from __future__ import annotations

from datetime import UTC, datetime, timedelta


def utc_now() -> datetime:
    return datetime.now(UTC)


def to_iso(value: datetime | None = None) -> str:
    current = value or utc_now()
    return current.astimezone(UTC).isoformat(timespec="milliseconds").replace("+00:00", "Z")


def from_iso(value: str) -> datetime:
    return datetime.fromisoformat(value.replace("Z", "+00:00"))


def expires_in(days: int) -> str:
    return to_iso(utc_now() + timedelta(days=days))