Set correct preview link when using WordPress MU Domain Mapping Plugin

fix-domain-mapping-preview.php

<?php
add_filter('get_sample_permalink_html', function($return, $id, $new_title, $new_slug) {

  $post_type_object = get_post_type_object(get_post_type($id));
  
  //Append rewrite slug if it exists
  if(isset($post_type_object->rewrite['slug'])) {
    $url_append = '/' . $post_type_object->rewrite['slug'];
  }
  else {
    $url_append = '';
  }
  
  //Bail if domain URL doesn't exist
  if(!function_exists('domain_mapping_siteurl')) {
    return $return;
  }
  
  //Try to find mapped domain
  global $wpdb;
  $domain = $wpdb->get_var( "SELECT domain FROM {$wpdb->dmtable} WHERE blog_id = '{$wpdb->blogid}' AND active='1' LIMIT 1" );
  
  //Mapped domain found
  if($domain) {
    //Replace the preview link
    $return = preg_replace('/(<span id=\"sample-permalink\"[^>]*>)(.*)(<span.*)/', "$1http://{$domain}{$url_append}/$3", $return);
  }
  
  return $return;
}, 10, 4);