def archive(base_dir: str) -> int:
        """
        Archive schema, cred def, revocation caches to disk as json.

        :param base_dir: archive base directory
        :return: timestamp (epoch seconds) used as subdirectory
        """

        LOGGER.debug('archive >>> base_dir: %s', base_dir)

        rv = int(time())
        timestamp_dir = join(base_dir, str(rv))
        makedirs(timestamp_dir, exist_ok=True)

        with SCHEMA_CACHE.lock:
            with open(join(timestamp_dir, 'schema'), 'w') as archive:
                print(json.dumps(SCHEMA_CACHE.schemata()), file=archive)

        with CRED_DEF_CACHE.lock:
            with open(join(timestamp_dir, 'cred_def'), 'w') as archive:
                print(json.dumps(CRED_DEF_CACHE), file=archive)

        with REVO_CACHE.lock:
            with open(join(timestamp_dir, 'revocation'), 'w') as archive:
                revo_cache_dict = {}
                for rr_id in REVO_CACHE:
                    revo_cache_dict[rr_id] = {
                        'rev_reg_def': REVO_CACHE[rr_id].rev_reg_def,
                        'rr_delta_frames': [vars(f) for f in REVO_CACHE[rr_id].rr_delta_frames],
                        'rr_state_frames': [vars(f) for f in REVO_CACHE[rr_id].rr_state_frames]
                    }
                print(json.dumps(revo_cache_dict), file=archive)

        LOGGER.debug('archive <<< %s', rv)
        return rv
Archive schema, cred def, revocation caches to disk as json.

        :param base_dir: archive base directory
        :return: timestamp (epoch seconds) used as subdirectory