/*
   $Id: greg.c,v 3.0.1.3 1994/04/25 15:25:33 sadinoff Exp $
   Hebcal - A Jewish Calendar Generator
   Copyright (C) 1994  Danny Sadinoff
     
     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., 675 Mass Ave, Cambridge, MA 02139, USA.

     Danny Sadinoff can be reached at 
     1 Cove La.
     Great Neck, NY
              11024
 
     sadinoff@panix.com
*/


#include <stdio.h>
#include "mytime.h"
#include "mystring.h"
#include "error.h"
#include "greg.h"

/* greg.c gregorian calendar module for hebrew calendar program
   By Danny Sadinoff
   (C) 1992

*/

char * eMonths[] = { 
  "UNUSED",
  "January","February","March","April","May","June","July",
  "August","September","October","November","December"
  };
		      
int MonthLengths[][13] ={ 
  {0,31,28,31,30,31,30,31,31,30,31,30,31},
  {0,31,29,31,30,31,30,31,31,30,31,30,31}
};

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


/*
 *Return the day number within the year of the date DATE.
 *For example, dayOfYear({1,1,1987}) returns the value 1
 *while dayOfYear({12,31,1980}) returns 366.
 */


int dayOfYear(d)
date_t d;
{
  int dOY = d.dd + 31 * (d.mm - 1);
  if (d.mm > FEB)
    {
      dOY -= (4 * d.mm + 23)/10;
      if (LEAP(d.yy))
	dOY++;
    }
  return dOY;
}


/*
 * The number of days elapsed between the Gregorian date 12/31/1 BC and DATE.
 * The Gregorian date Sunday, December 31, 1 BC is imaginary.
 */
long int greg2abs (d)		/* "absolute date" */
date_t d;
{
  return (  (long) dayOfYear(d)	/* days this year */
	  + 365L * (long)(d.yy - 1)	/* + days in prior years */
	  + (long)((d.yy - 1) / 4	/* + Julian Leap years */
	  - (d.yy - 1) / 100        /* - century years */
	  + (d.yy - 1) / 400));     /* + Gregorian leap years*/
}

/*
 * See the footnote on page 384 of ``Calendrical Calculations, Part II:
 * Three Historical Calendars'' by E. M. Reingold,  N. Dershowitz, and S. M.
 * Clamen, Software--Practice and Experience, Volume 23, Number 4
 * (April, 1993), pages 383-404 for an explanation.
 */
date_t abs2greg (theDate)
     long theDate;
{
  int  day, year, month, mlen;
  date_t d;
  long int d0,n400,d1,n100,d2,n4,d3,n1;

  d0 = theDate - 1L;
  n400 = d0 / 146097L;
  d1 = d0 % 146097L;
  n100 = d1 / 36524L;
  d2 = d1 % 36524L;
  n4 = d2 / 1461L;
  d3 = d2 % 1461L;
  n1 = d3 / 365L;
  
  day = (int)((d3 % 365L) + 1L);
  year = (int) (400L * n400 + 100L * n100 + 4L * n4 + n1);
  
  if (4L == n100 || 4L == n1) 
    {
      d.mm = 12;
      d.dd = 31;
      d.yy = year;
      return d;
    }
  else 
    {
      year++;
      month = 1;
      while ((mlen = MonthLengths[LEAP(year)][month]) < day) 
	{
	  day -= mlen;
	  month++;
	}
      d.yy = year;
      d.mm = month;
      d.dd = day;
      return d;
    }
}

void incDate (dt,n) /* decrements dt by n days */
date_t *dt;
long int n;
{
  *dt = abs2greg(greg2abs(*dt) + n);
}


int dayOfWeek(d1)  /* sunday = 0 */
date_t d1;
{
  return (int) (greg2abs(d1) % 7L) ;
}

void setDate (d) 
date_t *d;
{
/*
     asctime() converts a time value contained in a tm  structure
     to a 26-character string of the form:
          Sun Sep 16 01:03:52 1973\n\0
     Each field  has  a  constant  width.   asctime()  returns  a
     pointer to the string.
*/

  time_t time();
  char *ctime PROTO((const time_t *));  /* AMG added "const" */

  time_t secs = time(NULL); 
  char *timestr = ctime(&secs);
  
/* portability has driven me to truly shameful code.  
   please forgive this.
*/
  sscanf(timestr + 20,"%d",&d->yy);
  d->mm = lookup_string(timestr + 4,eMonths,13,3);
  sscanf (timestr + 8,"%d",&d->dd);
}


long day_on_or_before (day_of_week, date)
     int day_of_week;
     long date;
/* Returns the absolute date of the DAYNAME on or before absolute DATE.
 * DAYNAME=0 means Sunday, DAYNAME=1 means Monday, and so on.


 * Note: Applying this function to d+6 gives us the DAYNAME on or after an
 * absolute day d.  Similarly, applying it to d+3 gives the DAYNAME nearest to
 * absolute date d, applying it to d-1 gives the DAYNAME previous to absolute
 * date d, and applying it to d+7 gives the DAYNAME following absolute date d.

 */
{
  return date - ((date - (long)day_of_week) % 7L);
}



/* (defun calendar-nth-named-day (n dayname month year &optional day)
  "The date of Nth DAYNAME in MONTH, YEAR before/after optional DAY.
  A DAYNAME of 0 means Sunday, 1 means Monday, and so on.  If N<0,
  return the Nth DAYNAME before MONTH DAY, YEAR (inclusive).
  If N>0, return the Nth DAYNAME after MONTH DAY, YEAR (inclusive).

  If DAY is omitted, it defaults to 1 if N>0, and MONTH's last day otherwise.
  (calendar-gregorian-from-absolute
   (if (> n 0)
       (+ (* 7 (1- n))
	  (calendar-dayname-on-or-before
	   dayname
	   (+ 6 (calendar-absolute-from-gregorian
		 (list month (or day 1) year)))))
     (+ (* 7 (1+ n))
	(calendar-dayname-on-or-before
	 dayname
	 (calendar-absolute-from-gregorian
	  (list month
                (or day (calendar-last-day-of-month month year))
                year)))))))
*/