[web_dashboard] add logout (#447)

* logout wip

* Use AnimatedSwitcher, change lingo from "login" to signIn"

* add automatic sign-in

* fix flashing sign in button

* sign out of FirebaseAuth and GoogleSignIn

* formatting

* change isSignedIn() to getter

* Add error handling for sign in

* improve error handling at login screen

experimental/web_dashboard/lib/src/app.dart

@@ -23,7 +23,9 @@ class AppState {
   AppState(this.auth);
 }
 
-/// Creates a [DashboardApi] when the user is logged in.
+/// Creates a [DashboardApi] for the given user. This allows users of this
+/// widget to specify whether [MockDashboardApi] or [ApiBuilder] should be
+/// created when the user logs in.
 typedef DashboardApi ApiBuilder(User user);
 
 /// An app that displays a personalized dashboard.
@@ -63,41 +65,62 @@ class _DashboardAppState extends State<DashboardApp> {
     return Provider.value(
       value: _appState,
       child: MaterialApp(
-        home: Builder(
-          builder: (context) => SignInPage(
-            auth: _appState.auth,
-            onSuccess: (user) => _handleSignIn(user, context, _appState),
-          ),
+        home: SignInSwitcher(
+          appState: _appState,
+          apiBuilder: widget.apiBuilder,
         ),
       ),
     );
   }
+}
 
-  /// Sets the DashboardApi on AppState and navigates to the home page.
-  void _handleSignIn(User user, BuildContext context, AppState appState) {
-    appState.api = widget.apiBuilder(user);
+/// Switches between showing the [SignInPage] or [HomePage], depending on
+/// whether or not the user is signed in.
+class SignInSwitcher extends StatefulWidget {
+  final AppState appState;
+  final ApiBuilder apiBuilder;
 
-    _showPage(HomePage(), context);
-  }
+  SignInSwitcher({
+    this.appState,
+    this.apiBuilder,
+  });
 
-  /// Navigates to the home page using a fade transition.
-  void _showPage(Widget page, BuildContext context) {
-    var route = _fadeRoute(page);
-    Navigator.of(context).pushReplacement(route);
-  }
+  @override
+  _SignInSwitcherState createState() => _SignInSwitcherState();
+}
 
-  /// Creates a [Route] that shows [newPage] using a fade transition.
-  Route<FadeTransition> _fadeRoute(Widget newPage) {
-    return PageRouteBuilder<FadeTransition>(
-      pageBuilder: (context, animation, secondaryAnimation) {
-        return newPage;
-      },
-      transitionsBuilder: (context, animation, secondaryAnimation, child) {
-        return FadeTransition(
-          opacity: animation.drive(CurveTween(curve: Curves.ease)),
-          child: child,
-        );
-      },
+class _SignInSwitcherState extends State<SignInSwitcher> {
+  bool _isSignedIn = false;
+
+  @override
+  Widget build(BuildContext context) {
+    return AnimatedSwitcher(
+      switchInCurve: Curves.easeOut,
+      switchOutCurve: Curves.easeOut,
+      duration: Duration(milliseconds: 200),
+      child: _isSignedIn
+          ? HomePage(
+              onSignOut: _handleSignOut,
+            )
+          : SignInPage(
+              auth: widget.appState.auth,
+              onSuccess: _handleSignIn,
+            ),
     );
   }
+
+  void _handleSignIn(User user) {
+    widget.appState.api = widget.apiBuilder(user);
+
+    setState(() {
+      _isSignedIn = true;
+    });
+  }
+
+  Future _handleSignOut() async {
+    await widget.appState.auth.signOut();
+    setState(() {
+      _isSignedIn = false;
+    });
+  }
 }

experimental/web_dashboard/lib/src/auth/auth.dart

@@ -3,6 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 abstract class Auth {
+  Future<bool> get isSignedIn;
   Future<User> signIn();
   Future signOut();
 }
@@ -10,3 +11,5 @@ abstract class Auth {
 abstract class User {
   String get uid;
 }
+
+class SignInException implements Exception {}

experimental/web_dashboard/lib/src/auth/firebase.dart

@@ -2,6 +2,7 @@
 // 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 'package:flutter/services.dart';
 import 'package:google_sign_in/google_sign_in.dart';
 import 'package:firebase_auth/firebase_auth.dart' hide FirebaseUser;
 
@@ -11,9 +12,20 @@ class FirebaseAuthService implements Auth {
   final GoogleSignIn _googleSignIn = GoogleSignIn();
   final FirebaseAuth _auth = FirebaseAuth.instance;
 
+  Future<bool> get isSignedIn => _googleSignIn.isSignedIn();
+
   Future<User> signIn() async {
+    try {
+      return await _signIn();
+    } on PlatformException catch (e) {
+      print('Unable to sign in: $e');
+      throw SignInException();
+    }
+  }
+
+  Future<User> _signIn() async {
     GoogleSignInAccount googleUser;
-    if (await _googleSignIn.isSignedIn()) {
+    if (await isSignedIn) {
       googleUser = await _googleSignIn.signInSilently();
     } else {
       googleUser = await _googleSignIn.signIn();
@@ -30,7 +42,10 @@ class FirebaseAuthService implements Auth {
   }
 
   Future<void> signOut() async {
-    await _auth.signOut();
+    await Future.wait([
+      _auth.signOut(),
+      _googleSignIn.signOut(),
+    ]);
   }
 }
 
@@ -39,3 +54,4 @@ class _FirebaseUser implements User {
 
   _FirebaseUser(this.uid);
 }
+

experimental/web_dashboard/lib/src/auth/mock.dart

@@ -2,11 +2,20 @@
 // 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:math';
+
 import 'auth.dart';
 
 class MockAuthService implements Auth {
+  Future<bool> get isSignedIn async => false;
+
   @override
   Future<User> signIn() async {
+    // Sign in will randomly fail 25% of the time.
+    var random = Random();
+    if (random.nextInt(4) == 0)  {
+      throw SignInException();
+    }
     return MockUser();
   }
 

experimental/web_dashboard/lib/src/pages/home.dart

@@ -10,6 +10,12 @@ import 'dashboard.dart';
 import 'entries.dart';
 
 class HomePage extends StatefulWidget {
+  final VoidCallback onSignOut;
+
+  HomePage({
+    @required this.onSignOut,
+  });
+
   @override
   _HomePageState createState() => _HomePageState();
 }
@@ -20,6 +26,17 @@ class _HomePageState extends State<HomePage> {
   @override
   Widget build(BuildContext context) {
     return AdaptiveScaffold(
+      title: Text('Dashboard App'),
+      actions: [
+        Padding(
+          padding: const EdgeInsets.all(8.0),
+          child: FlatButton(
+            textColor: Colors.white,
+            onPressed: () => _handleSignOut(),
+            child: Text('Sign Out'),
+          ),
+        )
+      ],
       currentIndex: _pageIndex,
       destinations: [
         AdaptiveScaffoldDestination(title: 'Home', icon: Icons.home),
@@ -67,7 +84,36 @@ class _HomePageState extends State<HomePage> {
     }
   }
 
-  Widget _pageAtIndex(int index) {
+  Future<void> _handleSignOut() async {
+    var shouldSignOut = await showDialog<bool>(
+      context: context,
+      builder: (context) => AlertDialog(
+        title: Text('Are you sure you want to sign out?'),
+        actions: [
+          FlatButton(
+            child: Text('No'),
+            onPressed: () {
+              Navigator.of(context).pop(false);
+            },
+          ),
+          FlatButton(
+            child: Text('Yes'),
+            onPressed: () {
+              Navigator.of(context).pop(true);
+            },
+          ),
+        ],
+      ),
+    );
+
+    if (!shouldSignOut) {
+      return;
+    }
+
+    widget.onSignOut();
+  }
+
+  static Widget _pageAtIndex(int index) {
     if (index == 0) {
       return DashboardPage();
     }

experimental/web_dashboard/lib/src/pages/sign_in.dart

@@ -6,7 +6,7 @@ import 'package:flutter/material.dart';
 
 import '../auth/auth.dart';
 
-class SignInPage extends StatefulWidget {
+class SignInPage extends StatelessWidget {
   final Auth auth;
   final ValueChanged<User> onSuccess;
 
@@ -15,31 +15,89 @@ class SignInPage extends StatefulWidget {
     @required this.onSuccess,
   });
 
-  @override
-  _SignInPageState createState() => _SignInPageState();
-}
-
-class _SignInPageState extends State<SignInPage> {
-  @override
-  void initState() {
-    super.initState();
-  }
-
   @override
   Widget build(BuildContext context) {
     return Scaffold(
       body: Center(
-        child: RaisedButton(
-          child: Text('Sign In'),
-          onPressed: () async {
-            var user = await widget.auth.signIn();
-            if (user != null) {
-              widget.onSuccess(user);
-            } else {
-              throw ('Unable to sign in');
-            }
-          },
-        ),
+        child: SignInButton(auth: auth, onSuccess: onSuccess),
+      ),
+    );
+  }
+}
+
+class SignInButton extends StatefulWidget {
+  final Auth auth;
+  final ValueChanged<User> onSuccess;
+
+  SignInButton({
+    @required this.auth,
+    @required this.onSuccess,
+  });
+
+  @override
+  _SignInButtonState createState() => _SignInButtonState();
+}
+
+class _SignInButtonState extends State<SignInButton> {
+  Future<bool> _checkSignInFuture;
+
+  @override
+  void initState() {
+    super.initState();
+    _checkSignInFuture = _checkIfSignedIn();
+  }
+
+  // Check if the user is signed in. If the user is already signed in (for
+  // example, if they signed in and refreshed the page), invoke the `onSuccess`
+  // callback right away.
+  Future<bool> _checkIfSignedIn() async {
+    var alreadySignedIn = await widget.auth.isSignedIn;
+    if (alreadySignedIn) {
+      var user = await widget.auth.signIn();
+      widget.onSuccess(user);
+    }
+    return alreadySignedIn;
+  }
+
+  Future<void> _signIn() async {
+    try {
+      var user = await widget.auth.signIn();
+      widget.onSuccess(user);
+    } on SignInException {
+      _showError();
+    }
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return FutureBuilder<bool>(
+      future: _checkSignInFuture,
+      builder: (context, snapshot) {
+        // If signed in, or the future is incomplete, show a circular
+        // progress indicator.
+        var alreadySignedIn = snapshot.data;
+        if (snapshot.connectionState != ConnectionState.done ||
+            alreadySignedIn == true) {
+          return CircularProgressIndicator();
+        }
+
+        // If sign in failed, show toast and the login button
+        if (snapshot.hasError) {
+          _showError();
+        }
+
+        return RaisedButton(
+          child: Text('Sign In with Google'),
+          onPressed: () => _signIn(),
+        );
+      },
+    );
+  }
+
+  void _showError() {
+    Scaffold.of(context).showSnackBar(
+      SnackBar(
+        content: Text('Unable to sign in.'),
       ),
     );
   }

experimental/web_dashboard/lib/src/widgets/third_party/adaptive_scaffold.dart

@@ -28,6 +28,7 @@ class AdaptiveScaffoldDestination {
 /// defined in the [destinations] parameter.
 class AdaptiveScaffold extends StatefulWidget {
   final Widget title;
+  final List<Widget> actions;
   final Widget body;
   final int currentIndex;
   final List<AdaptiveScaffoldDestination> destinations;
@@ -37,6 +38,7 @@ class AdaptiveScaffold extends StatefulWidget {
   AdaptiveScaffold({
     this.title,
     this.body,
+    this.actions = const [],
     @required this.currentIndex,
     @required this.destinations,
     this.onNavigationIndexChange,
@@ -80,7 +82,9 @@ class _AdaptiveScaffoldState extends State<AdaptiveScaffold> {
           ),
           Expanded(
             child: Scaffold(
-              appBar: AppBar(),
+              appBar: AppBar(
+                actions: widget.actions,
+              ),
               body: widget.body,
               floatingActionButton: widget.floatingActionButton,
             ),
@@ -94,6 +98,7 @@ class _AdaptiveScaffoldState extends State<AdaptiveScaffold> {
       return Scaffold(
         appBar: AppBar(
           title: widget.title,
+          actions: widget.actions,
         ),
         body: Row(
           children: [
@@ -126,7 +131,10 @@ class _AdaptiveScaffoldState extends State<AdaptiveScaffold> {
     // Show a bottom app bar
     return Scaffold(
       body: widget.body,
-      appBar: AppBar(title: widget.title),
+      appBar: AppBar(
+        title: widget.title,
+        actions: widget.actions,
+      ),
       bottomNavigationBar: BottomNavigationBar(
         items: [
           ...widget.destinations.map(