/*
** dtime.c -- time/date routines
**
** This code is Copyright (c) 2002, by the authors of nmh.  See the
** COPYRIGHT file in the root directory of the nmh distribution for
** complete copyright information.
*/

#include <time.h>
#include <h/mh.h>   /* for snprintf() */
#include <h/tws.h>

#if !defined(HAVE_STRUCT_TM_TM_GMTOFF)
extern long timezone;
#endif

/*
** The number of days in the year, accounting for leap years
*/
#define dysize(y) \
	(((y) % 4) ? 365 : (((y) % 100) ? 366 : (((y) % 400) ? 365 : 366)))

char *tw_moty[] = {
	"Jan", "Feb", "Mar", "Apr",
	"May", "Jun", "Jul", "Aug",
	"Sep", "Oct", "Nov", "Dec",
	NULL
};

char *tw_dotw[] = {
	"Sun", "Mon", "Tue",
	"Wed", "Thu", "Fri",
	"Sat", NULL
};

char *tw_ldotw[] = {
	"Sunday", "Monday", "Tuesday",
	"Wednesday", "Thursday", "Friday",
	"Saturday",  NULL
};

static int dmsize[] = {
	31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31
};


/*
** Get current time (adjusted for local time
** zone and daylight savings time) expressed
** as nmh "broken-down" time structure.
*/

struct tws *
dlocaltimenow(void)
{
	time_t clock;

	time(&clock);
	return dlocaltime(&clock);
}


/*
** Take clock value and return pointer to nmh time structure
** containing "broken-down" time.  The time is adjusted for
** local time zone and daylight savings time.
*/

struct tws *
dlocaltime(time_t *clock)
{
	static struct tws tw;
	struct tm *tm;

	if (!clock)
		return NULL;

	tm = localtime(clock);

	tw.tw_sec  = tm->tm_sec;
	tw.tw_min  = tm->tm_min;
	tw.tw_hour = tm->tm_hour;
	tw.tw_mday = tm->tm_mday;
	tw.tw_mon  = tm->tm_mon;

	/* tm_year is always "year - 1900". So we correct for this. */
	tw.tw_year = tm->tm_year + 1900;
	tw.tw_wday = tm->tm_wday;
	tw.tw_yday = tm->tm_yday;

	tw.tw_flags = TW_NULL;
	if (tm->tm_isdst)
		tw.tw_flags |= TW_DST;

#ifdef HAVE_STRUCT_TM_TM_GMTOFF
	tw.tw_zone = tm->tm_gmtoff / 60;
	if (tm->tm_isdst)  /* if DST is in effect */
		tw.tw_zone -= 60;  /* reset to normal offset */
#else
	tzset();
	tw.tw_zone = -(timezone / 60);
#endif

	tw.tw_flags &= ~TW_SDAY;
	tw.tw_flags |= TW_SEXP;
	tw.tw_flags &= ~TW_SZONE;
	tw.tw_flags |= TW_SZEXP;

	tw.tw_clock = *clock;

	return (&tw);
}


/*
** Take clock value and return pointer to nmh time
** structure containing "broken-down" time.  Time is
** expressed in UTC (Coordinated Universal Time).
*/

struct tws *
dgmtime(time_t *clock)
{
	static struct tws tw;
	struct tm *tm;

	if (!clock)
		return NULL;

	tm = gmtime(clock);

	tw.tw_sec  = tm->tm_sec;
	tw.tw_min  = tm->tm_min;
	tw.tw_hour = tm->tm_hour;
	tw.tw_mday = tm->tm_mday;
	tw.tw_mon  = tm->tm_mon;

	/* tm_year is always "year - 1900". So we correct for this. */
	tw.tw_year = tm->tm_year + 1900;
	tw.tw_wday = tm->tm_wday;
	tw.tw_yday = tm->tm_yday;

	tw.tw_flags = TW_NULL;
	if (tm->tm_isdst)
		tw.tw_flags |= TW_DST;

	tw.tw_zone = 0;

	tw.tw_flags &= ~TW_SDAY;
	tw.tw_flags |= TW_SEXP;
	tw.tw_flags &= ~TW_SZONE;
	tw.tw_flags |= TW_SZEXP;

	tw.tw_clock = *clock;

	return (&tw);
}


/*
** Using a nmh "broken-down" time structure,
** produce a 26-byte date/time string, such as
**
**    Tue Jan 14 17:49:03 1992\n\0
*/

char *
dctime(struct tws *tw)
{
	static char buffer[26];

	if (!tw)
		return NULL;

	snprintf(buffer, sizeof(buffer), "%.3s %.3s %02d %02d:%02d:%02d %.4d\n",
		tw_dotw[tw->tw_wday], tw_moty[tw->tw_mon], tw->tw_mday,
		tw->tw_hour, tw->tw_min, tw->tw_sec,
		tw->tw_year < 100 ? tw->tw_year + 1900 : tw->tw_year);

	return buffer;
}


/*
** Produce a date/time string of the form
**
**    Mon, 16 Jun 1992 15:30:48 -0700
**
** for the current time, as specified by rfc822 and rfc1123.
*/
char *
dtimenow(void)
{
	time_t clock;

	time(&clock);
	return dtime(&clock);
}


/*
** Using a local calendar time value, produce
** a date/time string of the form
**
**    Mon, 16 Jun 1992 15:30:48 -0700
**
** as specified by rfc822 and rfc1123.
*/
char *
dtime(time_t *clock)
{
	return dasctime(dlocaltime(clock));
}


/*
** Using a nmh "broken-down" time structure, produce
** a date/time string of the form
**
**    Mon, 16 Jun 1992 15:30:48 -0700
**
** as specified by rfc822 and rfc1123.
*/
char *
dasctime(struct tws *tw)
{
	char buffer[80];
	static char result[80];

	if (!tw)
		return NULL;

	/* Display timezone if known */
	if ((tw->tw_flags & TW_SZONE) == TW_SZNIL)
		result[0] = '\0';
	else
		snprintf(result, sizeof(result), " %s", dtimezone(tw->tw_zone, tw->tw_flags));

	snprintf(buffer, sizeof(buffer), "%02d %s %0*d %02d:%02d:%02d%s",
		tw->tw_mday, tw_moty[tw->tw_mon],
		tw->tw_year < 100 ? 2 : 4, tw->tw_year,
		tw->tw_hour, tw->tw_min, tw->tw_sec, result);

	if ((tw->tw_flags & TW_SDAY) == TW_SEXP)
		snprintf(result, sizeof(result), "%s, %s", tw_dotw[tw->tw_wday], buffer);
	else
		if ((tw->tw_flags & TW_SDAY) == TW_SNIL)
			strncpy(result, buffer, sizeof(result));
		else
			snprintf(result, sizeof(result), "%s (%s)", buffer, tw_dotw[tw->tw_wday]);

	return result;
}


/*
** Get the timezone for given offset as numeric value.
*/
char *
dtimezone(int offset, int flags)
{
	int hours, mins;
	static char buffer[10];

	if (offset < 0) {
		mins = -((-offset) % 60);
		hours = -((-offset) / 60);
	} else {
		mins = offset % 60;
		hours = offset / 60;
	}

#ifdef ADJUST_NUMERIC_ONLY_TZ_OFFSETS_WRT_DST
	if (flags & TW_DST)
		hours += 1;
#endif /* ADJUST_NUMERIC_ONLY_TZ_OFFSETS_WRT_DST */
	snprintf(buffer, sizeof(buffer), "%s%02d%02d",
		offset < 0 ? "-" : "+", abs(hours), abs(mins));
	return buffer;
}


/*
** Convert nmh time structure for local "broken-down"
** time to calendar time (clock value).  This routine
** is based on the gtime() routine written by Steven Shafer
** at CMU.  It was forwarded to MTR by Jay Lepreau at Utah-CS.
*/

time_t
dmktime(struct tws *tw)
{
	int i, sec, min, hour, mday, mon, year;
	time_t result;

	if (tw->tw_clock != 0)
		return tw->tw_clock;

	if ((sec = tw->tw_sec) < 0 || sec > 61
		|| (min = tw->tw_min) < 0 || min > 59
		|| (hour = tw->tw_hour) < 0 || hour > 23
		|| (mday = tw->tw_mday) < 1 || mday > 31
		|| (mon = tw->tw_mon + 1) < 1 || mon > 12)
		return (tw->tw_clock = (time_t) -1);

	year = tw->tw_year;

	result = 0;
	if (year < 1970)
		year += 1900;

	if (year < 1970)
		year += 100;

	for (i = 1970; i < year; i++)
		result += dysize(i);
	if (dysize(year) == 366 && mon >= 3)
		result++;
	while (--mon)
		result += dmsize[mon - 1];
	result += mday - 1;
	result = 24 * result + hour;
	result = 60 * result + min;
	result = 60 * result + sec;
	result -= 60 * tw->tw_zone;
	if (tw->tw_flags & TW_DST)
		result -= 60 * 60;

	return (tw->tw_clock = result);
}


/*
** Simple calculation of day of the week.  Algorithm
** used is Zeller's congruence.  We assume that
** if tw->tw_year < 100, then the century = 19.
*/

void
set_dotw(struct tws *tw)
{
	int month, day, year, century;

	month = tw->tw_mon - 1;
	day = tw->tw_mday;
	year = tw->tw_year % 100;
	century = tw->tw_year < 100 ? 19 : tw->tw_year / 100;

	if (month <= 0) {
		month += 12;
		if (--year < 0) {
			year += 100;
			century--;
		}
	}

	tw->tw_wday = ((26 * month - 2) / 10 + day + year + year / 4
			- 3 * century / 4 + 1) % 7;
	if (tw->tw_wday < 0)
		tw->tw_wday += 7;

	tw->tw_flags &= ~TW_SDAY, tw->tw_flags |= TW_SIMP;
}


/*
** Copy nmh time structure
*/

void
twscopy(struct tws *tb, struct tws *tw)
{
	*tb = *tw;  /* struct copy */
}


/*
** Compare two nmh time structures
*/

int
twsort(struct tws *tw1, struct tws *tw2)
{
	time_t c1, c2;

	if (tw1->tw_clock == 0)
		dmktime(tw1);
	if (tw2->tw_clock == 0)
		dmktime(tw2);

	return ((c1 = tw1->tw_clock) > (c2 = tw2->tw_clock) ? 1
		: c1 == c2 ? 0 : -1);
}
