Perform payment transaction during checkout

So I have concerns about the event listener.

With 'commerce_order.place.post_transition' => 'onOrderPostPlace', the event will run on admin placed orders and checkout. Checkout and admin have two flows, in my opinion. With checkout an order collects payment information before being placed. An admin workflow probably leads to an order being placed then collecting payment. We cannot always assume we have payment method information on the placed transition, only when in the checkout context.

Steve, building on what bojanz said here in #2822056, could your code potentially work in CheckoutFlowBase::validateForm (with a similar condition to what's firing the complete event) to create the payment? We could trap any exceptions there and redirect back to the current step with an error message if the payment fails or proceed to complete if it's good.

I'm working on a payment processor implementation right now, so I went ahead and took Steve's code from the event listener and moved it to CheckoutFlowBase::validateForm (with appropriate conditionals and one minor fix, which was to use the $payment_gateway->id() for the payment gateway as opposed to the plugin ID, which only worked if the name of the plugin for the gateway was the same as the gateway plugin's ID). This seemed to work for me and could be used as a starting point at least. We'd needed a dependency on commerce_payment added to commerce_checkout if this is to work though.

Tested patch #12 with commerce braintree and dev version of commerce module and it seems to be working.

Going to take a stab at wrapping this up. Here's a tl;dr of what I discussed with bojanz that will help support onsite and offsite payment gateways

• All checkout flows have the offsite_payment step
• Rename aforementioned step to "payment"
• The payment_information will allow selecting payment gateway and selecting payment method if an onsite gateway
• Create a new pane called payment_process that lives on Payment page
• If the gateway is an onsite gateway, run createPayment w/ auth/capture setting
• If the gateway is offsite, do redirect

This then places all payment collection logic in one place. Onsite payments will provide the form redirect based on success or failure.

New PR: https://github.com/drupalcommerce/commerce/pull/542

Came across an issue that I think we should handle in a follow-up. On-site payment gateways will cause the payment page to be skipped (we have a payment method and we run it to create a payment.) This only needs to be present when the user has selected an offsite payment gateway.

I have messed around with ::isVisible a bit but there isn't a good solution. I tried to return FALSE if the gateway was OnSite, but then it caused the page to be skipped. But this was also an issue in 1.x with the checkout progress module.

Opened followup for #16: #2831945: The payment step is always present in the checkout progress block.

BOOM!