Generate the image HTML with a limited srcset range of sizes

wp-limit-srcset.php

<?php
namespace RMG\PageSpeed;
/**
 * Get the HTML for an image with limited srcset sizes
 *
 * @param string|int $image_id
 * @param string $size The image size name ex. `medium`, `thumb`
 * @param boolean $icon
 * @param null|array $attrs
 *
 * @return false|string
 */
function get_image_maxsize( $image_id, $size, $icon = false, $attrs = [] ) {
	if ( ! $image_src = wp_get_attachment_image( $image_id, $size, $icon, $attrs ) ) {
		return false;
	}

	$link_dom = new \DOMDocument();
	$link_dom->loadHTML( $image_src );
	foreach ($link_dom->getElementsByTagName('img') as $item) {

		$srcset = $item->getAttribute( 'srcset' );
		$updated_srcset = \RMG\PageSpeed\limit_srcset_values( $srcset, $size );

		$item->setAttribute('srcset', $updated_srcset);
		$image_src = $link_dom->saveHTML();
	}

	return $image_src;
}

function limit_srcset_values( $srcset, $size ) {
	$sizes = wp_get_registered_image_subsizes();

	if ( ! array_key_exists( $size, $sizes ) ) {
		return false;
	}

	$max_width = intval( $sizes[$size]['width'] );

	$sizes = [];

	$src_items = explode( ', ', $srcset );

	foreach( $src_items as $item ) {
		$item_props = explode( ' ', $item );
		$item_width = intval( str_replace( 'w', '', $item_props[1] ) );

		if ( $item_width <= $max_width ) {
			$sizes[] = $item;
		}
	}

	return implode( ', ', $sizes );
}