/*

 * Copyright (c) 1997, 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

 * questions.

 */

package sun.applet;

import java.util.EventListener;

import java.io.Serializable;

import java.io.ObjectOutputStream;

import java.io.IOException;

/**

 * AppletEventMulticaster class.  This class manages an immutable

 * structure consisting of a chain of AppletListeners and is

 * responsible for dispatching events to them.

 *

 * @author  Sunita Mani

 */

public class AppletEventMulticaster implements AppletListener {

    private final AppletListener a, b;

    public AppletEventMulticaster(AppletListener a, AppletListener b) {

        this.a = a; this.b = b;

    }

    public void appletStateChanged(AppletEvent e) {

        a.appletStateChanged(e);

        b.appletStateChanged(e);

    }

    /**

     * Adds Applet-listener-a with Applet-listener-b and

     * returns the resulting multicast listener.

     * @param a Applet-listener-a

     * @param b Applet-listener-b

     */

    public static AppletListener add(AppletListener a, AppletListener b) {

        return addInternal(a, b);

    }

    /**

     * Removes the old Applet-listener from Applet-listener-l and

     * returns the resulting multicast listener.

     * @param l Applet-listener-l

     * @param oldl the Applet-listener being removed

     */

    public static AppletListener remove(AppletListener l, AppletListener oldl) {

        return removeInternal(l, oldl);

    }

    /**

     * Returns the resulting multicast listener from adding listener-a

     * and listener-b together.

     * If listener-a is null, it returns listener-b;

     * If listener-b is null, it returns listener-a

     * If neither are null, then it creates and returns

     * a new AppletEventMulticaster instance which chains a with b.

     * @param a event listener-a

     * @param b event listener-b

     */

    private static AppletListener addInternal(AppletListener a, AppletListener b) {

        if (a == null)  return b;

        if (b == null)  return a;

        return new AppletEventMulticaster(a, b);

    }

    /**

     * Removes a listener from this multicaster and returns the

     * resulting multicast listener.

     * @param oldl the listener to be removed

     */

    protected AppletListener remove(AppletListener oldl) {

        if (oldl == a)  return b;

        if (oldl == b)  return a;

        AppletListener a2 = removeInternal(a, oldl);

        AppletListener b2 = removeInternal(b, oldl);

        if (a2 == a && b2 == b) {

            return this;        // it's not here

        }

        return addInternal(a2, b2);

    }

    /**

     * Returns the resulting multicast listener after removing the

     * old listener from listener-l.

     * If listener-l equals the old listener OR listener-l is null,

     * returns null.

     * Else if listener-l is an instance of AppletEventMulticaster

     * then it removes the old listener from it.

     * Else, returns listener l.

     * @param l the listener being removed from

     * @param oldl the listener being removed

     */

    private static AppletListener removeInternal(AppletListener l, AppletListener oldl) {

        if (l == oldl || l == null) {

            return null;

        } else if (l instanceof AppletEventMulticaster) {

            return ((AppletEventMulticaster)l).remove(oldl);

        } else {

            return l;           // it's not here

        }

    }

}