<?php
/*
 * URL auf 2nd.TLD kürzen www.meineurl.de -> meineurl.de
*/
function get_2nd_level_name($url) {
  // a list of decimal-separated TLDs
  static $doubleTlds = array(
      'co.uk', 'me.uk', 'net.uk', 'org.uk', 'sch.uk',
      'ac.uk', 'gov.uk', 'nhs.uk', 'police.uk', 'mod.uk',
      'asn.au', 'com.au', 'net.au', 'id.au', 'org.au',
      'edu.au', 'gov.au', 'csiro.au', 'br.com', 'com.cn',
      'com.tw', 'cn.com', 'de.com', 'eu.com', 'hu.com',
      'idv.tw', 'net.cn', 'no.com', 'org.cn', 'org.tw',
      'qc.com', 'ru.com', 'sa.com', 'se.com', 'se.net',
      'uk.com', 'uk.net', 'us.com', 'uy.com', 'za.com'
    );
  // sanitize the URL
  $url = trim( $url );
  // if no hostname, use the current by default
  if (empty($url) || '/' == $url[0]) $url = $_SERVER['HTTP_HOST'] . $url;  
  // if no scheme, use `http://` by default
  if (FALSE === strpos($url, '://')) $url = 'http://' . $url;
  // can we successfully parse the URL?
  if ($host = parse_url( $url, PHP_URL_HOST)) {
    // is this an IP?
    if (preg_match( '/^\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}$/', $host)) {
      return $host;
    }
    // sanitize the hostname
    $host = strtolower($host);
    // explode on the decimals
    $parts = explode('.', $host);
    // is there just one part? (`localhost`, etc)
    if (! isset( $parts[1])) return $parts[0];    
    // grab the TLD
    $tld = array_pop($parts);
    // grab the hostname
    $host = array_pop( $parts ) . '.' . $tld;
    // have we collected a double TLD?
    if (!empty( $parts) && in_array($host, $doubleTlds)) {
      $host = array_pop($parts) . '.' . $host;
    }
    // send it on it's way
    return $host;
  }
  // at this point, nah
  return FALSE;
}
?>