build full url

/**
  * builds a full url given a protocol, hostname, base path and url
  *
  * @param string $protocol
  * @param string $host
  * @param string $base_path
  * @param string $url
  * @return string
  *
  * Initially the trailing slash of $base_path was optional, and conditionally appended.
  * However on dynamically created sites, where the page is given as url parameter,
  * the base path might not end with an url.
  * Therefore do not append a slash, and **require** the $base_url to ending in a slash
  * when needed.
  * Vice versa, on using the local file system path of a file, make sure that the slash
  * is appended (o.k. also for Windows)
  */
function buildFullUrl($protocol, $host, $base_path, $url)
{
  $protocol = mb_strtolower($protocol);
  if (empty($protocol)) {
    $protocol = "file://";
  }
  if ($url === "") {
    return null;
  }

  $url_lc = mb_strtolower($url);

  // Is the url already fully qualified, a Data URI, or a reference to a named anchor?
  // File-protocol URLs may require additional processing (e.g. for URLs with a relative path)
  if (
    (mb_strpos($url_lc, "://") !== false
      && !in_array(substr($url_lc, 0, 7), ["file://", "phar://"], true)
    )
    || mb_substr($url_lc, 0, 1) === "#"
    || mb_strpos($url_lc, "data:") === 0
    || mb_strpos($url_lc, "mailto:") === 0
    || mb_strpos($url_lc, "tel:") === 0
  ) {
    return $url;
  }

  $res = "";
  if (strpos($url_lc, "file://") === 0) {
    $url = substr($url, 7);
    $protocol = "file://";
  } elseif (strpos($url_lc, "phar://") === 0) {
    $res = substr($url, strpos($url_lc, ".phar") + 5);
    $url = substr($url, 7, strpos($url_lc, ".phar") - 2);
    $protocol = "phar://";
  }

  $ret = "";

  $is_local_path = in_array($protocol, ["file://", "phar://"], true);

  if ($is_local_path) {
    //On Windows local file, an abs path can begin also with a '\' or a drive letter and colon
    //drive: followed by a relative path would be a drive specific default folder.
    //not known in php app code, treat as abs path
    //($url[1] !== ':' || ($url[2]!=='\\' && $url[2]!=='/'))
    if ($url[0] !== '/' && (strtoupper(substr(PHP_OS, 0, 3)) !== 'WIN' || (mb_strlen($url) > 1 && $url[0] !== '\\' && $url[1] !== ':'))) {
      // For rel path and local access we ignore the host, and run the path through realpath()
      $ret .= realpath($base_path) . '/';
    }
    $ret .= $url;
    $ret = preg_replace('/\?(.*)$/', "", $ret);

    $filepath = realpath($ret);
    if ($filepath === false) {
      return null;
    }

    $ret = "$protocol$filepath$res";

    return $ret;
  }

  $ret = $protocol;
  // Protocol relative urls (e.g. "//example.org/style.css")
  if (strpos($url, '//') === 0) {
    $ret .= substr($url, 2);
    //remote urls with backslash in html/css are not really correct, but lets be genereous
  } elseif ($url[0] === '/' || $url[0] === '\\') {
    // Absolute path
    $ret .= $host . $url;
  } else {
    // Relative path
    //$base_path = $base_path !== "" ? rtrim($base_path, "/\\") . "/" : "";
    $ret .= $host . $base_path . $url;
  }

  // URL should now be complete, final cleanup
  $parsed_url = parse_url($ret);

  // reproduced from https://www.php.net/manual/en/function.parse-url.php#106731
  $scheme   = isset($parsed_url['scheme']) ? $parsed_url['scheme'] . '://' : '';
  $host     = isset($parsed_url['host']) ? $parsed_url['host'] : '';
  $port     = isset($parsed_url['port']) ? ':' . $parsed_url['port'] : '';
  $user     = isset($parsed_url['user']) ? $parsed_url['user'] : '';
  $pass     = isset($parsed_url['pass']) ? ':' . $parsed_url['pass']  : '';
  $pass     = ($user || $pass) ? "$pass@" : '';
  $path     = isset($parsed_url['path']) ? $parsed_url['path'] : '';
  $query    = isset($parsed_url['query']) ? '?' . $parsed_url['query'] : '';
  $fragment = isset($parsed_url['fragment']) ? '#' . $parsed_url['fragment'] : '';

  // partially reproduced from https://stackoverflow.com/a/1243431/264628
  /* replace '//' or '/./' or '/foo/../' with '/' */
  $re = array('#(/\.?/)#', '#/(?!\.\.)[^/]+/\.\./#');
  for ($n = 1; $n > 0; $path = preg_replace($re, '/', $path, -1, $n)) {
  }

  $ret = "$scheme$user$pass$host$port$path$query$fragment";

  return $ret;
}