/*
 *  The Sun Project JXTA(TM) Software License
 *  
 *  Copyright (c) 2001-2007 Sun Microsystems, Inc. All rights reserved.
 *  
 *  Redistribution and use in source and binary forms, with or without 
 *  modification, are permitted provided that the following conditions are met:
 *  
 *  1. Redistributions of source code must retain the above copyright notice,
 *     this list of conditions and the following disclaimer.
 *  
 *  2. Redistributions in binary form must reproduce the above copyright notice, 
 *     this list of conditions and the following disclaimer in the documentation 
 *     and/or other materials provided with the distribution.
 *  
 *  3. The end-user documentation included with the redistribution, if any, must 
 *     include the following acknowledgment: "This product includes software 
 *     developed by Sun Microsystems, Inc. for JXTA(TM) technology." 
 *     Alternately, this acknowledgment may appear in the software itself, if 
 *     and wherever such third-party acknowledgments normally appear.
 *  
 *  4. The names "Sun", "Sun Microsystems, Inc.", "JXTA" and "Project JXTA" must 
 *     not be used to endorse or promote products derived from this software 
 *     without prior written permission. For written permission, please contact 
 *     Project JXTA at http://www.jxta.org.
 *  
 *  5. Products derived from this software may not be called "JXTA", nor may 
 *     "JXTA" appear in their name, without prior written permission of Sun.
 *  
 *  THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES,
 *  INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND 
 *  FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL SUN 
 *  MICROSYSTEMS OR ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, 
 *  INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 
 *  LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, 
 *  OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF 
 *  LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING 
 *  NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, 
 *  EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *  
 *  JXTA is a registered trademark of Sun Microsystems, Inc. in the United 
 *  States and other countries.
 *  
 *  Please see the license information page at :
 *  <http://www.jxta.org/project/www/license.html> for instructions on use of 
 *  the license in source files.
 *  
 *  ====================================================================

 *  This software consists of voluntary contributions made by many individuals 
 *  on behalf of Project JXTA. For more information on Project JXTA, please see 
 *  http://www.jxta.org.
 *  
 *  This license is based on the BSD license adopted by the Apache Foundation. 
 */

package net.jxta.content;

import java.util.List;

/**
 * This interface represents a content transfer which is acting as a front
 * for multiple ContentTransfer instances, all of which are working to
 * obtain a single Content instance.  This allows ContentService
 * implementations to provide failover mechanisms and provider
 * randomization while maintaining operational transparency to the
 * end user.
 * <p/>
 * An explicit effort was made to always expose the actual ContentTransfer
 * instances to the end-user.  This interface provides a mechanism by
 * which to accomplish this design goal.
 * 
 * @see net.jxta.content.ContentTransfer
 * @see net.jxta.content.ContentProvider
 * @see net.jxta.content.ContentService
 */
public interface ContentTransferAggregator extends ContentTransfer {

    /**
     * Adds an event listener to track the operation and progress of the
     * transfer.
     *
     * @param listener listener instance to add
     */
    void addContentTransferAggregatorListener(
            ContentTransferAggregatorListener listener);

    /**
     * Removes a previously registered event listener.
     *
     * @param listener listener instance to remove
     */
    void removeContentTransferAggregatorListener(
            ContentTransferAggregatorListener listener);

    /**
     * Returns the currently selected/active ContentTransfer instance being
     * actively used to retrieve the Content.  Note that many instances may
     * be actively seeking peers that have the requested Content (at the
     * aggregator's discretion), but only the instance actively downloading
     * from a remote peer will be returned by this method.
     *
     * @return current ContentTransfer instance, or null if no instance is
     *  currently retrieving data
     */
    ContentTransfer getCurrentContentTransfer();

    /**
     * Returns the current list ContentTransfer instances being managed
     * by the aggregated transfer object.
     *
     * @return list of ContentTransfer instances
     */
    List<ContentTransfer> getContentTransferList();

}