/*
   =============================================================================
	ctime.c -- time and date support ala' Unix
	Version 3 -- 1989-01-13 -- D.N. Lynx Crowe
   =============================================================================
*/

#define	HAS_ENV		0		/* define non-zero if getenv() exists */

/*
 * This routine converts time as follows.
 * The epoch is 0000 Jan 1 1970 GMT.
 * The argument time is in seconds since then.
 * The localtime(t) entry returns a pointer to an array containing:
 *
 *  seconds (0-59)
 *  minutes (0-59)
 *  hours (0-23)
 *  day of month (1-31)
 *  month (0-11)
 *  year-1900
 *  weekday (0-6, Sun is 0)
 *  day of the year
 *  daylight savings flag
 *
 * The routine corrects for daylight savings time and will work in any
 * time zone provided that "timezone" is adjusted to the difference between
 * Greenwich and local standard time (measured in seconds).
 *
 * In places like Michigan "daylight" must be initialized to 0 to prevent
 * the conversion to daylight savings time.
 *
 * There is a table which accounts for the peculiarities undergone by
 * daylight savings time in 1974-1975.
 *
 * This routine does not work for Saudi Arabia,  which runs on Solar time.
 *
 * asctime(tvec)
 *
 *	where tvec is produced by localtime()
 *
 *	Returns a ptr to a character string that has the ascii time in the form:
 *
 *		Thu Jan 01 00:00:00 1970n0\\
 *		01234567890123456789012345
 *		0	  1	    2
 *
 * ctime(t)
 *
 *	Just calls localtime(), then asctime()
 *
 * tzset()
 *
 *	Looks for an environment variable named TZ.
 *
 *	It should be in the form "ESTn" or "ESTnEDT",
 *	where "n" represents a string of digits with an optional
 *	negative sign (for locations east of Greenwich, England).
 *
 *	If the variable is present, it will set the external
 *	variables "timezone", "daylight", and "tzname"
 *	appropriately. It is called by localtime, and
 *	may also be called explicitly by the user.
 */

/*  */

#define	dysize(A) (((A)%4)? 365: 366)

#define	void	int

#include "time.h"

long	timezone = 8*60*60;
int	daylight = 0;
char	*tzname[] = {"PST", "PDT"};

struct tm *gmtime(), *localtime();
char	*ctime(), *asctime();
void	tzset();

static char cbuf[26];
static int dmsize[12] = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };

/*
 * The following table is used for 1974 and 1975 and
 * gives the day number of the first day after the Sunday of the
 * change.
 */

static struct {

	int	daylb;
	int	dayle;

} daytab[] = {

	5,	333,	/* 1974: Jan 6 - last Sun. in Nov */
	58,	303,	/* 1975: Last Sun. in Feb - last Sun in Oct */
};

/*  */

/*
   =============================================================================
	ctime(t)
   =============================================================================
*/

char *
ctime(t)
long	*t;
{
	return(asctime(localtime(t)));
}

/*  */

/*
   =============================================================================
	localtime(tim)
   =============================================================================
*/

struct tm *
localtime(tim)
long	*tim;
{
	register int dayno, daylbegin, daylend;
	register struct tm *ct;
	long copyt;

	tzset();
	copyt = *tim - timezone;
	ct = gmtime(&copyt);
	dayno = ct->tm_yday;
	daylbegin = 119;	/* last Sun in Apr */
	daylend = 303;		/* Last Sun in Oct */

	if(ct->tm_year == 74 || ct->tm_year == 75) {

		daylbegin = daytab[ct->tm_year-74].daylb;
		daylend = daytab[ct->tm_year-74].dayle;
	}

	daylbegin = sunday(ct, daylbegin);
	daylend = sunday(ct, daylend);

	if(daylight &&
	    (dayno>daylbegin || (dayno==daylbegin && ct->tm_hour>=2)) &&
	    (dayno<daylend || (dayno==daylend && ct->tm_hour<1))) {

		copyt += 1*60*60;
		ct = gmtime(&copyt);
		ct->tm_isdst++;
	}

	return(ct);
}

/*  */

/*
   =============================================================================
	sunday(t,d)

	The argument is a 0-origin day number.
	The value is the day number of the first
	Sunday on or after the day.
   =============================================================================
 */

static int
sunday(t, d)
register struct tm *t;
register int d;
{
	if(d >= 58)
		d += dysize(t->tm_year) - 365;

	return(d - (d - t->tm_yday + t->tm_wday + 700) % 7);
}

/*  */

/*
   =============================================================================
	gmtime(tim)
   =============================================================================
*/

struct tm *
gmtime(tim)
long	*tim;
{
	register int d0, d1;
	long hms, day;
	static struct tm xtime;

	/*
	 * break initial number into days
	 */

	hms = *tim % 86400L;
	day = *tim / 86400L;

	if(hms < 0) {
		hms += 86400L;
		day -= 1;
	}

	/*
	 * generate hours:minutes:seconds
	 */

	xtime.tm_sec = hms % 60;
	d1 = hms / 60;
	xtime.tm_min = d1 % 60;
	d1 /= 60;
	xtime.tm_hour = d1;

	/*
	 * day is the day number.
	 * generate day of the week.
	 * The addend is 4 mod 7 (1/1/1970 was Thursday)
	 */

	xtime.tm_wday = (day + 7340036L) % 7;

	/*
	 * year number
	 */

	if(day >= 0)
		for(d1=70; day >= dysize(d1); d1++)
			day -= dysize(d1);
	else
		for(d1=70; day < 0; d1--)
			day += dysize(d1-1);

	xtime.tm_year = d1;
	xtime.tm_yday = d0 = day;

	/*
	 * generate month
	 */

	if(dysize(d1) == 366)
		dmsize[1] = 29;

	for(d1=0; d0 >= dmsize[d1]; d1++)
		d0 -= dmsize[d1];

	dmsize[1] = 28;
	xtime.tm_mday = d0+1;
	xtime.tm_mon = d1;
	xtime.tm_isdst = 0;
	return(&xtime);
}

/*  */

/*
   =============================================================================
	asctime(t)
   =============================================================================
*/

char *
asctime(t)
struct tm *t;
{
	register char *cp, *ncp;
	register int *tp;
	char	*ct_numb();

	cp = cbuf;

	for(ncp = "Day Mon 00 00:00:00 1900\n"; *cp++ = *ncp++; );

	ncp = &"SunMonTueWedThuFriSat"[3*t->tm_wday];
	cp = cbuf;
	*cp++ = *ncp++;
	*cp++ = *ncp++;
	*cp++ = *ncp++;
	cp++;
	tp = &t->tm_mon;
	ncp = &"JanFebMarAprMayJunJulAugSepOctNovDec"[(*tp)*3];
	*cp++ = *ncp++;
	*cp++ = *ncp++;
	*cp++ = *ncp++;
	cp = ct_numb(cp, *--tp);
	cp = ct_numb(cp, *--tp+100);
	cp = ct_numb(cp, *--tp+100);
	cp = ct_numb(cp, *--tp+100);

	if(t->tm_year >= 100) {
		cp[1] = '2';
		cp[2] = '0';
	}

	cp += 2;
	cp = ct_numb(cp, t->tm_year+100);
	return(cbuf);
}

/*  */

/*
   =============================================================================
	ct_numb(cp,n)
   =============================================================================
*/

static char *
ct_numb(cp, n)
register char *cp;
int	n;
{
	cp++;

	if(n >= 10)
		*cp++ = (n/10)%10 + '0';
	else
		*cp++ = ' ';

	*cp++ = n%10 + '0';
	return(cp);
}

/*  */

/*
   =============================================================================
	tzset()
   =============================================================================
*/

void
tzset()
{
#if	HAS_ENV
	register char *p, *q;
	register int n;
	int sign;
	char *getenv();

	if((p = getenv ("TZ")) && *p) {

		n = 3;
		q = tzname[0];

		do {

			*q++ = *p? *p++: ' ';

		} while(--n);

		if(sign = *p == '-')
			p++;

		n = 0;

		while(*p >= '0' && *p <= '9')
			n = (n * 10) + *p++ - '0';

		if(sign)
			n = -n;

		timezone = ((long)(n * 60)) * 60;

		if(daylight = *p != '\0') {

			q = tzname[1];
			n = 3;

			do {

				*q++ = *p? *p++: ' ';

			} while(--n);
		}
	}
#endif
}