/*
 *
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.
 *
 */
using System;

namespace Qpid.Messaging
{
   /// <summary>
   /// Describes an object that can be used to receive (consume)
   /// messages from an AMQP queue.
   /// </summary>
   /// <remarks>
   /// Consumers are created using either 
   /// <see cref="IChannel.CreateConsumer"/> or using 
   /// the builder pattern (preferred) with 
   /// <see cref="IChannel.CreateConsumerBuilder"/>.
   /// 
   /// <para>
   /// Consumers offer two different ways of receiving messages:
   /// You can attach a delegate to the <see cref="OnMessage"/>
   /// event and be notified when a message arrives, or you can
   /// use the <see cref="Receive"/> and <see cref="ReceiveNoWait"/>
   /// methods to control when you receive messages. Be aware that you can use 
   /// one or the other, but not both at the same time.
   /// </para>
   /// <para>
   /// Regardless of which method you choose, the prefetch settings
   /// specified when creating the channel will still control when messages
   /// are actually received from the AMQP broker. Any messages that arrive
   /// between the prefetch window will be queued by the channel
   /// until they can be delivered to the consumer (either though the event
   /// or until the consumer actively calls <see cref="Receive"/>).
   /// </para>
   /// </remarks>
   public interface IMessageConsumer : IDisposable
   {
      /// <summary>
      /// Fired when a message is received from the broker by the consumer
      /// </summary>
      MessageReceivedDelegate OnMessage { get; set; }

      /// <summary>
      /// Wait infinitely for a message to be received from the broker
      /// </summary>
      /// <returns>The message received</returns>
      IMessage Receive();
      /// <summary>
      /// Wait the specified time until a message is receive from the broker
      /// </summary>
      /// <param name="delay">Maximum number of milliseconds to wait for a message</param>
      /// <returns>The message received, or null if the timeout expires</returns>
      IMessage Receive(long delay);
      /// <summary>
      /// Return a message if one is already available in the channel. 
      /// Does not wait for one to be received from the broker.
      /// </summary>
      /// <returns>The message, if it was available, otherwise null</returns>
      IMessage ReceiveNoWait();
   }
}
