def get_action(self, key):
        """
        returns the action to perform on this key based on its
        state before the last sync.
        """
        index_local_timestamp = self.get_index_local_timestamp(key)
        real_local_timestamp = self.get_real_local_timestamp(key)
        remote_timestamp = self.get_remote_timestamp(key)
        return get_sync_state(
            index_local_timestamp, real_local_timestamp, remote_timestamp
        )
returns the action to perform on this key based on its
        state before the last sync.