custom tax order total little help please

[balihr]

I have an order_total module (which I built) but can't get one desired effect on it.

I need it to collect info from the product in cart and check it's main category ID.

I have tried the following code but it doesn't work:
1) added anew function to includes/functions/functions_categories.php

function zen_get_main_category_by_product($products_id){
    global $db;
    $cPath = '';

    $category_query = "select p.products_id, p.master_categories_id
                       from " . TABLE_PRODUCTS . " p
                       where p.products_id = '" . (int)$products_id . "' limit 1";


    $category = $db->Execute($category_query);

    if ($category->RecordCount() > 0) {

      $categories = array();
      zen_get_parent_categories($categories, $category->fields['master_categories_id']);
      $categories = array_reverse($categories);
      
      return $categories[0];
}
}

2) next, I added this to functions_tax.php:

function zen_get_sales_tax(){
	 global $db;
	 $products = $_SESSION['cart']->get_products();
	 for ($i=0, $n=sizeof($products); $i<$n; $i++) {
	 $productArray[$i] = array(
                            'id'=>$products[$i]['id']);
	 }
	 $main_category_id = zen_get_main_category_by_product($productArray[0]['id']);
	
	$sales_tax_select = "SELECT sales_tax from " . TABLE_CATEGORIES . " where categories_id = '" . (int)$main_category_id . "'";
}

3) finally, I added this to my new ot_sales_tax.php file:

<?php
/**
 * ot_total order-total module
 *
 * @package orderTotal
 * @copyright Copyright 2003-2007 Zen Cart Development Team
 * @copyright Portions Copyright 2003 osCommerce
 * @license http://www.zen-cart.com/license/2_0.txt GNU Public License V2.0
 * @version $Id: ot_loworderfee.php 6101 2007-04-01 10:30:22Z wilt $
 */

  class ot_sales_tax {
    var $title, $output;

    function ot_sales_tax() {
      $this->code = 'ot_sales_tax';
      $this->title = MODULE_ORDER_TOTAL_SALES_TAX_TITLE;
      $this->description = MODULE_ORDER_TOTAL_SALES_TAX_DESCRIPTION;
      $this->sort_order = MODULE_ORDER_TOTAL_SALES_TAX_SORT_ORDER;

      $this->output = array();
    }

    function process() {
      global $order, $currencies;

      if (MODULE_ORDER_TOTAL_SALES_TAX == 'true') {

// calculate from flat fee or percentage
				$sales_tax_defined = zen_get_sales_tax($sales_tax);
              $sales_tax_value = ($order->info['subtotal'] * ($sales_tax_defined/100));

			$order->info['total'] += $sales_tax_value;

            $this->output[] = array('title' => $this->title . ':',
                                    'text' => $currencies->format($sales_tax_value, true, $order->info['currency'], $order->info['currency_value']),
                                    'value' => $sales_tax_value);
          }
        }

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

        $check_query = $db->Execute($check_query);
        $this->_check = $check_query->RecordCount();
      }

      return $this->_check;
    }

    function keys() {
      return array('MODULE_ORDER_TOTAL_SALES_TAX_STATUS', 'MODULE_ORDER_TOTAL_SALES_TAX_SORT_ORDER', 'MODULE_ORDER_TOTAL_SALES_TAX', 'MODULE_ORDER_TOTAL_SALES_TAX_FEE');
    }

    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_ORDER_TOTAL_SALES_TAX_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_ORDER_TOTAL_SALES_TAX_SORT_ORDER', '400', 'Sort order of display.', '6', '2', now())");
      $db->Execute("insert into " . TABLE_CONFIGURATION . " (configuration_title, configuration_key, configuration_value, configuration_description, configuration_group_id, sort_order, set_function, date_added) values ('Allow Low Order Fee', 'MODULE_ORDER_TOTAL_SALES_TAX', 'false', 'Do you want to allow low order fees?', '6', '3', 'zen_cfg_select_option(array(\'true\', \'false\'), ', now())");
      $db->Execute("insert into " . TABLE_CONFIGURATION . " (configuration_title, configuration_key, configuration_value, configuration_description, configuration_group_id, sort_order, use_function, date_added) values ('Order Fee', 'MODULE_ORDER_TOTAL_SALES_TAX_FEE', '5', 'Enter your percentage', '6', '5', '', now())");
    }

    function remove() {
	  global $db;
      $db->Execute("delete from " . TABLE_CONFIGURATION . " where configuration_key in ('" . implode("', '", $this->keys()) . "')");
    }
  }
?>

Basically, what I'm trying to achieve is to get the ot module to find out the following:
- check cart for current product
- check that product's top level category id
- select a DB entry based on category id
- use that entry as tax percentage

Can anyone help me out where I'm going wrong?

Ajeh, please? Will send another big pack of donuts if we work this out. :)