/**
 * Redistribution and use of this software and associated documentation
 * ("Software"), with or without modification, are permitted provided
 * that the following conditions are met:
 *
 * 1. Redistributions of source code must retain copyright
 *    statements and notices.  Redistributions must also contain a
 *    copy of this document.
 *
 * 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 name "Exolab" must not be used to endorse or promote
 *    products derived from this Software without prior written
 *    permission of Exoffice Technologies.  For written permission,
 *    please contact info@exolab.org.
 *
 * 4. Products derived from this Software may not be called "Exolab"
 *    nor may "Exolab" appear in their names without prior written
 *    permission of Exoffice Technologies. Exolab is a registered
 *    trademark of Exoffice Technologies.
 *
 * 5. Due credit should be given to the Exolab Project
 *    (http://www.exolab.org/).
 *
 * THIS SOFTWARE IS PROVIDED BY EXOFFICE TECHNOLOGIES AND CONTRIBUTORS
 * ``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
 * EXOFFICE TECHNOLOGIES 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.
 *
 * Copyright 2001-2005 (C) Exoffice Technologies Inc. All Rights Reserved.
 *
 * $Id: QueueBrowserEndpoint.java,v 1.2 2005/03/18 03:58:39 tanderson Exp $
 */
package org.exolab.jms.messagemgr;

import java.util.Vector;
import java.sql.Connection;
import javax.jms.InvalidSelectorException;
import javax.jms.JMSException;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.exolab.jms.client.JmsQueue;
import org.exolab.jms.message.MessageImpl;
import org.exolab.jms.scheduler.Scheduler;
import org.exolab.jms.server.JmsServerSession;


/**
 * A QueueBrowserEndpoint is a QueueListener to a QueueDestinationCache. This
 * enables it to receive all the messages, which it then feeds down to the
 * client side.
 *
 * @author <a href="mailto:jima@comware.com.au">Jim Alateras</a>
 * @author <a href="mailto:tma@netspace.net.au">Tim Anderson
 * @version $Revision: 1.2 $ $Date: 2005/03/18 03:58:39 $
 */
public class QueueBrowserEndpoint extends AbstractConsumerEndpoint {

    /**
     * Cache of all handles for this consumer.
     */
    private MessageQueue _handles = new MessageQueue();

    /**
     * The destination that this consumer subscribes to.
     */
    private QueueDestinationCache _cache;

    /**
     * The logger.
     */
    private static final Log _log =
            LogFactory.getLog(QueueBrowserEndpoint.class);


    /**
     * Create a new <code>QueueBrowserEndpoint</code>.
     *
     * @param consumerId the identity of this consumer
     * @param session    the owning session
     * @param queue      the queue to browse
     * @param selector   the message selector. May be <code>null</code>
     * @param scheduler  used to schedule asynchronous message delivery.
     * @throws InvalidSelectorException if <code>selector</code> is invalid
     * @throws JMSException             if the destination cache can't be
     *                                  created
     */
    public QueueBrowserEndpoint(long consumerId, JmsServerSession session,
                                JmsQueue queue, String selector,
                                Scheduler scheduler)
            throws InvalidSelectorException, JMSException {
        super(consumerId, session, queue, selector, false, scheduler);

        _cache = (QueueDestinationCache)
                DestinationManager.instance().getDestinationCache(queue);

        // set up the message cache and register itself as a listener to the
        // cache
        _cache.addQueueListener(this);
        _cache.playbackMessages(this);
    }

    /**
     * This event is called when a non-persistent message is added to a
     * <code>DestinationCache</code>..
     *
     * @param handle  a handle to the added message
     * @param message the added message
     * @return <code>true</code> if the listener accepted the message; otherwise
     *         <code>false</ode>
     */
    public boolean messageAdded(MessageHandle handle, MessageImpl message) {
        addMessage(handle);
        return true;
    }

    /**
     * This event is called when a persistent message is added to the
     * <code>DestinationCache</code>.
     *
     * @param handle     a handle to the added message
     * @param message    the added message
     * @param connection the database connection
     * @return <code>true</code>
     */
    public boolean persistentMessageAdded(MessageHandle handle,
                                          MessageImpl message,
                                          Connection connection) {
        return messageAdded(handle, message);
    }

    /**
     * This event is called when a message is removed from the
     * <code>DestinationCache</code>.
     *
     * @param messageId the identifier of the removed message
     */
    public void messageRemoved(String messageId) {
        _handles.remove(messageId);
    }

    /**
     * This event is called when a message is removed from the
     * <code>DestinationCache</code>.
     *
     * @param messageId     a handle to the removed message
     * @param connection the database connection
     */
    public void persistentMessageRemoved(String messageId,
                                         Connection connection) {
        messageRemoved(messageId);
    }

    /**
     * Return the next available message to the client.
     * <p/>
     * This operation is not supported for QueueBrowsers.
     *
     * @param wait number of milliseconds to wait
     * @return null
     * @throws JMSException if invoked
     */
    public MessageHandle receive(long wait) throws JMSException {
        throw new JMSException("Cannot call receive for QueueBrowser");
    }

    /**
     * Return, at most, count messages from the cache.
     *
     * @param count the max number of messages to receive
     * @return a list of <code>MessageHandle</code> instances
     */
    public Vector receiveMessages(int count) {
        Vector messages = new Vector();
        int index = 0;
        while (index < count) {

            // check if we should exit the loop
            if (isStopped() || getMessageCount() == 0) {
                break;
            }

            // remove the first message from the list and check
            // that it is not null. Synchronize the removal of
            // the message but not the sending to the remote
            // consumer
            try {
                MessageHandle handle = removeFirstMessage();
                if (handle != null) {
                    MessageImpl m = handle.getMessage();
                    if (m != null) {
                        // add it to the list of messages to send
                        // but only deliver messages that satisfy the
                        // selection criteria.
                        if (selects(m)) {
                            messages.addElement(handle);
                            ++index;
                        } else {
                            // drop the message
                        }
                    } else {
                        // message may have been consumed in the interim
                    }
                }
            } catch (Exception exception) {
                _log.error(exception, exception);
            }
        }

        return messages;
    }

    /**
     * Set the message listener for this consumer. If a message listener is set
     * then messages will be scheduled to be sent to it when they are available.
     *
     * @param listener the message listener to add, or <code>null</code> to
     *                 remove an existing listener
     */
    public void setMessageListener(ConsumerEndpointListener listener) {
        _log.error("QueueBrowserEndpoint.setMessageListener "
                    + "should never be called");
    }

    /**
     * Return the number of unsent messages in the cache for this consumer.
     *
     * @return the number of unsent messages
     */
    public int getMessageCount() {
        return _handles.size();
    }

    /**
     * Add the handle to the cache.
     *
     * @param handle the message handle to add
     */
    protected void addMessage(MessageHandle handle) {
        _handles.add(handle);

        // notify the consumer
        notifyMessageAvailable();
    }

    /**
     * Deliver messages in the cache to the consumer.
     * <p> This is not relevant to QueueBrowsers, and thus shouldn't be invoked.
     *
     * @return <code>false</code>
     */
    protected boolean deliverMessages() {
        _log.error(
                "QueueBrowserEndpoint.deliverMessages() should never be called",
                new Exception());
        return false;
    }

    /**
     * Remove the handle from the cache.
     *
     * @param handle the handle to remove
     * @return the removed handle, or <code>null</code> if it doesn't exist
     */
    protected MessageHandle removeMessage(MessageHandle handle) {
        return _handles.remove(handle);
    }

    /**
     * Return the first message handle in the cache.
     *
     * @return the first message or null if cache is empty
     */
    protected MessageHandle removeFirstMessage() {
        return _handles.removeFirst();
    }

    /**
     * Closes this endpoint.
     */
    protected void doClose() {
        // unregister from the DestinationCache
        _cache.removeQueueListener(this);
    }

}