docs: def reverse_media_url(target_type, url_string, *args, **kwargs):
      '''
      Given a target type and an resource URL, generates a valid URL to this via
      '''
      args_str = '<%s>' % '><'.join(args)
      kwargs_str = '<%s>' % '><'.join('%s:%s' % pair for pair in kwargs.items())
      url_str = ''.join([url_string, args_str, kwargs_str])
      normalized_url = str(ResourceURL(url_str))
  
      query_tuples = []
  
      if singletons.settings.SECURITY and 'Sha1' in singletons.settings.SECURITY:
          secret = singletons.settings.HMAC_SECRET
          digest = get_hmac_sha1_digest(secret, normalized_url, target_type)
          query_tuples.append(('digest', digest))
  
      # Add in URL as last querystring argument
      query_tuples.append(('url', normalized_url))
  
      querystring = urlencode(query_tuples)
      scheme = singletons.settings.EXTERNAL_SCHEME
      host = singletons.settings.EXTERNAL_HOST
      port = singletons.settings.EXTERNAL_PORT
      if not host:
          host = singletons.settings.HOST
      if not port:
          port = singletons.settings.PORT
  
      port_suffix = ':%s' % port if port != 80 else ''
  
      typestring_normalized = str(TypeString(target_type))
      return '%s://%s%s/media/%s/?%s' % (
          scheme,
          host,
          port_suffix,
          typestring_normalized,
          querystring,
      )