from datetime import datetime
from zoneinfo import ZoneInfo, available_timezones

ALLOWED_TIMEZONES = available_timezones()
DATETIME_FORMAT = '%Y-%m-%d %H:%M:%S'


def tz_aware_now(zone: str) -> datetime:
    """
    :param str zone: Zone name in DB
    :return: A timezone aware datetime object
    :raises: ValueError When zone name is not supported
    """
    # ZoneInfo uses a weak cache, no need to implement a local cache
    if zone not in ALLOWED_TIMEZONES:
        raise ValueError(f'Unsupported timezone "{zone}"')
    return datetime.now(tz=ZoneInfo(zone))


def real_utc_now() -> datetime:
    return tz_aware_now('UTC')