CRM-17281 Pledge payments: fix rounding bug with miscalculation for multiple payments against a pledge

[eileenmcnaughton]

Overview

FIX miscalculation of remaining pledge payments when a payment is made that exceeds them and the cent values do not accurately spread over the payments (e.g 12 payments to pay $100)
FROM @mlutfy #9585

Before

No test, payment miscalculates remaining payments when a payment is made that pays off multiple payments

After

Payments covered are set to zero rather than the overhang value remaining outstanding

Technical Details

Note that we added a placeholder function for the number of decimal places a payment can be in, rather than hard-coding it.

Comments

---

• CRM-17281: Pledges miscalculate when total amount is not an integer and a payment is received that covers three installments

[eileenmcnaughton]

This code is from #9585 - that patch also involved quite a lot of cleanup - unfortunately a lot of that cleanup can't be used now as it is stale :-(

The following comments are ones I added to the last commit but copying here to make them easier to see

This PR fixes a bug where payments are miscalculated with weird results. If a payment
changes the amount of future payments in such a way as to make an irregular amount
e.g 10 is split over 3 payments, the payment amount needs to be recorded as .33 not
.333333, assuming a currency with 2 decimal places. This commit
ensures the rounding takes place & is locked in by the accompanying unit test.

Note that we discussed this & agreed to use a function as a placeholder for the number
of decimal places.

[eileenmcnaughton]

I spent a lot of time trying to understand why the removed line

      $oldestPayment = self::getOldestPledgePayment($pledgeID);

3e0b390

Was there in the first place, & tbh I really couldn't. It's worth noting that there is a clear reproducable problem that this line causes which can be seen in the UI or the unit test & which removing it fixes in both instances. While I don't think it will, even if we just move the bug I think this is a step forwards since the test means this variant cannot come back & the code makes baby-steps towards legibility in this PR.

As a reviewers collaboration I would normally merge this at this stage but at the moment we have an unresolved process here so @colemanw would you be able to merge this please?

@mlutfy can you please confirm there is nothing in the final version you are uncomfortable with.

[eileenmcnaughton]

Screenshot of old borked behaviour - this is after paying $100 against a $100 pledge, still showing $0.04 on the last payment and pledge status not being Completed. This is fixed after this and we also tested making 2 payments which total $100 & confirmed no change.

[mlutfy]

I reviewed the changes and looks good!

[colemanw]

@civicrm-builder retest this please