Allow for retring individual tracks

src/store/downloads/selectors.ts

@@ -2,12 +2,28 @@ import { createSelector, EntityId } from '@reduxjs/toolkit';
 import { intersection } from 'lodash';
 import { AppState } from 'store';
 
+export const selectAllDownloads = (state: AppState) => state.downloads;
+export const selectDownloadedEntities = (state: AppState) => state.downloads.entities;
+
+/**
+ * Only retain the supplied trackIds that have successfully been downloaded
+ */
 export const selectDownloadedTracks = (trackIds: EntityId[]) => (
     createSelector(
-        (state: AppState) => state.downloads,
+        selectAllDownloads,
         ({ entities, ids }) => {
             return intersection(trackIds, ids)
                 .filter((id) => entities[id]?.isComplete);
         }
     )
 );
+
+/**
+ * Select a boolean that indicates whether the track is downloaded
+ */
+export const selectIsDownloaded = (trackId: string) => (
+    createSelector(
+        selectDownloadedEntities,
+        (entities) => entities[trackId]?.isComplete,
+    )
+);