Started to implement the main IntentService for background operations

app/src/main/java/de/mobcomp/grades/main/MainService.java

@@ -0,0 +1,67 @@
+package de.mobcomp.grades.main;
+
+import android.app.IntentService;
+import android.content.Intent;
+import android.util.Log;
+
+import java.util.HashSet;
+import java.util.Set;
+
+/**
+ * This service is used to handle ongoing operations in the background.
+ * It is mostly used for network operations.
+ *
+ * The incoming intent must specify two extra Strings (PROCESSOR_KEY, METHOD_KEY),
+ * so the service can decide which processor to create and which method to call.
+ */
+public class MainService extends IntentService {
+    private static final String TAG = MainService.class.getSimpleName();
+
+    // intent extra keys TODO: add corresponding values for processors and methods.
+    public static final String PROCESSOR_KEY = "processor_key";
+    public static final String METHOD_KEY = "method_key";
+    public static final String REQUEST_ID = "request_id";
+
+    // save request ids for pending request in this set, and remove them when its done.
+    private Set<Long> pendingRequest;
+
+    /**
+     * Creates an IntentService. Invoked by your subclass's constructor.
+     */
+    public MainService() {
+        super(TAG);
+        pendingRequest = new HashSet<>();
+    }
+
+    @Override
+    public void onStart(Intent intent, int startId) {
+        long requestId = intent.getLongExtra(REQUEST_ID, -1);
+        if (pendingRequest.contains(requestId)) {
+            // ignore intent if it is already pending
+            return;
+        }
+
+        // add request to pending requests
+        pendingRequest.add(requestId);
+
+        // add intent to message queue
+        super.onStart(intent, startId);
+    }
+
+    @Override
+    protected void onHandleIntent(Intent intent) {
+        // get desired processor and method from extras
+        int processor = intent.getIntExtra(PROCESSOR_KEY, -1);
+        int method = intent.getIntExtra(METHOD_KEY, -1);
+
+        switch (processor) {
+            default:
+                Log.e(TAG, "Invalid processor call to MainService: " + processor);
+                break;
+        }
+
+        // remove request id from pending requests
+        long requestId = intent.getLongExtra(REQUEST_ID, -1);
+        pendingRequest.remove(requestId);
+    }
+}