Move musicus package to seperate directory

musicus/lib/backend.dart

@@ -0,0 +1,166 @@
+import 'dart:io';
+import 'dart:isolate';
+
+import 'package:flutter/services.dart';
+import 'package:flutter/widgets.dart';
+import 'package:moor/isolate.dart';
+import 'package:moor/moor.dart';
+import 'package:moor_ffi/moor_ffi.dart';
+import 'package:path/path.dart' as p;
+import 'package:path_provider/path_provider.dart' as pp;
+import 'package:shared_preferences/shared_preferences.dart';
+
+import 'database.dart';
+import 'music_library.dart';
+import 'player.dart';
+
+// The following code was taken from
+// https://moor.simonbinder.eu/docs/advanced-features/isolates/ and just
+// slightly modified.
+
+Future<MoorIsolate> _createMoorIsolate() async {
+  // This method is called from the main isolate. Since we can't use
+  // getApplicationDocumentsDirectory on a background isolate, we calculate
+  // the database path in the foreground isolate and then inform the
+  // background isolate about the path.
+  final dir = await pp.getApplicationDocumentsDirectory();
+  final path = p.join(dir.path, 'db.sqlite');
+  final receivePort = ReceivePort();
+
+  await Isolate.spawn(
+    _startBackground,
+    _IsolateStartRequest(receivePort.sendPort, path),
+  );
+
+  // _startBackground will send the MoorIsolate to this ReceivePort.
+  return (await receivePort.first as MoorIsolate);
+}
+
+void _startBackground(_IsolateStartRequest request) {
+  // This is the entrypoint from the background isolate! Let's create
+  // the database from the path we received.
+  final executor = VmDatabase(File(request.targetPath));
+  // We're using MoorIsolate.inCurrent here as this method already runs on a
+  // background isolate. If we used MoorIsolate.spawn, a third isolate would be
+  // started which is not what we want!
+  final moorIsolate = MoorIsolate.inCurrent(
+    () => DatabaseConnection.fromExecutor(executor),
+  );
+  // Inform the starting isolate about this, so that it can call .connect().
+  request.sendMoorIsolate.send(moorIsolate);
+}
+
+// Used to bundle the SendPort and the target path, since isolate entrypoint
+// functions can only take one parameter.
+class _IsolateStartRequest {
+  final SendPort sendMoorIsolate;
+  final String targetPath;
+
+  _IsolateStartRequest(this.sendMoorIsolate, this.targetPath);
+}
+
+enum BackendStatus {
+  loading,
+  setup,
+  ready,
+}
+
+class Backend extends StatefulWidget {
+  final Widget child;
+
+  Backend({
+    @required this.child,
+  });
+
+  @override
+  BackendState createState() => BackendState();
+
+  static BackendState of(BuildContext context) =>
+      context.dependOnInheritedWidgetOfExactType<_InheritedBackend>().state;
+}
+
+class BackendState extends State<Backend> {
+  static const _platform = MethodChannel('de.johrpan.musicus/platform');
+
+  final player = Player();
+
+  BackendStatus status = BackendStatus.loading;
+  Database db;
+  String musicLibraryUri;
+  MusicLibrary ml;
+
+  MoorIsolate _moorIsolate;
+  SharedPreferences _shPref;
+
+  @override
+  void initState() {
+    super.initState();
+    _load();
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return _InheritedBackend(
+      child: widget.child,
+      state: this,
+    );
+  }
+
+  Future<void> _load() async {
+    _moorIsolate = await _createMoorIsolate();
+    final dbConnection = await _moorIsolate.connect();
+    player.setup();
+    db = Database.connect(dbConnection);
+
+    _shPref = await SharedPreferences.getInstance();
+    musicLibraryUri = _shPref.getString('musicLibraryUri');
+
+    _loadMusicLibrary();
+  }
+
+  Future<void> _loadMusicLibrary() async {
+    if (musicLibraryUri == null) {
+      setState(() {
+        status = BackendStatus.setup;
+      });
+    } else {
+      ml = MusicLibrary(musicLibraryUri);
+      await ml.load();
+      setState(() {
+        status = BackendStatus.ready;
+      });
+    }
+  }
+
+  Future<void> chooseMusicLibraryUri() async {
+    final uri = await _platform.invokeMethod<String>('openTree');
+
+    if (uri != null) {
+      musicLibraryUri = uri;
+      await _shPref.setString('musicLibraryUri', uri);
+      setState(() {
+        status = BackendStatus.loading;
+      });
+      await _loadMusicLibrary();
+    }
+  }
+
+  @override
+  void dispose() {
+    super.dispose();
+    _moorIsolate.shutdownAll();
+  }
+}
+
+class _InheritedBackend extends InheritedWidget {
+  final Widget child;
+  final BackendState state;
+
+  _InheritedBackend({
+    @required this.child,
+    @required this.state,
+  }) : super(child: child);
+
+  @override
+  bool updateShouldNotify(_InheritedBackend old) => true;
+}