Web Stories link utm_source sanitizer example

web-stories-link-sanitizer-utm-source.php

<?php
/**
 * Plugin Name: Web Stories Link sanitizer example
 * Description: Example sanitizer to add add "?utm_source=page_xx" to all links in a story.
 * Author: Pascal Birchler
 * Author URI: https://pascalbirchler.com/
 * Version: 0.0.1
 * Requires at least: 6.4
 * Requires PHP: 7.4
 * License: Apache License 2.0
 * License URI: https://www.apache.org/licenses/LICENSE-2.0
 *
 * @copyright 2023 Google LLC
 * @license   https://www.apache.org/licenses/LICENSE-2.0 Apache License 2.0
 */

if ( ! defined( 'ABSPATH' ) ) {
	exit;
}

add_action(
	'init',
	static function() {
		if ( ! class_exists( '\Google\Web_Stories_Dependencies\AMP_Base_Sanitizer' ) ) {
			return;
		}

		add_filter(
			'web_stories_amp_sanitizers',
			static function( $sanitizers ) {
				$sanitizers[ Your_Website_Example_AMP_Sanitizer::class ] = [];

				return $sanitizers;
			}
		);

		class Your_Website_Example_AMP_Sanitizer extends \Google\Web_Stories_Dependencies\AMP_Base_Sanitizer {
			/**
			 * Sanitize the HTML contained in the DOMDocument received by the constructor.
			 */
			public function sanitize(): void {
				$page_nubmer = 0;

				$pages = $this->dom->body->getElementsByTagName( 'amp-story-page' );

				/**
				 * The <amp-story-page> element
				 *
				 * @var DOMElement $page The <a> element
				 */
				foreach ( $pages as $page ) {
					$page_nubmer++;

					$links = $page->getElementsByTagName( 'a' );

					/**
					 * The <a> element
					 *
					 * @var DOMElement $link The <a> element
					 */
					foreach ( $links as $link ) {
						$url = $link->getAttribute( 'href' );

						$url = add_query_arg(
							[
								'utm_source' =>
									"page_$page_nubmer"
							],
							$url
						);

						$link->setAttribute( 'href', $url );
					}
				}
			}
		}
	}
);