Pull current track from Redux store

Fixes #40

src/components/App.tsx

@@ -11,7 +11,8 @@ import {
 } from '@react-navigation/native';
 import { useColorScheme } from 'react-native';
 import { ColorSchemeContext, themes } from './Colors';
-import ErrorReportingAlert from 'utility/ErrorReportingAlert';
+// import ErrorReportingAlert from 'utility/ErrorReportingAlert';
+import PlayerStateUpdater from './PlayerStateUpdater';
 
 export default function App(): JSX.Element {
     const colorScheme = useColorScheme();
@@ -41,6 +42,7 @@ export default function App(): JSX.Element {
                 <ColorSchemeContext.Provider value={theme}>
                     <NavigationContainer theme={colorScheme === 'dark' ? DarkTheme : DefaultTheme}>
                         <Routes />
+                        <PlayerStateUpdater />
                     </NavigationContainer>
                 </ColorSchemeContext.Provider>
             </PersistGate>

src/components/PlayerStateUpdater.ts

@@ -0,0 +1,54 @@
+import { useCallback, useEffect } from 'react';
+import TrackPlayer, { TrackPlayerEvents } from 'react-native-track-player';
+import { shallowEqual, useDispatch } from 'react-redux';
+import { useTypedSelector } from 'store';
+import player from 'store/player';
+
+function PlayerStateUpdater() {
+    const dispatch = useDispatch();
+    const trackId = useTypedSelector(state => state.player.currentTrack?.id, shallowEqual);
+
+    const handleUpdate = useCallback(async () => {
+        const currentTrackId = await TrackPlayer.getCurrentTrack();
+
+        // GUARD: Only retrieve new track if it is different from the one we
+        // have currently in state.
+        if (currentTrackId === trackId){
+            return;
+        }
+                
+        // GUARD: Only fetch current track if there is a current track
+        if (!currentTrackId) {
+            dispatch(player.actions.setCurrentTrack(undefined));
+        }
+
+        // If it is different, retrieve the track and save it
+        try {
+            const currentTrack = await TrackPlayer.getTrack(currentTrackId);
+            dispatch(player.actions.setCurrentTrack(currentTrack));
+        } catch {
+            // Due to the async nature, a track might be removed at the
+            // point when we try to retrieve it. If this happens, we'll just
+            // smother the error and wait for a new track update to
+            // finish.
+        }
+    }, [trackId, dispatch]);
+
+    useEffect(() => {
+        function handler() {
+            handleUpdate();
+        }
+
+        handler();
+
+        const subscription = TrackPlayer.addEventListener(TrackPlayerEvents.PLAYBACK_TRACK_CHANGED, handler);
+        
+        return () => {
+            subscription.remove();
+        };
+    }, []);
+
+    return null;
+}
+
+export default PlayerStateUpdater;