from datetime import datetime


def get_daily_filename(date: datetime = datetime.today()) -> str:
    """Returns the filename for the given date in the format:
    'yyyy-mm-dd-nnn-day.md'

    :param date [datetime.datetime] : Date for filename, defaults to datetime.today().
    :return (str) : Filename
    """
    iso_date = date.strftime("%Y-%m-%d")  # ISO date
    doy = date.strftime("%j")  # Day of year
    dow = date.strftime("%a").lower()  # Day of week
    return f"{iso_date}-{doy}-{dow}.md"