public function generateCoupon($priceRuleId, $expireDate)
    {
        $rule   = $this->getPriceRule($priceRuleId);
        $coupon = $rule->acquireCoupon();
        $coupon = $this->setUpCoupon($expireDate, $coupon, $rule);
        $this->couponResourceInterface->save($coupon);

        return $coupon->getCode();
    }