/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
 *
 * The contents of this file are subject to the Netscape Public
 * License Version 1.1 (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.mozilla.org/NPL/
 *
 * Software distributed under the License is distributed on an "AS
 * IS" basis, WITHOUT WARRANTY OF ANY KIND, either express or
 * implied. See the License for the specific language governing
 * rights and limitations under the License.
 *
 * The Original Code is Mozilla Communicator client code.
 *
 * The Initial Developer of the Original Code is Netscape Communications
 * Corporation.  Portions created by Netscape are
 * Copyright (C) 1998 Netscape Communications Corporation. All
 * Rights Reserved.
 *
 * Contributor(s): 
 */

#ifndef nsPIEventQueueChain_h__
#define nsPIEventQueueChain_h__

#include "nsISupports.h"

// {8f310040-82a7-11d3-95bc-0060083a0bcf}
#define NS_IEVENTQUEUECHAIN_IID \
{ 0x8f310040, 0x82a7, 0x11d3, { 0x95, 0xbc, 0x0, 0x60, 0x8, 0x3a, 0xb, 0xcf } }

class nsIEventQueue;

class nsPIEventQueueChain : public nsISupports
{
public:
    NS_DEFINE_STATIC_IID_ACCESSOR(NS_IEVENTQUEUECHAIN_IID);

    /**
     * Add the given queue as the new youngest member of our chain.
     * It will not be addrefed.
     * @param aQueue the queue. must not be null.
     * @return error indication
     */
    NS_IMETHOD AppendQueue(nsIEventQueue *aQueue) = 0;

    /**
     * Remove this element from the chain.
     * @return NS_OK
     */
    NS_IMETHOD Unlink() = 0;

    /**
     * Fetch (and addref) the youngest member of the chain.
     * @param *aQueue the youngest queue. aQueue must not be null.
     * @return error indication
     */
    NS_IMETHOD GetYoungest(nsIEventQueue **aQueue) = 0;

    /**
     * Fetch (and addref) the youngest member of the chain which is
     * still accepting events, or at least still contains events in need
     * of processing.
     * @param *aQueue the youngest such queue. aQueue must not be null.
     *        *aQueue will be returned null, if no such queue is found.
     * @return error indication -- can be NS_OK even if *aQueue is 0
     */
    NS_IMETHOD GetYoungestActive(nsIEventQueue **aQueue) = 0;

    NS_IMETHOD SetYounger(nsPIEventQueueChain *aQueue) = 0;
    NS_IMETHOD GetYounger(nsIEventQueue **aQueue) = 0;

    NS_IMETHOD SetElder(nsPIEventQueueChain *aQueue) = 0;
    NS_IMETHOD GetElder(nsIEventQueue **aQueue) = 0;
};

#endif /* nsPIEventQueueChain_h___ */