public static void UpdateSubscriber(Subscriber subscriber, Company company)
        {
            Subscriber currentSubscriber = GetSubscriber(subscriber.LicencePlates);
            DateTime   oldSubscription   = currentSubscriber.ValidTo;
            int        months            = Convert.ToInt32(Math.Ceiling((subscriber.ValidTo - oldSubscription).Days / 31.0));
            DateTime   validTo           = currentSubscriber.ValidTo.AddMonths(months);

            currentSubscriber.ValidTo = validTo;

            if (months > 0)
            {
                ChargeSubscriberController.ChargeSubscription(subscriber.LicencePlates, months, validTo, company);
                Database.Subscribers.UpdateSubscriber(currentSubscriber);
            }
            else
            {
                throw new Exception("Pretplata se ne može ukinuti.");
            }
        }
        public static void AddSubscriber(string licencePlates, DateTime validTo, Company company)
        {
            int months = 0;

            if (((validTo - DateTime.Now).Days / 31.0) == 0)
            {
                months  = 1;
                validTo = DateTime.Now;
            }
            else
            {
                months  = Convert.ToInt32(Math.Ceiling((validTo - DateTime.Now).Days / 31.0));
                validTo = DateTime.Now;
            }
            DateTime newValidTo = validTo.AddMonths(months);

            Database.Subscribers.AddSubscriber(licencePlates, newValidTo);

            if (months > 0)
            {
                ChargeSubscriberController.ChargeSubscription(licencePlates, months, newValidTo, company);
            }
        }