The code in the plugin needed a dramatic cleanup. This refactor collapses the Plan/Product/Subscription controllers on the backend into one new controller: `SubscribeController`.
This reduces N+1 calls to the back end during the subscription process and simplifies use of the code.
I've also removed a bunch of dead code and refactored some logic into methods for easier readability. No feature/functionality changes in this commit; only refactoring. However, refactoring will allow for implementation of better anonymous user handling, so this is largely a foundation to enable making that change.
Building off the foundation of using the Prices API, this PR adds the ability to create a one-time purchase plan for any product, which then can add a user to the specified plan group.
Some things to be aware of:
One-time purchases cannot have trials.
One-time purchases use the Invoice API instead of Subscriptions. Invoices are created then charged immediately.
Users should receive emails for these invoices directly from Stripe just like subscriptions.
Justin DiRose