code: def map_url_to_cache_id(self, url):
          
          base, _ = self.get_domain_home_from_url(url)
  
          if base == '':
              # invalid url
              _sub_page = ''
          elif base == url or base + '/' == url:
              # homepage
              _sub_page = 'homepage'
          else:
              # sub page
              _sub_page = url.replace(base, '').split('/')
              _sub_page = '/'.join([x for x in _sub_page if x])
  
          if _sub_page:
              full_name = os.path.join(self.cache['site_raw'], _sub_page)
              return full_name
          else:
              return _sub_page
docs: use of the url resource location as cached id
  
          e.g.: ``<domain>/foo/bar/a.html => <base>/domain/foo/bar/a.html``
  
          - map the url to local file
  
          :param url:
          :type url:
          :return:
          :rtype: