/*
 * Copyright (C) 1996-2000 Michael R. Elkins <me@cs.hmc.edu>
 * 
 *     This program 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 of the License, or
 *     (at your option) any later version.
 * 
 *     This program 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 this program; if not, write to the Free Software
 *     Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111, USA.
 */ 

#include "mutt.h"
#include <string.h>

/* From globals.h */
const char *Weekdays[] = { "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat" };
const char *Months[] = { "Jan", "Feb", "Mar", "Apr", "May",
  "Jun", "Jul","Aug", "Sep", "Oct", "Nov", "Dec", "ERR" };


/* returns the seconds east of UTC given `g' and its corresponding gmtime()
   representation */
static time_t compute_tz (time_t g, struct tm *utc)
{
  struct tm *lt = localtime (&g);
  time_t t;
  int yday;

  t = (((lt->tm_hour - utc->tm_hour) * 60) + (lt->tm_min - utc->tm_min)) * 60;

  if ((yday = (lt->tm_yday - utc->tm_yday)))
  {
    /* This code is optimized to negative timezones (West of Greenwich) */
    if (yday == -1 ||	/* UTC passed midnight before localtime */
	yday > 1)	/* UTC passed new year before localtime */
      t -= 24 * 60 * 60;
    else
      t += 24 * 60 * 60;
  }

  return t;
}

/* Returns the local timezone in seconds east of UTC for the time t,
 * or for the current time if t is zero.
 */
time_t mutt_local_tz (time_t t)
{
  struct tm *ptm;
  struct tm utc;

  if (!t)
    t = time (NULL);
  ptm = gmtime (&t);
  /* need to make a copy because gmtime/localtime return a pointer to
     static memory (grr!) */
  memcpy (&utc, ptm, sizeof (utc));
  return (compute_tz (t, &utc));
}

/* converts struct tm to time_t, but does not take the local timezone into
   account unless ``local'' is nonzero */
time_t mutt_mktime (struct tm *t, int local)
{
  time_t g;

  static int AccumDaysPerMonth[12] = {
    0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334
  };

  /* Compute the number of days since January 1 in the same year */
  g = AccumDaysPerMonth [t->tm_mon % 12];

  /* The leap years are 1972 and every 4. year until 2096,
   * but this algoritm will fail after year 2099 */
  g += t->tm_mday;
  if ((t->tm_year % 4) || t->tm_mon < 2)
    g--;
  t->tm_yday = g;

  /* Compute the number of days since January 1, 1970 */
  g += (t->tm_year - 70) * 365;
  g += (t->tm_year - 69) / 4;

  /* Compute the number of hours */
  g *= 24;
  g += t->tm_hour;

  /* Compute the number of minutes */
  g *= 60;
  g += t->tm_min;

  /* Compute the number of seconds */
  g *= 60;
  g += t->tm_sec;

  if (local)
    g -= compute_tz (g, t);

  return (g);
}

void mutt_normalize_time (struct tm *tm)
{
  static char DaysPerMonth[12] = {
    31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31
  };

  while (tm->tm_sec < 0)
  {
    tm->tm_sec += 60;
    tm->tm_min--;
  }
  while (tm->tm_min < 0)
  {
    tm->tm_min += 60;
    tm->tm_hour--;
  }
  while (tm->tm_hour < 0)
  {
    tm->tm_hour += 24;
    tm->tm_mday--;
  }
  while (tm->tm_mon < 0)
  {
    tm->tm_mon += 12;
    tm->tm_year--;
  }
  while (tm->tm_mday < 0)
  {
    if (tm->tm_mon)
      tm->tm_mon--;
    else
    {
      tm->tm_mon = 11;
      tm->tm_year--;
    }
    tm->tm_mday += DaysPerMonth[tm->tm_mon];
  }
}
