WordPress : Always force original domain when previewing posts and pages when using domain mapping

gistfile1.php

<?php 

/**
 * Forces original site for previewing posts and pages when using domain mapping
 *
 * @return URL of preview link using original site 
 **/
 
function original_site_preview_link($url, $post) {
  $parts = parse_url($url);
  $host = $parts['host'];
  $path = $parts['path'];
  $path_segments = explode('/', $path);
  $query = ('' != $parts['query']) ? "?{$parts['query']}" : '';

  $mapped = !strpos(network_site_url(), $host);
  
  if ( $mapped ) {
    // Remove leading slash only
    $path_segments = array_slice($path_segments, 1);
  
  } else {
    // Remove array elements for leading slash and blogname
    // If the domain isn't mapped, strip out the blog name from path, we'll add it later
    $path_segments = array_slice($path_segments, 2);
  }

  // Put the path back together
  $path = implode($path_segments, '/');

  // Blog site URL on original network domain
  $site = trailingslashit(site_url());

  // Return new link
  return $site . $path . $query;
}
add_filter( 'preview_post_link', 'original_site_preview_link');