Support asynchronous payment flows

[syjer]

For supporting other payment flow (where the ACK from the gateway can be hours or days later), we will need to an additional state for the TicketReservation I would guess.

Currently, as defined in the enum TicketReservationStatus we have the following states:

PENDING, IN_PAYMENT, COMPLETE, STUCK

The transition is, PENDING -> IN_PAYMENT -> COMPLETE | STUCK

The PENDING state is when the user has reserved a ticket but not paid, if the user has not completed the transaction in the configured timeout, the reservation will be removed.

The IN_PAYMENT state is when the user is paying (this is done in a transaction, so if there are no failure on the stripe side and our side this state is not visible (at the moment there is a error page for handling the IN_PAYMENT and STUCK page, see ReservationController#showReservationPage, last branch )).

So, for supporting the async case, we will need :

• decide where the user will select the payment method (first page or second page?)
• add an additional state between PENDING and IN_PAYMENT .
• add the additional gui for the payment provider + logic on the controller side (we will need to abstract this part, at the moment it's hardcoded)
• gui for the new state (where the user can still modify the ticket assignment) in ReservationController#showReservationPage.

When the payment has been confirmed, the reservation should transition directly to COMPLETE and it should send an email to the user(s) and let them download/see the tickets.

At the moment the user cannot see/interact with the TicketController until the reservation has a COMPLETE status, so on this side we are covered.

[cbellone]

done. To be tested