import calendar

from dateutil.relativedelta import relativedelta


def nth_date(month, nth):
    try:
        month = month.replace(month.year, month.month, nth)
    except ValueError:
        month = month.replace(month.year, month.month, calendar.monthrange(month.year, month.month)[1])
    return month


def dates(start, end, nth):
    """
    Given a start and end date, return a list of dates at nth date each month

    If nth is greater than last day of month, set to last day of month instead.
    """
    start = nth_date(start, nth)
    months = [start]
    rd = relativedelta(end, start)
    total_months = (12 * rd.years) + rd.months
    for _ in range(total_months):
        start += relativedelta(months=1)
        start = nth_date(start, nth)
        months.append(start)
    return months