public function calculate_shipping( $package = array() ) {
		$shipping_total = 0;

		switch ( $this->type ) {
			case 'fixed':
				$shipping_total = $this->fee;
				break;
			case 'percent':
				$shipping_total = $package['contents_cost'] * ( $this->fee / 100 );
				break;
			case 'product':
				foreach ( $package['contents'] as $item_id => $values ) {
					if ( $values['quantity'] > 0 && $values['data']->needs_shipping() ) {
						$shipping_total += $this->fee * $values['quantity'];
					}
				}
				break;
		}

		$rate = array(
			'id'      => $this->id,
			'label'   => $this->title,
			'cost'    => $shipping_total,
			'package' => $package,
		);

		$this->add_rate( $rate );
	}