import calendar
from datetime import date

from layercake.dateutils import now


def get_billing_period(
    billing_day: int,
    year: int | None = None,
    month: int | None = None,
) -> tuple[date, date]:
    today = now()
    year_ = year or today.year
    month_ = month or today.month

    _, last_day = calendar.monthrange(year_, month_)
    start_day = min(billing_day, last_day)
    start_date = date(year_, month_, start_day)

    if month_ == 12:
        next_month = 1
        next_year = year_ + 1
    else:
        next_month = month_ + 1
        next_year = year_

    _, last_day_next_month = calendar.monthrange(next_year, next_month)
    end_day = min(billing_day, last_day_next_month) - 1

    if end_day == 0:
        end_date = date(year_, month_, last_day)
    else:
        end_date = date(next_year, next_month, end_day)

    return start_date, end_date