Suggestion: Refactor and consolidate event handlers

[begedin]

Problem

Right now, our connect event handlers are being called with Stripe.Event as their first argument, but most of the other factors in how their being called are kind of all around the place.

Some require user_id (a Stripe.Account id) as the second argument, some inferr it, some get is as part of the object that's being handled, etc.

The thing is, we store the Stripe.Event as a local record, StripeEvent, every time before it gets handled. The local StripeEvent has the following info which ought to be enough for us to handle any event:

• object_id - id of the object stored in the event. For platform events, this is enough to retrieve the object from the stripe API.
• user_id - id of the connect account associated with the event object, with object_id, enough to retrieve the object from stripe API in the case of a connect event
• type - the type of the event. enough to figure out which handler should handle it
• endpoint - "platform" or "connect" - enough to figure out which handler module ought to be used to handle the event.

This means that, instead of passing in the Stripe.Event into our handlers, we ought to be able to pass in CodeCorps.StripeEvent instead and not deal with the problematic code in EventHandler.call_handler.

We can use the opportunity to consolidate our handler modules.

• Move all handlers of platform events under StripeService.PlatformEvents.
• Move all handlers of connect events under StripeService.ConnectEvents.
• For platform events, each handler should call their respective service module with just an id_from_stripe for that object. Everything else can be inferred after retrieving the object from the Stripe API
• For connect events, handler should call their respective service with id_from_stripe and user_id, which should then be enough to retrieve the object from stripe and read the rest from there. This means that our event handlers will all have the identical interface within their endpoint group.
• I would also consider renaming our XService.create functions (those that simply fetch the record from stripe and insert it locally), to create_from_stripe or even import_from_stripe, since this is what they in fact do.

Platform event handlers

• customer.source.updated - currently passes Stripe.Event.data.object.id into service, which can be StripeEvent.object_id`
• customer.updated - same as customer.source.updated

Connect event handlers

• account.updated - currently passes Stripe.Event.data.object.id into service, which can be StripeEvent.object_id. For the sake of connect events having the same interface, we should consider passing in StripeEvent.user_idas a second argument (the connect account id), even though it has the same value asobject_id` in this case.
• charge.succeeded - currently passes Stripe.Event.data.object.id into service, which can be StripeEvent.object_id. Also passes in user_id, which we've explicitly merged into the stripe object. If we switch to StripeEvent, we can just simply pass in StripeEvent.user_id`
• customer.subscription.deleted - currently passes Stripe.Event.data.object.id into service, which can be StripeEvent.object_id. Also passes in customer, so we can infer the account and then fetch the record. If we pass in StripeEvent.user_id` instead, we would not have to do all that.
• customer.subscription.updated - same as customer.subscription.deleted
• invoice.payment.succeeded- same as customer.subscription.deleted

[begedin]

@joshsmith Could use your thoughts on this. Seems like having a unified interface for handling our connect/platform events would be helpful.