Add sync button to playlist screen

lib/components/AlbumScreen/album_screen_content.dart

@@ -1,3 +1,4 @@
+import 'package:finamp/components/AlbumScreen/sync_playlist.dart';
 import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_gen/gen_l10n/app_localizations.dart';
@@ -77,7 +78,9 @@ class _AlbumScreenContentState extends State<AlbumScreenContent> {
                   !FinampSettingsHelper.finampSettings.isOffline)
                 PlaylistNameEditButton(playlist: widget.parent),
               FavoriteButton(item: widget.parent),
-              DownloadButton(parent: widget.parent, items: widget.children)
+              DownloadButton(parent: widget.parent, items: widget.children),
+              if (widget.parent.type == "Playlist" && !FinampSettingsHelper.finampSettings.isOffline)
+                SyncPlaylistButton(parent: widget.parent, items: widget.children)
             ],
           ),
           if (widget.children.length > 1 &&

lib/components/AlbumScreen/sync_playlist.dart

@@ -0,0 +1,86 @@
+import 'dart:collection';
+
+import 'package:finamp/models/finamp_models.dart';
+import 'package:finamp/models/jellyfin_models.dart';
+import 'package:finamp/services/downloads_helper.dart';
+import 'package:finamp/services/jellyfin_api_helper.dart';
+import 'package:flutter/material.dart';
+import 'package:get_it/get_it.dart';
+import 'package:logging/logging.dart';
+
+import '../../services/finamp_settings_helper.dart';
+import '../../services/finamp_user_helper.dart';
+
+class SyncPlaylistButton extends StatefulWidget {
+  const SyncPlaylistButton({
+    Key? key,
+    required this.parent,
+    required this.items,
+  }) : super(key: key);
+
+  final BaseItemDto parent;
+  final List<BaseItemDto> items;
+  @override
+  State<SyncPlaylistButton> createState() =>
+      _SyncPlaylistButtonState();
+}
+class _SyncPlaylistButtonState
+    extends State<SyncPlaylistButton> {
+  final _syncLogger = Logger("SyncPlaylistButton");
+  final DownloadsHelper downloadsHelper = GetIt.instance<DownloadsHelper>();
+  final JellyfinApiHelper jellyfinApiHelper = GetIt.instance<JellyfinApiHelper>();
+  final FinampUserHelper _finampUserHelper = GetIt.instance<FinampUserHelper>();
+
+  void syncPlaylist() async {
+    _syncLogger.info("Syncing playlist");
+
+    List<DownloadedSong> downloadedSongs = downloadsHelper.downloadedItems.toList();
+    Map<String, DownloadedSong> downloadedSongsCache = HashMap();
+    Map<String, BaseItemDto> playlistItems = HashMap();
+    String playlistParentId = widget.parent.id;
+    for (BaseItemDto item in widget.items) {
+      // songs actively in playlist
+      playlistItems.putIfAbsent(item.id, () => item);
+    }
+
+    for (DownloadedSong downloadedSong in downloadedSongs) {
+      if (downloadedSong.mediaSourceInfo.id != null &&
+          downloadedSong.requiredBy.contains(playlistParentId)) {
+        // songs actively downloaded
+        downloadedSongsCache.putIfAbsent(downloadedSong.mediaSourceInfo.id!, () => downloadedSong);
+      }
+    }
+
+    Set<String> playlistIds = playlistItems.keys.toSet();
+    Set<String> downloadedIds = downloadedSongsCache.keys.toSet();
+    Set<String> idsToAdd = playlistIds.difference(downloadedIds);
+    Set<String> idsToRemove = downloadedIds.difference(playlistIds);
+    Set<String> unchangedIds = playlistIds.intersection(downloadedIds);
+
+    _syncLogger.info("Items to be added $idsToAdd");
+    _syncLogger.info("Items to be removed $idsToRemove");
+    _syncLogger.info("Items with no change $unchangedIds");
+    await downloadsHelper.deleteDownloads(jellyfinItemIds: idsToRemove.toList());
+    await downloadsHelper.removeChildFromParent(parentId: playlistParentId, childIds: idsToRemove.toList());
+
+    DownloadLocation location = FinampSettingsHelper.finampSettings.downloadLocationsMap.values.first;
+    for (String itemToAdd in idsToAdd) {
+      BaseItemDto? item = playlistItems.remove(itemToAdd);
+      if (item != null) {
+        await downloadsHelper.addDownloads(
+          items: [item],
+          parent: widget.parent,
+          useHumanReadableNames: location.useHumanReadableNames,
+          downloadLocation: location,
+          viewId: _finampUserHelper.currentUser!.currentViewId!,
+        );
+      }
+    }
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return IconButton(
+        onPressed: () => syncPlaylist(), icon: const Icon(Icons.sync));
+  }
+}

lib/services/downloads_helper.dart

@@ -246,6 +246,13 @@ class DownloadsHelper {
     }
   }
 
+  Future<void> removeChildFromParent({required String parentId, required List<String> childIds}) async {
+    var album = _downloadedParentsBox.get(parentId);
+    for (String childId in childIds) {
+      album?.downloadedChildren.removeWhere((key, value) => key == childId);
+    }
+  }
+
   /// Deletes download tasks for items with ids in jellyfinItemIds from storage
   /// and removes the Hive entries for that download task. If deletedFor is
   /// specified, also do checks to delete the parent album. The only time