from app.services.oa_confirmation_date import add_months_ymd


def test_simple_month_add():
    assert add_months_ymd("2026-01-15", 3) == "2026-04-15"


def test_clamp_end_of_month():
    assert add_months_ymd("2026-01-31", 1) == "2026-02-28"


def test_zero_months_returns_same_day():
    assert add_months_ymd("2026-07-30", 0) == "2026-07-30"


def test_invalid_returns_none():
    assert add_months_ymd("", 3) is None
    assert add_months_ymd("2026-01-15", -1) is None
    assert add_months_ymd("2026-01-15", True) is None  # type: ignore[arg-type]
    assert add_months_ymd("2026-02-30", 1) is None