from datetime import datetime, timezone


def utc_now() -> datetime:
    """Naive UTC datetime for existing SQLAlchemy DateTime columns."""
    return datetime.now(timezone.utc).replace(tzinfo=None)


def to_utc_naive(value: datetime | None) -> datetime | None:
    if value is None:
        return None
    if value.tzinfo is None:
        return value
    return value.astimezone(timezone.utc).replace(tzinfo=None)


def to_utc_aware(value: datetime | None) -> datetime | None:
    if value is None:
        return None
    if value.tzinfo is None:
        return value.replace(tzinfo=timezone.utc)
    return value.astimezone(timezone.utc)


def to_zulu_iso(value: datetime) -> str:
    return to_utc_aware(value).isoformat().replace("+00:00", "Z")


def unix_ms_utc(value: datetime) -> int:
    return int(to_utc_aware(value).timestamp() * 1000)