#!/usr/bin/env python3
# ---------------------------------------------------------------------
#
#   Module:      cal.py
#
#   Description: Calendar formulas
#
#        Input:  year-mm-dd [offset]
#
#        Output: day of the week, date, Julian day number,
#                day of the year, week of the year
#
#   Example: cal 1777-04-30 +84005
#            Mon 2007-04-30 J# 2454221 D# 120 W# 18
#
#   Documentation: 
#       http://berndt-schwerdtfeger.de/wp-content/uploads/pdf/calj.pdf
#
# ---------------------------------------------------------------------
#   Copyright (C) 2023 Berndt E. Schwerdtfeger
#
#   Licensed under the Apache License, Version 2.0 (the "License");
#   you may not use this file except in compliance with the License.
#   You may obtain a copy of the License at
#       http://www.apache.org/licenses/LICENSE-2.0
#   Unless required by applicable law or agreed to in writing, software
#   distributed under the License is distributed on an "AS IS" BASIS,
#   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
#   See the License for the specific language governing permissions and
#   limitations under the License.
# ---------------------------------------------------------------------

# ---------------------------------------------------------------------
# function definitions
# ---------------------------------------------------------------------

def leap(y):
    leap = False
    if   y%4   == 0 :
        leap = True
    if (y > 1582 and y%100 == 0 and y%400 != 0):
        leap = False
    if leap:
        return 1
    else:
        return 0

# ---------------------------------------------------------------------
def date(n):
    global y,m,d
    while (n > 365 + leap(y)):          # if offset larger than # of
        n -= 365 + leap(y)              # ... days in a year
        y += 1                          # ... find the correct year
 
    while (n <= 0):                     # if offset is negative
        y -= 1                          # ... find the correct year
        n += 365 + leap(y)              # ... and offset
    i = leap(y)                         # adjust for leap day
    m = 12
    while (n <= e[m] + i):              # searching for the month
        m -= 1
        if (m<3): i=0
    d = n - e[m] - i;                   # setting the day


# ---------------------------------------------------------------------
# main program
# ---------------------------------------------------------------------
import sys

argc=len(sys.argv)
if (argc==1 or sys.argv[1]  == '?'):
    print("\ncal v1.3.2, 2023-12-25")
    print("-- Copyright (C) 2010-2023 Berndt E. Schwerdtfeger --\n")
    print("Input:  year-mm-dd [offset]");
    print("Output: {Mon|..|Sun} year-mm-dd J# jjjjjjj D# nnn W# ww");
else:   
    s=sys.argv[1]
    # set constants  -- move them to some spot below
    wd = ["Mon", "Tue", "Wed", "Thu", "Fri", "Sat", "Sun"]
    e = [0,0,31,59,90,120,151,181,212,243,273,304,334]

    if (argc >= 3):
        n=int(sys.argv[2])
    else:                               # if no offset provided
        n=0                             # ... initialize to 0

    # parse the argument, should be in format y-m-d, with 
    # y integer (so: may have a minus sign in front!)	
	# m in the range 1 <= m <= 12
	# d in the range 1 <= d <= 31
	
    ymd = s.split('-')
    if (len(ymd[0])==0):                # vorzeichen
        y = -int(ymd[1])
        m = int(ymd[2])
        d = int(ymd[3])
    else:
        y = int(ymd[0])
        m = int(ymd[1])
        d = int(ymd[2])
	
    if (y==1582 and m==10 and d>4 and d<15):
        print("Invalid date")
        sys.exit()                      # abort
    # test if we are in Julian or Gregorian era
    if (y < 1582 or y == 1582 and m*100+d < 1005):
        j = 1721423 + d + e[m] + (y-1)*365 + (y-1)//4
    else:                               # Gregorian era
        x = y - 2001
        j = 2451910 + d + e[m] + x*365 + x//4 - x//100 + x//400

    if (m>2): j+=leap(y)                # correction for leap year
    j += n                              # add offset
    if (j < 2299161):                   # Julian era
        y=1582
        date(j-2298883)                 # calculate the date
    else:                               # Gregorian era
        y=1583
        date(j-2299238)                 # calculate the date
    n = d + e[m]                        # offset into this year
    if (m > 2): n += leap(y)            # adjust for leap day
    if (y==1582 and n>278): n-=10       # ten days dropped in 1582
    w = j%7                             # set weekday
#   if (w<0): w+=7                        does not occur in Python
    print('%s %d-%d-%d J# %d D# %d W# %d' % (wd[w],y,m,d,j,n,(n-w+9)/7))