How to add a new custom Webhook topic in WooCommerce, with example of order filtering.

adding_new_webhook_topics.php

<?php // do not copy this line


/**
 * add_new_topic_hooks will add a new webhook topic hook. 
 * @param array $topic_hooks Esxisting topic hooks.
 */
function add_new_topic_hooks( $topic_hooks ) {

	// Array that has the topic as resource.event with arrays of actions that call that topic.
	$new_hooks = array(
		'order.custom_filter' => array(
			'custom_order_filter',
			),
		);

	return array_merge( $topic_hooks, $new_hooks );
}
add_filter( 'woocommerce_webhook_topic_hooks', 'add_new_topic_hooks' );

/**
 * add_new_topic_events will add new events for topic resources.
 * @param array $topic_events Existing valid events for resources.
 */
function add_new_topic_events( $topic_events ) {

	// New events to be used for resources.
	$new_events = array(
		'custom_filter',
		);

	return array_merge( $topic_events, $new_events );
}
add_filter( 'woocommerce_valid_webhook_events', 'add_new_topic_events' );

/**
 * add_new_webhook_topics adds the new webhook to the dropdown list on the Webhook page.
 * @param array $topics Array of topics with the i18n proper name.
 */
function add_new_webhook_topics( $topics ) {

	// New topic array to add to the list, must match hooks being created.
	$new_topics = array( 
		'order.custom_filter' => __( 'Order Custom Filter', 'woocommerce' ),
		);

	return array_merge( $topics, $new_topics );
}
add_filter( 'woocommerce_webhook_topics', 'add_new_webhook_topics' );

/**
 * my_order_item_check will check an order when it is created through the checkout form,
 * if it has product ID 10603 as one of the items, it will fire off the action `custom_order_filter`
 * 
 * @param  int    $order_id    The ID of the order that was just created.
 * @param  array  $posted_data Array of all of the data that was posted through checkout form.
 * @param  object $order       The order object.
 * @return null
 */
function my_order_item_check( $order_id, $posted_data, $order ) {
	
	$order = wc_get_order( $order_id );
	$items = $order->get_items();

	foreach ( $items as $item ) {
		
		if ( is_a( $item, 'WC_Order_Item_Product' ) ) {
			
			if ( 10603 === $item->get_product_id() ) {
				
				do_action( 'custom_order_filter', $order_id, $posted_data, $order );
				return;
			}
		}
	}
}
add_action( 'woocommerce_checkout_order_processed', 'my_order_item_check', 10, 3 );

/**
 *  The two below actions are what the order.created webhook is tied into, it is up to you to use these if you wish. 
 */
// add_action( 'woocommerce_process_shop_order_meta', 'my_order_item_check' );
// add_action( 'woocommerce_api_create_order', 'my_order_item_check' );