/*

   Licensed to the Apache Software Foundation (ASF) under one or more
   contributor license agreements.  See the NOTICE file distributed with
   this work for additional information regarding copyright ownership.
   The ASF licenses this file to You 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 org.apache.batik.ext.awt.image;

import org.apache.batik.ext.awt.image.renderable.Filter;
import org.apache.batik.util.ParsedURL;
import org.apache.batik.util.SoftReferenceCache;

/**
 * This class manages a cache of soft references to Images that
 * we have already loaded.
 *
 * <p>
 *   Adding an image is two fold. First you add the ParsedURL, this lets
 *   the cache know that someone is working on this ParsedURL.  Then when
 *   the completed RenderedImage is ready you put it into the cache.
 * </p>
 * <p>
 *   If someone requests a ParsedURL after it has been added but before it has
 *   been put they will be blocked until the put.
 * </p>
 *
 * @author <a href="mailto:thomas.deweese@kodak.com">Thomas DeWeese</a>
 * @version $Id$
 */
public class URLImageCache extends SoftReferenceCache {

    static URLImageCache theCache = new URLImageCache();

    public static URLImageCache getDefaultCache() { return theCache; }

    /**
     * Let people create there own caches.
     */
    public URLImageCache() { }

    /**
     * Check if <tt>request(url)</tt> will return with a Filter
     * (not putting you on the hook for it).  Note that it is possible
     * that this will return true but between this call and the call
     * to request the soft-reference will be cleared.  So it
     * is still possible for request to return NULL, just much less
     * likely (you can always call 'clear' in that case). 
     */
    public synchronized boolean isPresent(ParsedURL purl) {
        return super.isPresentImpl(purl);
    }

    /**
     * Check if <tt>request(url)</tt> will return immediately with the
     * Filter.  Note that it is possible that this will return
     * true but between this call and the call to request the
     * soft-reference will be cleared.
     */
    public synchronized boolean isDone(ParsedURL purl) {
        return super.isDoneImpl(purl);
    }

    /**
     * If this returns null then you are now 'on the hook'.
     * to put the Filter associated with ParsedURL into the
     * cache.  */
    public synchronized Filter request(ParsedURL purl) {
        return (Filter)super.requestImpl(purl);
    }

    /**
     * Clear the entry for ParsedURL.
     * This is the easiest way to 'get off the hook'.
     * if you didn't indend to get on it.
     */
    public synchronized void clear(ParsedURL purl) {
        super.clearImpl(purl);
    }

    /**
     * Associate bi with purl.  bi is only referenced through
     * a soft reference so don't rely on the cache to keep it
     * around.  If the map no longer contains our purl it was
     * probably cleared or flushed since we were put on the hook
     * for it, so in that case we will do nothing.
     */
    public synchronized void put(ParsedURL purl, Filter filt) {
        super.putImpl(purl, filt);
    }
}