A powerful and easy freeshipping remainder block for Magento based on shopping cart promo rules

freeshipping_remainder.php

<?php
/*

Just create as many shopping cart price rules that are elligible for free shipping
and this block class will use the most appropriate one to define: 

- minimum amount to get freeshipping
- remaining amount to purchase to get freeshipping.

If no rule is elligible, the block falls back to a CMS block.

Just call this block from layout and define a template from which you can call:

- $this->getMinimumPurchaseAmount()
- $this->getRemainingShippingAmount()

*/

/**
 * Checkout_Freeshipping_Remainder Block
 */
class Namespace_Module_Block_Checkout_Freeshipping_Remainder extends Mage_Core_Block_Template
{
  
    /**
     * CMS block identifier for fallback
     */
    const CMS_BLOCK_ID = 'my_cms_block_id';

    /**
     * Amount remaining to get freeshipping
     *
     * @var int
     */
    protected $_remainingShippingAmount = 0;

    /**
     * Minimum purchase amount to get freeshipping
     *
     * @var int
     */
    protected $_minimumPurchaseAmount = 0;

    /**
     * Retrieve minimum purchase amount to get freeshipping
     *
     * @return float
     */
    public function getMinimumPurchaseAmount()
    {
        return $this->_minimumPurchaseAmount;
    }

    /**
     * Retrieve remaining shipping amount
     *
     * @return float
     */
    public function getRemainingShippingAmount()
    {
        return $this->_remainingShippingAmount;
    }

    /**
     * Retrieve shipping cart promo rules that may be used
     *
     * @return array
     */
    protected function _getApplicableRules()
    {

        $currentWebsiteId = Mage::app()->getStore()->getWebsiteId();
        $currentCustomerGroup = (Mage::helper('customer')->isLoggedIn()) ? Mage::helper('customer')->getCustomer()->getGroupId() : Mage_Customer_Model_Group::NOT_LOGGED_IN_ID;

        // Get sales rules that are active, with free shipping enabled and without any coupon
        $availableRules = Mage::getModel('salesrule/rule')->getCollection()
            ->addWebsiteGroupDateFilter($currentWebsiteId, $currentCustomerGroup)
            ->addFieldToFilter('simple_free_shipping', Mage_SalesRule_Model_Rule::FREE_SHIPPING_ADDRESS)
            ->addFieldToFilter('coupon_type', Mage_SalesRule_Model_Rule::COUPON_TYPE_NO_COUPON)
        ;

        $applicableRules = array();

        foreach($availableRules as $rule) {

            /* @var $rule Mage_SalesRule_Model_Rule */

            /**
             * Check if rule may be a candidate to be applicable.
             * This is done by removing all conditions based on cart subtotal amount and testing rule against remaining conditions
             */
            $originalConditions = $rule->getConditionsSerialized();
            $conditions = unserialize($originalConditions);

            // If there is no condition, rule is a candidate!
            if(!isset($conditions['conditions'])) {
                $applicableRules[] = $rule;
                continue;
            }

            // If there is a condition based on cart subtotal, remove it...
            foreach($conditions['conditions'] as $k => $condition) {
                if(isset($condition['attribute']) && $condition['attribute'] == 'base_subtotal') {
                    unset($conditions['conditions'][$k]);
                }
            }

            // ... and rebase conditions
            $conditions['conditions'] = array_values($conditions['conditions']);

            // If there is no condition anymore, remove its entry in its associated rule
            if(count($conditions['conditions']) < 1) {
                unset($conditions['conditions']);
            }

            // Update rule with reworked conditions
            $rule->setConditionsSerialized(serialize($conditions));

            // And check if updated rule is valid. If so, push it into $applicableRules array.
            $address = Mage::helper('checkout/cart')->getQuote()->getShippingAddress();
            if($rule->validate($address)) {
                // Rollback rule to its original state for further processing
                $rule->setConditionsSerialized($originalConditions);
                $applicableRules[] = $rule;
            }
        }

        return $applicableRules;
    }

    /**
     * Calculate remaining amount to get free shipping
     *
     * @param array $rules
     * @return Undiz_Local_Block_Checkout_Freeshipping_Remainder
     */
    public function setRemainingShippingAmount($rules)
    {
        $lowestValue = null;

        // Retrieve lowest minimum value to get free shipping
        foreach($rules as $rule) {
            $conditions = unserialize($rule->getConditionsSerialized());

            // If there is no condition, value for free shipping is 0
            if(!isset($conditions['conditions'])) {
                $value = 0;
            }
            else {
                foreach($conditions['conditions'] as $condition) {
                    if(isset($condition['attribute']) && $condition['attribute'] == 'base_subtotal') {
                        $value = $condition['value'];
                        if(is_null($lowestValue) || $value < $lowestValue) {
                            $lowestValue = $value;
                        }
                    }
                }
            }

            if(is_null($lowestValue) || $value < $lowestValue) {
                $lowestValue = $value;
            }
        }

        if($lowestValue) {

            $store = Mage::app()->getStore();

            // Get cart subtotal excl. tax
            $cartSubtotal = Mage::helper('checkout/cart')->getQuote()->getBaseSubtotal();

            // Check if tax application for shipping is required
            // If so, retrieve tax rate based on current store and using shipping tax class
            $taxRate = 0;
            if(Mage::getStoreConfig('tax/calculation/discount_tax') == 1) { // @see Mage_Tax_Model_System_Config_Source_PriceType
                $request = Mage::getSingleton('tax/calculation')->getRateRequest(false, false, false, $store);
                $taxRate = Mage::getSingleton('tax/calculation')
                    ->getRate($request->setProductClassId(Mage::getStoreConfig('tax/classes/shipping_tax_class')));
            }

            // Get cart subtotal updated with tax rate
            $cartSubtotal = $cartSubtotal * (1 + $taxRate/100);

            // Calculate remaining shipping amount. If < 0, set it to 0
            $remainingShippingAmount = ($lowestValue - $cartSubtotal < 0) ? 0 : $lowestValue - $cartSubtotal;

            // Calculate remaining shipping amount for real
            $this->_remainingShippingAmount = $store->roundPrice($remainingShippingAmount);

            // Update minimum purchase amount to get free shiupping
            $this->_minimumPurchaseAmount = $store->roundPrice($lowestValue);
        }

        return $this;
    }

    /**
     * Switch html rendering:
     * - if there is some available sales rule => calculate remaining shipping amount
     * - else => render some CMS block
     *
     * @return string
     */
    protected function _toHtml()
    {
        $applicableRules = $this->_getApplicableRules();

        if(count($applicableRules) < 1) {
            $cmsBlock = $this->getLayout()
                ->createBlock('cms/block')
                ->setBlockId(self::CMS_BLOCK_ID);

            return $cmsBlock->toHtml();
        }

        $this->setRemainingShippingAmount($applicableRules);

        return parent::_toHtml();
    }
}