/*
 * Copyright (C) 2010 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License
 */
package io.pivotal.arca.dispatcher;

import android.annotation.SuppressLint;
import android.os.AsyncTask;
import android.os.Handler;
import android.os.Looper;
import android.os.Message;
import android.support.v4.content.Loader;
import android.support.v4.content.Loader.OnLoadCompleteListener;
import android.test.AndroidTestCase;

import java.util.concurrent.ArrayBlockingQueue;

/**
 * A convenience class for testing {@link android.support.v4.content.Loader}s. This test case
 * provides a simple way to synchronously get the result from a Loader making
 * it easy to assert that the Loader returns the expected result.
 */
public class SupportLoaderTestCase extends AndroidTestCase {

	    static {
	        // Force class loading of AsyncTask on the main thread so that it's handlers are tied to
	        // the main thread and responses from the worker thread get delivered on the main thread.
	        // The tests are run on another thread, allowing them to block waiting on a response from
	        // the code running on the main thread. The main thread can't block since the AysncTask
	        // results come in via the event loop.
	        new AsyncTask<Void, Void, Void>() {
	            @Override
	            protected Void doInBackground(Void... args) {return null;}
	            @Override
	            protected void onPostExecute(Void result) {}
	        };
	    }

	    /**
	     * Runs a Loader synchronously and returns the result of the load. The loader will
	     * be started, stopped, and destroyed by this method so it cannot be reused.
	     *
	     * @param loader The loader to run synchronously
	     * @return The result from the loader
	     */
	    @SuppressLint("HandlerLeak")
		public <T> T getLoaderResultSynchronously(final Loader<T> loader) {
	        // The test thread blocks on this queue until the loader puts it's result in
	        final ArrayBlockingQueue<T> queue = new ArrayBlockingQueue<T>(1);

	        // This callback runs on the "main" thread and unblocks the test thread
	        // when it puts the result into the blocking queue
	        final OnLoadCompleteListener<T> listener = new OnLoadCompleteListener<T>() {
	            @Override
	            public void onLoadComplete(Loader<T> completedLoader, T data) {
	                // Shut the loader down
	                completedLoader.unregisterListener(this);
	                completedLoader.stopLoading();
	                completedLoader.reset();

	                // Store the result, unblocking the test thread
	                queue.add(data);
	            }
	        };

	        // This handler runs on the "main" thread of the process since AsyncTask
	        // is documented as needing to run on the main thread and many Loaders use
	        // AsyncTask
	        final Handler mainThreadHandler = new Handler(Looper.getMainLooper()) {
	            @Override
	            public void handleMessage(Message msg) {
	                loader.registerListener(0, listener);
	                loader.startLoading();
	            }
	        };

	        // Ask the main thread to start the loading process
	        mainThreadHandler.sendEmptyMessage(0);

	        // Block on the queue waiting for the result of the load to be inserted
	        T result;
	        while (true) {
	            try {
	                result = queue.take();
	                break;
	            } catch (InterruptedException e) {
	                throw new RuntimeException("waiting thread interrupted", e);
	            }
	        }

	        return result;
	    }
	}