from __future__ import annotations

from datetime import datetime, timezone


def to_naive_utc(dt: datetime | None) -> datetime | None:
    """
    Convert a timezone-aware datetime to naive UTC (tzinfo removed).

    Our DB columns are DateTime without timezone. Persisting timezone-aware
    datetimes can cause runtime errors (especially on Postgres).
    """
    if dt is None:
        return None
    if dt.tzinfo is None:
        return dt
    return dt.astimezone(timezone.utc).replace(tzinfo=None)


def to_iso_utc(dt: datetime | None) -> str | None:
    """
    Serialize a datetime as an ISO-8601 UTC string.

    - If dt is timezone-aware: convert to UTC and use "Z".
    - If dt is naive: treat it as UTC and use "Z".
    """
    if dt is None:
        return None
    if dt.tzinfo is None:
        dt = dt.replace(tzinfo=timezone.utc)
    else:
        dt = dt.astimezone(timezone.utc)
    return dt.isoformat().replace("+00:00", "Z")