.amountOfProduct(product));
+    final cartStore = context.read<CartStore>();
     return ListTile(
       title: Text('${product.title} (${product.priceAsString}€/Stück)'),
-      trailing: NumberPicker(value: 5, onUp: () {}, onDown: () {}),
+      trailing: NumberPicker(
+        value: numberOfProduct,
+        onUp: () => cartStore.increaseAmount(product),
+        onDown: () => cartStore.decreaseAmount(product),
+      ),
     );
   }
 }

lib/store/cart_store.dart

@@ -0,0 +1,77 @@
+import 'package:flutter/material.dart';
+import 'package:provider/provider.dart';
+import 'package:thesis_shop/models/cart_item.dart';
+import 'package:thesis_shop/models/product.dart';
+import 'package:thesis_shop/models/remote_resource.dart';
+import 'package:thesis_shop/store/product_store.dart';
+
+class CartStore extends ChangeNotifier {
+  List<CartItem> _cart = [];
+  List<CartItem> get cart => _cart;
+
+  int get numberOfProducts => _cart.length;
+  double get totalPrice => _cart.fold<double>(
+        0.0,
+        (value, item) => value + item.product.price * item.amount,
+      );
+
+  int amountOfProduct(Product product) => cart
+      .firstWhere((item) => product == item.product,
+          orElse: () => CartItem(product: product, amount: 0))
+      .amount;
+
+  void updateProductList(RemoteResource<List<Product>> remoteProducts) {
+    if (remoteProducts is LoadingRemoteResource) {
+      return;
+    }
+    late final List<Product> products;
+    if (remoteProducts is ErrorRemoteResource) {
+      products = [];
+    } else {
+      products = remoteProducts.asFinished().value;
+    }
+    final productsByKey = {
+      for (final product in products) product.title: product,
+    };
+    _cart = _cart
+        .where((item) => productsByKey.containsKey(item.product.title))
+        .map((item) => CartItem(
+            product: productsByKey[item.product.title]!, amount: item.amount))
+        .toList();
+    notifyListeners();
+  }
+
+  void _addAmount(Product product, int amount) {
+    final old = _cart.cast<CartItem?>().firstWhere(
+        (item) => item?.product.title == product.title,
+        orElse: () => null);
+    if (old == null) {
+      if (amount <= 0) return;
+      _cart = _cart..add(CartItem(product: product, amount: amount));
+      notifyListeners();
+      return;
+    }
+    if (old.amount + amount < 0) return;
+    final newItem = CartItem(product: product, amount: old.amount + amount);
+    _cart = _cart
+        .map(
+          (item) => item.product.title == product.title ? newItem : item,
+        )
+        .toList();
+    notifyListeners();
+  }
+
+  void increaseAmount(Product product) => _addAmount(product, 1);
+  void decreaseAmount(Product product) => _addAmount(product, -1);
+}
+
+class CartStoreProvider
+    extends ChangeNotifierProxyProvider<ProductStore, CartStore> {
+  CartStoreProvider({Key? key, Widget? child})
+      : super(
+            key: key,
+            child: child,
+            create: (context) => CartStore(),
+            update: (context, productStore, cartStore) =>
+                cartStore!..updateProductList(productStore.products));
+}