How to simulate paid features?

Question

Business Informatics

The web service has regulated resources. Their presence / absence / value is what they charge for. You can buy a separate chip, or raise a separate parameter for a while. You can buy a "tariff plan" that includes a set of advanced options and a valid month.
The question is: what is the best way to describe/manage these resources within the application? Probably, for game developers, hosting or mobile operators, the topic is hackneyed and resolved long ago.
It is interesting to hear the opinion of those who have implemented something similar in their projects.
Difficulties arose when considering collisions. For example, I bought a tariff TA , in which the parameter P1 rises to 100. This TAvalid for 1 calendar month. But the user took, and two weeks later bought a separate upgrade P1 to 200, for a period of 2 weeks.
For some parameters, addition is possible: i.e. for two weeks the user will have P1 = 100+200 = 300 . For some, addition is impossible, and you need to consistently keep P1 = 200 , and after the upgrade, continue at the tariff level P1 = 100 . And another question, whether to extend it for 2 weeks, or turn it off as soon as the month of the tariff has passed? (Honestly, it should be extended, perhaps.)
The system is growing, and there will be new "bargaining items" and new business logic. How is it more or less reasonable to foresee the possible complications of marketing in advance?
While everyoneThe parameter is entered into the database, along with a description of its properties: added or sequential, etc. Upon purchase, the user acquires the Product , which consists of one or more Parameters , and has an expiration date. And the purchased Parameters are entered in the Activation table : today with a plus sign, and at the end of the action, with a minus sign. If several identical Parameters appear for one User , their dates are adjusted.

Answer 1

You should study the issue of accounting for contracts in the insurance business. Judging by the conditions that you described - offhand ...
But it's better to simplify the concept model as much as possible, since it will still have to be optimized.