async Task <bool> ExistsAsync(string topicPath, string subscriptionName, string metadata, INamespaceManager namespaceClient, bool removeCacheEntry = false)
        {
            logger.Info($"Checking existence cache for subscription '{subscriptionName}' aka '{metadata}' in namespace '{namespaceClient.Address.Host}'.");

            var key = GenerateSubscriptionKey(namespaceClient.Address, topicPath, subscriptionName);

            if (removeCacheEntry)
            {
                Task <bool> dummy;
                rememberExistence.TryRemove(key, out dummy);
            }

            var exists = await rememberExistence.GetOrAdd(key, notFoundKey =>
            {
                logger.Info($"Checking namespace '{namespaceClient.Address.Host}' for existence of subscription '{subscriptionName}' for the topic '{topicPath}'.");
                return(namespaceClient.SubscriptionExists(topicPath, subscriptionName));
            }).ConfigureAwait(false);

            logger.Info($"Determined, from cache, that the subscription '{subscriptionName}' in namespace '{namespaceClient.Address.Host}' {(exists ? "exists" : "does not exist")}.");

            return(exists);
        }
        private void EnsureMessagingEntityExists(MessageTypeMessagingEntityMappingDetails mappingDetails, IEnumerable <MessageTypeMessagingEntityMappingDetails> allMessageTypePathMappings)
        {
            MessagingEntityCreationOptions creationOptions = mappingDetails.CreationOptions;

            if (creationOptions != MessagingEntityCreationOptions.None
                &&
                !_verifiedExistingMessagingEntities.Contains(mappingDetails))
            {
                Func <bool> exists;
                Action      create;
                Action      delete;

                string path = mappingDetails.Path;

                switch (mappingDetails.MessagingEntityType)
                {
                case MessagingEntityType.Queue:
                    exists = () => _namespaceManager.QueueExists(path);
                    create = () => _namespaceManager.CreateQueue(path);
                    delete = () => _namespaceManager.DeleteQueue(path);

                    break;

                case MessagingEntityType.Topic:
                    exists = () => _namespaceManager.TopicExists(path);
                    create = () => _namespaceManager.CreateTopic(path);
                    delete = () => _namespaceManager.DeleteTopic(path);

                    break;

                case MessagingEntityType.Subscription:
                    string[] parts            = path.Split('/');
                    string   topicPath        = parts[0];
                    string   subscriptionName = parts[2];

                    exists = () => _namespaceManager.SubscriptionExists(topicPath, subscriptionName);
                    create = () =>
                    {
                        MessageTypeMessagingEntityMappingDetails topicMessageTypePathMapping = allMessageTypePathMappings.FirstOrDefault(mtpmd => mtpmd.MessagingEntityType == MessagingEntityType.Topic && mtpmd.Path == topicPath);

                        if (topicMessageTypePathMapping == null)
                        {
                            topicMessageTypePathMapping = new MessageTypeMessagingEntityMappingDetails(mappingDetails.MessageType, topicPath, MessagingEntityType.Topic, MessagingEntityCreationOptions.VerifyAlreadyExists);
                        }

                        EnsureMessagingEntityExists(topicMessageTypePathMapping, allMessageTypePathMappings);

                        _namespaceManager.CreateSubscription(topicPath, subscriptionName);
                    };
                    delete = () => _namespaceManager.DeleteSubscription(topicPath, subscriptionName);

                    break;

                default:
                    throw new NotSupportedException(string.Format("Unsupported messaging entity type, {0}, requested for creation (path {1}).", mappingDetails.MessagingEntityType, mappingDetails.Path));
                }

                bool alreadyExists = exists();

                if (alreadyExists)
                {
                    if ((creationOptions & MessagingEntityCreationOptions.CreateAsTemporary) != 0)
                    {
                        if ((creationOptions & MessagingEntityCreationOptions.RecreateExistingTemporary) == 0)
                        {
                            throw new MessagingEntityAlreadyExistsException(mappingDetails.Path, mappingDetails.MessagingEntityType);
                        }

                        try
                        {
                            delete();

                            alreadyExists = false;
                        }
                        catch (UnauthorizedAccessException exception)
                        {
                            throw new UnauthorizedAccessException(string.Format("Unable to delete temporary messaging that already exists at path \"{0}\" due to insufficient access. Make sure the policy being used has 'Manage' permission for the namespace.", mappingDetails.Path), exception);
                        }
                    }
                }

                if (!alreadyExists)
                {
                    if ((creationOptions & (MessagingEntityCreationOptions.CreateIfDoesntExist | MessagingEntityCreationOptions.CreateAsTemporary)) == 0)
                    {
                        throw new MessagingEntityDoesNotAlreadyExistException(mappingDetails.Path, mappingDetails.MessagingEntityType);
                    }

                    try
                    {
                        create();
                    }
                    catch (UnauthorizedAccessException exception)
                    {
                        throw new UnauthorizedAccessException(string.Format("Unable to create messaging entity at path \"{0}\" due to insufficient access. Make sure the policy being used has 'Manage' permission for the namespace.", mappingDetails.Path), exception);
                    }
                }

                _verifiedExistingMessagingEntities.Add(mappingDetails);
            }
        }