/*
   =============================================================================
	calndr.c -- print a calendar
	Version 1 -- 1986-10-06
   =============================================================================
*/

#include <time.h>

char	dayw[] = {
	" S  M Tu  W Th  F  S"
};

char	*smon[]= {
	"January", "February", "March", "April",
	"May", "June", "July", "August",
	"September", "October", "November", "December",
};

char	mon[] = {
	0,
	31, 29, 31, 30,
	31, 30, 31, 31,
	30, 31, 30, 31,
};


char	string[432];

extern struct tm *localtime();
extern long time();

struct tm *thetime;
long timbuf;

/*
   =============================================================================
	main function for calndr command
   =============================================================================
*/

main(argc, argv)
char *argv[];
{
	register y, i, j;
	int m;

	switch(argc) {

	case 1:
		timbuf = time(&timbuf);
		thetime = localtime(&timbuf);
		m = thetime->tm_mon + 1;
		y = thetime->tm_year + 1900;
		break;

	case 2:
		goto xlong;

	case 3:
		m = number(argv[1]);
		y = number(argv[2]);
		break;

	default:
		printf("usage: calndr [ [month] year ]\n");
		exit(0);
	}

	/* print out just month */

	if(m<1 || m>12)
		goto badarg;

	if(y<1 || y>9999)
		goto badarg;

	printf("   %s %u\n\n", smon[m-1], y);
	printf("%s\n", dayw);

	cal(m, y, string, 24);

	for(i=0; i<6*24; i+=24)
		pstr(string+i, 24);

	exit(0);

	/* print out complete year */

xlong:
	y = number(argv[1]);

	if(y<1 || y>9999)
		goto badarg;

	printf("\n\n\n");
	printf("				%u\n", y);
	printf("\n");

	for(i=0; i<12; i+=3) {

		for(j=0; j<6*72; j++)
			string[j] = '\0';

		printf("	 %.3s", smon[i]);
		printf("			%.3s", smon[i+1]);
		printf("		       %.3s\n", smon[i+2]);
		printf("%s   %s   %s\n", dayw, dayw, dayw);

		cal(i+1, y, string, 72);
		cal(i+2, y, string+23, 72);
		cal(i+3, y, string+46, 72);

		for(j=0; j<6*72; j+=72)
			pstr(string+j, 72);
	}

	printf("\n\n\n");
	exit(0);

badarg:
	printf("calndr:  Bad argument\n");
	exit(1);
}

/*
   =============================================================================
	number(str) -- extract an integer from str
   =============================================================================
*/

number(str)
char *str;
{
	register n, c;
	register char *s;

	n = 0;
	s = str;

	while(c = *s++) {

		if(c<'0' || c>'9')
			return(0);

		n = n*10 + c-'0';
	}

	return(n);
}

/*
   =============================================================================
	pstr(str, n)
   =============================================================================
*/

pstr(str, n)
char *str;
{
	register i;
	register char *s;

	s = str;
	i = n;

	while(i--)
		if(*s++ == '\0')
			s[-1] = ' ';

	i = n+1;

	while(i--)
		if(*--s != ' ')
			break;

	s[1] = '\0';
	printf("%s\n", str);
}

/*
   =============================================================================
	cal(m, y, p, w) -- calculate calendar string
   =============================================================================
*/

cal(m, y, p, w)
char *p;
{
	register d, i;
	register char *s;

	s = p;
	d = jan1(y);
	mon[2] = 29;
	mon[9] = 30;

	switch((jan1(y+1)+7-d)%7) {

	/*
	 *	non-leap year
	 */
	case 1:
		mon[2] = 28;
		break;

	/*
	 *	1752
	 */
	default:
		mon[9] = 19;
		break;

	/*
	 *	leap year
	 */
	case 2:
		;
	}

	for(i=1; i<m; i++)
		d += mon[i];

	d %= 7;
	s += 3*d;

	for(i=1; i<=mon[m]; i++) {

		if(i==3 && mon[m]==19) {
			i += 11;
			mon[m] += 11;
		}

		if(i > 9)
			*s = i/10+'0';

		s++;
		*s++ = i%10+'0';
		s++;

		if(++d == 7) {
			d = 0;
			s = p+w;
			p = s;
		}
	}
}

/*
   =============================================================================
	jan1(yr) -- return day of the week
	of jan 1 of given year
   =============================================================================
 */

jan1(yr)
{
	register y, d;

	/* normal gregorian calendar -- one extra day per four years */

	y = yr;
	d = 4+y+(y+3)/4;

	/* julian calendar -- regular gregorian less three days per 400 */

	if(y > 1800) {
		d -= (y-1701)/100;
		d += (y-1601)/400;
	}

	/* great calendar changeover instant */

	if(y > 1752)
		d += 3;

	return(d%7);
}