Magento – Apply coupon observer to set message in cart view

I found answer of above question.

Created event of sales_order_status_after

<events>
        <sales_order_save_commit_after>
            <observers>
                <modulename>
                    <type>singleton</type>
                    <class>Mycompany_Offer_Model_Observer</class>
                    <method>sales_order_save_commit_after</method>
                </modulename> 
            </observers>
        </sales_order_save_commit_after> 
    </events>

Added Method sales_order_save_commit_after in observer:

<?php

class Mycompany_Offer_Model_Observer {

    public function sales_order_save_commit_after(Varien_Event_Observer $observer)
    {               


        $order = $observer->getOrder();
        if($order->getState() == Mage_Sales_Model_Order::STATE_COMPLETE){
            $orderTotal = $order->getBaseSubTotal();
            $customerId = 0;
            if($customerId = $order->getCustomerId())
            { 
                $customer_id = $customer->getId();
            }  
            $discountAmount = 10;
            $duration = 30;  
            $discountIn = 'by_fixed'; 
            Mage::getModel('offer/offer')->createCoupon($customer_id, $discountAmount, $duration, $discountIn); 

        } 
    } 

}

Added above function createCoupon in model file:

class Mycompany_Offer_Model_Offer extends Mage_Core_Model_Abstract

        /**
         * Function to create coupon dynamically
         *
         * @param int $customer_id
         * @param int $discount
         * @param int $days
         * @param text $type
         * @return nothing
         */
        public function createCoupon($customer_id, $discount,$days,$type)
        {
            $customer = Mage::getModel('customer/customer')->load($customer_id);

            $customerGroupIds = Mage::getModel('customer/group')->getCollection()->getAllIds();
            $websitesId = Mage::getModel('core/website')->getCollection()->getAllIds();

            $customer_name = $customer->getName();
            $couponCode = Mage::helper('core')->getRandomString(9);

            $model = Mage::getModel('salesrule/rule');
            $model->setName('Discount for ' . $customer_name);
            $model->setDescription('Discount for ' . $customer_name);
            $model->setFromDate(date('Y-m-d'));
            $model->setToDate(date('Y-m-d', strtotime('+'.$days.' days'))); 
            $model->setCouponType(2);
            $model->setCouponCode($couponCode);
            $model->setUsesPerCoupon(1);
            $model->setUsesPerCustomer(1);
            $model->setCustomerGroupIds($customerGroupIds);
            $model->setIsActive(1);
            $model->setConditionsSerialized('');
            $model->setActionsSerialized('');
            $model->setStopRulesProcessing(0);
            $model->setIsAdvanced(1);
            $model->setProductIds('');
            $model->setSortOrder(1);
            $model->setSimpleAction($type);//$model->setSimpleAction('by_fixed');
            $model->setDiscountAmount($discount);
            $model->setDiscountStep(0);
            $model->setSimpleFreeShipping(0);
            $model->setTimesUsed(0);
            $model->setIsRss(0);
            $model->setWebsiteIds($websitesId);

            try {
                $model->save();  
                return $model->getData();
            } catch (Exception $e) {
                print_r($e->getMessage());exit;
                Mage::log($e->getMessage());
            }
        }
}


Mage::getModel('offer/offer')->createCoupon($customer_id, $discountAmount, $duration, $discountIn);

As per above syntax we have to pass parameters like 'customer id', 'discount amount', 'duration' (in days), and 'discountIn'( like 'by_percent' or 'by_fixed')

class NameSpace_Module_Model_Observer
{
    $productId = 1;
    $couponId = 'xyz';

    public function yourObserverMethod($observer)
    {
     $quote = $event->getQuote();
     $item = $event->getItem();
        // add
        if ($quote->getCouponCode() == $this->couponId && !in_array($this->productId, $item->getAllIds())){
            // add product
        }

         //remove
        if($quote->getCouponCode() != $this->couponId && in_array($this->productId, $item->getAllIds()){
             // remove product
        }
    }
}

See

Mage::dispatchEvent('salesrule_validator_process', array(
    'rule'    => $rule,
    'item'    => $item,
    'address' => $address,
    'quote'   => $quote,
    'qty'     => $qty,
    'result'  => $result,
));