Add SubscriptionType to differentiate between auto-renewable and non-renewing subscriptions.

[bizz84]

For auto-renewable, receipt["latest_receipt_info"] is used.
For non-renewing, receipt["receipt"]?["in_app"] is used.

This fixes a bug where receipt verification fails for non-renewing subscriptions (which were previously using "latest_receipt_info".

[bryanbartow]

Pushing new build using this branch to my test users shortly. I'll report results back.

[griddle]

thanks @bizz84

I've never worked with StoreKit until a couple days ago so take this with a grain of salt, but one thing I've noticed is that for auto-renewing subscriptions in a Subscription Group, if the user switches between groups (ie: upgrades or downgrades), there's no way to know that. This code will return that they're on both subscriptions and neither are expired.

I've read a few blogs that solve this by doing:

let currentReceipt = receipts["latest_receipt_info"].last

I'm not sure if that will work if you have more than one Subscription Group though.

I'm still learning and I will submit a PR if I can provide a helpful update on this problem.

[bizz84]

@griddle seems like this page explains Subscription Groups in detail: https://developer.apple.com/library/content/documentation/LanguagesUtilities/Conceptual/iTunesConnectInAppPurchase_Guide/Chapters/CreatingInAppPurchaseProducts.html

If you found more documentation/blogs with practical notes about how to make it work, could you share links here?

If we can understand how this is meant to work, then it can be implemented accordingly.

[bryanbartow]

Beta testers all report the build using this PR is working as expected. Thanks for the fix @bizz84.