<?php
    // load product
    /** @var Mage_Catalog_Model_Product $product */
    $product = Mage::getModel(‘catalog/product’)
                    ->setStoreId($storeId)
                    ->load($productId);

    // set length of coupon code
    /** @var Mage_SalesRule_Model_Coupon_Codegenerator $generator */
    $generator = Mage::getModel(‘salesrule/coupon_codegenerator’)
                        ->setLength(8);
    /** @var Mage_SalesRule_Model_Rule_Condition_Product $conditionProduct */
    $conditionProduct = Mage::getModel(‘salesrule/rule_condition_product’)
                                                ->setType(‘salesrule/rule_condition_product’)
                                                ->setAttribute(‘sku’)
                                                ->setOperator(‘==’)
                                                ->setValue($product->getSku());
                                               
    /** @var Mage_SalesRule_Model_Rule_Condition_Product_Found $conditionProductFound */
    $conditionProductFound = Mage::getModel(‘salesrule/rule_condition_product_found’)
                                            ->setConditions(array($conditionProduct));
    /** @var Mage_SalesRule_Model_Rule_Condition_Combine $condition */
    $condition = Mage::getModel(‘salesrule/rule_condition_combine’)
                    ->setConditions(array($conditionProductFound));
                                               
    /** @var Mage_SalesRule_Model_Coupon $coupon */
    $coupon = Mage::getModel(‘salesrule/coupon’);
    // try to generate unique coupon code
    $attempts = 0;
    do {
        if ($attempts++ >= 8) {
            Mage::throwException(Mage::helper(‘mymodule’)->__(‘Unable to create requested Coupons. Please try again.’));
        }
        $code = $generator->generateCode();
    } while ($coupon->getResource()->exists($code));

    // create rule
    /** @var Mage_SalesRule_Model_Rule $rule */
    $rule = Mage::getModel(‘salesrule/rule’);
    $rule->setName(Mage::helper(‘mymodule’)->__(‘Name of the coupon’))
        ->setDescription($rule->getName())
        ->setFromDate(date(‘Y-m-d’))
        ->setCustomerGroupIds($this->_getCustomerGroups())
        ->setIsActive(1)
        ->setConditionsSerialized(serialize($condition->asArray()))
        //->setActionsSerialized  
        //->setStopRulesProcessing
        //->setIsAdvanced                  
        ->setSimpleAction(Mage_SalesRule_Model_Rule::BY_FIXED_ACTION)
        ->setDiscountAmount($product->getFinalPrice())
        ->setDiscountQty(1)
        //->setDiscountStep                  
        ->setStopRulesProcessing(0)
        ->setIsRss(0)
        ->setWebsiteIds(array(1))
        ->setCouponType(Mage_SalesRule_Model_Rule::COUPON_TYPE_SPECIFIC)
        ->setConditions($condition)
        ->save();         
   
    // create coupon
    $coupon->setId(null)
        ->setRuleId($rule->getRuleId())
        ->setCode($code)
        ->setUsageLimit(1)
        //->setUsagePerCustomer
        //->setTimesUsed
        //->setExpirationDate
        ->setIsPrimary(1)
        ->setCreatedAt(time())
        ->setType(Mage_SalesRule_Helper_Coupon::COUPON_TYPE_SPECIFIC_AUTOGENERATED)
        ->save();
?>