/*******************************************************************************
 * Copyright (c) 2007, 2018 Association for Decentralized Information Management
 * in Industry THTH ry.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *     VTT Technical Research Centre of Finland - initial API and implementation
 *     Semantum Oy - added shutdown facilities
 *******************************************************************************/

package org.simantics.utils.threads;

import java.util.concurrent.Callable;
import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.ScheduledThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;

/**
 * @author Toni Kalajainen
 * @author Tuukka Lehtonen
 */
public class ExecutorWorker {

	private static volatile ExecutorWorker instance;

	public static ExecutorWorker getInstance() {
		if (instance == null) {
			synchronized (ExecutorWorker.class) {
				if (instance == null)
					instance = new ExecutorWorker();
			}
		}
		return instance;
	}

	private ExecutorWorker() {}

	private final AtomicInteger counter = new AtomicInteger(0);
	private final ThreadGroup threadGroup = new ThreadGroup("ExecutorWorker-Group");
	private ScheduledThreadPoolExecutor pool = new ScheduledThreadPoolExecutor(1, r -> {
		Thread t = new Thread(threadGroup, r, "ExecutorWorker-" + (counter.incrementAndGet()));
		if (!t.isDaemon())
			t.setDaemon(true);
		if (t.getPriority() != Thread.NORM_PRIORITY)
			t.setPriority(Thread.NORM_PRIORITY);
		return t;
	});

	public synchronized ScheduledFuture<Object> timerExec(final Executable executable, int delay)
	{
		Callable<Object> c = () -> {
			ThreadUtils.asyncExec(executable.threadAccess, executable.runnable);
			return null;
		};
		return pool.schedule(c, delay, TimeUnit.MILLISECONDS);
	}

	private void shutdownThis() {
		ScheduledThreadPoolExecutor e = pool;
		if (e != null) {
			pool = null;
			ThreadUtils.shutdownAndAwaitTermination(e, 1000);
		}
	}

	public static synchronized void shutdown() {
		ExecutorWorker i = instance;
		if (i != null) {
			instance = null;
			i.shutdownThis();
		}
	}

}