Maximum Coupon Discount

Problem/Motivation

The question came up recently as to whether or not the Ubercart Coupons (uc_coupon) module had any "up to" functionality with respect to the application of percentage-based coupons. This functionality is also known as "Maximum Coupon Discount".

OpenCart: Maximum Coupon Discount
The OpenCart Shopping Cart Offers this functionality as an add-on:
Maximum Coupon Discount is an Opencart extension designed to limit the discount per coupon code. By default, there is no limit on the amount of discount that can be given. So if you want to restrict with some maximum discount for coupons this extension is for you. This extension allows you to set a maximum discount that can be given. Example: Let's say the coupon code is Flat 50% Off, and the order total is $100. So by default, the discount would be $50. But if you wanted to restrict the maximum discount to $20. It won't be possible with default Opencart features. This extension fills that gap.
https://www.cartbinder.com/store/maximum-coupon-discount-limit-discount-...

Steps to reproduce

I looked around in the Coupons area of Ubercart at:

Home » Administration » Store » Coupons

or:

/admin/store/coupons/add

But couldn't find anything that limited the monetary discount of a percentage coupon to some ceiling.

Proposed resolution

New code?

Remaining tasks

User interface changes

- Change Administrative GUI area by adding an area to manage field maximum_coupon_discount?
- Add (optional) checkout notification if order hits maximum coupon discount

API changes

- Add hook?

Data model changes

- Add field in database / stored variable?
- Alter cart checkout code