/* Convert struct partime into time_t.  */

/* Copyright 1992, 1993, 1994, 1995 Paul Eggert
   Distributed under license by the Free Software Foundation, Inc.

This file is part of RCS.

RCS is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.

RCS is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with RCS; see the file COPYING.
If not, write to the Free Software Foundation,
59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.

Report problems and direct all questions to:

    rcs-bugs@cs.purdue.edu

*/

#include "rcsbase.h"

#include "partime.h"
#include "maketime.h"

char const maketId[]
  = "$Id: maketime.c,v 5.11 1995/06/16 06:19:24 eggert Exp $";

static int isleap P((int));
static int month_days P((struct tm const*));
static time_t maketime P((struct partime const*,time_t));

/*
* For maximum portability, use only localtime and gmtime.
* Make no assumptions about the time_t epoch or the range of time_t values.
* Avoid mktime because it's not universal and because there's no easy,
* portable way for mktime to yield the inverse of gmtime.
*/

#define TM_YEAR_ORIGIN 1900

	static int
isleap(y)
	int y;
{
	return (y&3) == 0  &&  (y%100 != 0 || y%400 == 0);
}

static int const month_yday[] = {
	/* days in year before start of months 0-12 */
	0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365
};

/* Yield the number of days in TM's month.  */
	static int
month_days(tm)
	struct tm const *tm;
{
	int m = tm->tm_mon;
	return month_yday[m+1] - month_yday[m]
		+ (m==1 && isleap(tm->tm_year + TM_YEAR_ORIGIN));
}

/*
* Convert UNIXTIME to struct tm form.
* Use gmtime if available and if !LOCALZONE, localtime otherwise.
*/
	struct tm *
time2tm(unixtime, localzone)
	time_t unixtime;
	int localzone;
{
	struct tm *tm;
#	if TZ_must_be_set
		static char const *TZ;
		if (!TZ  &&  !(TZ = getenv("TZ")))
			faterror("The TZ environment variable is not set; please set it to your timezone");
#	endif
	if (localzone  ||  !(tm = gmtime(&unixtime)))
		tm = localtime(&unixtime);
	return tm;
}

/* Yield A - B, measured in seconds.  */
	time_t
difftm(a, b)
	struct tm const *a, *b;
{
	int ay = a->tm_year + (TM_YEAR_ORIGIN - 1);
	int by = b->tm_year + (TM_YEAR_ORIGIN - 1);
	int difference_in_day_of_year = a->tm_yday - b->tm_yday;
	int intervening_leap_days = (
		((ay >> 2) - (by >> 2))
		- (ay/100 - by/100)
		+ ((ay/100 >> 2) - (by/100 >> 2))
	);
	time_t difference_in_years = ay - by;
	time_t difference_in_days = (
		difference_in_years*365
		+ (intervening_leap_days + difference_in_day_of_year)
	);
	return
		(
			(
				24*difference_in_days
				+ (a->tm_hour - b->tm_hour)
			)*60 + (a->tm_min - b->tm_min)
		)*60 + (a->tm_sec - b->tm_sec);
}

/*
* Adjust time T by adding SECONDS.  SECONDS must be at most 24 hours' worth.
* Adjust only T's year, mon, mday, hour, min and sec members;
* plus adjust wday if it is defined.
*/
	void
adjzone(t, seconds)
	register struct tm *t;
	long seconds;
{
	/*
	* This code can be off by a second if SECONDS is not a multiple of 60,
	* if T is local time, and if a leap second happens during this minute.
	* But this bug has never occurred, and most likely will not ever occur.
	* Liberia, the last country for which SECONDS % 60 was nonzero,
	* switched to UTC in May 1972; the first leap second was in June 1972.
	*/
	int leap_second = t->tm_sec == 60;
	long sec = seconds + (t->tm_sec - leap_second);
	if (sec < 0) {
	    if ((t->tm_min -= (59-sec)/60) < 0) {
		if ((t->tm_hour -= (59-t->tm_min)/60) < 0) {
		    t->tm_hour += 24;
		    if (TM_DEFINED(t->tm_wday)  &&  --t->tm_wday < 0)
			t->tm_wday = 6;
		    if (--t->tm_mday <= 0) {
			if (--t->tm_mon < 0) {
			    --t->tm_year;
			    t->tm_mon = 11;
			}
			t->tm_mday = month_days(t);
		    }
		}
		t->tm_min += 24 * 60;
	    }
	    sec += 24L * 60 * 60;
	} else
	    if (60 <= (t->tm_min += sec/60))
		if (24 <= (t->tm_hour += t->tm_min/60)) {
		    t->tm_hour -= 24;
		    if (TM_DEFINED(t->tm_wday)  &&  ++t->tm_wday == 7)
			t->tm_wday = 0;
		    if (month_days(t) < ++t->tm_mday) {
			if (11 < ++t->tm_mon) {
			    ++t->tm_year;
			    t->tm_mon = 0;
			}
			t->tm_mday = 1;
		    }
		}
	t->tm_min %= 60;
	t->tm_sec = (int) (sec%60) + leap_second;
}

/*
* Convert TM to time_t, using localtime if LOCALZONE and gmtime otherwise.
* Use only TM's year, mon, mday, hour, min, and sec members.
* Ignore TM's old tm_yday and tm_wday, but fill in their correct values.
* Yield -1 on failure (e.g. a member out of range).
* Posix 1003.1-1990 doesn't allow leap seconds, but some implementations
* have them anyway, so allow them if localtime/gmtime does.
*/
	time_t
tm2time(tm, localzone)
	struct tm *tm;
	int localzone;
{
	/* Cache the most recent t,tm pairs; 1 for gmtime, 1 for localtime.  */
	static time_t t_cache[2];
	static struct tm tm_cache[2];

	time_t d, gt;
	struct tm const *gtm;
	/*
	* The maximum number of iterations should be enough to handle any
	* combinations of leap seconds, time zone rule changes, and solar time.
	* 4 is probably enough; we use a bigger number just to be safe.
	*/
	int remaining_tries = 8;

	/* Avoid subscript errors.  */
	if (12 <= (unsigned)tm->tm_mon)
	    return -1;

	tm->tm_yday = month_yday[tm->tm_mon] + tm->tm_mday
		-  (tm->tm_mon<2  ||  ! isleap(tm->tm_year + TM_YEAR_ORIGIN));

	/* Make a first guess.  */
	gt = t_cache[localzone];
	gtm = gt ? &tm_cache[localzone] : time2tm(gt,localzone);

	/* Repeatedly use the error from the guess to improve the guess.  */
	while ((d = difftm(tm, gtm)) != 0) {
		if (--remaining_tries == 0)
			return -1;
		gt += d;
		gtm = time2tm(gt,localzone);
	}
	t_cache[localzone] = gt;
	tm_cache[localzone] = *gtm;

	/*
	* Check that the guess actually matches;
	* overflow can cause difftm to yield 0 even on differing times,
	* or tm may have members out of range (e.g. bad leap seconds).
	*/
	if (   (tm->tm_year ^ gtm->tm_year)
	    |  (tm->tm_mon  ^ gtm->tm_mon)
	    |  (tm->tm_mday ^ gtm->tm_mday)
	    |  (tm->tm_hour ^ gtm->tm_hour)
	    |  (tm->tm_min  ^ gtm->tm_min)
	    |  (tm->tm_sec  ^ gtm->tm_sec))
		return -1;

	tm->tm_wday = gtm->tm_wday;
	return gt;
}

/*
* Check *PT and convert it to time_t.
* If it is incompletely specified, use DEFAULT_TIME to fill it out.
* Use localtime if PT->zone is the special value TM_LOCAL_ZONE.
* Yield -1 on failure.
* ISO 8601 day-of-year and week numbers are not yet supported.
*/
	static time_t
maketime(pt, default_time)
	struct partime const *pt;
	time_t default_time;
{
	int localzone, wday;
	struct tm tm;
	struct tm *tm0 = 0;
	time_t r;

	tm0 = 0; /* Keep gcc -Wall happy.  */
	localzone = pt->zone==TM_LOCAL_ZONE;

	tm = pt->tm;

	if (TM_DEFINED(pt->ymodulus) || !TM_DEFINED(tm.tm_year)) {
	    /* Get tm corresponding to current time.  */
	    tm0 = time2tm(default_time, localzone);
	    if (!localzone)
		adjzone(tm0, pt->zone);
	}

	if (TM_DEFINED(pt->ymodulus))
	    tm.tm_year +=
		(tm0->tm_year + TM_YEAR_ORIGIN)/pt->ymodulus * pt->ymodulus;
	else if (!TM_DEFINED(tm.tm_year)) {
	    /* Set default year, month, day from current time.  */
	    tm.tm_year = tm0->tm_year + TM_YEAR_ORIGIN;
	    if (!TM_DEFINED(tm.tm_mon)) {
		tm.tm_mon = tm0->tm_mon;
		if (!TM_DEFINED(tm.tm_mday))
		    tm.tm_mday = tm0->tm_mday;
	    }
	}

	/* Convert from partime year (Gregorian) to Posix year.  */
	tm.tm_year -= TM_YEAR_ORIGIN;

	/* Set remaining default fields to be their minimum values.  */
	if (!TM_DEFINED(tm.tm_mon)) tm.tm_mon = 0;
	if (!TM_DEFINED(tm.tm_mday)) tm.tm_mday = 1;
	if (!TM_DEFINED(tm.tm_hour)) tm.tm_hour = 0;
	if (!TM_DEFINED(tm.tm_min)) tm.tm_min = 0;
	if (!TM_DEFINED(tm.tm_sec)) tm.tm_sec = 0;

	if (!localzone)
	    adjzone(&tm, -pt->zone);
	wday = tm.tm_wday;

	/* Convert and fill in the rest of the tm.  */
	r = tm2time(&tm, localzone);

	/* Check weekday.  */
	if (r != -1  &&  TM_DEFINED(wday)  &&  wday != tm.tm_wday)
		return -1;

	return r;
}

/* Parse a free-format date in SOURCE, yielding a Unix format time.  */
	time_t
str2time(source, default_time, default_zone)
	char const *source;
	time_t default_time;
	long default_zone;
{
	struct partime pt;

	if (*partime(source, &pt))
	    return -1;
	if (pt.zone == TM_UNDEFINED_ZONE)
	    pt.zone = default_zone;
	return maketime(&pt, default_time);
}

#if TEST
#include <stdio.h>
	int
main(argc, argv) int argc; char **argv;
{
	time_t default_time = time((time_t *)0);
	long default_zone = argv[1] ? atol(argv[1]) : 0;
	char buf[1000];
	while (gets(buf)) {
		time_t t = str2time(buf, default_time, default_zone);
		printf("%s", asctime(gmtime(&t)));
	}
	return 0;
}
#endif
