/*
 *
 * Copyright (c) 2006 The Apache Software Foundation
 *
 * Licensed under the Apache License, Version 2.0 (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.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 */
package org.apache.qpid.server.queue;

import org.apache.qpid.AMQException;

import java.util.concurrent.Executor;
import java.util.List;

interface DeliveryManager
{
    /**
     * Determines whether there are queued messages. Sets _queueing to false if
     * there are no queued messages. This needs to be atomic.
     *
     * @return true if there are queued messages
     */
    boolean hasQueuedMessages();

    /**
     * This method should not be used to determin if there are messages in the queue.
     *
     * @return int The number of messages in the queue
     * @use hasQueuedMessages() for all controls relating to having messages on the queue.
     */
    int getQueueMessageCount();

    /**
     * Requests that the delivery manager start processing the queue asynchronously
     * if there is work that can be done (i.e. there are messages queued up and
     * subscribers that can receive them.
     * <p/>
     * This should be called when subscribers are added, but only after the consume-ok
     * message has been returned as message delivery may start immediately. It should also
     * be called after unsuspending a client.
     * <p/>
     *
     * @param executor the executor on which the delivery should take place
     */
    void processAsync(Executor executor);

    /**
     * Handles message delivery. The delivery manager is always in one of two modes;
     * it is either queueing messages for asynchronous delivery or delivering
     * directly.
     *
     * @param name the name of the entity on whose behalf we are delivering the message
     * @param msg  the message to deliver
     * @throws org.apache.qpid.server.queue.FailedDequeueException if the message could not be dequeued
     */
    void deliver(String name, AMQMessage msg) throws FailedDequeueException;

    void removeAMessageFromTop() throws AMQException;

    void clearAllMessages() throws AMQException;

    List<AMQMessage> getMessages();
}
