using System;

using System.Threading.Tasks;

using System.Collections.Generic;

​

namespace MassTransit

{

    public interface ConsumeContext

    {

    }

    public interface MessageContext

    {

    }

    public interface PipeContext {}

    public interface IPublishEndpoint {}

    public interface IPublishObserverConnector {}

    public interface ISendEndpointProvider {}

    public interface IMessage

    {

        Guid? MessageId { get; set; }

    }

    public class Message : IMessage

    {

        public Guid? MessageId { get; set; }

    }

    public class SpecificMessage : Message

    {

    }

    public interface ConsumeContext<out T> : ConsumeContext, MessageContext, PipeContext, IPublishEndpoint, IPublishObserverConnector, ISendEndpointProvider where T : class

    {

        T Message { get; }

​

        /// <summary>Notify that the message has been consumed</summary>

        /// <param name="duration"></param>

        /// <param name="consumerType">The consumer type</param>

        Task NotifyConsumed(TimeSpan duration, string consumerType);

​

        /// <summary>

        /// Notify that a fault occurred during message consumption

        /// </summary>

        /// <param name="duration"></param>

        /// <param name="consumerType"></param>

        /// <param name="exception"></param>

        Task NotifyFaulted(TimeSpan duration, string consumerType, Exception exception);

    }

​

    public class MyClass <T>: ConsumeContext<T> where T : class

    {

        public T Message { get; set; }

        public Task NotifyConsumed(TimeSpan duration, string consumerType) { return null; }

        public Task NotifyFaulted(TimeSpan duration, string consumerType, Exception exception) { return null; }

    }

    public class Program

    {

        public static Guid? GetMessageId<T>(ConsumeContext<T> input) where T : class

        {

            var casted = input as ConsumeContext<IMessage>;

            if (casted == null) return null;

            return casted.Message.MessageId;

        }

        public static void Main()

        {

            var exampleObject = new MyClass<SpecificMessage>();

            exampleObject.Message = new SpecificMessage { MessageId = new Guid("00000001-0002-0003-0004-000000000005") };

            var messageId = GetMessageId(exampleObject);

            Console.WriteLine(messageId.Value);

        }

    }

}

​