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Powerful and flexible instrument for asynchronous image loading, caching and displaying on Android
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/*******************************************************************************
 * Copyright 2011-2013 Sergey Tarasevich
 *
 * 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 com.nostra13.universalimageloader.core;

import android.view.View;
import com.nostra13.universalimageloader.core.assist.FailReason;
import com.nostra13.universalimageloader.core.assist.FlushedInputStream;
import com.nostra13.universalimageloader.core.assist.ImageLoadingListener;
import com.nostra13.universalimageloader.core.imageaware.ImageAware;

import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import java.util.WeakHashMap;
import java.util.concurrent.Executor;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.locks.ReentrantLock;

/**
 * {@link ImageLoader} engine which responsible for {@linkplain LoadAndDisplayImageTask display task} execution.
 *
 * @author Sergey Tarasevich (nostra13[at]gmail[dot]com)
 * @since 1.7.1
 */
class ImageLoaderEngine {

	final ImageLoaderConfiguration configuration;

	private Executor taskExecutor;
	private Executor taskExecutorForCachedImages;
	private ExecutorService taskDistributor;

	private final Map cacheKeysForImageAwares = Collections
			.synchronizedMap(new HashMap());
	private final Map uriLocks = new WeakHashMap();

	private final AtomicBoolean paused = new AtomicBoolean(false);
	private final AtomicBoolean networkDenied = new AtomicBoolean(false);
	private final AtomicBoolean slowNetwork = new AtomicBoolean(false);

	private final Object pauseLock = new Object();

	ImageLoaderEngine(ImageLoaderConfiguration configuration) {
		this.configuration = configuration;

		taskExecutor = configuration.taskExecutor;
		taskExecutorForCachedImages = configuration.taskExecutorForCachedImages;

		taskDistributor = Executors.newCachedThreadPool();
	}

	/** Submits task to execution pool */
	void submit(final LoadAndDisplayImageTask task) {
		taskDistributor.execute(new Runnable() {
			@Override
			public void run() {
				boolean isImageCachedOnDisc = configuration.discCache.get(task.getLoadingUri()).exists();
				initExecutorsIfNeed();
				if (isImageCachedOnDisc) {
					taskExecutorForCachedImages.execute(task);
				} else {
					taskExecutor.execute(task);
				}
			}
		});
	}

	/** Submits task to execution pool */
	void submit(ProcessAndDisplayImageTask task) {
		initExecutorsIfNeed();
		taskExecutorForCachedImages.execute(task);
	}

	private void initExecutorsIfNeed() {
		if (!configuration.customExecutor && ((ExecutorService) taskExecutor).isShutdown()) {
			taskExecutor = createTaskExecutor();
		}
		if (!configuration.customExecutorForCachedImages && ((ExecutorService) taskExecutorForCachedImages)
				.isShutdown()) {
			taskExecutorForCachedImages = createTaskExecutor();
		}
	}

	private Executor createTaskExecutor() {
		return DefaultConfigurationFactory
				.createExecutor(configuration.threadPoolSize, configuration.threadPriority,
								configuration.tasksProcessingType);
	}

	/**
	 * Returns URI of image which is loading at this moment into passed {@link com.nostra13.universalimageloader.core.imageaware.ImageAware}
	 */
	String getLoadingUriForView(ImageAware imageAware) {
		return cacheKeysForImageAwares.get(imageAware.getId());
	}

	/**
	 * Associates memoryCacheKey with imageAware. Then it helps to define image URI is loaded into View at
	 * exact moment.
	 */
	void prepareDisplayTaskFor(ImageAware imageAware, String memoryCacheKey) {
		cacheKeysForImageAwares.put(imageAware.getId(), memoryCacheKey);
	}

	/**
	 * Cancels the task of loading and displaying image for incoming imageAware.
	 *
	 * @param imageAware {@link com.nostra13.universalimageloader.core.imageaware.ImageAware} for which display task
	 *                   will be cancelled
	 */
	void cancelDisplayTaskFor(ImageAware imageAware) {
		cacheKeysForImageAwares.remove(imageAware.getId());
	}

	/**
	 * Denies or allows engine to download images from the network.
 
 If downloads are denied and if image
	 * isn't cached then {@link ImageLoadingListener#onLoadingFailed(String, View, FailReason)} callback will be fired
	 * with {@link FailReason.FailType#NETWORK_DENIED}
	 *
	 * @param denyNetworkDownloads pass true - to deny engine to download images from the network; false -
	 *                             to allow engine to download images from network.
	 */
	void denyNetworkDownloads(boolean denyNetworkDownloads) {
		networkDenied.set(denyNetworkDownloads);
	}

	/**
	 * Sets option whether ImageLoader will use {@link FlushedInputStream} for network downloads to handle this known problem or not.
	 *
	 * @param handleSlowNetwork pass true - to use {@link FlushedInputStream} for network downloads; false
	 *                          - otherwise.
	 */
	void handleSlowNetwork(boolean handleSlowNetwork) {
		slowNetwork.set(handleSlowNetwork);
	}

	/**
	 * Pauses engine. All new "load&display" tasks won't be executed until ImageLoader is {@link #resume() resumed}.
 Already running tasks are not paused.
	 */
	void pause() {
		paused.set(true);
	}

	/** Resumes engine work. Paused "load&display" tasks will continue its work. */
	void resume() {
		paused.set(false);
		synchronized (pauseLock) {
			pauseLock.notifyAll();
		}
	}

	/** Stops engine, cancels all running and scheduled display image tasks. Clears internal data. */
	void stop() {
		if (!configuration.customExecutor) {
			((ExecutorService) taskExecutor).shutdownNow();
		}
		if (!configuration.customExecutorForCachedImages) {
			((ExecutorService) taskExecutorForCachedImages).shutdownNow();
		}

		cacheKeysForImageAwares.clear();
		uriLocks.clear();
	}

	ReentrantLock getLockForUri(String uri) {
		ReentrantLock lock = uriLocks.get(uri);
		if (lock == null) {
			lock = new ReentrantLock();
			uriLocks.put(uri, lock);
		}
		return lock;
	}

	AtomicBoolean getPause() {
		return paused;
	}

	Object getPauseLock() {
		return pauseLock;
	}

	boolean isNetworkDenied() {
		return networkDenied.get();
	}

	boolean isSlowNetwork() {
		return slowNetwork.get();
	}
}