kyunomi on "Custom function in child theme"

Hi,

I was trying to create a custom function in a child theme that i created.

<?php

add_action('woocommerce_order_details_after_order_table', 'My_additional_shipping_info');

function My_additional_shipping_info() {
	if ( $totals = $order->get_order_item_totals() ) {
		if ($totals['shipping']['value']=="Self-Pickup @ Raffles Place MRT") {
			echo 'Self-Pickup: ';
		} else {
			echo 'Delivery: ';
		}
	}
	if ( $delivery_time = get_post_meta( $order->id, '_delivery_time', true ) ) {
		echo "{$delivery_time}"; }
}
?>

However, after i wrote it, the following error will occur
Fatal error: Call to a member function get_order_item_totals() on a non-object in /home/.../wp-content/themes/theme-child/functions.php

I guess it has something to do with me trying to call upon a function from wordpress without linking to it. but i dont know how to do it as i am still learning. would anyone kindly assists me? Thanks!