PurchaseScreen: Move to purchasing code to its own widget

All of this is way too complicated

lib/screens/purchase_screen.dart

@@ -12,84 +12,8 @@ import 'package:gitjournal/settings.dart';
 
 import 'package:purchases_flutter/purchases_flutter.dart';
 
-class PurchaseScreen extends StatefulWidget {
-  @override
-  _PurchaseScreenState createState() => _PurchaseScreenState();
-}
-
-class _PurchaseScreenState extends State<PurchaseScreen> {
-  List<Offering> _offerings;
-  Offering _selectedOffering;
-  var _scaffoldKey = GlobalKey<ScaffoldState>();
-
-  @override
-  void initState() {
-    super.initState();
-    initPlatformState();
-  }
-
-  Future<void> initPlatformState() async {
-    await InAppPurchases.confirmProPurchase();
-    if (Settings.instance.proMode) {
-      Navigator.of(context).pop();
-    }
-
-    await Purchases.setup(
-      environment['revenueCat'],
-      appUserId: Settings.instance.pseudoId,
-    );
-
-    Offerings offerings;
-    try {
-      offerings = await Purchases.getOfferings();
-    } catch (e) {
-      if (e is PlatformException) {
-        var snackBar = SnackBar(content: Text(e.message));
-        _scaffoldKey.currentState
-          ..removeCurrentSnackBar()
-          ..showSnackBar(snackBar);
-        return;
-      }
-    }
-    var offeringList = offerings.all.values.toList();
-    offeringList.retainWhere((Offering o) => o.identifier.contains("monthly"));
-    offeringList.sort((Offering a, Offering b) =>
-        a.monthly.product.price.compareTo(b.monthly.product.price));
-    print("Offerings: $offeringList");
-
-    // If the widget was removed from the tree while the asynchronous platform
-    // message was in flight, we want to discard the reply rather than calling
-    // setState to update our non-existent appearance.
-    if (!mounted) return;
-
-    setState(() {
-      _offerings = offeringList;
-      _selectedOffering = _offerings.isNotEmpty ? _offerings.first : null;
-
-      if (_offerings.length > 1) {
-        _selectedOffering = _offerings[1];
-      } else {
-        var fakePackageJson = {
-          'identifier': 'monthly_fake',
-          'product': {
-            'identifier': 'fake_product',
-            'title': 'Fake Product',
-            'priceString': '0 Fake',
-            'price': 0.0,
-          },
-        };
-
-        var fakeOffer = Offering.fromJson(<String, dynamic>{
-          'identifier': 'monthly_fake_offering',
-          'monthly': fakePackageJson,
-          'availablePackages': [fakePackageJson],
-        });
-
-        _offerings = [fakeOffer];
-        _selectedOffering = _offerings[0];
-      }
-    });
-  }
+class PurchaseScreen extends StatelessWidget {
+  final _scaffoldKey = GlobalKey<ScaffoldState>();
 
   @override
   Widget build(BuildContext context) {
@@ -97,7 +21,7 @@ class _PurchaseScreenState extends State<PurchaseScreen> {
       child: Scaffold(
         key: _scaffoldKey,
         appBar: EmptyAppBar(),
-        body: _offerings == null ? const LoadingWidget() : buildBody(context),
+        body: buildBody(context),
       ),
       onWillPop: _onWillPop,
     );
@@ -150,36 +74,6 @@ class _PurchaseScreenState extends State<PurchaseScreen> {
 
     var titleStyle =
         textTheme.headline3.copyWith(color: textTheme.headline6.color);
-    var slider = Slider(
-      min: _offerings.first.monthly.product.price,
-      max: _offerings.last.monthly.product.price + 0.50,
-      value: _selectedOffering.monthly.product.price,
-      onChanged: (double val) {
-        int i = -1;
-        for (i = 1; i < _offerings.length; i++) {
-          var prev = _offerings[i - 1].monthly.product;
-          var cur = _offerings[i].monthly.product;
-
-          if (prev.price < val && val <= cur.price) {
-            i--;
-            break;
-          }
-        }
-        if (val == _offerings.first.monthly.product.price) {
-          i = 0;
-        } else if (val >= _offerings.last.monthly.product.price) {
-          i = _offerings.length - 1;
-        }
-
-        if (i != -1) {
-          setState(() {
-            _selectedOffering = _offerings[i];
-          });
-        }
-      },
-      label: _selectedOffering.monthly.product.priceString,
-      divisions: _offerings.length,
-    );
 
     Widget w = Column(
       children: <Widget>[
@@ -189,8 +83,7 @@ class _PurchaseScreenState extends State<PurchaseScreen> {
           textAlign: TextAlign.center,
         ),
         body,
-        slider,
-        PurchaseButton(_selectedOffering?.monthly),
+        PurchaseWidget(),
       ],
       mainAxisAlignment: MainAxisAlignment.spaceAround,
     );
@@ -373,3 +266,130 @@ class _SingleChildScrollViewExpanded extends StatelessWidget {
     );
   }
 }
+
+class PurchaseWidget extends StatefulWidget {
+  @override
+  _PurchaseWidgetState createState() => _PurchaseWidgetState();
+}
+
+class _PurchaseWidgetState extends State<PurchaseWidget> {
+  List<Offering> _offerings;
+  Offering _selectedOffering;
+  var _scaffoldKey = GlobalKey<ScaffoldState>();
+
+  @override
+  void initState() {
+    super.initState();
+    initPlatformState();
+  }
+
+  Future<void> initPlatformState() async {
+    await InAppPurchases.confirmProPurchase();
+    if (Settings.instance.proMode) {
+      Navigator.of(context).pop();
+    }
+
+    await Purchases.setup(
+      environment['revenueCat'],
+      appUserId: Settings.instance.pseudoId,
+    );
+
+    Offerings offerings;
+    try {
+      offerings = await Purchases.getOfferings();
+    } catch (e) {
+      if (e is PlatformException) {
+        var snackBar = SnackBar(content: Text(e.message));
+        _scaffoldKey.currentState
+          ..removeCurrentSnackBar()
+          ..showSnackBar(snackBar);
+        return;
+      }
+    }
+    var offeringList = offerings.all.values.toList();
+    offeringList.retainWhere((Offering o) => o.identifier.contains("monthly"));
+    offeringList.sort((Offering a, Offering b) =>
+        a.monthly.product.price.compareTo(b.monthly.product.price));
+    print("Offerings: $offeringList");
+
+    // If the widget was removed from the tree while the asynchronous platform
+    // message was in flight, we want to discard the reply rather than calling
+    // setState to update our non-existent appearance.
+    if (!mounted) return;
+
+    setState(() {
+      _offerings = offeringList;
+      _selectedOffering = _offerings.isNotEmpty ? _offerings.first : null;
+
+      if (_offerings.length > 1) {
+        _selectedOffering = _offerings[1];
+      } else {
+        var fakePackageJson = {
+          'identifier': 'monthly_fake',
+          'product': {
+            'identifier': 'fake_product',
+            'title': 'Fake Product',
+            'priceString': '0 Fake',
+            'price': 0.0,
+          },
+        };
+
+        var fakeOffer = Offering.fromJson(<String, dynamic>{
+          'identifier': 'monthly_fake_offering',
+          'monthly': fakePackageJson,
+          'availablePackages': [fakePackageJson],
+        });
+
+        _offerings = [fakeOffer];
+        _selectedOffering = _offerings[0];
+      }
+    });
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return _offerings == null ? const LoadingWidget() : buildBody(context);
+  }
+
+  Widget buildBody(BuildContext context) {
+    var slider = Slider(
+      min: _offerings.first.monthly.product.price,
+      max: _offerings.last.monthly.product.price + 0.50,
+      value: _selectedOffering.monthly.product.price,
+      onChanged: (double val) {
+        int i = -1;
+        for (i = 1; i < _offerings.length; i++) {
+          var prev = _offerings[i - 1].monthly.product;
+          var cur = _offerings[i].monthly.product;
+
+          if (prev.price < val && val <= cur.price) {
+            i--;
+            break;
+          }
+        }
+        if (val == _offerings.first.monthly.product.price) {
+          i = 0;
+        } else if (val >= _offerings.last.monthly.product.price) {
+          i = _offerings.length - 1;
+        }
+
+        if (i != -1) {
+          setState(() {
+            _selectedOffering = _offerings[i];
+          });
+        }
+      },
+      label: _selectedOffering.monthly.product.priceString,
+      divisions: _offerings.length,
+    );
+
+    return Column(
+      children: <Widget>[
+        slider,
+        const SizedBox(height: 16.0),
+        PurchaseButton(_selectedOffering?.monthly),
+      ],
+      mainAxisAlignment: MainAxisAlignment.spaceAround,
+    );
+  }
+}