Advanced discount rule plugin

Hi

We have an issue that we cant seem to find a solution for in our existing installation.
Nop 4.50.

We would like to have a discount related to a discount code.
Lets say for 10% of any product.

However, this discount should only effect products that is not yet on any discount.
So if the product is general discounted with 20% the cart should still give 20%. (Not 10% and not 30%). But if the product is general discounted with 8% of course the discount code with 10% should apply, so 10% discount is given.
In other words, the calculation for each product should always give the best discount for the customer, but never combine them.

Any one know a way to do this, or a plugin that can do this?

Best regards,
Axel

Please clarify "product is general discounted".
Do you have other "Assigned to product" type discounts?
Or, does "general" mean something like "Price" being less than "Old Price"?

New York wrote:

Yes, i mean if Price is set lower than Old price, then the product is on sale, and Nop will show it like that. But then you cannot add additional discount by coupon code or other discount.
Then it needs to calculate what is the best price for each product for this customer

There is no built-in feature to prevent applying a Discount to a product just because it is having an Old Price.  One would have to create a custom Discount Requirement Rule Plugin for it.