Am I in developer hell already? A shitty project is about to come to an end (hopefully), or should I rather say: It needs to come to an end. But I am still quite lost in how to deal with it, hence procrastinating on it - making the deadline come closer and with it the realization that I'll probably have to rewrite almost everything. I'm not sure how, but I do know that the current code is a dumpster fire.

Basically what I need to do is dealing with the APIs of different payment providers/gateways (like PayPal, AmazonPay). For most cases I'll get a payment ID from the shop and need to act on it later, e.g. capture the authorized money in the case of a credit card transaction or do refunds (without user interaction, unless there is an error). Now at first I put something together where I try to abstract the payment information into two tables:
orders{1}<->{0..n}payments
payments{1}<->{1..n}paymentDetails

Unfortunately trying to abstract the different payment methods and to squeeze them (and their different possible stati and functions) in these tables was not very successful, it's a total mess with magic numbers, half-broken behavior and without any consideration for partial payments/captures or unfinished requests (i.e. if there is an exception before the response is dealt with, there is no indication that anything has ever been sent). Also the current amount is calculated through the history of the paymentDetails table, which basically works differently for each payment type.

How to fix this mess in a way that I'll still have a job by next week?

I'm trying to improve the db schema first, as I think my biggest problems are lying there. Through some research I've come across a recommendation for making payment type specific subtables (with a magic number/string in the main table to prevent having to look up all subtables). That way I can record what I send and receive without having to abstract it too much, so I'll have an acceptable transaction log. The paymentDetails table can be removed (necessary fields go to the payments table). The payments table gets multiple fields for the amount (differentiating between open, authorized, captured, processing and refunded values) and always reflects the current status.

Tables:
payments
paymentRequestsPaypal
paymentRequestsAmazonpay
paymentRequestsXyz

I think I'm going in the right direction here. hm. Maybe there's some light at the end of this long, dark tunnel. Or a train. I'll have two days to find out.