/*
 *    GeoTools - The Open Source Java GIS Toolkit
 *    http://geotools.org
 *
 *    (C) 2007-2008, Open Source Geospatial Foundation (OSGeo)
 *
 *    This library is free software; you can redistribute it and/or
 *    modify it under the terms of the GNU Lesser General Public
 *    License as published by the Free Software Foundation;
 *    version 2.1 of the License.
 *
 *    This library is distributed in the hope that it will be useful,
 *    but WITHOUT ANY WARRANTY; without even the implied warranty of
 *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 *    Lesser General Public License for more details.
 */
package org.geotools.caching;

import java.util.Collections;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.Map;

import org.geotools.caching.spatialindex.NodeIdentifier;

/**
 * Least-Recently Used Eviction Policy
 * <p>
 * Removes the oldest items from the cache.
 * </p>
 *
 *
 *
 * @source $URL$
 */
public class LRUEvictionPolicy implements EvictionPolicy {
	private Map<NodeIdentifier, Object> queue;
	private EvictableTree tree;

	public LRUEvictionPolicy(EvictableTree tree) {
		this.queue = Collections.synchronizedMap(new LinkedHashMap<NodeIdentifier, Object>(100, .75f, true));
		this.tree = tree;
	}

	public boolean evict() {
		synchronized (queue) {
			Iterator<NodeIdentifier> it = queue.keySet().iterator();
			while (it.hasNext()) {
				NodeIdentifier node = it.next();
				if (!node.isLocked()) {
					try {
						node.writeLock();
						try {
							tree.evict(node);
							queue.remove(node);
						} finally {
							node.writeUnLock();
						}
					} catch (Exception ex) {
						ex.printStackTrace();
						return false;
					}
					return true;
				}
			}
		}
		return false;
	}

	public void access(NodeIdentifier node) {
		if (queue.containsKey(node)) {
			queue.get(node);
		} else if (node.isValid()) {
			queue.put(node, null);
		}
	}
}