Find closest promo rule

Question

We are offering free products on certain order limits, over Magento CE 1.7.

In order to encourage customer to go for more purchase, we have to show notices/alerts on cart's page with the closest promo that could be applied on the cart.

I have found a similar post, but this seems to be exhaustive process, as it would require to iterate through all the shopping cart promo rules to find the appropriate rule: Read promotion rule condition - Magento

Looking forward to know if there is any filter available to simplify the process.

Answer 1

Found few filters, and build up above the previously mentioned solution:

$attr_match = sprintf('%%%s%%', substr(serialize(array('attribute' => 'base_subtotal')), 5, -1));
$type_match = sprintf('%%%s%%', substr(serialize(array('type' => 'salesrule/rule_condition_address')), 5, -1));
$opr_grt_match = sprintf('%%%s%%', substr(serialize(array('operator' => '>')), 5, -1));
$opr_grteq_match = sprintf('%%%s%%', substr(serialize(array('operator' => '>=')), 5, -1));

$collection = Mage::getResourceModel('salesrule/rule_collection')
        ->addWebsiteGroupDateFilter(Mage::app()->getWebsite()->getId(), $group_id)
        ->addFieldToFilter('main_table.coupon_type', Mage_SalesRule_Model_Rule::COUPON_TYPE_NO_COUPON)
        ->addFieldToFilter('main_table.conditions_serialized', array(
           'like' => $attr_match,
            ))
        ->addFieldToFilter('main_table.conditions_serialized', array(
            'like' => $type_match,
            ))
        ->addFieldToFilter('main_table.conditions_serialized', array(array(
            'like'  =>  $opr_grt_match
            ),array(
            'like'  =>  $opr_grteq_match
            )))
    ;
    $quote = Mage::getSingleton('checkout/session')->getQuote();
    $applied_rules = $quote->getAppliedRuleIds();
    if($applied_rules) {
        $collection->addFieldToFilter('main_table.rule_id',array(
           'nin' => explode(",", $applied_rules),
            ));
    }
    $rules = $collection->setOrder('main_table.sort_order', Varien_Data_Collection::SORT_ORDER_ASC)->load();

Looking forward to comments, to improvise it.

Added an article on my blog, with a more descriptive solution: Magento – Closest Promo Rule