from .dates_add_days import epoch_day_from_iso


def days_between(start_iso: str, end_iso: str) -> int:
    """Calendar days from one date to another: end minus start, negative when
    the end is earlier. Both dates are parsed strictly, so an impossible date
    fails rather than being rolled into the next month.
    """
    return epoch_day_from_iso(end_iso) - epoch_day_from_iso(start_iso)