Exp:resso Store discount extension

ext.store_discount.php

<?php  if ( ! defined('BASEPATH')) exit('No direct script access allowed');

/**
 * Store Discount Extension
 *
 * @package     ExpressionEngine
 * @subpackage  Addons
 * @category    Extension
 * @author      Eli Van Zoeren
 * @link        http://elivz.com
 */

class Store_discount_ext {

    public $settings        = array();
    public $description     = 'Apply quantity-based discounts to Exp:resso Store';
    public $docs_url        = 'http://elivz.com';
    public $name            = 'Store Discount';
    public $settings_exist  = 'n';
    public $version         = '1.0';

    private $EE;

    /**
     * Constructor
     *
     * @param   mixed   Settings array or empty string if none exist.
     */
    public function __construct($settings = '')
    {
        $this->EE =& get_instance();
        $this->settings = $settings;
    }

    // ----------------------------------------------------------------------

    /**
     * Activate Extension
     *
     * This function enters the extension into the exp_extensions table
     *
     * @see http://codeigniter.com/user_guide/database/index.html for
     * more information on the db class.
     *
     * @return void
     */
    public function activate_extension()
    {
        // Setup custom settings in this array.
        $this->settings = array();

        // Add hooks
        $data = array(
            'class'     => __CLASS__,
            'method'    => 'update_cart',
            'hook'      => 'store_cart_update_end',
            'settings'  => serialize($this->settings),
            'priority'  => 10,
            'version'   => $this->version,
            'enabled'   => 'y'
        );

        $this->EE->db->insert('extensions', $data);
    }

    // ----------------------------------------------------------------------

    /**
     * Disable Extension
     *
     * This method removes information from the exp_extensions table
     *
     * @return void
     */
    function disable_extension()
    {
        $this->EE->db->where('class', __CLASS__);
        $this->EE->db->delete('extensions');
    }

    // ----------------------------------------------------------------------

    /**
     * Update Extension
     *
     * This function performs any necessary db updates when the extension
     * page is visited
     *
     * @return  mixed   void on update / false if none
     */
    function update_extension($current = '')
    {
        if ($current == '' OR $current == $this->version)
        {
            return FALSE;
        }

        $this->EE->db->where('class', __CLASS__);
        $this->EE->db->update(
                    'extensions',
                    array('version' => $this->version)
        );
    }

    // ----------------------------------------------------------------------

    /**
     * Responds to the store_cart_update_end hook in Exp:resso Store
     * to apply a discount to each product, as needed
     *
     * @return array of cart items
     */
    function update_cart($cart_contents)
    {
        $this->EE->load->helper(array('store'));

        // Get the number of products currently in the user's cart
        $count = count($cart_contents['items']);

        // Only apply the discount if there is more than one item
        if ($count > 1)
        {
            // Take $10 off all but the first product
            // This calculation can easily be adjusted as needed
            $discount = ($count - 1) * 10;

            // Add the quantity discount to any existing discount (promo code)
            $cart_contents['order_discount_val'] += $discount;
            // Make sure we don't end up with a negative total
            if ($cart_contents['order_discount_val'] > $cart_contents['order_subtotal_val'])
            {
                $cart_contents['order_discount_val'] = $cart_contents['order_subtotal_val'];
            }
            $cart_contents['order_discount'] = store_format_currency($cart_contents['order_discount_val']);

            // Update the cart total to reflect the new discount
            $cart_contents['order_total_val'] = $cart_contents['order_subtotal_val'] - $cart_contents['order_discount_val'];
            $cart_contents['order_total'] = store_format_currency($cart_contents['order_total_val']);
        }

        return $cart_contents;
    }
}

/* End of file ext.store_discount.php */
/* Location: /system/expressionengine/third_party/store_discount/ext.store_discount.php */

Right... this is a starting point for developing your own discount extension. If you need a click-and-play interface for discounts, you'll probably need to wait until Exp:resso adds it to Store, or use a different e-commerce add-on (CartThrob has very flexible discounting, although at the expense of a more complex system all around).

Yeah I really should start learning as it will make things a lot easier.
Thanks for this extension Eli it will work as a great starting point. I will ask a mate of mine to have a look and show me how we can extend the code to what I need. I will gist the result when it is done.

Cheers
Dan

Dan.. try something like this (untested, may be some slight errors):

foreach ($cart_contents['items'] as $item)
{
    if ($item['item_qty'] >= 3)
    {
         $cart_contents['order_discount_val'] += 10;
    }
}

then add the rest of the code from above:

        if ($cart_contents['order_discount_val'] > $cart_contents['order_total_val'])
            $cart_contents['order_discount_val'] = $cart_contents['order_total_val'];
        $cart_contents['order_discount'] = store_format_currency($cart_contents['order_discount_val']);

        // Update the cart total to reflect the new discount
        $cart_contents['order_total_val'] = $cart_contents['order_subtotal_val'] - $cart_contents['order_discount_val'];
        $cart_contents['order_total'] = store_format_currency($cart_contents['order_total_val']);

        return $cart_contents;

That should add a $10 discount for every item which has qty >= 3. Notice all the variables are exactly the same as what you use in the template (item_qty, order_total etc).

Works great thanks guys.