Implement product 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/product_store.dart';
 import 'package:thesis_shop/stores/user_store.dart';
 import 'package:thesis_shop/utils/map_keys_extension.dart';
 
@@ -12,7 +13,12 @@ class ThesisShopApp extends StatelessWidget {
       : super(key: key);
 
   Widget injectStores(BuildContext context, {required Widget child}) {
-    return UserStoreImplementation(child: child);
+    return UserStoreImplementation(
+      child: ProductStoreImplementation(
+        productService: productService,
+        child: child,
+      ),
+    );
   }
 
   @override

lib/models/remote_resource.dart

@@ -0,0 +1,38 @@
+abstract class RemoteResource<T> {
+  RemoteResource._();
+
+  factory RemoteResource.loading() {
+    return LoadingRemoteResource();
+  }
+
+  factory RemoteResource.error(String errorMessage) {
+    return ErrorRemoteResource(errorMessage);
+  }
+
+  factory RemoteResource.finished(T value) {
+    return FinishedRemoteResource(value);
+  }
+
+  FinishedRemoteResource<T> asFinished() {
+    return this as FinishedRemoteResource<T>;
+  }
+
+  ErrorRemoteResource<T> asError() {
+    return this as ErrorRemoteResource<T>;
+  }
+}
+
+class ErrorRemoteResource<T> extends RemoteResource<T> {
+  final String errorMessage;
+
+  ErrorRemoteResource(this.errorMessage) : super._();
+}
+
+class LoadingRemoteResource<T> extends RemoteResource<T> {
+  LoadingRemoteResource() : super._();
+}
+
+class FinishedRemoteResource<T> extends RemoteResource<T> {
+  final T value;
+  FinishedRemoteResource(this.value) : super._();
+}

lib/screens/product_list/product_list_screen.dart

@@ -1,31 +1,44 @@
 import 'package:flutter/material.dart';
-import 'package:thesis_shop/models/product.dart';
+import 'package:thesis_shop/models/remote_resource.dart';
+import 'package:thesis_shop/screens/product_list/cart_button_overlay.dart';
+import 'package:thesis_shop/screens/product_list/product_list.dart';
+import 'package:thesis_shop/stores/product_store.dart';
 import 'package:thesis_shop/widgets/user_switch.dart';
 
-import 'cart_button_overlay.dart';
-import 'product_list.dart';
-
-const _productPlaceholder = [
-  Product(title: 'Bananen', price: 3),
-  Product(title: 'Äpfel', price: 2),
-  Product(title: 'Birnen', price: 2.5),
-  Product(title: 'Kirschen', price: 1.2),
-];
-
 class ProductListScreen extends StatelessWidget {
   const ProductListScreen({Key? key}) : super(key: key);
 
   @override
   Widget build(BuildContext context) {
-    const products = _productPlaceholder;
     return Scaffold(
       appBar: AppBar(
         title: const Text('Thesis Shop'),
         actions: const [UserSwitch()],
       ),
-      body: const CartButtonOverlay(
-        child: ProductList(products: products),
-      ),
+      body: const _ProductStateSwitch(),
     );
   }
 }
+
+class _ProductStateSwitch extends StatelessWidget {
+  const _ProductStateSwitch({Key? key}) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    final remoteProducts = ProductStore.of(context).products;
+    if (remoteProducts is FinishedRemoteResource) {
+      final products = remoteProducts.asFinished().value;
+      return CartButtonOverlay(
+        child: ProductList(
+          products: products,
+        ),
+      );
+    } else if (remoteProducts is ErrorRemoteResource) {
+      return Center(child: Text(remoteProducts.asError().errorMessage));
+    } else if (remoteProducts is LoadingRemoteResource) {
+      return const Center(child: CircularProgressIndicator.adaptive());
+    } else {
+      throw UnimplementedError();
+    }
+  }
+}

lib/stores/product_store.dart

@@ -0,0 +1,70 @@
+import 'package:flutter/widgets.dart';
+import 'package:thesis_shop/models/product.dart';
+import 'package:thesis_shop/models/remote_resource.dart';
+import 'package:thesis_shop/service/product_service.dart';
+
+class ProductStoreImplementation extends StatefulWidget {
+  final Widget child;
+  final ProductService productService;
+  const ProductStoreImplementation({
+    Key? key,
+    required this.child,
+    required this.productService,
+  }) : super(key: key);
+
+  @override
+  _ProductStoreImplementationState createState() =>
+      _ProductStoreImplementationState();
+}
+
+class _ProductStoreImplementationState
+    extends State<ProductStoreImplementation> {
+  RemoteResource<List<Product>> products = RemoteResource.loading();
+
+  @override
+  void initState() {
+    super.initState();
+    loadProducts().catchError(
+      (err) => setState(
+        () {
+          products = RemoteResource.error(err.toString());
+        },
+      ),
+    );
+  }
+
+  Future<void> loadProducts() async {
+    final remoteProducts = await widget.productService.fetchProducts();
+    setState(() {
+      products = RemoteResource.finished(remoteProducts);
+    });
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return ProductStore(products: products, child: widget.child);
+  }
+}
+
+class ProductStore extends InheritedWidget {
+  const ProductStore({
+    Key? key,
+    required this.products,
+    required Widget child,
+  }) : super(key: key, child: child);
+
+  final RemoteResource<List<Product>> products;
+  List<Product> get mustProducts => products.asFinished().value;
+
+  static ProductStore of(BuildContext context) {
+    final ProductStore? result =
+        context.dependOnInheritedWidgetOfExactType<ProductStore>();
+    assert(result != null, 'No ProductStore found in context');
+    return result!;
+  }
+
+  @override
+  bool updateShouldNotify(ProductStore oldWidget) {
+    return oldWidget.products != products;
+  }
+}