Initial commit

lib/app.dart

@@ -0,0 +1,78 @@
+import 'package:flutter/material.dart';
+
+import 'backend.dart';
+import 'screens/home.dart';
+import 'widgets/player_bar.dart';
+
+class App extends StatefulWidget {
+  @override
+  _AppState createState() => _AppState();
+}
+
+class _AppState extends State<App> with SingleTickerProviderStateMixin {
+  final nestedNavigator = GlobalKey<NavigatorState>();
+
+  AnimationController playerBarAnimation;
+  Backend backend;
+
+  @override
+  void initState() {
+    super.initState();
+
+    playerBarAnimation = AnimationController(
+      vsync: this,
+      duration: Duration(milliseconds: 300),
+    );
+  }
+
+  @override
+  void didChangeDependencies() {
+    super.didChangeDependencies();
+
+    backend = Backend.of(context);
+    backend.playerActive.listen((active) =>
+        active ? playerBarAnimation.forward() : playerBarAnimation.reverse());
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return MaterialApp(
+      title: 'Musicus',
+      theme: ThemeData(
+        brightness: Brightness.dark,
+        accentColor: Colors.amber,
+        textSelectionColor: Colors.grey[600],
+        cursorColor: Colors.amber,
+        textSelectionHandleColor: Colors.amber,
+        toggleableActiveColor: Colors.amber,
+        fontFamily: 'Libertinus Sans',
+      ),
+      // The nested Navigator is for every screen from which the player bar at
+      // the bottom should be accessible. The WillPopScope widget intercepts
+      // taps on the system back button and redirects them to the nested
+      // navigator.
+      home: WillPopScope(
+        onWillPop: () async => !(await nestedNavigator.currentState.maybePop()),
+        child: Scaffold(
+          body: Navigator(
+            key: nestedNavigator,
+            onGenerateRoute: (settings) => settings.name == '/'
+                ? MaterialPageRoute(
+                    builder: (context) => HomeScreen(),
+                  )
+                : null,
+            initialRoute: '/',
+          ),
+          bottomNavigationBar: SizeTransition(
+            sizeFactor: CurvedAnimation(
+              curve: Curves.easeOut,
+              parent: playerBarAnimation,
+            ),
+            axisAlignment: -1.0,
+            child: PlayerBar(),
+          ),
+        ),
+      ),
+    );
+  }
+}

lib/backend.dart

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+import 'package:flutter/widgets.dart';
+import 'package:rxdart/rxdart.dart';
+
+class Backend extends InheritedWidget {
+  static Backend of(BuildContext context) =>
+      context.inheritFromWidgetOfExactType(Backend);
+
+  final Widget child;
+
+  final playerActive = BehaviorSubject.seeded(false);
+  final playing = BehaviorSubject.seeded(false);
+  final position = BehaviorSubject.seeded(0.0);
+
+  Backend({
+    @required this.child,
+  }) : super(child: child);
+
+  void startPlayer() {
+    playerActive.add(true);
+  }
+
+  void playPause() {
+    playing.add(!playing.value);
+    if (playing.value) {
+      simulatePlay();
+    }
+  }
+
+  void seekTo(double pos) {
+    position.add(pos);
+  }
+
+  Future<void> simulatePlay() async {
+    while (playing.value) {
+      await Future.delayed(Duration(milliseconds: 200));
+      if (position.value >= 0.99) {
+        position.add(0.0);
+      } else {
+        position.add(position.value + 0.01);
+      }
+    }
+  }
+
+  @override
+  bool updateShouldNotify(Backend old) =>
+      playerActive != old.playerActive ||
+      playing != old.playing ||
+      position != old.position;
+}

lib/main.dart

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+import 'package:flutter/widgets.dart';
+
+import 'app.dart';
+import 'backend.dart';
+
+void main() {
+  runApp(Backend(
+    child: App(),
+  ));
+}

lib/screens/home.dart

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+import 'package:flutter/material.dart';
+
+import '../backend.dart';
+
+class HomeScreen extends StatelessWidget {
+  @override
+  Widget build(BuildContext context) {
+    final backend = Backend.of(context);
+
+    return Scaffold(
+      appBar: AppBar(
+        title: Text('Musicus'),
+      ),
+      // For debugging purposes
+      body: ListView(
+        children: <Widget>[
+          ListTile(
+            title: Text('Start player'),
+            onTap: backend.startPlayer,
+          ),
+          ListTile(
+            title: Text('Play/Pause'),
+            onTap: backend.playPause,
+          ),
+        ],
+      ),
+    );
+  }
+}

lib/screens/program.dart

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+import 'package:flutter/material.dart';
+
+class ProgramScreen extends StatelessWidget {
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      appBar: AppBar(
+        leading: IconButton(
+          icon: const Icon(Icons.keyboard_arrow_down),
+          onPressed: () => Navigator.pop(context),
+        ),
+        title: Text('Program'),
+      ),
+    );
+  }
+}

lib/widgets/play_pause_button.dart

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+import 'package:flutter/material.dart';
+
+import '../backend.dart';
+
+class PlayPauseButton extends StatefulWidget {
+  @override
+  _PlayPauseButtonState createState() => _PlayPauseButtonState();
+}
+
+class _PlayPauseButtonState extends State<PlayPauseButton>
+    with SingleTickerProviderStateMixin {
+  AnimationController playPauseAnimation;
+  Backend backend;
+
+  @override
+  void initState() {
+    super.initState();
+
+    playPauseAnimation =
+        AnimationController(vsync: this, duration: Duration(milliseconds: 300));
+  }
+
+  @override
+  void didChangeDependencies() {
+    super.didChangeDependencies();
+
+    backend = Backend.of(context);
+    backend.playing.listen((playing) =>
+        playing ? playPauseAnimation.forward() : playPauseAnimation.reverse());
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return IconButton(
+      icon: AnimatedIcon(
+        icon: AnimatedIcons.play_pause,
+        progress: playPauseAnimation,
+      ),
+      onPressed: backend.playPause,
+    );
+  }
+}

lib/widgets/player_bar.dart

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+import 'package:flutter/material.dart';
+
+import '../backend.dart';
+import '../screens/program.dart';
+
+import 'play_pause_button.dart';
+
+class PlayerBar extends StatelessWidget {
+  @override
+  Widget build(BuildContext context) {
+    final backend = Backend.of(context);
+
+    return BottomAppBar(
+      child: InkWell(
+        child: Column(
+          mainAxisSize: MainAxisSize.min,
+          children: <Widget>[
+            StreamBuilder(
+              stream: backend.position,
+              builder: (context, snapshot) => LinearProgressIndicator(
+                value: snapshot.data,
+              ),
+            ),
+            Row(
+              children: <Widget>[
+                Padding(
+                  padding: const EdgeInsets.all(8.0),
+                  child: Icon(Icons.keyboard_arrow_up),
+                ),
+                Expanded(
+                  child: Column(
+                    crossAxisAlignment: CrossAxisAlignment.start,
+                    children: <Widget>[
+                      Text(
+                        'Composer',
+                        style: TextStyle(fontWeight: FontWeight.bold),
+                      ),
+                      Text('Work: Movement'),
+                    ],
+                  ),
+                ),
+                PlayPauseButton(),
+              ],
+            ),
+          ],
+        ),
+        onTap: () => Navigator.push(
+          context,
+          MaterialPageRoute(
+            builder: (context) => ProgramScreen(),
+          ),
+        ),
+      ),
+    );
+  }
+}