/*

 * 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

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

 *

 * 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.

 *

 */

package sun.awt.image;

import java.lang.ref.WeakReference;

import java.awt.Image;

import java.awt.image.ImageObserver;

public abstract class ImageWatched {

    public static Link endlink = new Link();

    public Link watcherList;

    public ImageWatched() {

        watcherList = endlink;

    }

    /*

     * This class defines a node on a linked list of ImageObservers.

     * The base class defines the dummy implementation used for the

     * last link on all chains and a subsequent subclass then

     * defines the standard implementation that manages a weak

     * reference to a real ImageObserver.

     */

    public static class Link {

        /*

         * Check if iw is the referent of this Link or any

         * subsequent Link objects on this chain.

         */

        public boolean isWatcher(ImageObserver iw) {

            return false;  // No "iw" down here.

        }

        /*

         * Remove this Link from the chain if its referent

         * is the indicated target or if it has been nulled

         * out by the garbage collector.

         * Return the new remainder of the chain.

         * The argument may be null which will trigger

         * the chain to remove only the dead (null) links.

         * This method is only ever called inside a

         * synchronized block so Link.next modifications

         * will be safe.

         */

        public Link removeWatcher(ImageObserver iw) {

            return this;  // Leave me as the end link.

        }

        /*

         * Deliver the indicated image update information

         * to the referent of this Link and return a boolean

         * indicating whether or not some referent became

         * null or has indicated a lack of interest in

         * further updates to its imageUpdate() method.

         * This method is not called inside a synchronized

         * block so Link.next modifications are not safe.

         */

        public boolean newInfo(Image img, int info,

                               int x, int y, int w, int h)

        {

            return false;  // No disinterested parties down here.

        }

    }

    /*

     * Standard Link implementation to manage a Weak Reference

     * to an ImageObserver.

     */

    public static class WeakLink extends Link {

        private WeakReference<ImageObserver> myref;

        private Link next;

        public WeakLink(ImageObserver obs, Link next) {

            myref = new WeakReference<ImageObserver>(obs);

            this.next = next;

        }

        public boolean isWatcher(ImageObserver iw) {

            return (myref.get() == iw || next.isWatcher(iw));

        }

        public Link removeWatcher(ImageObserver iw) {

            ImageObserver myiw = myref.get();

            if (myiw == null) {

                // Remove me from the chain, but continue recursion.

                return next.removeWatcher(iw);

            }

            // At this point myiw is not null so we know this test will

            // never succeed if this is a pruning pass (iw == null).

            if (myiw == iw) {

                // Remove me from the chain and end the recursion here.

                return next;

            }

            // I am alive, but not the one to be removed, recurse

            // and update my next link and leave me in the chain.

            next = next.removeWatcher(iw);

            return this;

        }

        public boolean newInfo(Image img, int info,

                               int x, int y, int w, int h)

        {

            // Note tail recursion because items are added LIFO.

            boolean ret = next.newInfo(img, info, x, y, w, h);

            ImageObserver myiw = myref.get();

            if (myiw == null) {

                // My referent is null so we must prune in a second pass.

                ret = true;

            } else if (myiw.imageUpdate(img, info, x, y, w, h) == false) {

                // My referent has lost interest so clear it and ask

                // for a pruning pass to remove it later.

                myref.clear();

                ret = true;

            }

            return ret;

        }

    }

    public synchronized void addWatcher(ImageObserver iw) {

        if (iw != null && !isWatcher(iw)) {

            watcherList = new WeakLink(iw, watcherList);

        }

    }

    public synchronized boolean isWatcher(ImageObserver iw) {

        return watcherList.isWatcher(iw);

    }

    public void removeWatcher(ImageObserver iw) {

        synchronized (this) {

            watcherList = watcherList.removeWatcher(iw);

        }

        if (watcherList == endlink) {

            notifyWatcherListEmpty();

        }

    }

    public boolean isWatcherListEmpty() {

        synchronized (this) {

            watcherList = watcherList.removeWatcher(null);

        }

        return (watcherList == endlink);

    }

    public void newInfo(Image img, int info, int x, int y, int w, int h) {

        if (watcherList.newInfo(img, info, x, y, w, h)) {

            // Some Link returned true so we now need to prune dead links.

            removeWatcher(null);

        }

    }

    protected abstract void notifyWatcherListEmpty();

}