Adds products found by sku and gtin to wp search query (WooCommerce)

woo_inject_sku_into_search_query.php

<?php
 /**
 * Returns an array of product ids similar to the given sku / gtin
 * @param $sku - the search key
 * @param int $limit - maximum number of returned items
 *
 * @return array|bool
 */
function prefix_get_product_arr_by_sku( $sku, $limit = 10 ) {
  global $wpdb;
  $products_id = $wpdb->get_results( $wpdb->prepare( "SELECT post_id FROM {$wpdb->postmeta} WHERE ( meta_key = '_sku' OR meta_key = '_gtin') AND meta_value LIKE '%s' LIMIT {$limit}", '%'.$sku.'%' ) );
  if ( $products_id ) {
    foreach ($products_id as $product_id) $products[$product_id->post_id] = $product_id->post_id;
  }
  return !empty($products) ? array_unique($products) : false;
}

function prefix_search_inject_sku_gtin( $search, $query ) {
  global $wpdb;

  if(isset($query->query['s']) && !empty($query->query['s'])){
    $products = prefix_get_product_arr_by_sku($query->query['s']);

    if( !empty( $products ) ) {
      $search =  str_replace( 'AND (((', " AND ((({$wpdb->posts}.ID IN (" . implode( ',', $products ) . ")) OR (", $search);
    }
  }

  return $search;

}
add_filter( 'posts_search', 'prefix_search_inject_sku_gtin', 999, 2 );