def METHOD_NAME(date_string):
    """Validate that a provided string matches the right format and is a report date."""
    try:
        date = datetime.datetime.strptime(date_string, "%Y-%m-%d")
    except ValueError:
        return False
    # If the day after a date is the first day of a month, then
    # that date is the last day of a month
    if date.day == 15 or (date + datetime.timedelta(days=1)).day == 1:
        return True
    else:
        return False