Add game_template (#1180)

Adds a template / sample for games built in Flutter, with all the bells and whistles, like ads, in-app purchases, audio, main menu, settings, and so on.

Co-authored-by: Parker Lougheed
Co-authored-by: Shams Zakhour

game_template/lib/src/in_app_purchase/ad_removal.dart

@@ -0,0 +1,41 @@
+// Copyright 2022, the Flutter project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// Represents the state of an in-app purchase of ad removal such as
+/// [AdRemovalPurchase.notStarted()] or [AdRemovalPurchase.active()].
+class AdRemovalPurchase {
+  /// The representation of this product on the stores.
+  static const productId = 'remove_ads';
+
+  /// This is `true` if the `remove_ad` product has been purchased and verified.
+  /// Do not show ads if so.
+  final bool active;
+
+  /// This is `true` when the purchase is pending.
+  final bool pending;
+
+  /// If there was an error with the purchase, this field will contain
+  /// that error.
+  final Object? error;
+
+  const AdRemovalPurchase.active() : this._(true, false, null);
+
+  const AdRemovalPurchase.error(Object error) : this._(false, false, error);
+
+  const AdRemovalPurchase.notStarted() : this._(false, false, null);
+
+  const AdRemovalPurchase.pending() : this._(false, true, null);
+
+  const AdRemovalPurchase._(this.active, this.pending, this.error);
+
+  @override
+  int get hashCode => Object.hash(active, pending, error);
+
+  @override
+  bool operator ==(Object other) =>
+      other is AdRemovalPurchase &&
+      other.active == active &&
+      other.pending == pending &&
+      other.error == error;
+}

game_template/lib/src/in_app_purchase/in_app_purchase.dart

@@ -0,0 +1,193 @@
+// Copyright 2022, the Flutter project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:flutter/foundation.dart';
+import 'package:in_app_purchase/in_app_purchase.dart';
+import 'package:logging/logging.dart';
+
+import '../style/snack_bar.dart';
+import 'ad_removal.dart';
+
+/// Allows buying in-app. Facade of `package:in_app_purchase`.
+class InAppPurchaseController extends ChangeNotifier {
+  static final Logger _log = Logger('InAppPurchases');
+
+  StreamSubscription<List<PurchaseDetails>>? _subscription;
+
+  InAppPurchase inAppPurchaseInstance;
+
+  AdRemovalPurchase _adRemoval = const AdRemovalPurchase.notStarted();
+
+  /// Creates a new [InAppPurchaseController] with an injected
+  /// [InAppPurchase] instance.
+  ///
+  /// Example usage:
+  ///
+  ///     var controller = InAppPurchaseController(InAppPurchase.instance);
+  InAppPurchaseController(this.inAppPurchaseInstance);
+
+  /// The current state of the ad removal purchase.
+  AdRemovalPurchase get adRemoval => _adRemoval;
+
+  /// Launches the platform UI for buying an in-app purchase.
+  ///
+  /// Currently, the only supported in-app purchase is ad removal.
+  /// To support more, ad additional classes similar to [AdRemovalPurchase]
+  /// and modify this method.
+  Future<void> buy() async {
+    if (!await inAppPurchaseInstance.isAvailable()) {
+      _reportError('InAppPurchase.instance not available');
+      return;
+    }
+
+    _adRemoval = const AdRemovalPurchase.pending();
+    notifyListeners();
+
+    _log.info('Querying the store with queryProductDetails()');
+    final response = await inAppPurchaseInstance
+        .queryProductDetails({AdRemovalPurchase.productId});
+
+    if (response.error != null) {
+      _reportError('There was an error when making the purchase: '
+          '${response.error}');
+      return;
+    }
+
+    if (response.productDetails.length != 1) {
+      _log.info(
+        'Products in response: '
+        '${response.productDetails.map((e) => '${e.id}: ${e.title}, ').join()}',
+      );
+      _reportError('There was an error when making the purchase: '
+          'product ${AdRemovalPurchase.productId} does not exist?');
+      return;
+    }
+    final productDetails = response.productDetails.single;
+
+    _log.info('Making the purchase');
+    final purchaseParam = PurchaseParam(productDetails: productDetails);
+    try {
+      final success = await inAppPurchaseInstance.buyNonConsumable(
+          purchaseParam: purchaseParam);
+      _log.info('buyNonConsumable() request was sent with success: $success');
+      // The result of the purchase will be reported in the purchaseStream,
+      // which is handled in [_listenToPurchaseUpdated].
+    } catch (e) {
+      _log.severe(
+          'Problem with calling inAppPurchaseInstance.buyNonConsumable(): '
+          '$e');
+    }
+  }
+
+  @override
+  void dispose() {
+    _subscription?.cancel();
+    super.dispose();
+  }
+
+  /// Asks the underlying platform to list purchases that have been already
+  /// made (for example, in a previous session of the game).
+  Future<void> restorePurchases() async {
+    if (!await inAppPurchaseInstance.isAvailable()) {
+      _reportError('InAppPurchase.instance not available');
+      return;
+    }
+
+    try {
+      await inAppPurchaseInstance.restorePurchases();
+    } catch (e) {
+      _log.severe('Could not restore in-app purchases: $e');
+    }
+    _log.info('In-app purchases restored');
+  }
+
+  /// Subscribes to the [inAppPurchaseInstance.purchaseStream].
+  void subscribe() {
+    _subscription?.cancel();
+    _subscription =
+        inAppPurchaseInstance.purchaseStream.listen((purchaseDetailsList) {
+      _listenToPurchaseUpdated(purchaseDetailsList);
+    }, onDone: () {
+      _subscription?.cancel();
+    }, onError: (dynamic error) {
+      _log.severe('Error occurred on the purchaseStream: $error');
+    });
+  }
+
+  Future<void> _listenToPurchaseUpdated(
+      List<PurchaseDetails> purchaseDetailsList) async {
+    for (final purchaseDetails in purchaseDetailsList) {
+      _log.info(() => 'New PurchaseDetails instance received: '
+          'productID=${purchaseDetails.productID}, '
+          'status=${purchaseDetails.status}, '
+          'purchaseID=${purchaseDetails.purchaseID}, '
+          'error=${purchaseDetails.error}, '
+          'pendingCompletePurchase=${purchaseDetails.pendingCompletePurchase}');
+
+      if (purchaseDetails.productID != AdRemovalPurchase.productId) {
+        _log.severe("The handling of the product with id "
+            "'${purchaseDetails.productID}' is not implemented.");
+        _adRemoval = const AdRemovalPurchase.notStarted();
+        notifyListeners();
+        continue;
+      }
+
+      switch (purchaseDetails.status) {
+        case PurchaseStatus.pending:
+          _adRemoval = const AdRemovalPurchase.pending();
+          notifyListeners();
+          break;
+        case PurchaseStatus.purchased:
+        case PurchaseStatus.restored:
+          bool valid = await _verifyPurchase(purchaseDetails);
+          if (valid) {
+            _adRemoval = const AdRemovalPurchase.active();
+            if (purchaseDetails.status == PurchaseStatus.purchased) {
+              showSnackBar('Thank you for your support!');
+            }
+            notifyListeners();
+          } else {
+            _log.severe('Purchase verification failed: $purchaseDetails');
+            _adRemoval = AdRemovalPurchase.error(
+                StateError('Purchase could not be verified'));
+            notifyListeners();
+          }
+          break;
+        case PurchaseStatus.error:
+          _log.severe('Error with purchase: ${purchaseDetails.error}');
+          _adRemoval = AdRemovalPurchase.error(purchaseDetails.error!);
+          notifyListeners();
+          break;
+        case PurchaseStatus.canceled:
+          _adRemoval = const AdRemovalPurchase.notStarted();
+          notifyListeners();
+          break;
+      }
+
+      if (purchaseDetails.pendingCompletePurchase) {
+        // Confirm purchase back to the store.
+        await inAppPurchaseInstance.completePurchase(purchaseDetails);
+      }
+    }
+  }
+
+  void _reportError(String message) {
+    _log.severe(message);
+    showSnackBar(message);
+    _adRemoval = AdRemovalPurchase.error(message);
+    notifyListeners();
+  }
+
+  Future<bool> _verifyPurchase(PurchaseDetails purchaseDetails) async {
+    _log.info('Verifying purchase: ${purchaseDetails.verificationData}');
+    // TODO: verify the purchase.
+    // See the info in [purchaseDetails.verificationData] to learn more.
+    // There's also a codelab that explains purchase verification
+    // on the backend:
+    // https://codelabs.developers.google.com/codelabs/flutter-in-app-purchases#9
+    return true;
+  }
+}