Sale Coupon Multi Use

This module extends the standard coupon feature so one coupon code can be applied to more than one sale order, as long as the coupon is a fixed-amount discount.

• On a coupon program, a new 'Multi Use Coupons' checkbox appears. When ticked, the program is forced to be a Coupon Program with a Discount reward of type Fixed Amount; other combinations are refused.
• Once coupons have been generated, the multi-use option and the fixed amount can no longer be changed.
• On each coupon, you see whether it is multi-use, the orders it has been applied to, and a list of consumption lines showing the order line, its state and the amount consumed. A 'Fixed Amount Delta' shows how much of the coupon value is still available.
• When a multi-use coupon is applied to an order, only the remaining value is used, capped at the order total. A consumption line is created and the coupon leaves the order so it can be reused.
• The coupon status switches between 'new' and 'used' automatically depending on whether value remains. Removing the reward line or cancelling the order deletes the consumption line and updates the coupon status.
• The same multi-use coupon cannot be applied twice to the same reward on one order.