// Copyright (C) 2008-2021 Lily Anatia Wilson <hotaru@thinkindifferent.net>

// This file is part of cal.

//

// cal is non-violent software: you can use, redistribute,

// and/or modify it under the terms of the CNPLv6 as found

// in the LICENSE file in the source code root directory or

// at <https://git.pixie.town/thufie/CNPL>.

//

// cal comes with ABSOLUTELY NO WARRANTY, to the extent

// permitted by applicable law. See the CNPL for details.

#include <inttypes.h>

#include <limits.h>

#include <locale.h>

#include <stdint.h>

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include <time.h>

#include <wchar.h>

#include <sys/param.h>

#include <gmp.h>

int main(int argc, char **argv){

mpz_t year, tmp1, tmp2, tmp3, tmp4;

unsigned long day_of_week = 0;

uintmax_t month_min = 1, month_max = 12;

int_fast8_t month_days = 0;

const int_fast8_t months_days[12] = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31,

30, 31 };

time_t t = time(NULL);

char weekday[13] = {0}, weekdays[92] = {0}, month_name[13] = {0};

wchar_t w_weekday[3] = {0}, w_month_name[13] = {0};

struct tm *time_struct = localtime(&t);

setlocale(LC_ALL, "");

mpz_init(year);

switch(argc){

case 1:

mpz_set_ui(year, time_struct->tm_year + 1900);

month_min = month_max = time_struct->tm_mon + 1;

break;

case 2:

mpz_set_str(year, argv[1], 10);

break;

default:

month_min = month_max = strtoumax(argv[1], NULL, 10);

mpz_set_str(year, argv[2], 10);

}

if(mpz_sgn(year) < 1 || !month_min || month_min > 12){

fputs("http://opengroup.org/onlinepubs/9699919799/utilities/cal.html\n",

stderr);

exit(1);

}

for(int_fast8_t i = 0; i < 7; ++i){

time_struct->tm_wday = i;

strftime(weekday, 13, "%a", time_struct);

mbstowcs(w_weekday, weekday, 2);

wcstombs(weekday, w_weekday, 13);

strcat(weekdays, weekday);

strcat(weekdays, " ");

}

strcat(weekdays, "\n");

for(uintmax_t month = month_min; month <= month_max; ++month){

time_struct->tm_mon = month - 1;

strftime(month_name, 13, "%B", time_struct);

mbstowcs(w_month_name, month_name, 13);

if(month > month_min) putchar('\n');

for(int_fast8_t i = MAX(0, 20 - wcslen(w_month_name) - strlen(mpz_get_str(NULL, 10, year))) / 2; i > 0; --i)

putchar(' ');

fputs(month_name, stdout);

putchar(' ');

printf("%s\n", mpz_get_str(NULL, 10, year));

fputs(weekdays, stdout);

if(!mpz_cmp_ui(year, 1752) && month == 9){

puts(" 1 2 14 15 16");

puts("17 18 19 20 21 22 23");

puts("24 25 26 27 28 29 30");

}else{

month_days = months_days[month - 1];

mpz_init(tmp1);

mpz_init(tmp2);

mpz_init(tmp3);

mpz_init(tmp4);

if(mpz_cmp_ui(year, 1752) > 0 || (!mpz_cmp_ui(year, 1752) && month > 9)){

/* Gregorian */

if(month == 2 && mpz_divisible_ui_p(year, 4) && (!mpz_divisible_ui_p(year,

100) || mpz_divisible_ui_p(year, 400))) month_days = 29;

mpz_add_ui(tmp4, year, 4800 - (14 - month) / 12);

mpz_tdiv_q_ui(tmp1, tmp4, 4);

mpz_tdiv_q_ui(tmp2, tmp4, 100);

mpz_tdiv_q_ui(tmp3, tmp4, 400);

mpz_mul_ui(tmp4, tmp4, 365);

mpz_add(tmp4, tmp4, tmp1);

mpz_sub(tmp4, tmp4, tmp2);

mpz_add(tmp4, tmp4, tmp3);

mpz_add_ui(tmp4, tmp4, (153 * (month + 12 * ((14 - month) / 12) - 3) + 2) /

5);

mpz_sub_ui(tmp4, tmp4, 32043);

day_of_week = mpz_tdiv_ui(tmp4, 7);

}else{

/* Julian */

if(month == 2 && mpz_divisible_ui_p(year, 4))

month_days = 29;

mpz_add_ui(tmp2, year, 4800 - (14 - month) / 12);

mpz_tdiv_q_ui(tmp1, tmp2, 4);

mpz_mul_ui(tmp2, tmp2, 365);

mpz_add(tmp2, tmp2, tmp1);

mpz_add_ui(tmp2, tmp2, (153 * (month + 12 * ((14 - month) / 12) - 3) + 2) /

5);

mpz_sub_ui(tmp2, tmp2, 32081);

day_of_week = mpz_tdiv_ui(tmp2, 7);

}

mpz_clear(tmp1);

mpz_clear(tmp2);

mpz_clear(tmp3);

mpz_clear(tmp4);

for(uint_fast8_t i = 0; i < day_of_week; ++i) fputs(" ", stdout);

for(int_fast8_t i = 1; i <= month_days; ++i){

printf("%2u", i);

++day_of_week;

if(i < month_days)

fputs((day_of_week %= 7) ? " " : "\n", stdout);

}

}

putchar('\n');

}

mpz_clear(year);

return 0;

}