from datetime import datetime, timezone

DEFAULT_TIME_ZONE = timezone.utc


def utcnow():
    return datetime.now(timezone.utc)


def as_utc(value):
    if value.tzinfo is None:
        value = value.replace(tzinfo=DEFAULT_TIME_ZONE)
    return value.astimezone(timezone.utc)


def as_local(value):
    return value.astimezone(DEFAULT_TIME_ZONE)


def start_of_local_day():
    return utcnow().astimezone(DEFAULT_TIME_ZONE).replace(hour=0, minute=0, second=0, microsecond=0)