def safe_unlink(path):
    try:
        unlink(path)
    except OSError, e:
        if e.errno != ENOENT:
            raise

def safe_float(s):
    try:
        return float(s)
    except ValueError:
        return 0.0

def _basearchive_name(config_name):
    return path(_basedir) / config_name + '.tgz'

def _timestamp_name(config_name):
    return _basearchive_name + '.timestamp'

def _basearchive_needs_updating(config_name):
    timestamp_file = _timestamp_name(config_name)
    if timestamp_file.access(R_OK):
        timestamp = safe_float(timestamp_file.bytes())
        cur_time = time()
        return timestamp + _update_timeout < cur_time
    return True

def _gen_basearchive(pb_options):
    if _run(pb_options):
        timestamp.write_text(str(time()))
        return True
    else:
        safe_unlink(basearchive)

def _prepare_basearchive(config_name):
    basearchive = _basearchive_name(config_name)
    timestamp = _timestamp_name(config_name)
    if basearchive.exists():
        if _basearchive_needs_updating(config_name):
            pb = _get_args(config_name, '--update')
            return _gen_basearchive(pb)
        else:
            return True
    else:
        pb = _get_args(config_name, '--create')
        return _gen_basearchive(pb)