/*

 * Copyright (c) 2011, 2014, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code 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 General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

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 */

package sun.awt.image;

import java.awt.*;

import java.lang.ref.*;

import java.util.*;

import java.util.concurrent.locks.*;

import sun.awt.AppContext;

/**

 * ImageCache - A fixed pixel count sized cache of Images keyed by arbitrary

 * set of arguments. All images are held with SoftReferences so they will be

 * dropped by the GC if heap memory gets tight. When our size hits max pixel

 * count least recently requested images are removed first.

 *

 * The ImageCache must be used from the thread with an AppContext only.

 *

 */

final public class ImageCache {

    // Ordered Map keyed by args hash, ordered by most recent accessed entry.

    private final LinkedHashMap<PixelsKey, ImageSoftReference> map

            = new LinkedHashMap<>(16, 0.75f, true);

    // Maximum number of pixels to cache, this is used if maxCount

    private final int maxPixelCount;

    // The current number of pixels stored in the cache

    private int currentPixelCount = 0;

    // Lock for concurrent access to map

    private final ReadWriteLock lock = new ReentrantReadWriteLock();

    // Reference queue for tracking lost softreferences to images in the cache

    private final ReferenceQueue<Image> referenceQueue = new ReferenceQueue<>();

    public static ImageCache getInstance() {

        return AppContext.getSoftReferenceValue(ImageCache.class,

                () -> new ImageCache());

    }

    ImageCache(final int maxPixelCount) {

        this.maxPixelCount = maxPixelCount;

    }

    ImageCache() {

        this((8 * 1024 * 1024) / 4); // 8Mb of pixels

    }

    public void flush() {

        lock.writeLock().lock();

        try {

            map.clear();

        } finally {

            lock.writeLock().unlock();

        }

    }

    public Image getImage(final PixelsKey key){

        final ImageSoftReference ref;

        lock.readLock().lock();

        try {

            ref = map.get(key);

        } finally {

            lock.readLock().unlock();

        }

        return ref == null ? null : ref.get();

    }

    /**

     * Sets the cached image for the specified constraints.

     *

     * @param key The key with which the specified image is to be associated

     * @param image  The image to store in cache

     */

    public void setImage(final PixelsKey key, final Image image) {

        lock.writeLock().lock();

        try {

            ImageSoftReference ref = map.get(key);

            // check if currently in map

            if (ref != null) {

                if (ref.get() != null) {

                    return;

                }

                // soft image has been removed

                currentPixelCount -= key.getPixelCount();

                map.remove(key);

            };

            // add new image to pixel count

            final int newPixelCount = key.getPixelCount();

            currentPixelCount += newPixelCount;

            // clean out lost references if not enough space

            if (currentPixelCount > maxPixelCount) {

                while ((ref = (ImageSoftReference)referenceQueue.poll()) != null) {

                    //reference lost

                    map.remove(ref.key);

                    currentPixelCount -= ref.key.getPixelCount();

                }

            }

            // remove old items till there is enough free space

            if (currentPixelCount > maxPixelCount) {

                final Iterator<Map.Entry<PixelsKey, ImageSoftReference>>

                        mapIter = map.entrySet().iterator();

                while ((currentPixelCount > maxPixelCount) && mapIter.hasNext()) {

                    final Map.Entry<PixelsKey, ImageSoftReference> entry =

                            mapIter.next();

                    mapIter.remove();

                    final Image img = entry.getValue().get();

                    if (img != null) img.flush();

                    currentPixelCount -= entry.getValue().key.getPixelCount();

                }

            }

            // finally put new in map

            map.put(key, new ImageSoftReference(key, image, referenceQueue));

        } finally {

            lock.writeLock().unlock();

        }

    }

    public interface PixelsKey {

        int getPixelCount();

    }

    private static class ImageSoftReference extends SoftReference<Image> {

        final PixelsKey key;

        ImageSoftReference(final PixelsKey key, final Image referent,

                final ReferenceQueue<? super Image> q) {

            super(referent, q);

            this.key = key;

        }

    }

}