/* Copyright (c) 2008 Anonymous
 *
 * Permission to use, copy, modify, and/or distribute this software for any
 * purpose with or without fee is hereby granted, provided that you grant this
 * same permission to anyone you distribute it to without any additional
 * restrictions.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <inttypes.h>
#include <limits.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>

int main(int argc, char **argv){
 uintmax_t year = 0;
 uintmax_t month = 0;
 int_fast8_t month_days = 0, day_of_week = 0;
 const char *month_names[12] = { "January", "February", "March", "April", "May",
  "June", "July", "August", "September", "October", "November", "December" };
 const int_fast8_t months_days[12] = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31,
  30, 31 };
 time_t t = time(NULL);
 struct tm *time_struct = localtime(&t);
 switch(argc){
  case 1:
   year = time_struct->tm_year + 1900;
   month = time_struct->tm_mon + 1;
   break;
  case 2:
   year = strtoumax(argv[1], NULL, 10);
   month = time_struct->tm_mon + 1;
   break;
  default:
   month = strtoumax(argv[1], NULL, 10);
   year = strtoumax(argv[2], NULL, 10);
 }
 if(!year || !month || month > 12){
  fputs("learn to use cal, you idiot: http://opengroup.org/susv3xcu/cal.html\n",
   stderr);
  abort();
 }
#ifndef OVER_9999
 if(year > 9999){
  fputs("learn to use cal, you idiot: http://opengroup.org/susv3xcu/cal.html\n",
   stderr);
  abort();
 }
#endif
 if(year == 1752 && month == 9){
  puts("September 1752");
  puts("Su Mo Tu We Th Fr Sa");
  puts("       1  2 14 15 16");
  puts("17 18 19 20 21 22 23");
  puts("24 25 26 27 28 29 30");
  return 0;
 }else{
  printf("%s %" PRIuMAX "\n", month_names[month - 1], year);
  puts("Su Mo Tu We Th Fr Sa");
  month_days = months_days[month - 1];
  if(year > 1752 || (year == 1752 && month > 9)){
   /* Gregorian */
   if(month == 2 && !(year % 4) && year % 100 || !(year % 400))
    month_days = 29;
   day_of_week = ((153 * (month + 12 * ((14 - month) / 12) - 3) + 2) / 5 +
    365 * (year + 4800 - ((14 - month) / 12)) + (year + 4800 - ((14 - month) /
    12)) / 4 - (year + 4800 - ((14 - month) / 12)) / 100 + (year + 4800 - ((14 -
    month) / 12)) / 400 - 32043) % 7;
  }else{
   /* Julian */
   if(month == 2 && !(year % 4))
    month_days = 29;
   day_of_week = ((153 * (month + 12 * ((14 - month) / 12) - 3) + 2) / 5 +
    365 * (year + 4800 - ((14 - month) / 12)) + (year + 4800 - ((14 - month) /
    12)) / 4 - 32081) % 7;
  }
  for(int i = 0; i < day_of_week; ++i) fputs("   ", stdout);
  for(int i = 1; i <= month_days; ++i){
   printf("% 2u", i);
   ++day_of_week;
   putchar((day_of_week %= 7) ? ' ' : '\n');
  }
 }
 putchar('\n');
 return 0;
}