INFRA: Set Up Project.

lib/widget/story_view/controller/story_controller.dart

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+import 'package:rxdart/rxdart.dart';
+
+enum PlaybackState { pause, play, next, previous }
+
+/// Controller to sync playback between animated child (story) views. This
+/// helps make sure when stories are paused, the animation (gifs/slides) are
+/// also paused.
+/// Another reason for using the controller is to place the stories on `paused`
+/// state when a media is loading.
+class StoryController {
+  /// Stream that broadcasts the playback state of the stories.
+  final playbackNotifier = BehaviorSubject<PlaybackState>();
+
+  /// Notify listeners with a [PlaybackState.pause] state
+  void pause() {
+    playbackNotifier.add(PlaybackState.pause);
+  }
+
+  /// Notify listeners with a [PlaybackState.play] state
+  void play() {
+    playbackNotifier.add(PlaybackState.play);
+  }
+
+  void next() {
+    playbackNotifier.add(PlaybackState.next);
+  }
+
+  void previous() {
+    playbackNotifier.add(PlaybackState.previous);
+  }
+
+  /// Remember to call dispose when the story screen is disposed to close
+  /// the notifier stream.
+  void dispose() {
+    playbackNotifier.close();
+  }
+}