def _iso_8601(dt: datetime.datetime) -> str:
    return dt.isoformat() + 'Z'


def _parse_dt(s: str) -> datetime.datetime:
    return datetime.datetime.strptime(s, '%Y-%m-%dT%H:%M:%S.%fZ')


def _get_sync_dt() -> datetime.datetime:
    s3 = boto3.client('s3')
    try:
        resp = s3.get_object(Bucket=SYNC_KEY.bucket, Key=SYNC_KEY.prefix)
    except ClientError:
        return datetime.datetime.min
    else:
        return _parse_dt(resp['Body'].read().decode().strip())


def _set_sync_dt(dt: datetime.datetime) -> None:
    now = _iso_8601(dt).encode()
    s3 = boto3.client('s3')
    s3.put_object(
        Body=now, Bucket=SYNC_KEY.bucket, Key=SYNC_KEY.prefix,
        ServerSideEncryption='AES256',
    )


def main(event: Dict[str, Any], context: Any) -> int:
    event_dt = _parse_dt(event['Records'][0]['eventTime'])
    sync_dt = _get_sync_dt()
    now_dt = datetime.datetime.utcnow()
    if sync_dt > event_dt:
        print(f'skipping (synced at {sync_dt}, event at {event_dt})')
        return 0

    # (snip...) creation and sync here

    _set_sync_dt(now_dt)
    return 0


# Strictly for testing
if __name__ == '__main__':
    now = _iso_8601(datetime.datetime.utcnow())
    exit(main({'Records': [{'eventTime': now}]}, None))