## This program calculates a new date given an old date and
## a number of days in the future

import time

months = ['January','February','March','April','May', 'June', \
          'July', 'August', 'September', 'October','November','December']

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

months_30 = ['April','June','September','November']

anchor_sunday = ['November', 14, 2010]

anchor_year = 2010

def is_leap_year(year):
    ## let's assume that years divisible by 4 are leap years
    return((year % 4) == 0)

def calculate_day_number(month, day, year):
    leap_days = 0
    day_total = 0
    month_number = months.index(month)
    if is_leap_year(year) and \
        (((month_number == 1) and (day > 28)) \
       or (month_number >= 2)):
        leap_days = 1
    for month in months[:month_number]:
        if month == 'February':
            day_total = day_total + 28 + leap_days
        elif month in months_30:
            day_total = day_total + 30
        else:
            day_total = day_total + 31
    day_total = day_total+ day
    return(day_total)

def year_days(year):
    if is_leap_year(year):
        return(366)
    else:
        return(365)

anchor_day = calculate_day_number(anchor_sunday[0],anchor_sunday[1],anchor_sunday[2])

def get_day_difference(new_year, old_year, new_day, old_day):
    ## print('Get_day_differrence: ',new_year,old_year,new_day,old_day)
    ## Used for debugging
    import math
    days = 0
    max_year = max(new_year,old_year)
    min_year = min(new_year,old_year)
    if old_year == new_year:
        ## if the same year, subtract days
        return (new_day - old_day)
    else:
        if max_year==new_year:
            max_day = new_day
            min_day = old_day
        else:
            max_day = old_day
            min_day = new_day
        if (is_leap_year(min_year) and (min_day < 59)):
            days = 366 - min_day
        else:
            days = 365 - min_day
        ## set days to the days left in the current year
        for year in range(min_year+1, max_year):
            ## add on the number of days in each year in between
            if is_leap_year(year):
                days = days + 366
                days = days + 365
        days = days + max_day
        ## add the days into the final year
        if new_day == max_day:
            return(days)
        else:
            return(0 - days)

def remaining_days_after_year(year, days_left):
    if is_leap_year(year):
        return(days_left > 366)
    else:
        return(days_left>365)

def days_in_month(month,year):
    if month=='February':
        if is_leap_year(year):
            return(29)
        else:
            return(28)
    elif month in months_30:
        return(30)
    else:
        return(31)

def day_in_future(month, day, year, future):
    today = calculate_day_number(month,day, year)
    future_day = today + future
    ## anchor day is a known Sunday
    days_from_anchor = get_day_difference(year, \
                                          anchor_year, \
                                          today, \
                                          anchor_day)
    today_day_of_week = days_from_anchor%7
    future_day_of_week_number = (today_day_of_week+future)%7
    future_day_of_week = weekdays[future_day_of_week_number]
    days_left = future_day
    new_year = year
    while remaining_days_after_year(year, days_left):
        ## remaining_days_after_year = boolean function
        ## that determines if there are any more days in
        ## year
        if is_leap_year(new_year):
            days_left=days_left-366
        else:
            days_left=days_left-365
        new_year=new_year+1
    new_month = 'January'
    days_in_current_month = days_in_month(new_month,year)
    month_number = 0
    while days_in_current_month < days_left:
        days_left = days_left-days_in_current_month
        month_number = (month_number + 1)
        new_month = months[month_number]
        days_in_current_month = days_in_month(new_month,year)
    return([new_year,new_month,days_left,future_day_of_week])

def main():
    input_string = input('Please enter the current date \
in the form month/day/year: ')
    input_list = input_string.split('/')
    input_list[0] = int(input_list[0])
    input_list[1] = int(input_list[1])
    input_list[2] = int(input_list[2])
    month = months[input_list[0]-1] ## Human month 1 = index 0
    day = input_list[1]
    year = input_list[2]
    print('You entered', month, str(day)+',',year)
    future = int(input('How many days in the future would \
you like your appointment? '))
    new_day_list = day_in_future(month,day,year,future)
    new_year=new_day_list[0]
    new_month=new_day_list[1]
    new_day=new_day_list[2]
    week_day=new_day_list[3]
    print('Your appointment will be on',week_day,\
          new_month,str(new_day)+',',new_year)
    time.sleep(5)
        
main()