== How payment works? ==

User selects a plan at sign-up. He is redirect to the home page.
When she hits the homepage, she is invited to select an amount
(based on period: monthly or yearly). Then she press "Pay" button.
We call 'pay_square_create_link' (passing an id which is payments.id)
to create a payment link and we redirect the user to it.
Sample link: https://sandbox.square.link/u/IgOz82xk
The rg id, uid, operator name, 'plan' type and 'y' interval, 'init'
state are inserted by calling 'pay_insert' function.
	pay_needed_high_level
		pay_square_create_link
			pay_insert
We receive an order_id.

Next step is to go to the external payment page.
Payment takes place.
External site redirects back to RocketGit (passing back the payment id).
https://rg.embedromix.ro:9003/user/price1?paid=e09964ef29b3d886

Now, we received the payment id and we thank the user for the purchase.
We need to schedule the checking of the payment, as an event, to be able
to confirm it and mark it as paid. Should we? I think yes, because only now
the user confirmed the payment. Yes, but what if we cannot update the db?
Isn't it better to just check all initiated payments? I think yes.
We connect to the payment provider and we will check the state of the payment.
We also need to be able to compute the last paid day, to not bother the user
earlier than needed.
How should I compute it? And where to store this info?
	- case 1, user is paying immediately after sign-up (2023-02-10), pays for 1 month
		first day not paid is after exactly 1 month (2023-03-10)
	- case 2, user is paying after some days after sign-up (2023-02-10), pays for 1 month
		first day not paid is after exactly 1 month (2023-03-10)
	- what happens if we suspend the account for not paying?
		we still have resources used. Ask user to pay before unlocking resources?

TODO:
- We need to show correctly 12999 euro as 12.99 euro.
	1299/12990/USD 1/10/RON -> 1299=12.99/12990=129.90/USD 99=0.99/999=9.99/RON
- What if the user does not pay and does not return to rg? We should
reuse a previous payment if amount/period/plan match.
- What if the user changes the plan on-th-fly?
We need to think to multiple scenarios (cheaper plan or a more expensive one).
- Should we offer one (last?) month free?
-