amp-anim-to-amp-img.php

<?php
/**
 * Convert amp-anim to amp-img
 *
 * @package   AMP_Anim_To_AMP_Img
 * @author    Weston Ruter, Google
 * @license   GPL-2.0-or-later
 * @copyright 2019 Google Inc.
 *
 * @wordpress-plugin
 * Plugin Name: Convert amp-anim to amp-img
 * Description: Force animated GIFs to be rendered in <code>amp-img</code> instead of <code>amp-anim</code> after the image sanitizer has processed the underlying <code>img</code> tags. See <a href="https://github.com/ampproject/amphtml/issues/24306#issuecomment-527688934">amphtml#24306</a>.
 * Plugin URI: https://gist.github.com/westonruter/1eeb2224004c0e904fa2a35fc92899c0
 * Version: 0.1.0
 * Author: Weston Ruter, Google
 * Author URI: https://weston.ruter.net/
 * License: GNU General Public License v2 (or later)
 * License URI: http://www.gnu.org/licenses/gpl-2.0.html
 * Gist Plugin URI: https://gist.github.com/westonruter/1eeb2224004c0e904fa2a35fc92899c0
 */

namespace AMP_Anim_To_AMP_Img;

/**
 * Define sanitizer and register it.
 */
function init() {

	/**
	 * Class Sanitizer
	 */
	class Sanitizer extends \AMP_Base_Sanitizer {

		/**
		 * Convert.
		 */
		public function sanitize() {

			/**
			 * Elements.
			 *
			 * @var \DOMElement[] $amp_anims
			 */

			// Convert live node list to array.
			$amp_anims = [];
			foreach ( $this->dom->getElementsByTagName( 'amp-anim' ) as $amp_anim ) {
				$amp_anims[] = $amp_anim;
			}

			// Now replace them.
			foreach ( $amp_anims as $amp_anim ) {
				$amp_img = $this->dom->createElement( 'amp-img' );
				foreach ( $amp_anim->attributes as $attribute ) {
					$amp_img->setAttribute( $attribute->nodeName, $attribute->nodeValue );
					while ( $amp_anim->firstChild ) {
						$amp_img->appendChild( $amp_anim->firstChild );
					}
				}
				$amp_anim->parentNode->replaceChild( $amp_img, $amp_anim );
			}
		}
	} // End class Sanitizer.

	// Inject the new sanitizer right after the image sanitizer.
	add_filter(
		'amp_content_sanitizers',
		function( $old_sanitizers ) {
			$new_sanitizers = [];
			foreach ( $old_sanitizers as $sanitizer_class => $sanitizer_args ) {
				$new_sanitizers[ $sanitizer_class ] = $sanitizer_args;
				if ( 'AMP_Img_Sanitizer' === $sanitizer_class ) {
					$new_sanitizers[ __NAMESPACE__ . '\Sanitizer' ] = $sanitizer_args;
				}
			}
			return $new_sanitizers;
		}
	);
}

add_action( 'amp_init', __NAMESPACE__ . '\init' );

Installation instructions: https://gist.github.com/westonruter/6110fbc4bef0c4b8c021a112012f7e9c