Shopp Shipping Order Rates based on sub total after discounts

OrderAfterDiscountsRates.php

<?php
/**
 * Order Amount After Discounts Tiers
 *
 * Provides shipping calculations based on order amount ranges
 *
 * @author Jonathan Davis, Matthew Sigley, Ben Hutchings
 * @version 1.3
 * @copyright Ingenesis Limited, 27 April, 2008
 * @package shopp
 * @since 1.3
 * @subpackage OrderAmountAfterDiscounts
 *
 **/

defined( 'WPINC' ) || header( 'HTTP/1.1 403' ) & exit; // Prevent direct access

class OrderAmountAfterDiscounts extends ShippingFramework implements ShippingModule {

	public function init () {
		/* Not implemented */
	}

	public function calcitem ($id,$Item) {
		/* Not implemented */
	}

	public function methods () {
		return Shopp::__('Order Amount After Discounts Tiers');
	}

	public function calculate ( &$options, $Order ) {

		foreach ( $this->methods as $slug => $method ) {
			$tiers = isset($method['table']) ? $this->tablerate($method['table']) : false;
			if ( $tiers === false ) continue; // Skip methods that don't match at all

			$amount = 0;
			$matched = false;
			$tiers = array_reverse($tiers);

			$sub_total_after_discounts = $Order->Cart->total('order') + $Order->Cart->total('discount');
			if( $sub_total_after_discounts < 0 ) {
					$sub_total_after_discounts = 0;
			}

			foreach ( $tiers as $tier ) {
				extract($tier);
				$amount = Shopp::floatval($rate);			// Capture the rate amount
				if ( Shopp::floatval($sub_total_after_discounts) >= Shopp::floatval($threshold) ) {
					$matched = true;
					break;
				}
			}

			if ( ! $matched ) return $options;

			$rate = array(
				'slug' => $slug,
				'name' => $method['label'],
				'amount' => $amount,
				'delivery' => $this->delivery($method),
				'items' => false
			);

			$options[$slug] = new ShippingOption($rate);

		}

		return $options;
	}

	public function settings () {

		$this->setup('table');

		$this->ui->tablerates(0,array(
			'unit' => array( Shopp::__('Order Amount') ),
			'table' => $this->settings['table'],
			'threshold_class' => 'money',
			'rate_class' => 'money'
		));

	}

}