"""iso(): the single datetime→JSON serializer the routes share (R6 S1a)."""
from datetime import datetime, timezone

from app.utils import iso


def test_none_maps_to_none():
    assert iso(None) is None


def test_aware_datetime_keeps_offset():
    dt = datetime(2026, 7, 26, 12, 30, 0, tzinfo=timezone.utc)
    assert iso(dt) == "2026-07-26T12:30:00+00:00"


def test_naive_datetime_serializes_without_offset():
    dt = datetime(2026, 7, 26, 12, 30, 0)
    assert iso(dt) == "2026-07-26T12:30:00"


def test_matches_datetime_isoformat_contract():
    # iso is exactly `dt.isoformat()` for a present value — guards the routes that used to
    # hand-roll `x.isoformat() if x else None`.
    dt = datetime(2020, 1, 2, 3, 4, 5, 678901, tzinfo=timezone.utc)
    assert iso(dt) == dt.isoformat()