Zencart order total module example

ot_handling_charges.php

<?php
/*  Write this code on order.php   */
$customer_whole_obj = $db->Execute('select `customers_whole` from `'.TABLE_CUSTOMERS.'` where `customers_id` ='.$_SESSION['customer_id']);
$customer_whole = $customer_whole_obj->fields['customers_whole'];
if($customer_whole == 4){
  if($_SESSION['payment'] == 'paypal' || $_SESSION['payment'] =='authorizenet'){
    $this->info['charges'] = 2.5;
    $this->info['total_without_charges'] = $this->info['total'];
    $this->info['charges_amt'] = ($this->info['total'] * $this->info['charges'])/100;
    $this->info['total'] = $this->info['total'] + $this->info['charges_amt'];
  }
}

/* Module Language file */
define('MODULE_HANDLING_CHARGES_TITLE', 'Charges');
define('MODULE_HANDLING_CHARGES_DESCRIPTION', 'Handling Charges');

/* Module */
class ot_charges
{
    var $title, $output;

    function ot_charges()
    {
        $this->code = 'ot_charges';
        $this->title = MODULE_HANDLING_CHARGES_TITLE;
        $this->description = MODULE_HANDLING_CHARGES_DESCRIPTION;
        $this->sort_order = MODULE_HANDLING_CHARGES_SORT_ORDER;
        $this->output = array();
    }

    function process()
    {
        global $order, $currencies;
        if (isset($order->info['charges'])) {
            $this->output[] = array('title' => $this->title . ':',
                'text' => $currencies->format($order->info['charges_amt'], true, $order->info['currency'], $order->info['currency_value']),
                'value' => $order->info['charges_amt']);
            $this->output[] = array('title' => 'Total without charges:',
                'text' => $currencies->format($order->info['total_without_charges'], true, $order->info['currency'], $order->info['currency_value']),
                'value' => $order->info['total_without_charges']);
        } else {
            $this->output[] = array('title' => '',
                'text' => '',
                'value' => '');
        }
    }

    function check()
    {
        global $db;
        if (!isset($this->_check)) {
            $check_query = $db->Execute("select configuration_value from " . TABLE_CONFIGURATION . " where configuration_key = 'MODULE_HANDLING_CHARGES_STATUS'");
            $this->_check = $check_query->RecordCount();
        }
        return $this->_check;
    }

    function keys()
    {
        return array('MODULE_HANDLING_CHARGES_STATUS', 'MODULE_HANDLING_CHARGES_SORT_ORDER');
    }

    function install()
    {
        global $db;
        $db->Execute("insert into " . TABLE_CONFIGURATION . " (configuration_title, configuration_key, configuration_value, configuration_description, configuration_group_id, sort_order, set_function, date_added) values ('This module is installed', 'MODULE_HANDLING_CHARGES_STATUS', 'true', '', '6', '1','zen_cfg_select_option(array(\'true\'), ', now())");
        $db->Execute("insert into " . TABLE_CONFIGURATION . " (configuration_title, configuration_key, configuration_value, configuration_description, configuration_group_id, sort_order, date_added) values ('Sort Order', 'MODULE_HANDLING_CHARGES_SORT_ORDER', '777', 'Sort order of display.', '6', '2', now())");
    }

    function remove()
    {
        global $db, $messageStack;
        if (!isset($_GET['override']) && $_GET['override'] != '1') {
        $messageStack->add('header', ERROR_MODULE_REMOVAL_PROHIBITED . $this->code);
        return false;
    }
        $db->Execute("delete from " . TABLE_CONFIGURATION . " where configuration_key in ('" . implode("', '", $this->keys()) . "')");
    }
}