#! /usr/bin/env python3

# Calculate your unbirthday count (see Alice in Wonderland).
# This is defined as the number of days from your birth until today
# that weren't your birthday.  (The day you were born is not counted).
# Leap years make it interesting.

import sys
import time
import calendar

def main():
    if sys.argv[1:]:
        year = int(sys.argv[1])
    else:
        year = int(input('In which year were you born? '))
    if 0 <= year < 100:
        print("I'll assume that by", year, end=' ')
        year = year + 1900
        print('you mean', year, 'and not the early Christian era')
    elif not (1850 <= year <= time.localtime()[0]):
        print("It's hard to believe you were born in", year)
        return

    if sys.argv[2:]:
        month = int(sys.argv[2])
    else:
        month = int(input('And in which month? (1-12) '))
    if not (1 <= month <= 12):
        print('There is no month numbered', month)
        return

    if sys.argv[3:]:
        day = int(sys.argv[3])
    else:
        day = int(input('And on what day of that month? (1-31) '))
    if month == 2 and calendar.isleap(year):
        maxday = 29
    else:
        maxday = calendar.mdays[month]
    if not (1 <= day <= maxday):
        print('There are no', day, 'days in that month!')
        return

    bdaytuple = (year, month, day)
    bdaydate = mkdate(bdaytuple)
    print('You were born on', format(bdaytuple))

    todaytuple = time.localtime()[:3]
    todaydate = mkdate(todaytuple)
    print('Today is', format(todaytuple))

    if bdaytuple > todaytuple:
        print('You are a time traveler.  Go back to the future!')
        return

    if bdaytuple == todaytuple:
        print('You were born today.  Have a nice life!')
        return

    days = todaydate - bdaydate
    print('You have lived', days, 'days')

    age = 0
    for y in range(year, todaytuple[0] + 1):
        if bdaytuple < (y, month, day) <= todaytuple:
            age = age + 1

    print('You are', age, 'years old')

    if todaytuple[1:] == bdaytuple[1:]:
        print('Congratulations!  Today is your', nth(age), 'birthday')
        print('Yesterday was your', end=' ')
    else:
        print('Today is your', end=' ')
    print(nth(days - age), 'unbirthday')

def format(date):
    (year, month, day) = date
    return '%d %s %d' % (day, calendar.month_name[month], year)

def nth(n):
    if n == 1: return '1st'
    if n == 2: return '2nd'
    if n == 3: return '3rd'
    return '%dth' % n

def mkdate(date):
    # January 1st, in 0 A.D. is arbitrarily defined to be day 1,
    # even though that day never actually existed and the calendar
    # was different then...
    (year, month, day) = date
    days = year*365                  # years, roughly
    days = days + (year+3)//4        # plus leap years, roughly
    days = days - (year+99)//100     # minus non-leap years every century
    days = days + (year+399)//400    # plus leap years every 4 centirues
    for i in range(1, month):
        if i == 2 and calendar.isleap(year):
            days = days + 29
        else:
            days = days + calendar.mdays[i]
    days = days + day
    return days

if __name__ == "__main__":
    main()
