schwerdtfegers_method

DAYS = ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday', 'Sunday']


def schwerdtfegers_method(year, month, day):
    """
    Implementation of Schwerdtfeger's_method
    of Julian calendar.

    Look here:
    https://en.wikipedia.org/wiki/Determination_of_the_day_of_the_week#Schwerdtfeger's_method
    """
    if year < 0:
        raise ValueError('Year must be a positive integer')
    if not 1 <= month <= 12:
        raise ValueError('Month must between 1 and 12')
    if not 1 <= day <= 31:
        raise ValueError('Day must between 1 and 31')
    m_table = [None, 0, 3, 2, 5, 0, 3, 5, 1, 4, 6, 2, 4]
    if month >= 3:
        c = year // 100
        g = year - 100 * c
    else:
        c = (year - 1) // 100
        g = year - 1 - 100 * c
    f = c % 7
    w = (day + m_table[month] + f + g + ( g // 4)) % 7
    return w