It would take ages to go through all files now and assess all belongs_to
associations. So I just declare the old default and then we can move on
and apply the new default for the application while these classes still
use the old one. All new models will then use the new default which is
the goal of this excercise and we can refactor old classes when we touch
them anyway.
They're all numbers, so we can reliably validate in the browser, removing the need for additional validation logic.
They will still be validated server-side, and in the unlikely even that there is an error, the generic 'Calculator is invalid' message will appear, with the relevant fields highlighted red. I think that's fine.
This is much simpler. Multiple messages get combined onto one line though, which is not perfect.
And.. it still seems to duplicate the errors. Weird, it's fine on my frontend though.
The checkout was holding a lot of responsibility for knowing which kinds of payment gateways are available and how to initiate the process of redirecting to the external payment page (if needed). This was being hidden somewhat by the way the logic was tucked away in services.
PaymentMethod objects now know whether or not they require an external payment process, and know how that process should be started and how to build the required URL.
So we can now *ask* any payment method if it requires external payment processing or not, and *tell* it to start the process and return the relevant URL (if needed).
We set this value to `true` unconditionally in an initializer, and then check the value in various places via Spree::Config. It's never false, and it's not configurable, so we can just drop it and remove the related conditionals. 🔥
