def VShadowPathSpecGetStoreIndex(path_spec):
    """Retrieves the store index from the path specification.

  Args:
    path_spec (PathSpec): path specification.

  Returns:
    int: store index or None if not available.
  """
    store_index = getattr(path_spec, 'store_index', None)
    if store_index is None:
        location = getattr(path_spec, 'location', None)
        if location is None or not location.startswith('/vss'):
            return None
        store_index = None
        try:
            store_index = int(location[4:], 10) - 1
        except (TypeError, ValueError):
            pass
        if store_index is None or store_index < 0:
            return None
    return store_index
