Method: Get the number of times the coupon has been used

Method: Determine if the main (non-trial) price is discounted by this coupon

Method: Determine if trial amount discount is enabled for the coupon

Method: Determine if a coupon is expired

Method: Perform all available validations and return a success or error message

Method: Get an array of all products the coupon can be used with Combines $this->coupon_courses & $this->coupon_membership

Method: Get the number of remaining uses calculated by subtracting # of uses from the usage limit