Order::getCouponDiscount PHP Method

    public function getCouponDiscount(array $coupons)
    {
        $productsTotalPrice = $this->getProductsCost();
        $delta = 0.0;
        // суммарная скидка по купонам
        /* посчитаем скидку */
        if ($this->isCouponsAvailable()) {
            foreach ($coupons as $coupon) {
                switch ($coupon->type) {
                    case Coupon::TYPE_SUM:
                        $delta += $coupon->value;
                        break;
                    case Coupon::TYPE_PERCENT:
                        $delta += $coupon->value / 100 * $productsTotalPrice;
                        break;
                }
            }
        }
        return $delta;
    }