Add music library

android/app/src/main/kotlin/de/johrpan/musicus/MainActivity.kt

@@ -40,6 +40,22 @@ class MainActivity : FlutterActivity() {
                 val parentId = call.argument<String>("parentId")
                 val children = getChildren(treeUri, parentId)
                 result.success(children.map { it.toMap() })
+            } else if (call.method == "readFile") {
+                val treeUri = Uri.parse(call.argument<String>("treeUri"))
+                val id = call.argument<String>("id")!!
+                result.success(readFile(treeUri, id))
+            } else if (call.method == "readFileByName") {
+                val treeUri = Uri.parse(call.argument<String>("treeUri"))
+                val parentId = call.argument<String>("parentId")!!
+                val fileName = call.argument<String>("fileName")!!
+                result.success(readFileByName(treeUri, parentId, fileName))
+            } else if (call.method == "writeFileByName") {
+                val treeUri = Uri.parse(call.argument<String>("treeUri"))
+                val parentId = call.argument<String>("parentId")!!
+                val fileName = call.argument<String>("fileName")!!
+                val content = call.argument<String>("content")!!
+                writeFileByName(treeUri, parentId, fileName, content)
+                result.success(null)
             } else {
                 result.notImplemented()
             }
@@ -114,4 +130,104 @@ class MainActivity : FlutterActivity() {
 
         return children
     }
+
+    /**
+     * Look for a file by name
+     *
+     * @param treeUri The treeUri from the ACTION_OPEN_DOCUMENT_TREE request
+     * @param parentId The directory in which the file is searched for
+     * @param fileName Name of the file
+     * @return The URI of the file or null
+     */
+    private fun getUriByName(treeUri: Uri, parentId: String, fileName: String): Uri? {
+        var uri: Uri? = null
+
+        val childrenUri = DocumentsContract.buildChildDocumentsUriUsingTree(treeUri, parentId)
+        val projection = arrayOf(DocumentsContract.Document.COLUMN_DOCUMENT_ID, DocumentsContract.Document.COLUMN_DISPLAY_NAME)
+        
+        // The file system provider doesn't support a select clause.
+        val cursor = contentResolver.query(childrenUri, projection, null, null, null)
+
+        if (cursor != null) {
+            while (cursor.moveToNext()) {
+                val id = cursor.getString(0)
+                val name = cursor.getString(1)
+
+                if (name == fileName) {
+                    uri = DocumentsContract.buildDocumentUriUsingTree(treeUri, id)
+                    break
+                }
+            }
+
+            cursor.close()
+        }
+
+        return uri
+    }
+
+    /**
+     * Read content of a file
+     *
+     * @param treeUri The URI from ACTION_OPEN_DOCUMENT_TREE
+     * @param id The document ID of the file
+     * @return File content or null
+     */
+    private fun readFile(treeUri: Uri, id: String): String? {
+        val uri = DocumentsContract.buildDocumentUriUsingTree(treeUri, id)
+
+        // TODO: Handle errors.
+        val input = contentResolver.openInputStream(uri)!!
+        val result = input.reader().readText()
+        input.close()
+
+        return result
+    }
+
+    /**
+     * Read content of a file by name
+     *
+     * @param treeUri The URI from ACTION_OPEN_DOCUMENT_TREE
+     * @param parentId Document ID of the parent directory
+     * @param fileName Name of the file
+     * @return File content or null
+     */
+    private fun readFileByName(treeUri: Uri, parentId: String, fileName: String): String? {
+        var uri = getUriByName(treeUri, parentId, fileName)
+
+        return if (uri != null) {
+            // TODO: Handle errors.
+            val input = contentResolver.openInputStream(uri)!!
+            val result = input.reader().readText()
+            input.close()
+
+            return result
+        } else {
+            null
+        }
+    }
+
+    /**
+     * Write to file by name
+     * 
+     * The file will always have the MIME type application/json.
+     *
+     * @param treeUri The URI from ACTION_OPEN_DOCUMENT_TREE
+     * @param parentId Document ID of the parent directory
+     * @param fileName Name of the file
+     * @param content Content to write
+     * @return File content or null
+     */
+    private fun writeFileByName(treeUri: Uri, parentId: String, fileName: String, content: String) {
+        var uri = getUriByName(treeUri, parentId, fileName);
+
+        if (uri == null) {
+            val parentUri = DocumentsContract.buildDocumentUriUsingTree(treeUri, parentId)
+            uri = DocumentsContract.createDocument(contentResolver, parentUri, "application/json", fileName)
+        }
+
+        // TODO: Handle errors.
+        val output = contentResolver.openOutputStream(uri!!)!!;
+        output.writer().write(content)
+        output.close()
+    }
 }

lib/backend.dart

@@ -11,6 +11,7 @@ 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
@@ -86,6 +87,7 @@ class BackendState extends State<Backend> {
   BackendStatus status = BackendStatus.loading;
   Database db;
   String musicLibraryUri;
+  MusicLibrary ml;
 
   MoorIsolate _moorIsolate;
   SharedPreferences _shPref;
@@ -122,6 +124,8 @@ class BackendState extends State<Backend> {
         status = BackendStatus.setup;
       });
     } else {
+      ml = MusicLibrary(musicLibraryUri);
+      await ml.load();
       setState(() {
         status = BackendStatus.ready;
       });

lib/editors/tracks.dart

@@ -2,15 +2,15 @@ import 'package:flutter/material.dart';
 
 import '../backend.dart';
 import '../database.dart';
+import '../music_library.dart';
 import '../selectors/files.dart';
 import '../selectors/recording.dart';
 import '../widgets/recording_tile.dart';
 
-// TODO: Update for storage access framework.
 class TrackModel {
-  String path;
+  String fileName;
 
-  TrackModel(this.path);
+  TrackModel(this.fileName);
 }
 
 class TracksEditor extends StatefulWidget {
@@ -20,7 +20,8 @@ class TracksEditor extends StatefulWidget {
 
 class _TracksEditorState extends State<TracksEditor> {
   int recordingId;
-  List<TrackModel> tracks = [];
+  String parentId;
+  List<TrackModel> trackModels = [];
 
   @override
   Widget build(BuildContext context) {
@@ -33,7 +34,22 @@ class _TracksEditorState extends State<TracksEditor> {
           FlatButton(
             child: Text('DONE'),
             onPressed: () async {
-              // TODO: Save tracks.
+              final List<Track> tracks = [];
+
+              for (var i = 0; i < trackModels.length; i++) {
+                final trackModel = trackModels[i];
+
+                tracks.add(Track(
+                  fileName: trackModel.fileName,
+                  recordingId: recordingId,
+                  index: i,
+                  partIds: [],
+                ));
+              }
+
+              backend.ml.addTracks(parentId, tracks);
+
+              Navigator.pop(context);
             },
           ),
         ],
@@ -63,22 +79,27 @@ class _TracksEditorState extends State<TracksEditor> {
                   );
 
                   if (result != null) {
-                    // TODO: Add tracks.
+                    setState(() {
+                      parentId = result.parentId;
+                      for (final document in result.selection) {
+                        trackModels.add(TrackModel(document.name));
+                      }
+                    });
                   }
                 },
               ),
             ),
           ],
         ),
-        children: tracks
+        children: trackModels
             .map((t) => ListTile(
                   key: Key(t.hashCode.toString()),
-                  title: Text(t.path),
+                  title: Text(t.fileName),
                   trailing: IconButton(
                     icon: const Icon(Icons.delete),
                     onPressed: () {
                       setState(() {
-                        tracks.remove(t);
+                        trackModels.remove(t);
                       });
                     },
                   ),
@@ -86,9 +107,9 @@ class _TracksEditorState extends State<TracksEditor> {
             .toList(),
         onReorder: (i1, i2) {
           setState(() {
-            final track = tracks.removeAt(i1);
+            final track = trackModels.removeAt(i1);
             final newIndex = i2 > i1 ? i2 - 1 : i2;
-            tracks.insert(newIndex, track);
+            trackModels.insert(newIndex, track);
           });
         },
       ),

lib/music_library.dart

@@ -0,0 +1,155 @@
+import 'dart:convert';
+
+import 'package:flutter/services.dart';
+
+import 'platform.dart';
+
+/// Description of a concrete audio file.
+///
+/// This gets stored in the folder of the audio file and links the audio file
+/// to a recording in the database.
+class Track {
+  /// The name of the file that contains the track's audio.
+  ///
+  /// This corresponds to a document ID in terms of the Android Storage Access
+  /// Framework.
+  final String fileName;
+
+  /// Index within the list of tracks for the corresponding recording.
+  final int index;
+
+  /// Of which recording this track is a part of.
+  final int recordingId;
+
+  /// Which work parts of the recorded work are contained in this track.
+  final List<int> partIds;
+
+  Track({
+    this.fileName,
+    this.index,
+    this.recordingId,
+    this.partIds,
+  });
+
+  factory Track.fromJson(Map<String, dynamic> json) => Track(
+        fileName: json['fileName'],
+        index: json['index'],
+        recordingId: json['recording'],
+        partIds: List.from(json['parts']),
+      );
+
+  Map<String, dynamic> toJson() => {
+        'fileName': fileName,
+        'index': index,
+        'recording': recordingId,
+        'parts': partIds,
+      };
+}
+
+/// Representation of all tracked audio files in one folder.
+class MusicusFile {
+  /// Current version of the Musicus file format.
+  ///
+  /// If incompatible changes are made, this will be increased by one.
+  static const currentVersion = 0;
+
+  /// Musicus file format version in use.
+  ///
+  /// This will be used in the future, if incompatible changes are made.
+  final int version;
+
+  /// List of [Track] objects.
+  final List<Track> tracks;
+
+  MusicusFile({
+    this.version = currentVersion,
+    List<Track> tracks,
+  }) : tracks = tracks ?? [];
+
+  factory MusicusFile.fromJson(Map<String, dynamic> json) => MusicusFile(
+        version: json['version'],
+        tracks: json['tracks']
+            .map<Track>((trackJson) => Track.fromJson(trackJson))
+            .toList(growable: true),
+      );
+
+  Map<String, dynamic> toJson() => {
+        'version': version,
+        'tracks': tracks.map((t) => t.toJson()).toList(),
+      };
+}
+
+/// Manager for all available tracks and their representation on disk.
+class MusicLibrary {
+  static const platform = MethodChannel('de.johrpan.musicus/platform');
+
+  /// URI of the music library folder.
+  ///
+  /// 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.
+  final Map<int, List<Track>> tracks = {};
+
+  MusicLibrary(this.treeUri);
+
+  /// Load all available tracks.
+  ///
+  /// This recursively searches through the whole music library, reads the
+  /// content of all files called musicus.json and stores all track information
+  /// that it found.
+  Future<void> load() async {
+    // TODO: Consider capping the recursion somewhere.
+    Future<void> recurse([String parentId]) async {
+      final children = await Platform.getChildren(treeUri, 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 musicusFile = MusicusFile.fromJson(jsonDecode(content));
+          for (final track in musicusFile.tracks) {
+            if (tracks.containsKey(track.recordingId)) {
+              tracks[track.recordingId].add(track);
+            } else {
+              tracks[track.recordingId] = [track];
+            }
+          }
+        }
+      }
+    }
+
+    await recurse();
+  }
+
+  /// Add a list of new tracks to the music library.
+  /// 
+  /// They are stored in this instance and on disk in the directory denoted by
+  /// [parentId].
+  Future<void> addTracks(String parentId, List<Track> newTracks) async {
+    MusicusFile musicusFile;
+
+    final oldContent =
+        await Platform.readFileByName(treeUri, parentId, 'musicus.json');
+
+    if (oldContent != null) {
+      musicusFile = MusicusFile.fromJson(jsonDecode(oldContent));
+    } else {
+      musicusFile = MusicusFile();
+    }
+
+    for (final track in newTracks) {
+      musicusFile.tracks.add(track);
+
+      if (tracks.containsKey(track.recordingId)) {
+        tracks[track.recordingId].add(track);
+      } else {
+        tracks[track.recordingId] = [track];
+      }
+    }
+
+    await Platform.writeFileByName(
+        treeUri, parentId, 'musicus.json', jsonEncode(musicusFile.toJson()));
+  }
+}

lib/platform.dart

@@ -47,4 +47,51 @@ class Platform {
         .map((childJson) => Document.fromJson(childJson))
         .toList();
   }
+
+  /// Read contents of file.
+  ///
+  /// [treeId] is the base URI from the SAF, [id] is the document ID of the
+  /// file.
+  static Future<String> readFile(String treeUri, String id) async {
+    return await _platform.invokeMethod(
+      'readFile',
+      {
+        'treeUri': treeUri,
+        'id': id,
+      },
+    );
+  }
+
+  /// 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,
+        'parentId': parentId,
+        'fileName': fileName,
+      },
+    );
+  }
+
+  /// Write to file by name
+  ///
+  /// [treeId] is the base URI from the SAF, [parentId] is the document ID of
+  /// the parent directory.
+  static Future<void> writeFileByName(
+      String treeUri, String parentId, String fileName, String content) async {
+    await _platform.invokeMethod(
+      'writeFileByName',
+      {
+        'treeUri': treeUri,
+        'parentId': parentId,
+        'fileName': fileName,
+        'content': content,
+      },
+    );
+  }
 }

lib/selectors/files.dart

@@ -12,10 +12,10 @@ class FilesSelectorResult {
   /// This will be null, if they are in the toplevel directory.
   final String parentId;
 
-  /// Document IDs of the selected files.
-  final List<String> trackIds;
+  /// Selected files.
+  final Set<Document> selection;
 
-  FilesSelectorResult(this.parentId, this.trackIds);
+  FilesSelectorResult(this.parentId, this.selection);
 }
 
 class FilesSelector extends StatefulWidget {
@@ -27,7 +27,7 @@ class _FilesSelectorState extends State<FilesSelector> {
   BackendState backend;
   List<Document> history = [];
   List<Document> children = [];
-  Set<String> selectedIds = {};
+  Set<Document> selection = {};
 
   @override
   void didChangeDependencies() {
@@ -57,7 +57,7 @@ class _FilesSelectorState extends State<FilesSelector> {
                   context,
                   FilesSelectorResult(
                     history.isNotEmpty ? history.last.id : null,
-                    selectedIds.toList(),
+                    selection,
                   ),
                 );
               },
@@ -99,13 +99,13 @@ class _FilesSelectorState extends State<FilesSelector> {
                       controlAffinity: ListTileControlAffinity.trailing,
                       secondary: const Icon(Icons.insert_drive_file),
                       title: Text(document.name),
-                      value: selectedIds.contains(document.id),
+                      value: selection.contains(document),
                       onChanged: (selected) {
                         setState(() {
                           if (selected) {
-                            selectedIds.add(document.id);
+                            selection.add(document);
                           } else {
-                            selectedIds.remove(document.id);
+                            selection.remove(document);
                           }
                         });
                       },
@@ -124,6 +124,10 @@ class _FilesSelectorState extends State<FilesSelector> {
   Future<void> loadChildren() async {
     setState(() {
       children = [];
+
+      // We reset the selection here, because the user should not be able to
+      // select files from multiple directories for now.
+      selection = {};
     });
 
     final newChildren = await Platform.getChildren(