docs: def remote_path(self):
          """ turns an ebook_id into a path on PG's server(s)
              4443  -> 4/4/4/4443/ """
          # TODO: move this property into independent object for PG
          if len(self.book_id) > 1:
              path_parts = list(self.book_id[:-1])
          else:
              path_parts = ['0']
          path_parts.append(self.book_id)
          return os.path.join(*path_parts) + '/'