Move reusable code from mobile to common

This will be useful for a future desktop application.

README.md

@@ -12,17 +12,20 @@ depend on other ones. All packages are written in [Dart](https://dart.dev).
 `database` – A Database of classical music. This package will be used by all
 standalone Musicus applications for storing classical music metadata.
 
+`server` – A simple http server hosting a Musicus database. The server is
+developed using the [Aqueduct framework](https://aqueduct.io).
+
+`client` – A client library for the Musicus server.
+
+`common` – Common building blocks for Musicus client apps. This includes shared
+UI and backend code for the mobile app and the (future) desktop app.
+
 `mobile` – The Musicus mobile app. It is being developed using
 [Flutter toolkit](https://flutter.dev) and only runs on Android for now.
 
 `player` – The simplest possible audio player plugin. This is used by the
 mobile app for playback.
 
-`server` – A simple http server hosting a Musicus database. The server is
-developed using the [Aqueduct framework](https://aqueduct.io).
-
-`client` – A client library for the Musicus server.
-
 ## Hacking
 
 Picking up Dart as a programming language and Flutter as an UI toolkit should

common/.gitignore

@@ -0,0 +1,31 @@
+# Miscellaneous
+*.class
+*.log
+*.pyc
+*.swp
+.DS_Store
+.atom/
+.buildlog/
+.history
+.svn/
+
+# IntelliJ related
+*.iml
+*.ipr
+*.iws
+.idea/
+
+# VS Code related
+.vscode/
+
+# Flutter/Dart/Pub related
+**/*.g.dart
+**/doc/api/
+.dart_tool/
+pubspec.lock
+.flutter-plugins
+.flutter-plugins-dependencies
+.packages
+.pub-cache/
+.pub/
+/build/

common/lib/musicus_common.dart

@@ -0,0 +1,24 @@
+export 'src/editors/ensemble.dart';
+export 'src/editors/instrument.dart';
+export 'src/editors/performance.dart';
+export 'src/editors/person.dart';
+export 'src/editors/recording.dart';
+export 'src/editors/tracks.dart';
+export 'src/editors/work.dart';
+
+export 'src/selectors/ensemble.dart';
+export 'src/selectors/files.dart';
+export 'src/selectors/instruments.dart';
+export 'src/selectors/person.dart';
+export 'src/selectors/recording.dart';
+export 'src/selectors/work.dart';
+
+export 'src/widgets/lists.dart';
+export 'src/widgets/recording_tile.dart';
+export 'src/widgets/texts.dart';
+
+export 'src/backend.dart';
+export 'src/library.dart';
+export 'src/platform.dart';
+export 'src/playback.dart';
+export 'src/settings.dart';

common/lib/src/backend.dart

@@ -0,0 +1,221 @@
+import 'dart:io';
+import 'dart:isolate';
+import 'dart:ui';
+
+import 'package:flutter/widgets.dart';
+import 'package:moor/isolate.dart';
+import 'package:moor/moor.dart';
+import 'package:moor_ffi/moor_ffi.dart';
+import 'package:musicus_client/musicus_client.dart';
+import 'package:musicus_database/musicus_database.dart';
+
+import 'library.dart';
+import 'platform.dart';
+import 'playback.dart';
+import 'settings.dart';
+
+/// Current status of the backend.
+enum MusicusBackendStatus {
+  /// The backend is loading.
+  ///
+  /// It is not allowed to call any methods on the backend in this state.
+  loading,
+
+  /// Required settings are missing.
+  ///
+  /// Currently this only includes the music library path. It is not allowed to
+  /// call any methods on the backend in this state.
+  setup,
+
+  /// The backend is ready to be used.
+  ///
+  /// This is the only state, in which it is allowed to call methods on the
+  /// backend.
+  ready,
+}
+
+/// Meta widget holding all backend ressources for Musicus.
+///
+/// This widget is intended to sit near the top of the widget tree. Widgets
+/// below it can get the current backend state using the static [of] method.
+/// The backend is intended to be used exactly once and live until the UI is
+/// exited. Because of that, consuming widgets don't need to care about a
+/// change of the backend state object.
+///
+/// The backend maintains a Musicus database within a Moor isolate. The connect
+/// port will be registered as 'moor' in the [IsolateNameServer].
+class MusicusBackend extends StatefulWidget {
+  /// Path to the database file.
+  final String dbPath;
+
+  /// An object to persist the settings.
+  final MusicusSettingsStorage settingsStorage;
+
+  /// An object handling playback.
+  final MusicusPlayback playback;
+
+  /// An object handling platform dependent functionality.
+  final MusicusPlatform platform;
+
+  /// The first child below the backend widget.
+  ///
+  /// This widget should keep track of the current backend status and block
+  /// other widgets from accessing the backend until its status is set to
+  /// [MusicusBackendStatus.ready].
+  final Widget child;
+
+  MusicusBackend({
+    @required this.dbPath,
+    @required this.settingsStorage,
+    @required this.playback,
+    @required this.platform,
+    @required this.child,
+  });
+
+  @override
+  MusicusBackendState createState() => MusicusBackendState();
+
+  static MusicusBackendState of(BuildContext context) =>
+      context.dependOnInheritedWidgetOfExactType<_InheritedBackend>().state;
+}
+
+class MusicusBackendState extends State<MusicusBackend> {
+  /// Starts the Moor isolate.
+  ///
+  /// It will create a database connection for [request.path] and will send the
+  /// Moor send port through [request.sendPort].
+  static void _moorIsolateEntrypoint(_IsolateStartRequest request) {
+    final executor = VmDatabase(File(request.path));
+    final moorIsolate =
+        MoorIsolate.inCurrent(() => DatabaseConnection.fromExecutor(executor));
+    request.sendPort.send(moorIsolate.connectPort);
+  }
+
+  /// The current backend status.
+  ///
+  /// If this is not [MusicusBackendStatus.ready], the [child] widget should
+  /// prevent all access to the backend.
+  MusicusBackendStatus status = MusicusBackendStatus.loading;
+
+  Database db;
+  MusicusPlayback playback;
+  MusicusSettings settings;
+  MusicusClient client;
+  MusicusPlatform platform;
+  MusicusLibrary library;
+
+  @override
+  void initState() {
+    super.initState();
+    _load();
+  }
+
+  /// Initialize resources.
+  Future<void> _load() async {
+    SendPort moorPort = IsolateNameServer.lookupPortByName('moor');
+    if (moorPort == null) {
+      final receivePort = ReceivePort();
+      await Isolate.spawn(_moorIsolateEntrypoint,
+          _IsolateStartRequest(receivePort.sendPort, widget.dbPath));
+      moorPort = await receivePort.first;
+      IsolateNameServer.registerPortWithName(moorPort, 'moor');
+    }
+
+    final moorIsolate = MoorIsolate.fromConnectPort(moorPort);
+    db = Database.connect(await moorIsolate.connect());
+
+    playback = widget.playback;
+    await playback.setup();
+
+    settings = MusicusSettings(widget.settingsStorage);
+    await settings.load();
+
+    settings.musicLibraryPath.listen((path) {
+      setState(() {
+        status = MusicusBackendStatus.loading;
+      });
+      _updateMusicLibrary(path);
+    });
+
+    settings.server.listen((serverSettings) {
+      _updateClient(serverSettings);
+    });
+
+    _updateClient(settings.server.value);
+
+    final path = settings.musicLibraryPath.value;
+
+    platform = widget.platform;
+    platform.setBasePath(path);
+
+    // This will change the status for us.
+    _updateMusicLibrary(path);
+  }
+
+  /// Create a music library according to [path].
+  Future<void> _updateMusicLibrary(String path) async {
+    if (path == null) {
+      setState(() {
+        status = MusicusBackendStatus.setup;
+      });
+    } else {
+      platform.setBasePath(path);
+      library = MusicusLibrary(path, platform);
+      await library.load();
+      setState(() {
+        status = MusicusBackendStatus.ready;
+      });
+    }
+  }
+
+  /// Create a new client based on [settings].
+  void _updateClient(MusicusServerSettings settings) {
+    client?.dispose();
+    client = MusicusClient(
+      host: settings.host,
+      port: settings.port,
+      basePath: settings.apiPath,
+    );
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return _InheritedBackend(
+      child: widget.child,
+      state: this,
+    );
+  }
+
+  @override
+  void dispose() {
+    super.dispose();
+
+    settings.dispose();
+
+    /// We don't stop the Moor isolate, because it can be used elsewhere.
+    db.close();
+    client.dispose();
+  }
+}
+
+/// Bundles arguments for the moor isolate.
+class _IsolateStartRequest {
+  final SendPort sendPort;
+  final String path;
+
+  _IsolateStartRequest(this.sendPort, this.path);
+}
+
+/// Helper widget passing the current backend state down the widget tree.
+class _InheritedBackend extends InheritedWidget {
+  final Widget child;
+  final MusicusBackendState state;
+
+  _InheritedBackend({
+    @required this.child,
+    @required this.state,
+  }) : super(child: child);
+
+  @override
+  bool updateShouldNotify(_InheritedBackend old) => true;
+}

common/lib/src/editors/ensemble.dart

@@ -30,7 +30,7 @@ class _EnsembleEditorState extends State<EnsembleEditor> {
 
   @override
   Widget build(BuildContext context) {
-    final backend = Backend.of(context);
+    final backend = MusicusBackend.of(context);
 
     return Scaffold(
       appBar: AppBar(

common/lib/src/editors/instrument.dart

@@ -30,7 +30,7 @@ class _InstrumentEditorState extends State<InstrumentEditor> {
 
   @override
   Widget build(BuildContext context) {
-    final backend = Backend.of(context);
+    final backend = MusicusBackend.of(context);
 
     return Scaffold(
       appBar: AppBar(

common/lib/src/editors/person.dart

@@ -32,7 +32,7 @@ class _PersonEditorState extends State<PersonEditor> {
 
   @override
   Widget build(BuildContext context) {
-    final backend = Backend.of(context);
+    final backend = MusicusBackend.of(context);
 
     return Scaffold(
       appBar: AppBar(

common/lib/src/editors/recording.dart

@@ -36,7 +36,7 @@ class _RecordingEditorState extends State<RecordingEditor> {
     super.initState();
 
     if (widget.recordingInfo != null) {
-      final backend = Backend.of(context);
+      final backend = MusicusBackend.of(context);
 
       () async {
         workInfo = await backend.db.getWork(widget.recordingInfo.recording.id);
@@ -47,7 +47,7 @@ class _RecordingEditorState extends State<RecordingEditor> {
 
   @override
   Widget build(BuildContext context) {
-    final backend = Backend.of(context);
+    final backend = MusicusBackend.of(context);
 
     Future<void> selectWork() async {
       final WorkInfo newWorkInfo = await Navigator.push(

common/lib/src/editors/tracks.dart

@@ -2,7 +2,7 @@ import 'package:flutter/material.dart';
 import 'package:musicus_database/musicus_database.dart';
 
 import '../backend.dart';
-import '../music_library.dart';
+import '../library.dart';
 import '../selectors/files.dart';
 import '../selectors/recording.dart';
 import '../widgets/recording_tile.dart';
@@ -21,7 +21,7 @@ class TracksEditor extends StatefulWidget {
 }
 
 class _TracksEditorState extends State<TracksEditor> {
-  BackendState backend;
+  MusicusBackendState backend;
   WorkInfo workInfo;
   RecordingInfo recordingInfo;
   String parentId;
@@ -29,7 +29,7 @@ class _TracksEditorState extends State<TracksEditor> {
 
   @override
   Widget build(BuildContext context) {
-    backend = Backend.of(context);
+    backend = MusicusBackend.of(context);
 
     return Scaffold(
       appBar: AppBar(
@@ -57,7 +57,7 @@ class _TracksEditorState extends State<TracksEditor> {
               backend.db.updateWork(workInfo);
               backend.db.updateRecording(recordingInfo);
 
-              backend.ml.addTracks(parentId, tracks);
+              backend.library.addTracks(parentId, tracks);
 
               Navigator.pop(context);
             },

common/lib/src/editors/work.dart

@@ -200,7 +200,7 @@ class _WorkEditorState extends State<WorkEditor> {
 
   @override
   Widget build(BuildContext context) {
-    final backend = Backend.of(context);
+    final backend = MusicusBackend.of(context);
 
     final List<Widget> partTiles = [];
     for (var i = 0; i < parts.length; i++) {

common/lib/src/library.dart

@@ -1,32 +1,31 @@
 import 'dart:convert';
 
-import 'package:flutter/services.dart';
-
 import 'platform.dart';
 
-/// Bundles a [Track] with the URI of the audio file it represents.
+/// Bundles a [Track] with information on how to find the corresponding file.
-///
-/// The uri shouldn't be stored on disk, but will be used at runtime.
 class InternalTrack {
   /// The represented track.
   final Track track;
 
-  /// The URI of the represented audio file as retrieved from the SAF.
+  /// A string identifying the track for playback.
-  final String uri;
+  ///
+  /// This will be the result of calling the platform objects getIdentifier()
+  /// function with the file name of the track.
+  final String identifier;
 
   InternalTrack({
     this.track,
-    this.uri,
+    this.identifier,
   });
 
   factory InternalTrack.fromJson(Map<String, dynamic> json) => InternalTrack(
         track: Track.fromJson(json['track']),
-        uri: json['uri'],
+        identifier: json['identifier'],
       );
 
   Map<String, dynamic> toJson() => {
         'track': track.toJson(),
-        'uri': uri,
+        'identifier': identifier,
       };
 }
 
@@ -106,13 +105,12 @@ class MusicusFile {
 }
 
 /// Manager for all available tracks and their representation on disk.
-class MusicLibrary {
+class MusicusLibrary {
-  static const platform = MethodChannel('de.johrpan.musicus/platform');
+  /// String representing the music library base path.
+  final String basePath;
 
-  /// URI of the music library folder.
+  /// Access to platform dependent functionality.
-  ///
+  final MusicusPlatform platform;
-  /// This is a tree URI in the terms of the Android Storage Access Framework.
-  final String treeUri;
 
   /// Map of all available tracks by recording ID.
   ///
@@ -120,7 +118,7 @@ class MusicLibrary {
   /// audio file alongside the real [Track] object.
   final Map<int, List<InternalTrack>> tracks = {};
 
-  MusicLibrary(this.treeUri);
+  MusicusLibrary(this.basePath, this.platform);
 
   /// Load all available tracks.
   ///
@@ -130,13 +128,13 @@ class MusicLibrary {
   Future<void> load() async {
     // TODO: Consider capping the recursion somewhere.
     Future<void> recurse([String parentId]) async {
-      final children = await Platform.getChildren(treeUri, parentId);
+      final children = await platform.getChildren(parentId);
 
       for (final child in children) {
         if (child.isDirectory) {
           recurse(child.id);
         } else if (child.name == 'musicus.json') {
-          final content = await Platform.readFile(treeUri, child.id);
+          final content = await platform.readDocument(child.id);
           final musicusFile = MusicusFile.fromJson(jsonDecode(content));
           for (final track in musicusFile.tracks) {
             _indexTrack(parentId, track);
@@ -156,7 +154,7 @@ class MusicLibrary {
     MusicusFile musicusFile;
 
     final oldContent =
-        await Platform.readFileByName(treeUri, parentId, 'musicus.json');
+        await platform.readDocumentByName(parentId, 'musicus.json');
 
     if (oldContent != null) {
       musicusFile = MusicusFile.fromJson(jsonDecode(oldContent));
@@ -169,15 +167,15 @@ class MusicLibrary {
       musicusFile.tracks.add(track);
     }
 
-    await Platform.writeFileByName(
+    await platform.writeDocumentByName(
-        treeUri, parentId, 'musicus.json', jsonEncode(musicusFile.toJson()));
+        parentId, 'musicus.json', jsonEncode(musicusFile.toJson()));
   }
 
   /// Add a track to the map of available tracks.
   Future<void> _indexTrack(String parentId, Track track) async {
     final iTrack = InternalTrack(
       track: track,
-      uri: await Platform.getUriByName(treeUri, parentId, track.fileName),
+      identifier: await platform.getIdentifier(parentId, track.fileName),
     );
 
     if (tracks.containsKey(track.recordingId)) {

common/lib/src/platform.dart

@@ -0,0 +1,76 @@
+/// Object representing a document in Storage Access Framework terms.
+class Document {
+  /// Unique ID for the document.
+  ///
+  /// The platform implementation thould be able to get the content of the
+  /// document based on this value.
+  final String id;
+
+  /// Name of the document (i.e. file name).
+  final String name;
+
+  /// Document ID of the parent document.
+  final String parent;
+
+  /// Whether this document represents a directory.
+  final bool isDirectory;
+
+  Document({
+    this.id,
+    this.name,
+    this.parent,
+    this.isDirectory,
+  });
+
+  // Use Map<dynamic, dynamic> here, as we get casting errors otherwise. This
+  // won't be typesafe anyway.
+  Document.fromJson(Map<dynamic, dynamic> json)
+      : id = json['id'],
+        name = json['name'],
+        parent = json['parent'],
+        isDirectory = json['isDirectory'];
+}
+
+/// Platform dependent code for the Musicus backend.
+abstract class MusicusPlatform {
+  /// An identifier for the root directory of the music library.
+  ///
+  /// This will be the string, that is stored as musicLibraryPath in the
+  /// settings object.
+  String basePath;
+
+  MusicusPlatform();
+
+  /// This will be called, when the music library path was changed.
+  void setBasePath(String path) {
+    basePath = path;
+  }
+
+  /// Get all documents in a directory.
+  ///
+  /// [parentId] will be the ID of the directory document. If [parentId] is
+  /// null, the children of the root directory will be returned.
+  Future<List<Document>> getChildren(String parentId);
+
+  /// Read the contents of a document by ID.
+  Future<String> readDocument(String id);
+
+  /// Read from a document by name.
+  /// 
+  /// [parentId] is the document ID of the parent directory.
+  Future<String> readDocumentByName(String parentId, String fileName);
+
+  /// Get a string identifying a document.
+  ///
+  /// [parentId] is the document ID of the parent directory. The return value
+  /// should be a string, that the playback object can use to find and play the
+  /// file. It will be included in [InternalTrack] objects by the music
+  /// library.
+  Future<String> getIdentifier(String parentId, String fileName);
+
+  /// Write to a document by name.
+  ///
+  /// [parentId] is the document ID of the parent directory.
+  Future<void> writeDocumentByName(
+      String parentId, String fileName, String contents);
+}

common/lib/src/playback.dart

@@ -0,0 +1,96 @@
+import 'package:meta/meta.dart';
+import 'package:rxdart/rxdart.dart';
+
+import 'library.dart';
+
+/// Base class for Musicus playback.
+abstract class MusicusPlayback {
+  /// Whether the player is active.
+  ///
+  /// This means, that there is at least one item in the queue and the playback
+  /// service is ready to play.
+  final active = BehaviorSubject.seeded(false);
+
+  /// The current playlist.
+  ///
+  /// If the player is not active, this will be an empty list.
+  final playlist = BehaviorSubject.seeded(<InternalTrack>[]);
+
+  /// Index of the currently played (or paused) track within the playlist.
+  ///
+  /// This will be zero, if the player is not active!
+  final currentIndex = BehaviorSubject.seeded(0);
+
+  /// The currently played track.
+  ///
+  /// This will be null, if there is no  current track.
+  final currentTrack = BehaviorSubject<InternalTrack>.seeded(null);
+
+  /// Whether we are currently playing or not.
+  ///
+  /// This will be false, if the player is not active.
+  final playing = BehaviorSubject.seeded(false);
+
+  /// Current playback position.
+  ///
+  /// If the player is not active, this will default to zero.
+  final position = BehaviorSubject.seeded(const Duration());
+
+  /// Duration of the current track.
+  ///
+  /// If the player is not active, the duration will default to 1 s.
+  final duration = BehaviorSubject.seeded(const Duration(seconds: 1));
+
+  /// Playback position normalized to the range from zero to one.
+  final normalizedPosition = BehaviorSubject.seeded(0.0);
+
+  /// Initialize the player.
+  /// 
+  /// This will be called after the database was initialized.
+  Future<void> setup();
+
+  /// Add a list of tracks to the players playlist.
+  Future<void> addTracks(List<InternalTrack> tracks);
+
+  /// Remove the track at [index] from the playlist.
+  Future<void> removeTrack(int index);
+
+  /// Toggle whether the player is playing or paused.
+  Future<void> playPause();
+
+  /// Seek to [pos], which is a value between (and including) zero and one.
+  Future<void> seekTo(double pos);
+
+  /// Skip to the previous track in the playlist.
+  Future<void> skipToPrevious();
+
+  /// Play the next track in the playlist.
+  Future<void> skipToNext();
+
+  /// Switch to the track with the index [index] in the playlist.
+  Future<void> skipTo(int index);
+
+  /// Set all values to their default.
+  void reset() {
+    active.add(false);
+    playlist.add([]);
+    currentTrack.add(null);
+    playing.add(false);
+    position.add(const Duration());
+    duration.add(const Duration(seconds: 1));
+    normalizedPosition.add(0.0);
+  }
+
+  /// Tidy up.
+  @mustCallSuper
+  void dispose() {
+    active.close();
+    playlist.close();
+    currentIndex.close();
+    currentTrack.close();
+    playing.close();
+    position.close();
+    duration.close();
+    normalizedPosition.close();
+  }
+}

common/lib/src/selectors/files.dart

@@ -24,7 +24,7 @@ class FilesSelector extends StatefulWidget {
 }
 
 class _FilesSelectorState extends State<FilesSelector> {
-  BackendState backend;
+  MusicusBackendState backend;
   List<Document> history = [];
   List<Document> children = [];
   Set<Document> selection = {};
@@ -33,7 +33,7 @@ class _FilesSelectorState extends State<FilesSelector> {
   void didChangeDependencies() {
     super.didChangeDependencies();
 
-    backend = Backend.of(context);
+    backend = MusicusBackend.of(context);
     loadChildren();
   }
 
@@ -130,9 +130,8 @@ class _FilesSelectorState extends State<FilesSelector> {
       selection = {};
     });
 
-    final newChildren = await Platform.getChildren(
+    final newChildren = await backend.platform
-        backend.settings.musicLibraryUri.value,
+        .getChildren(history.isNotEmpty ? history.last.id : null);
-        history.isNotEmpty ? history.last.id : null);
 
     newChildren.sort((d1, d2) {
       if (d1.isDirectory != d2.isDirectory) {

common/lib/src/selectors/instruments.dart

@@ -35,7 +35,7 @@ class _InstrumentsSelectorState extends State<InstrumentsSelector> {
 
   @override
   Widget build(BuildContext context) {
-    final backend = Backend.of(context);
+    final backend = MusicusBackend.of(context);
 
     return Scaffold(
       appBar: AppBar(

common/lib/src/settings.dart

@@ -0,0 +1,112 @@
+import 'package:meta/meta.dart';
+import 'package:rxdart/rxdart.dart';
+
+/// Interface for persisting settings.
+/// 
+/// The methods should return null, if there is no value associated with the
+/// provided key.
+abstract class MusicusSettingsStorage {
+  Future<void> load();
+  Future<int> getInt(String key);
+  Future<String> getString(String key);
+  Future<void> setInt(String key, int value);
+  Future<void> setString(String key, String value);
+}
+
+/// Settings concerning the Musicus server to connect to.
+///
+/// We don't support setting a scheme here, because there may be password being
+/// submitted in the future, so we default to HTTPS.
+class MusicusServerSettings {
+  /// Host to connect to, e.g. 'musicus.johrpan.de';
+  final String host;
+
+  /// Port to connect to.
+  final int port;
+
+  /// Path to the API.
+  ///
+  /// This can be either null or empty, if the API is at the root of the host.
+  final String apiPath;
+
+  MusicusServerSettings({
+    @required this.host,
+    @required this.port,
+    @required this.apiPath,
+  });
+}
+
+/// Manager for all settings that are persisted.
+class MusicusSettings {
+  static const defaultHost = 'musicus.johrpan.de';
+  static const defaultPort = 443;
+  static const defaultApiPath = '/api';
+
+  /// The storage method to use.
+  final MusicusSettingsStorage storage;
+
+  /// A identifier for the base path of the music library.
+  /// 
+  /// This could be a file path on destop systems or a tree URI in terms of the
+  /// Android storage access framework.
+  final musicLibraryPath = BehaviorSubject<String>();
+
+  /// Musicus server to connect to.
+  final server = BehaviorSubject<MusicusServerSettings>();
+
+  /// Create a settings instance.
+  MusicusSettings(this.storage);
+
+  /// Initialize the settings.
+  Future<void> load() async {
+    await storage.load();
+    
+    final path = await storage.getString('musicLibraryPath');
+    if (path != null) {
+      musicLibraryPath.add(path);
+    }
+
+    final host = await storage.getString('serverHost') ?? defaultHost;
+    final port = await storage.getInt('serverPort') ?? defaultPort;
+    final apiPath = await storage.getString('serverApiPath') ?? defaultApiPath;
+
+    server.add(MusicusServerSettings(
+      host: host,
+      port: port,
+      apiPath: apiPath,
+    ));
+  }
+
+  /// Set a new music library path.
+  /// 
+  /// This will persist the new value and update the stream.
+  Future<void> setMusicLibraryPath(String path) async {
+    await storage.setString('musicLibraryPath', path);
+    musicLibraryPath.add(path);
+  }
+
+  /// Update the server settings.
+  /// 
+  /// This will persist the new values and update the stream.
+  Future<void> setServer(MusicusServerSettings serverSettings) async {
+    await storage.setString('serverHost', serverSettings.host);
+    await storage.setInt('serverPort', serverSettings.port);
+    await storage.setString('severApiPath', serverSettings.apiPath);
+    server.add(serverSettings);
+  }
+
+  /// Reset the server settings to their defaults.
+  Future<void> resetServer() async {
+    await setServer(MusicusServerSettings(
+      host: defaultHost,
+      port: defaultPort,
+      apiPath: defaultApiPath,
+    ));
+  }
+
+  /// Tidy up.
+  void dispose() {
+    musicLibraryPath.close();
+    server.close();
+  }
+}

common/lib/src/widgets/lists.dart

@@ -161,7 +161,7 @@ class _PersonsListState extends State<PersonsList> {
 
   @override
   Widget build(BuildContext context) {
-    final backend = Backend.of(context);
+    final backend = MusicusBackend.of(context);
 
     return Column(
       children: <Widget>[
@@ -222,7 +222,7 @@ class _EnsemblesListState extends State<EnsemblesList> {
 
   @override
   Widget build(BuildContext context) {
-    final backend = Backend.of(context);
+    final backend = MusicusBackend.of(context);
 
     return Column(
       children: <Widget>[
@@ -287,7 +287,7 @@ class _WorksListState extends State<WorksList> {
 
   @override
   Widget build(BuildContext context) {
-    final backend = Backend.of(context);
+    final backend = MusicusBackend.of(context);
 
     return Column(
       children: <Widget>[
@@ -346,7 +346,7 @@ class RecordingsList extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    final backend = Backend.of(context);
+    final backend = MusicusBackend.of(context);
 
     return PagedListView<RecordingInfo>(
       fetch: (page, _) async {

common/lib/src/widgets/texts.dart

@@ -45,7 +45,7 @@ class WorkText extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    final backend = Backend.of(context);
+    final backend = MusicusBackend.of(context);
 
     return StreamBuilder<Work>(
       stream: backend.db.workById(workId).watchSingle(),
@@ -61,7 +61,7 @@ class ComposersText extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    final backend = Backend.of(context);
+    final backend = MusicusBackend.of(context);
 
     return StreamBuilder<List<Person>>(
       stream: backend.db.composersByWork(workId).watch(),

common/pubspec.yaml

@@ -0,0 +1,18 @@
+name: musicus_common
+version: 0.1.0
+description: Common building blocks for Musicus client apps.
+
+environment:
+  sdk: ">=2.3.0 <3.0.0"
+
+dependencies:
+  flutter:
+    sdk: flutter
+  meta:
+  moor:
+  moor_ffi:
+  musicus_client:
+    path: ../client
+  musicus_database:
+    path: ../database
+  rxdart:

mobile/lib/app.dart

@@ -1,15 +1,18 @@
 import 'dart:async';
 
 import 'package:flutter/material.dart';
+import 'package:flutter/services.dart';
+import 'package:musicus_common/musicus_common.dart';
 
-import 'backend.dart';
 import 'screens/home.dart';
 import 'widgets/player_bar.dart';
 
 class App extends StatelessWidget {
+  static const _platform = MethodChannel('de.johrpan.musicus/platform');
+
   @override
   Widget build(BuildContext context) {
-    final backend = Backend.of(context);
+    final backend = MusicusBackend.of(context);
 
     return MaterialApp(
       title: 'Musicus',
@@ -36,11 +39,11 @@ class App extends StatelessWidget {
       ),
       home: Builder(
         builder: (context) {
-          if (backend.status == BackendStatus.loading) {
+          if (backend.status == MusicusBackendStatus.loading) {
             return Material(
               color: Theme.of(context).scaffoldBackgroundColor,
             );
-          } else if (backend.status == BackendStatus.setup) {
+          } else if (backend.status == MusicusBackendStatus.setup) {
             return Material(
               color: Theme.of(context).scaffoldBackgroundColor,
               child: Column(
@@ -57,8 +60,13 @@ class App extends StatelessWidget {
                   ListTile(
                     leading: const Icon(Icons.folder_open),
                     title: Text('Choose path'),
-                    onTap: () {
+                    onTap: () async {
-                      backend.settings.chooseMusicLibraryUri();
+                      final uri =
+                          await _platform.invokeMethod<String>('openTree');
+
+                      if (uri != null) {
+                        backend.settings.setMusicLibraryPath(uri);
+                      }
                     },
                   ),
                 ],
@@ -82,7 +90,7 @@ class _ContentState extends State<Content> with SingleTickerProviderStateMixin {
   final nestedNavigator = GlobalKey<NavigatorState>();
 
   AnimationController playerBarAnimation;
-  BackendState backend;
+  MusicusBackendState backend;
   StreamSubscription<bool> playerActiveSubscription;
 
   @override
@@ -99,14 +107,14 @@ class _ContentState extends State<Content> with SingleTickerProviderStateMixin {
   void didChangeDependencies() {
     super.didChangeDependencies();
 
-    backend = Backend.of(context);
+    backend = MusicusBackend.of(context);
-    playerBarAnimation.value = backend.player.active.value ? 1.0 : 0.0;
+    playerBarAnimation.value = backend.playback.active.value ? 1.0 : 0.0;
 
     if (playerActiveSubscription != null) {
       playerActiveSubscription.cancel();
     }
 
-    playerActiveSubscription = backend.player.active.listen((active) =>
+    playerActiveSubscription = backend.playback.active.listen((active) =>
         active ? playerBarAnimation.forward() : playerBarAnimation.reverse());
   }
 

mobile/lib/backend.dart

@@ -1,176 +0,0 @@
-import 'dart:io';
-import 'dart:isolate';
-import 'dart:ui';
-
-import 'package:flutter/widgets.dart';
-import 'package:moor/isolate.dart';
-import 'package:moor/moor.dart';
-import 'package:moor_ffi/moor_ffi.dart';
-import 'package:musicus_client/musicus_client.dart';
-import 'package:musicus_database/musicus_database.dart';
-import 'package:path/path.dart' as p;
-import 'package:path_provider/path_provider.dart' as pp;
-
-import 'music_library.dart';
-import 'player.dart';
-import 'settings.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> {
-  final player = Player();
-  final settings = Settings();
-
-  BackendStatus status = BackendStatus.loading;
-  Database db;
-  MusicusClient client;
-  MusicLibrary ml;
-
-  @override
-  void initState() {
-    super.initState();
-    _load();
-  }
-
-  @override
-  Widget build(BuildContext context) {
-    return _InheritedBackend(
-      child: widget.child,
-      state: this,
-    );
-  }
-
-  Future<void> _load() async {
-    MoorIsolate moorIsolate;
-
-    final moorPort = IsolateNameServer.lookupPortByName('moorPort');
-    if (moorPort != null) {
-      moorIsolate = MoorIsolate.fromConnectPort(moorPort);
-    } else {
-      moorIsolate = await _createMoorIsolate();
-      IsolateNameServer.registerPortWithName(
-          moorIsolate.connectPort, 'moorPort');
-    }
-
-    final dbConnection = await moorIsolate.connect();
-    db = Database.connect(dbConnection);
-
-    player.setup();
-
-    await settings.load();
-
-    _updateMusicLibrary(settings.musicLibraryUri.value);
-    settings.musicLibraryUri.listen((uri) {
-      _updateMusicLibrary(uri);
-    });
-
-    _updateClient(settings.server.value);
-    settings.server.listen((serverSettings) {
-      _updateClient(serverSettings);
-    });
-  }
-
-  Future<void> _updateMusicLibrary(String uri) async {
-    if (uri == null) {
-      setState(() {
-        status = BackendStatus.setup;
-      });
-    } else {
-      ml = MusicLibrary(uri);
-      await ml.load();
-      setState(() {
-        status = BackendStatus.ready;
-      });
-    }
-  }
-
-  Future<void> _updateClient(ServerSettings serverSettings) async {
-    client = MusicusClient(
-      host: serverSettings.host,
-      port: serverSettings.port,
-      basePath: serverSettings.basePath,
-    );
-  }
-
-  @override
-  void dispose() {
-    super.dispose();
-    client.dispose();
-  }
-}
-
-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;
-}

mobile/lib/main.dart

@@ -1,12 +1,26 @@
 import 'package:audio_service/audio_service.dart';
 import 'package:flutter/widgets.dart';
+import 'package:musicus_common/musicus_common.dart';
+import 'package:path/path.dart' as p;
+import 'package:path_provider/path_provider.dart' as pp;
 
 import 'app.dart';
-import 'backend.dart';
+import 'settings.dart';
+import 'platform.dart';
+import 'playback.dart';
+
+Future<void> main() async {
+  WidgetsFlutterBinding.ensureInitialized();
+
+  final dir = await pp.getApplicationDocumentsDirectory();
+  final dbPath = p.join(dir.path, 'db.sqlite');
 
-void main() {
   runApp(AudioServiceWidget(
-    child: Backend(
+    child: MusicusBackend(
+      dbPath: dbPath,
+      settingsStorage: SettingsStorage(),
+      platform: MusicusAndroidPlatform(),
+      playback: Playback(),
       child: App(),
     ),
   ));

mobile/lib/platform.dart

@@ -1,44 +1,16 @@
 import 'package:flutter/services.dart';
+import 'package:musicus_common/musicus_common.dart';
 
-/// Object representing a document in Storage Access Framework terms.
+class MusicusAndroidPlatform extends MusicusPlatform {
-class Document {
-  /// Unique document ID given by the SAF.
-  final String id;
-
-  /// Name of the document (i.e. file name).
-  final String name;
-
-  /// Document ID of the parent document.
-  final String parent;
-
-  /// Whether this document represents a directory.
-  final bool isDirectory;
-
-  // Use Map<dynamic, dynamic> here, as we get casting errors otherwise. This
-  // won't be typesafe anyway.
-  Document.fromJson(Map<dynamic, dynamic> json)
-      : id = json['id'],
-        name = json['name'],
-        parent = json['parent'],
-        isDirectory = json['isDirectory'];
-}
-
-/// Collection of methods that are implemented platform dependent.
-class Platform {
   static const _platform = MethodChannel('de.johrpan.musicus/platform');
 
-  /// Get child documents.
+  @override
-  ///
+  Future<List<Document>> getChildren(String parentId) async {
-  /// [treeId] is the base URI as requested from the SAF.
-  /// [parentId] is the document ID of the parent. If this is null, the children
-  /// of the tree base will be returned.
-  static Future<List<Document>> getChildren(
-      String treeUri, String parentId) async {
     final List<Map<dynamic, dynamic>> childrenJson =
         await _platform.invokeListMethod(
       'getChildren',
       {
-        'treeUri': treeUri,
+        'treeUri': basePath,
         'parentId': parentId,
       },
     );
@@ -48,65 +20,51 @@ class Platform {
         .toList();
   }
 
-  /// Read contents of file.
+  @override
-  ///
+  Future<String> getIdentifier(String parentId, String fileName) async {
-  /// [treeId] is the base URI from the SAF, [id] is the document ID of the
+    return await _platform.invokeMethod(
-  /// file.
+      'getUriByName',
-  static Future<String> readFile(String treeUri, String id) async {
+      {
+        'treeUri': basePath,
+        'parentId': parentId,
+        'fileName': fileName,
+      },
+    );
+  }
+
+  @override
+  Future<String> readDocument(String id) async {
     return await _platform.invokeMethod(
       'readFile',
       {
-        'treeUri': treeUri,
+        'treeUri': basePath,
         'id': id,
       },
     );
   }
 
-  /// Get document URI by file name
+  @override
-  ///
+  Future<String> readDocumentByName(String parentId, String fileName) async {
-  /// [treeId] is the base URI from the SAF, [parentId] is the document ID of
-  /// the parent directory.
-  static Future<String> getUriByName(
-      String treeUri, String parentId, String fileName) async {
-    return await _platform.invokeMethod(
-      'getUriByName',
-      {
-        'treeUri': treeUri,
-        'parentId': parentId,
-        'fileName': fileName,
-      },
-    );
-  }
-
-  /// Read contents of file by name
-  ///
-  /// [treeId] is the base URI from the SAF, [parentId] is the document ID of
-  /// the parent directory.
-  static Future<String> readFileByName(
-      String treeUri, String parentId, String fileName) async {
     return await _platform.invokeMethod(
       'readFileByName',
       {
-        'treeUri': treeUri,
+        'treeUri': basePath,
         'parentId': parentId,
         'fileName': fileName,
       },
     );
   }
 
-  /// Write to file by name
+  @override
-  ///
+  Future<void> writeDocumentByName(
-  /// [treeId] is the base URI from the SAF, [parentId] is the document ID of
+      String parentId, String fileName, String contents) async {
-  /// the parent directory.
-  static Future<void> writeFileByName(
-      String treeUri, String parentId, String fileName, String content) async {
     await _platform.invokeMethod(
       'writeFileByName',
       {
-        'treeUri': treeUri,
+        'treeUri': basePath,
         'parentId': parentId,
         'fileName': fileName,
-        'content': content,
+        'content': contents,
       },
     );
   }

mobile/lib/playback.dart

@@ -6,10 +6,8 @@ import 'dart:ui';
 import 'package:audio_service/audio_service.dart';
 import 'package:moor/isolate.dart';
 import 'package:musicus_database/musicus_database.dart';
+import 'package:musicus_common/musicus_common.dart';
 import 'package:musicus_player/musicus_player.dart';
-import 'package:rxdart/rxdart.dart';
-
-import 'music_library.dart';
 
 const _portName = 'playbackService';
 
@@ -18,61 +16,11 @@ void _playbackServiceEntrypoint() {
   AudioServiceBackground.run(() => _PlaybackService());
 }
 
-class Player {
+class Playback extends MusicusPlayback {
-  /// Whether the player is active.
-  ///
-  /// This means, that there is at least one item in the queue and the playback
-  /// service is ready to play.
-  final active = BehaviorSubject.seeded(false);
-
-  /// The current playlist.
-  ///
-  /// If the player is not active, this will be an empty list.
-  final playlist = BehaviorSubject.seeded(<InternalTrack>[]);
-
-  /// Index of the currently played (or paused) track within the playlist.
-  ///
-  /// This will be zero, if the player is not active!
-  final currentIndex = BehaviorSubject.seeded(0);
-
-  /// The currently played track.
-  ///
-  /// This will be null, if there is no  current track.
-  final currentTrack = BehaviorSubject<InternalTrack>.seeded(null);
-
-  /// Whether we are currently playing or not.
-  ///
-  /// This will be false, if the player is not active.
-  final playing = BehaviorSubject.seeded(false);
-
-  /// Current playback position.
-  ///
-  /// If the player is not active, this will default to zero.
-  final position = BehaviorSubject.seeded(const Duration());
-
-  /// Duration of the current track.
-  ///
-  /// If the player is not active, the duration will default to 1 s.
-  final duration = BehaviorSubject.seeded(const Duration(seconds: 1));
-
-  /// Playback position normalized to the range from zero to one.
-  final normalizedPosition = BehaviorSubject.seeded(0.0);
-
   StreamSubscription _playbackServiceStateSubscription;
 
-  /// Set everything to its default because the playback service was stopped.
-  void _stop() {
-    active.add(false);
-    playlist.add([]);
-    currentIndex.add(0);
-    playing.add(false);
-    position.add(const Duration());
-    duration.add(const Duration(seconds: 1));
-    normalizedPosition.add(0.0);
-  }
-
   /// Start playback service.
-  Future<void> start() async {
+  Future<void> _start() async {
     if (!AudioService.running) {
       await AudioService.start(
         backgroundTaskEntrypoint: _playbackServiceEntrypoint,
@@ -109,8 +57,8 @@ class Player {
     currentTrack.add(playlist.value[index]);
   }
 
-  /// Connect listeners and initialize streams.
+  @override
-  void setup() {
+  Future<void> setup() async {
     if (_playbackServiceStateSubscription != null) {
       _playbackServiceStateSubscription.cancel();
     }
@@ -125,8 +73,12 @@ class Player {
     ).listen((msg) {
       // If state is null, the background audio service has stopped.
       if (msg == null) {
-        _stop();
+        dispose();
       } else {
+        if (!active.value) {
+          active.add(true);
+        }
+
         if (msg is _StatusMessage) {
           playing.add(msg.playing);
         } else if (msg is _PositionMessage) {
@@ -154,9 +106,23 @@ class Player {
     }
   }
 
-  /// Toggle whether the player is playing or paused.
+  @override
-  ///
+  Future<void> addTracks(List<InternalTrack> tracks) async {
-  /// If the player is not active, this will do nothing.
+    if (!AudioService.running) {
+      await _start();
+    }
+
+    await AudioService.customAction('addTracks', jsonEncode(tracks));
+  }
+
+  @override
+  Future<void> removeTrack(int index) async {
+    if (AudioService.running) {
+      await AudioService.customAction('removeTrack', index);
+    }
+  }
+
+  @override
   Future<void> playPause() async {
     if (active.value) {
       if (playing.value) {
@@ -167,29 +133,7 @@ class Player {
     }
   }
 
-  /// Add a list of tracks to the players playlist.
+  @override
-  Future<void> addTracks(List<InternalTrack> tracks) async {
-    if (!AudioService.running) {
-      await start();
-    }
-
-    await AudioService.customAction('addTracks', jsonEncode(tracks));
-  }
-
-  /// Remove the track at [index] from the playlist.
-  ///
-  /// If the player is not active or an invalid value is provided, this will do
-  /// nothing.
-  Future<void> removeTrack(int index) async {
-    if (AudioService.running) {
-      await AudioService.customAction('removeTrack', index);
-    }
-  }
-
-  /// Seek to [pos], which is a value between (and including) zero and one.
-  ///
-  /// If the player is not active or an invalid value is provided, this will do
-  /// nothing.
   Future<void> seekTo(double pos) async {
     if (active.value && pos >= 0.0 && pos <= 1.0) {
       final durationMs = duration.value.inMilliseconds;
@@ -197,45 +141,31 @@ class Player {
     }
   }
 
-  /// Play the previous track in the playlist.
+  @override
-  ///
-  /// If the player is not active or there is no previous track, this will do
-  /// nothing.
-  Future<void> skipToNext() async {
-    if (AudioService.running) {
-      await AudioService.skipToNext();
-    }
-  }
-
-  /// Skip to the next track in the playlist.
-  ///
-  /// If the player is not active or there is no next track, this will do
-  /// nothing. If more than five seconds of the current track have been played,
-  /// this will go back to its beginning instead.
   Future<void> skipToPrevious() async {
     if (AudioService.running) {
       await AudioService.skipToPrevious();
     }
   }
 
-  /// Switch to the track with the index [index] in the playlist.
+  @override
+  Future<void> skipToNext() async {
+    if (AudioService.running) {
+      await AudioService.skipToNext();
+    }
+  }
+
+  @override
   Future<void> skipTo(int index) async {
     if (AudioService.running) {
       await AudioService.customAction('skipTo', index);
     }
   }
 
-  /// Tidy up.
+  @override
   void dispose() {
+    super.dispose();
     _playbackServiceStateSubscription.cancel();
-    active.close();
-    playlist.close();
-    currentIndex.close();
-    currentTrack.close();
-    playing.close();
-    position.close();
-    duration.close();
-    normalizedPosition.close();
   }
 }
 
@@ -363,7 +293,7 @@ class _PlaybackService extends BackgroundAudioTask {
 
   /// Initialize database.
   Future<void> _load() async {
-    final moorPort = IsolateNameServer.lookupPortByName('moorPort');
+    final moorPort = IsolateNameServer.lookupPortByName('moor');
     final moorIsolate = MoorIsolate.fromConnectPort(moorPort);
     db = Database.connect(await moorIsolate.connect());
     _loading.complete();
@@ -397,7 +327,7 @@ class _PlaybackService extends BackgroundAudioTask {
       final title = workInfo.work.title;
 
       AudioServiceBackground.setMediaItem(MediaItem(
-        id: track.uri,
+        id: track.identifier,
         album: composers,
         title: title,
       ));
@@ -456,7 +386,7 @@ class _PlaybackService extends BackgroundAudioTask {
   /// Set the current track, update the player and notify the system.
   Future<void> _setCurrentTrack(int index) async {
     _currentTrack = index;
-    _durationMs = await _player.setUri(_playlist[_currentTrack].uri);
+    _durationMs = await _player.setUri(_playlist[_currentTrack].identifier);
     _setState();
   }
 
@@ -508,7 +438,7 @@ class _PlaybackService extends BackgroundAudioTask {
   }
 
   @override
-  void onCustomAction(String name, dynamic arguments) {
+  Future<void> onCustomAction(String name, dynamic arguments) async {
     super.onCustomAction(name, arguments);
 
     // addTracks expects a List<Map<String, dynamic>> as its argument.

mobile/lib/screens/home.dart

@@ -1,10 +1,8 @@
 import 'package:flutter/material.dart';
+import 'package:musicus_common/musicus_common.dart';
 import 'package:musicus_database/musicus_database.dart';
 
-import '../backend.dart';
-import '../editors/tracks.dart';
 import '../icons.dart';
-import '../widgets/lists.dart';
 
 import 'person.dart';
 import 'settings.dart';
@@ -19,7 +17,7 @@ class _HomeScreenState extends State<HomeScreen> {
 
   @override
   Widget build(BuildContext context) {
-    final backend = Backend.of(context);
+    final backend = MusicusBackend.of(context);
 
     return Scaffold(
       appBar: AppBar(

mobile/lib/screens/person.dart

@@ -1,10 +1,7 @@
 import 'package:flutter/material.dart';
+import 'package:musicus_common/musicus_common.dart';
 import 'package:musicus_database/musicus_database.dart';
 
-import '../backend.dart';
-import '../editors/person.dart';
-import '../widgets/lists.dart';
-
 import 'work.dart';
 
 class PersonScreen extends StatefulWidget {
@@ -23,7 +20,7 @@ class _PersonScreenState extends State<PersonScreen> {
 
   @override
   Widget build(BuildContext context) {
-    final backend = Backend.of(context);
+    final backend = MusicusBackend.of(context);
 
     return Scaffold(
       appBar: AppBar(

mobile/lib/screens/program.dart

@@ -1,12 +1,10 @@
 import 'dart:async';
 
 import 'package:flutter/material.dart';
+import 'package:musicus_common/musicus_common.dart';
 import 'package:musicus_database/musicus_database.dart';
 
-import '../backend.dart';
-import '../music_library.dart';
 import '../widgets/play_pause_button.dart';
-import '../widgets/recording_tile.dart';
 
 class ProgramScreen extends StatefulWidget {
   @override
@@ -14,7 +12,7 @@ class ProgramScreen extends StatefulWidget {
 }
 
 class _ProgramScreenState extends State<ProgramScreen> {
-  BackendState backend;
+  MusicusBackendState backend;
 
   StreamSubscription<bool> playerActiveSubscription;
 
@@ -29,14 +27,14 @@ class _ProgramScreenState extends State<ProgramScreen> {
   void didChangeDependencies() {
     super.didChangeDependencies();
 
-    backend = Backend.of(context);
+    backend = MusicusBackend.of(context);
 
     if (playerActiveSubscription != null) {
       playerActiveSubscription.cancel();
     }
 
     // Close the program screen, if the player is no longer active.
-    playerActiveSubscription = backend.player.active.listen((active) {
+    playerActiveSubscription = backend.playback.active.listen((active) {
       if (!active) {
         Navigator.pop(context);
       }
@@ -46,7 +44,7 @@ class _ProgramScreenState extends State<ProgramScreen> {
       playlistSubscription.cancel();
     }
 
-    playlistSubscription = backend.player.playlist.listen((playlist) {
+    playlistSubscription = backend.playback.playlist.listen((playlist) {
       updateProgram(playlist);
     });
 
@@ -54,7 +52,7 @@ class _ProgramScreenState extends State<ProgramScreen> {
       positionSubscription.cancel();
     }
 
-    positionSubscription = backend.player.normalizedPosition.listen((pos) {
+    positionSubscription = backend.playback.normalizedPosition.listen((pos) {
       if (!seeking) {
         setState(() {
           position = pos;
@@ -154,7 +152,7 @@ class _ProgramScreenState extends State<ProgramScreen> {
         title: Text('Program'),
       ),
       body: StreamBuilder<int>(
-        stream: backend.player.currentIndex,
+        stream: backend.playback.currentIndex,
         builder: (context, snapshot) {
           if (snapshot.hasData) {
             return ListView.builder(
@@ -181,7 +179,7 @@ class _ProgramScreenState extends State<ProgramScreen> {
                     ],
                   ),
                   onTap: () {
-                    backend.player.skipTo(index);
+                    backend.playback.skipTo(index);
                   },
                   onLongPress: () {
                     showDialog(
@@ -192,7 +190,7 @@ class _ProgramScreenState extends State<ProgramScreen> {
                             ListTile(
                               title: Text('Remove from playlist'),
                               onTap: () {
-                                backend.player.removeTrack(index);
+                                backend.playback.removeTrack(index);
                                 Navigator.pop(context);
                               },
                             ),
@@ -220,7 +218,7 @@ class _ProgramScreenState extends State<ProgramScreen> {
               },
               onChangeEnd: (pos) {
                 seeking = false;
-                backend.player.seekTo(pos);
+                backend.playback.seekTo(pos);
               },
               onChanged: (pos) {
                 setState(() {
@@ -233,7 +231,7 @@ class _ProgramScreenState extends State<ProgramScreen> {
                 Padding(
                   padding: const EdgeInsets.only(left: 24.0),
                   child: StreamBuilder<Duration>(
-                    stream: backend.player.position,
+                    stream: backend.playback.position,
                     builder: (context, snapshot) {
                       if (snapshot.hasData) {
                         return DurationText(snapshot.data);
@@ -247,21 +245,21 @@ class _ProgramScreenState extends State<ProgramScreen> {
                 IconButton(
                   icon: const Icon(Icons.skip_previous),
                   onPressed: () {
-                    backend.player.skipToPrevious();
+                    backend.playback.skipToPrevious();
                   },
                 ),
                 PlayPauseButton(),
                 IconButton(
                   icon: const Icon(Icons.skip_next),
                   onPressed: () {
-                    backend.player.skipToNext();
+                    backend.playback.skipToNext();
                   },
                 ),
                 Spacer(),
                 Padding(
                   padding: const EdgeInsets.only(right: 20.0),
                   child: StreamBuilder<Duration>(
-                    stream: backend.player.duration,
+                    stream: backend.playback.duration,
                     builder: (context, snapshot) {
                       if (snapshot.hasData) {
                         return DurationText(snapshot.data);

mobile/lib/screens/server_settings.dart

@@ -1,9 +1,7 @@
 import 'dart:async';
 
 import 'package:flutter/material.dart';
-
+import 'package:musicus_common/musicus_common.dart';
-import '../backend.dart';
-import '../settings.dart';
 
 class ServerSettingsScreen extends StatefulWidget {
   @override
@@ -13,16 +11,16 @@ class ServerSettingsScreen extends StatefulWidget {
 class _ServerSettingsScreenState extends State<ServerSettingsScreen> {
   final hostController = TextEditingController();
   final portController = TextEditingController();
-  final basePathController = TextEditingController();
+  final apiPathController = TextEditingController();
 
-  BackendState backend;
+  MusicusBackendState backend;
-  StreamSubscription<ServerSettings> serverSubscription;
+  StreamSubscription<MusicusServerSettings> serverSubscription;
 
   @override
   void didChangeDependencies() {
     super.didChangeDependencies();
 
-    backend = Backend.of(context);
+    backend = MusicusBackend.of(context);
 
     if (serverSubscription != null) {
       serverSubscription.cancel();
@@ -34,10 +32,10 @@ class _ServerSettingsScreenState extends State<ServerSettingsScreen> {
     });
   }
 
-  void _settingsChanged(ServerSettings settings) {
+  void _settingsChanged(MusicusServerSettings settings) {
     hostController.text = settings.host;
     portController.text = settings.port.toString();
-    basePathController.text = settings.basePath;
+    apiPathController.text = settings.apiPath;
   }
 
   @override
@@ -50,15 +48,15 @@ class _ServerSettingsScreenState extends State<ServerSettingsScreen> {
             icon: const Icon(Icons.restore),
             tooltip: 'Reset to default',
             onPressed: () {
-              backend.settings.resetServerSettings();
+              backend.settings.resetServer();
             },
           ),
           FlatButton(
             onPressed: () async {
-              await backend.settings.setServerSettings(ServerSettings(
+              await backend.settings.setServer(MusicusServerSettings(
                 host: hostController.text,
                 port: int.parse(portController.text),
-                basePath: basePathController.text,
+                apiPath: apiPathController.text,
               ));
 
               Navigator.pop(context);
@@ -91,7 +89,7 @@ class _ServerSettingsScreenState extends State<ServerSettingsScreen> {
           Padding(
             padding: const EdgeInsets.all(16.0),
             child: TextField(
-              controller: basePathController,
+              controller: apiPathController,
               decoration: InputDecoration(
                 labelText: 'API path',
               ),

mobile/lib/screens/settings.dart

@@ -1,14 +1,15 @@
 import 'package:flutter/material.dart';
-
+import 'package:flutter/services.dart';
-import '../backend.dart';
+import 'package:musicus_common/musicus_common.dart';
-import '../settings.dart';
 
 import 'server_settings.dart';
 
 class SettingsScreen extends StatelessWidget {
+  static const _platform = MethodChannel('de.johrpan.musicus/platform');
+
   @override
   Widget build(BuildContext context) {
-    final backend = Backend.of(context);
+    final backend = MusicusBackend.of(context);
     final settings = backend.settings;
 
     return Scaffold(
@@ -18,18 +19,23 @@ class SettingsScreen extends StatelessWidget {
       body: ListView(
         children: <Widget>[
           StreamBuilder<String>(
-              stream: settings.musicLibraryUri,
+              stream: settings.musicLibraryPath,
               builder: (context, snapshot) {
                 return ListTile(
                   title: Text('Music library path'),
                   subtitle: Text(snapshot.data ?? 'Choose folder'),
                   isThreeLine: snapshot.hasData,
-                  onTap: () {
+                  onTap: () async {
-                    settings.chooseMusicLibraryUri();
+                    final uri =
+                        await _platform.invokeMethod<String>('openTree');
+
+                    if (uri != null) {
+                      settings.setMusicLibraryPath(uri);
+                    }
                   },
                 );
               }),
-          StreamBuilder<ServerSettings>(
+          StreamBuilder<MusicusServerSettings>(
               stream: settings.server,
               builder: (context, snapshot) {
                 final s = snapshot.data;
@@ -37,10 +43,10 @@ class SettingsScreen extends StatelessWidget {
                 return ListTile(
                   title: Text('Musicus server'),
                   subtitle: Text(
-                      s != null ? '${s.host}:${s.port}${s.basePath}' : '...'),
+                      s != null ? '${s.host}:${s.port}${s.apiPath}' : '...'),
                   trailing: const Icon(Icons.chevron_right),
                   onTap: () async {
-                    final ServerSettings result = await Navigator.push(
+                    final MusicusServerSettings result = await Navigator.push(
                       context,
                       MaterialPageRoute(
                         builder: (context) => ServerSettingsScreen(),
@@ -48,7 +54,7 @@ class SettingsScreen extends StatelessWidget {
                     );
 
                     if (result != null) {
-                      settings.setServerSettings(result);
+                      settings.setServer(result);
                     }
                   },
                 );

mobile/lib/screens/work.dart

@@ -1,11 +1,7 @@
 import 'package:flutter/material.dart';
+import 'package:musicus_common/musicus_common.dart';
 import 'package:musicus_database/musicus_database.dart';
 
-import '../backend.dart';
-import '../editors/work.dart';
-import '../widgets/texts.dart';
-import '../widgets/lists.dart';
-
 class WorkScreen extends StatelessWidget {
   final WorkInfo workInfo;
 
@@ -15,7 +11,7 @@ class WorkScreen extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    final backend = Backend.of(context);
+    final backend = MusicusBackend.of(context);
 
     return Scaffold(
       appBar: AppBar(
@@ -46,11 +42,11 @@ class WorkScreen extends StatelessWidget {
             performanceInfos: recordingInfo.performances,
           ),
           onTap: () {
-            final tracks = backend.ml.tracks[recordingInfo.recording.id];
+            final tracks = backend.library.tracks[recordingInfo.recording.id];
             tracks.sort((t1, t2) => t1.track.index.compareTo(t2.track.index));
 
-            backend.player
+            backend.playback
-                .addTracks(backend.ml.tracks[recordingInfo.recording.id]);
+                .addTracks(backend.library.tracks[recordingInfo.recording.id]);
           },
         ),
       ),

mobile/lib/settings.dart

@@ -1,102 +1,30 @@
-import 'package:flutter/services.dart';
+import 'package:musicus_common/musicus_common.dart';
-import 'package:meta/meta.dart';
-import 'package:rxdart/rxdart.dart';
 import 'package:shared_preferences/shared_preferences.dart';
 
-/// Settings concerning the Musicus server to connect to.
+class SettingsStorage extends MusicusSettingsStorage {
-///
+  SharedPreferences _pref;
-/// We don't support setting a scheme here, because there may be password being
-/// submitted in the future, so we default to HTTPS.
-class ServerSettings {
-  static const defaultHost = 'musicus.johrpan.de';
-  static const defaultPort = 1833;
-  static const defaultBasePath = '/api';
 
-  /// Host to connect to, e.g. 'musicus.johrpan.de';
-  final String host;
-
-  /// Port to connect to.
-  final int port;
-
-  /// Path to the API.
-  ///
-  /// This should be null, if the API is at the root of the host.
-  final String basePath;
-
-  ServerSettings({
-    @required this.host,
-    @required this.port,
-    @required this.basePath,
-  });
-}
-
-/// Manager for all settings that are persisted.
-class Settings {
-  static const defaultHost = 'musicus.johrpan.de';
-  static const defaultPort = 443;
-  static const defaultBasePath = '/api';
-
-  static const _platform = MethodChannel('de.johrpan.musicus/platform');
-
-  /// The tree storage access framework tree URI of the music library.
-  final musicLibraryUri = BehaviorSubject<String>();
-
-  /// Musicus server to connect to.
-  final server = BehaviorSubject<ServerSettings>();
-
-  SharedPreferences _shPref;
-
-  /// Initialize the settings.
   Future<void> load() async {
-    _shPref = await SharedPreferences.getInstance();
+    _pref = await SharedPreferences.getInstance();
-
-    final uri = _shPref.getString('musicLibraryUri');
-    if (uri != null) {
-      musicLibraryUri.add(uri);
   }
 
-    final host = _shPref.getString('serverHost') ?? defaultHost;
+  @override
-    final port = _shPref.getInt('serverPort') ?? defaultPort;
+  Future<int> getInt(String key) {
-    final basePath = _shPref.getString('serverBasePath') ?? defaultBasePath;
+    return Future.value(_pref.getInt(key));
-
-    server.add(ServerSettings(
-      host: host,
-      port: port,
-      basePath: basePath,
-    ));
   }
 
-  /// Open the system picker to select a new music library URI.
+  @override
-  Future<void> chooseMusicLibraryUri() async {
+  Future<String> getString(String key) {
-    final uri = await _platform.invokeMethod<String>('openTree');
+    return Future.value(_pref.getString(key));
-
-    if (uri != null) {
-      musicLibraryUri.add(uri);
-      await _shPref.setString('musicLibraryUri', uri);
-    }
   }
 
-  /// Change the Musicus server settings.
+  @override
-  Future<void> setServerSettings(ServerSettings settings) async {
+  Future<void> setInt(String key, int value) async {
-    await _shPref.setString('serverHost', settings.host);
+    await _pref.setInt(key, value);
-    await _shPref.setInt('serverPort', settings.port);
-    await _shPref.setString('serverBasePath', settings.basePath);
-
-    server.add(settings);
   }
 
-  /// Reset the server settings to their defaults.
+  @override
-  Future<void> resetServerSettings() async {
+  Future<void> setString(String key, String value) async {
-    await setServerSettings(ServerSettings(
+    await _pref.setString(key, value);
-      host: defaultHost,
-      port: defaultPort,
-      basePath: defaultBasePath,
-    ));
-  }
-
-  /// Tidy up.
-  void dispose() {
-    musicLibraryUri.close();
-    server.close();
   }
 }

mobile/lib/widgets/play_pause_button.dart

@@ -1,8 +1,7 @@
 import 'dart:async';
 
 import 'package:flutter/material.dart';
-
+import 'package:musicus_common/musicus_common.dart';
-import '../backend.dart';
 
 class PlayPauseButton extends StatefulWidget {
   @override
@@ -12,7 +11,7 @@ class PlayPauseButton extends StatefulWidget {
 class _PlayPauseButtonState extends State<PlayPauseButton>
     with SingleTickerProviderStateMixin {
   AnimationController playPauseAnimation;
-  BackendState backend;
+  MusicusBackendState backend;
   StreamSubscription<bool> playingSubscription;
 
   @override
@@ -29,14 +28,14 @@ class _PlayPauseButtonState extends State<PlayPauseButton>
   void didChangeDependencies() {
     super.didChangeDependencies();
 
-    backend = Backend.of(context);
+    backend = MusicusBackend.of(context);
-    playPauseAnimation.value = backend.player.playing.value ? 1.0 : 0.0;
+    playPauseAnimation.value = backend.playback.playing.value ? 1.0 : 0.0;
 
     if (playingSubscription != null) {
       playingSubscription.cancel();
     }
 
-    playingSubscription = backend.player.playing.listen((playing) =>
+    playingSubscription = backend.playback.playing.listen((playing) =>
         playing ? playPauseAnimation.forward() : playPauseAnimation.reverse());
   }
 
@@ -47,7 +46,7 @@ class _PlayPauseButtonState extends State<PlayPauseButton>
         icon: AnimatedIcons.play_pause,
         progress: playPauseAnimation,
       ),
-      onPressed: backend.player.playPause,
+      onPressed: backend.playback.playPause,
     );
   }
 

mobile/lib/widgets/player_bar.dart

@@ -1,17 +1,15 @@
 import 'package:flutter/material.dart';
+import 'package:musicus_common/musicus_common.dart';
 import 'package:musicus_database/musicus_database.dart';
 
-import '../backend.dart';
-import '../music_library.dart';
 import '../screens/program.dart';
 
 import 'play_pause_button.dart';
-import 'texts.dart';
 
 class PlayerBar extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
-    final backend = Backend.of(context);
+    final backend = MusicusBackend.of(context);
 
     return BottomAppBar(
       child: InkWell(
@@ -19,7 +17,7 @@ class PlayerBar extends StatelessWidget {
           mainAxisSize: MainAxisSize.min,
           children: <Widget>[
             StreamBuilder(
-              stream: backend.player.normalizedPosition,
+              stream: backend.playback.normalizedPosition,
               builder: (context, snapshot) => LinearProgressIndicator(
                 value: snapshot.data,
               ),
@@ -32,7 +30,7 @@ class PlayerBar extends StatelessWidget {
                 ),
                 Expanded(
                   child: StreamBuilder<InternalTrack>(
-                    stream: backend.player.currentTrack,
+                    stream: backend.playback.currentTrack,
                     builder: (context, snapshot) {
                       if (snapshot.data != null) {
                         final recordingId = snapshot.data.track.recordingId;

mobile/pubspec.yaml

@@ -17,6 +17,8 @@ dependencies:
   moor_ffi:
   musicus_client:
     path: ../client
+  musicus_common:
+    path: ../common
   musicus_database:
     path: ../database
   musicus_player: