Calculate only highest discount

Hi!

I’m thinking of creating my own module for this, but it seems like such a basic function that maybe someone has tackled it already:
Let’s say I have a user group that gets 15% discount on all products. Later I make some temporary discount of 20% on all products of a certain category. Now I don’t want my 15%-enters to get a 35% discount on those products - only the 20% because that’s the higher discount. So the general rule would be: in all cases when multiple discounts apply to a basket item only apply the highest discount.
This is pretty common practice in shops, so has anyone tried to do something like this in Oxid? I definitely don’t see any options in the admin.

apparently this has not been solved yet - at least no one has shared a solution

Thanks for the info! I’ll get down to creating a module for this as soon as I manage to get my images into the new shop.