public IEnumerable <string> GetEmailListOfSoonToBeExpiredSubscription(int threshold)
        {
            var soonToExpire = subscriptionRepository.GetAll()
                               .Where(sub => sub.FixedContract && IsSubscriptionExpiringSoon(threshold, sub));
            var userIdsWithExpiringSub = soonToExpire
                                         .Where(sub => userRepository.GetById(sub.ClientId).Type == UserType.User)
                                         .Select(sub => sub.ClientId);
            var emailsOfUserWithExpiringSub = userIdsWithExpiringSub.Select(id => loginRepository.ByUserId(id).Email);

            return(emailsOfUserWithExpiringSub.ToList());
        }