Stackability Resolution Strategy

[brendan-shea-pm]

Most promotions with be set to not stack with promotions of the same type. For Order promos, they don't stack with other Order promos. Same for Item and Shipping, but the stacking is checked per Item and Shipping Method.

When a promotion is added to a cart that already has a conflicting promotion, the outcome should be that the promotion that gives the customer the highest value discount should remain on the cart, and the lesser one removed.

When a promotion is triggered, check whether there are any conflicting promotion types in the order, item(s), or shipping method

If there is a conflict, calculate the value of each conflicting promotion

Remove any promotion that does not have the highest value, so that only the highest value promotion remains