Copyright (c) 2013 IBM Corporation and others.
This program and the accompanying materials
are made available under the terms of the Eclipse Public License 2.0
which accompanies this distribution, and is available at
https://www.eclipse.org/legal/epl-2.0/
SPDX-License-Identifier: EPL-2.0
Contributors:
    IBM Corporation - initial API and implementation
/*******************************************************************************
 * Copyright (c) 2013 IBM Corporation and others.
 *
 * This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License 2.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-2.0/
 *
 * SPDX-License-Identifier: EPL-2.0
 * 
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.osgi.internal.framework;

import java.io.IOException;
import java.util.concurrent.*;
import org.eclipse.osgi.framework.log.FrameworkLogEntry;

public final class StorageSaver {
	private static class StorageSaverTask implements Runnable {
		private final EquinoxContainer container;

		public StorageSaverTask(EquinoxContainer container) {
			this.container = container;
		}

		@Override
		public void run() {
			try {
				container.getStorage().save();
			} catch (IOException e) {
				container.getLogServices().log(EquinoxContainer.NAME, FrameworkLogEntry.ERROR, "Error saving on update", e); //$NON-NLS-1$
			}
		}
	}

	private final EquinoxContainer container;
	private final long delay;
	private final ScheduledFuture<?> future;
	private final Thread hook;
	private final StorageSaverTask task;

	public StorageSaver(EquinoxContainer container) {
		this.container = container;
		task = new StorageSaverTask(container);
		delay = computeDelay();
		future = scheduleTask();
		hook = registerShutdownHook();
	}

	public void close() {
		unregisterShutdownHook();
		unscheduleTask();
	}

	public void save() {
		if (delay != 0)
			// Periodic saves are enabled or saves are disabled altogether.
			return;
		// Immediately save on request.
		task.run();
	}

	private Thread registerShutdownHook() {
		Thread thread = new Thread(task, "Equinox Shutdown Hook"); //$NON-NLS-1$
		Runtime.getRuntime().addShutdownHook(thread);
		return thread;
	}

	private long computeDelay() {
		EquinoxConfiguration configuration = container.getConfiguration();
		// Default provided by the configuration, if necessary.
		String delayProp = configuration.getConfiguration(EquinoxConfiguration.PROP_STATE_SAVE_DELAY_INTERVAL);
		// Type compatibility verified by the configuration.
		return Long.parseLong(delayProp);
	}

	private ScheduledFuture<?> scheduleTask() {
		// Negative delay disables saves. Zero delay results in immediate saves.
		if (delay <= 0)
			return null;
		ScheduledExecutorService executor = container.getScheduledExecutor();
		return executor.scheduleWithFixedDelay(task, delay, delay, TimeUnit.MILLISECONDS);
	}

	private void unregisterShutdownHook() {
		try {
			Runtime.getRuntime().removeShutdownHook(hook);
		} catch (IllegalStateException e) {
			// Ignore.
		}
	}

	private void unscheduleTask() {
		if (future != null)
			future.cancel(false);
	}
}