add download service with limited functionality

app/src/main/java/com/dkanada/gramophone/service/DownloadService.java

@@ -0,0 +1,88 @@
+package com.dkanada.gramophone.service;
+
+import android.app.Service;
+import android.content.Intent;
+import android.os.Environment;
+import android.os.Handler;
+import android.os.IBinder;
+import android.os.Looper;
+
+import com.dkanada.gramophone.App;
+import com.dkanada.gramophone.BuildConfig;
+import com.dkanada.gramophone.model.Song;
+import com.dkanada.gramophone.util.MusicUtil;
+
+import java.io.File;
+import java.io.FileOutputStream;
+import java.io.InputStream;
+import java.io.OutputStream;
+import java.net.URL;
+import java.net.URLConnection;
+import java.util.concurrent.Executor;
+import java.util.concurrent.Executors;
+
+public class DownloadService extends Service {
+    public static final String PACKAGE_NAME = BuildConfig.APPLICATION_ID;
+    public static final String EXTRA_SONG = PACKAGE_NAME + ".extra.song";
+
+    private Executor executor;
+    private Handler handler;
+
+    @Override
+    public void onCreate() {
+        super.onCreate();
+
+        Looper looper = Looper.myLooper();
+        if (looper == null) {
+            looper = Looper.getMainLooper();
+        }
+
+        executor = Executors.newFixedThreadPool(4);
+        handler = new Handler(looper);
+    }
+
+    @Override
+    public int onStartCommand(Intent intent, int flags, int startId) {
+        if (intent == null) return super.onStartCommand(null, flags, startId);
+        Song song = intent.getParcelableExtra(EXTRA_SONG);
+
+        executor.execute(() -> {
+            try {
+                URL url = new URL(MusicUtil.getDownloadUri(song));
+                URLConnection connection = url.openConnection();
+
+                File root = new File(App.getInstance().getCacheDir(), "music");
+                String path = song.artistName + "/" + song.albumName + "/";
+                String name = song.discNumber + "." + song.trackNumber + " - " + song.title + "." + song.container;
+                File audio = new File(root, path + name);
+
+                audio.getParentFile().mkdirs();
+                audio.createNewFile();
+
+                InputStream input = connection.getInputStream();
+                OutputStream output = new FileOutputStream(audio);
+
+                connection.connect();
+
+                byte[] data = new byte[4096];
+                int count;
+
+                while ((count = input.read(data)) != -1) {
+                    output.write(data, 0, count);
+                }
+
+                input.close();
+                output.close();
+            } catch (Exception e) {
+                e.printStackTrace();
+            }
+        });
+
+        return super.onStartCommand(intent, flags, startId);
+    }
+
+    @Override
+    public IBinder onBind(Intent intent) {
+        return null;
+    }
+}