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//$Id: UpdateTimestampsCache.java 10811 2006-11-15 14:44:34Z [email protected] $
package org.hibernate.cache;

import java.io.Serializable;
import java.util.Iterator;
import java.util.Properties;
import java.util.Set;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.hibernate.HibernateException;
import org.hibernate.cfg.Settings;

/**
 * Tracks the timestamps of the most recent updates to particular tables. It is
 * important that the cache timeout of the underlying cache implementation be set
 * to a higher value than the timeouts of any of the query caches. In fact, we
 * recommend that the the underlying cache not be configured for expiry at all.
 * Note, in particular, that an LRU cache expiry policy is never appropriate.
 *
 * @author Gavin King
 * @author Mikheil Kapanadze
 */
public class UpdateTimestampsCache {

	public static final String REGION_NAME = UpdateTimestampsCache.class.getName();

	private static final Log log = LogFactory.getLog(UpdateTimestampsCache.class);

	private Cache updateTimestamps;
	private final String regionName;

	public void clear() throws CacheException {
		updateTimestamps.clear();
	}

	public UpdateTimestampsCache(Settings settings, Properties props) throws HibernateException {
		String prefix = settings.getCacheRegionPrefix();
		regionName = prefix == null ? REGION_NAME : prefix + '.' + REGION_NAME;
		log.info( "starting update timestamps cache at region: " + regionName );
		this.updateTimestamps = settings.getCacheProvider().buildCache( regionName, props );
	}

	public synchronized void preinvalidate(Serializable[] spaces) throws CacheException {
		//TODO: to handle concurrent writes correctly, this should return a Lock to the client
		Long ts = new Long( updateTimestamps.nextTimestamp() + updateTimestamps.getTimeout() );
		for ( int i=0; i= timestamp.longValue() ) {
					return false;
				}
			}
		}
		return true;
	}

	public void destroy() {
		try {
			updateTimestamps.destroy();
		}
		catch (Exception e) {
			log.warn("could not destroy UpdateTimestamps cache", e);
		}
	}

	public Cache getCache() {
		return updateTimestamps;
	}
	
	public String getRegionName() {
		return regionName;
	}
	
	public String toString() {
		return "UpdateTimestampeCache";
	}

}