messengerapi.SubscriptionClient/code/MessengerApi.SubscriptionClient/Model/Subscription.cs

using MessengerApi.Model.Messages;

namespace MessengerApi.Model
{
    /// <summary>
    /// See <see cref="SubscriptionClient"/> if you need to subscribe. It will give you one of these upon subscribing. 
    /// Also see <see cref="OnMessage"/> for what happens where you actually receive message for this sub.
    /// </summary>
    public class Subscription : IDisposable
    {
        public string MessageTypeMask { get; private set; }

        public event EventHandler<InboxMessage> OnMessage;

        internal SubscriptionClient client;

        private bool isDisposed;

        internal Subscription(string messageTypeMask, SubscriptionClient client)
        {
            MessageTypeMask = messageTypeMask;
            this.client = client;
        }

        internal void Message(InboxMessage message)
        {
            OnMessage?.Invoke(this, message);
        }

        public void Dispose()
        {
            if (isDisposed)
            {
                return;
            }

            AssertNotDisposedOrThrow();
            client.Unsubscribe(this);
            Dispose();

            isDisposed = true;
        }

        private void AssertNotDisposedOrThrow()
        {
            if (isDisposed)
            {
                throw new ObjectDisposedException(MessageTypeMask);
            }
        }
    }
}