gistfile1.php

<?php

  define("ALTERNATE_LANGUAGE_DIRECTORY", "sp");
  
  $referer = $_SERVER['HTTP_REFERER'];

  $redirect = create_redirect($referer);
  header("Location: $redirect");

  function create_redirect($referer) {
    $domain = clean_domain($referer);
    
    $domain_array = domain_to_array($domain);

    $language = get_language($domain_array);

    if($language == "english") {
      $redirect = build_spanish_link($domain_array);
    } else if ($language == "spanish") {
      $redirect = build_english_link($domain_array);
    } else {
      $redirect = build_spanish_link($domain_array);
    }

    return $redirect;  
  }

  function clean_domain($domain) {
    return str_replace("http://", "", $domain);
  }

  function domain_to_array($domain){
    return explode('/', $domain);
  }

  function get_language($domain_array) {    
    if(array_search(ALTERNATE_LANGUAGE_DIRECTORY, $domain_array)) {
      return "spanish";
    } else {
      return "english";
    }
  }
  
  function build_english_link($domain_array) {    
    $cleaned_domain_array = array_remove_needle(ALTERNATE_LANGUAGE_DIRECTORY, $domain_array);

    $redirect = "http://" . implode("/", $cleaned_domain_array);

    return $redirect;
  }

  function build_spanish_link($domain_array) {
    $spanish_domain_array = add_spanish($domain_array);
    
    $redirect = "http://" . implode("/", $spanish_domain_array);

    return $redirect;
  }

  function array_remove_needle($needle, $haystack) {
    $cleaned_array = array();
    foreach($haystack as $item) {
      if($item != $needle) {
        $cleaned_array[] = $item;
      }
    }
    return $cleaned_array;
  }

  function add_spanish($domain_array) {    
    $last = array_pop($domain_array);
    $domain_array[] = ALTERNATE_LANGUAGE_DIRECTORY;
    $domain_array[] = $last;
    return $domain_array;
  }

?>