Resolves #412 Add 'Support app development' option

lib/pages/purchase.page.dart

@@ -0,0 +1,107 @@
+part of '../main.dart';
+
+class PurchasePage extends StatefulWidget {
+  PurchasePage({Key key, this.title}) : super(key: key);
+
+  final String title;
+
+  @override
+  _PurchasePageState createState() => new _PurchasePageState();
+}
+
+class _PurchasePageState extends State<PurchasePage> {
+  
+  bool _loaded = false;
+  String _error = "";
+  List<ProductDetails> _products;
+  List<PurchaseDetails> _purchases;
+
+  @override
+  void initState() {
+    super.initState();
+    _loadProducts();
+  }
+
+  _loadProducts() async {
+    final bool available = await InAppPurchaseConnection.instance.isAvailable();
+    if (!available) {
+      setState(() {
+        _error = "Error connecting to store";
+      });
+    } else {
+      const Set<String> _kIds = {'just_few_bucks', 'flat_white_a_month', 'lunch_a_year', 'lunch_a_month'};
+      final ProductDetailsResponse response = await InAppPurchaseConnection.instance.queryProductDetails(_kIds);
+      if (!response.notFoundIDs.isEmpty) {
+        Logger.d("Products not found: ${response.notFoundIDs}");
+      }
+      _products = response.productDetails;
+      _loadPreviousPurchases();
+    }
+  }
+
+  _loadPreviousPurchases() async {
+    final QueryPurchaseDetailsResponse response = await InAppPurchaseConnection.instance.queryPastPurchases();
+    if (response.error != null) {
+      setState(() {
+        _error = "Error loading previous purchases";
+      });
+    } else {
+      _purchases = response.pastPurchases;
+      for (PurchaseDetails purchase in _purchases) {
+        Logger.d("Previous purchase: ${purchase.status}");
+      }
+      if (_products.isEmpty) {
+        setState(() {
+          _error = "No data found in store";
+        });
+      } else {
+        setState(() {
+          _loaded = true;
+        });
+      }
+    }
+  }
+  
+  Widget _buildProducts() {
+    List<Widget> productWidgets = [];
+    for (ProductDetails product in _products) {
+      productWidgets.add(
+        ProductPurchase(
+          product: product,
+          onBuy: (product) => _buyProduct(product),
+          purchased: _purchases.any((purchase) { return purchase.productID == product.id;}),)
+      );
+    }
+    return ListView(
+        scrollDirection: Axis.vertical,
+        children: productWidgets
+      );
+  }
+
+  void _buyProduct(ProductDetails product) {
+    Logger.d("Starting purchase of ${product.id}");
+    final PurchaseParam purchaseParam = PurchaseParam(productDetails: product);
+    InAppPurchaseConnection.instance.buyNonConsumable(purchaseParam: purchaseParam);
+    Navigator.of(context).pop();
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    Widget body;
+    if (!_loaded) {
+      body = _error.isEmpty ? PageLoadingIndicator() : PageLoadingError(errorText: _error);
+    } else {
+      body = _buildProducts();
+    }
+    return new Scaffold(
+      appBar: new AppBar(
+        leading: IconButton(icon: Icon(Icons.arrow_back), onPressed: (){
+          Navigator.pop(context);
+        }),
+        title: new Text(widget.title),
+      ),
+      body: body,
+    );
+  }
+  
+}