/* Islamic calendar utility functions
 *
 * Copyright (C) 1999 Ali Abdin <aliabdin aucegypt 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 02111-1307, USA.
 */
#include <stdlib.h>

#include <gnome.h>
#include <time.h>


static int
last_day_of_gregorian_month (int month, int year) {
	int monthdays[12] = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
	/* Last day of gregorian month during year */
	if ((month == 2) && ((year % 4) == 0) && ((year % 400) != 100) &&
	    ((year % 400) != 200) && ((year % 400)  != 300))
		return 29;
	else
		return monthdays[month-1];
}	

#if 1 
glong
absolute_from_gregorian (int month, int day, int year) {
	/* WARNING: This uses 1/1/1 == '1' as the absolute date */
	/* Absolute date given gregorian */
	long absolutedays, monthdays;
	int m;
        long dayyears;
	div_t tmpdiv;

	absolutedays = day; /* Days so far this month */
	monthdays = 0;
	for (m = 1; m < month; m++)
		monthdays =
		       monthdays + last_day_of_gregorian_month (m, year);
		/* Days in prior months /this/ year */
	dayyears = 365.0 * (year-1); /* days in prior years */
/*	g_print ("dayyears is: %d\n", dayyears); */
	tmpdiv = div (year-1, 4);
	dayyears = dayyears + tmpdiv.quot;
/*	g_print ("dayyears is: %d\n", dayyears); */
       		/* add julian leap days in prior years */
	tmpdiv = div(year-1, 100);
	dayyears = dayyears - (tmpdiv.quot); /* minus prior century
						       years */
	tmpdiv = div(year-1, 400);
	dayyears = dayyears + (tmpdiv.quot); /* Add back the years
						       divisible by 400 */
/*	g_print ("days is: %d\ndayyears is: %d\n",absolutedays,dayyears); */
	return (absolutedays + dayyears + monthdays);
}
#endif


static gboolean
islamic_leap_year (gint year) {
	/* Given Islamic year return TRUE if it is a leap year */
	if ((((year * 11) + 14) % 30) < 11)
		return TRUE;
	else
		return FALSE;
}

static gint
last_day_of_islamic_month (gint month, gint year) {
	/* Given the islamic month/year it returns the size of the month */
	
	if (((month % 2) == 1) || ((month == 12) && islamic_leap_year (year)))
		return 30; /* Odd months and 12th month of a leap year are
			      both 30 days */
	else
		return 29;
}

static glong
absolute_from_islamic (gint month, gint day, gint year) {
	glong absolutedays;
	div_t tmpdiv;

	/* Add days so far this month + days so far this year excluding leap
	 * years */
	absolutedays = day + (29 * (month-1));
	tmpdiv = div (month,2);
	absolutedays = absolutedays + tmpdiv.quot; /* Number of days this year
						    */
	absolutedays = absolutedays + ((year-1) * 354); /* non-leap days in
							   prior years */
	tmpdiv = div(((11 * year) + 3), 30);
	absolutedays = absolutedays + 
		             tmpdiv.quot; /* leap days in prior years */
//	g_print ("absolutedays is %d\n",absolutedays);
	/* you have to subtract an extra '1' since you pass over '0' */
		absolutedays = absolutedays + (-492148) - 1;
	/* The above is the 'magic' number since '0' is the epoch (1/1/1970)
	 * and 7/19/622 is the first day of the Islamic calendar (-492148 or
	 * 492,148 days before the epoch)
	 */
	return absolutedays;
}

static void
islamic_from_absolute (glong absolute, gint *month, gint *day, gint *year) {
	
	if (absolute < -492148) {
		/* This is before Islam */
		*month = 0;
		*day = 0;
		*year = 0;
	}
	else {
		gint y,m;
		gint tmpsum = 0;
		div_t tmpdiv;
		glong tmplong; /* We need a temp 'long' value for the day */
		
		/* Approximate the islamic year from the absolute date */
		tmpdiv = div ( absolute - (-492148), 355);
		*year = tmpdiv.quot;
		for (y = tmpdiv.quot;
		     absolute >= absolute_from_islamic (1, 1, y+1);
		     y++) {
			tmpsum = tmpsum++;
		}	/* Forward search for the exact islamic year */
		*year = *year + tmpsum;
		tmpsum = 0;
		for (m = 1;
	  	     absolute > 
		     	absolute_from_islamic (m, 
				last_day_of_islamic_month (m, *year), *year);
		     m++) {
			tmpsum = tmpsum++;
		}
		*month = 1 + tmpsum;
		/* Calculate the days by subtraction */
		tmplong = absolute - (1 - (absolute_from_islamic (*month, 1, *year)));
		*day = absolute + (1 - (absolute_from_islamic (*month, 1, *year)));
	}
}


time_t
time_from_islamic_date (int imonth, int iday, int iyear)
{
	struct tm tm;
	glong totaldays;
	gint addyears, month, day;
	gint y;

	memset (&tm, 0, sizeof (tm));
	
	totaldays = absolute_from_islamic (imonth, iday, iyear);
//	if (totaldays > 0) {
		

		addyears = (gint) totaldays / 366;
		g_print ("addyears is: %d\n",addyears);
		for (y = addyears; totaldays >= absolute_from_gregorian (1,1, 1970 + y) ;y++);

		addyears = y; /* Number of years to add to 1970 */

		for (month = 1;
			totaldays > (absolute_from_gregorian (month,
         	       	     last_day_of_gregorian_month (month, addyears + 1970), addyears + 1970)) -
			absolute_from_gregorian (1,1,1970);
					month++);
		g_print ("totaldays = %d - %d - %d;\n",totaldays, absolute_from_gregorian (month,1, 1970 + addyears), absolute_from_gregorian (1,1,1970));

		day = totaldays + (1 - (absolute_from_gregorian (month, 1, 1970 + addyears) - 
					absolute_from_gregorian (1,2,1970)));

		g_print ("addyears is %d\nmonth is %d\nday is %d\n",addyears, month, day);

		tm.tm_year = 70 + addyears;
		tm.tm_mon = month-1;
		tm.tm_mday = day;
//	}

	return mktime (&tm);
}

void
islamic_from_time (time_t time, gint *month, gint *day, gint *year) {
	glong absolute;

	absolute = (gint) time / (60*60*24); /* Turn from seconds into days */

	islamic_from_absolute (absolute, month, day, year);
}


int
main (int argc, char **argv) {
	gint month,day,year,x;
	gboolean failed = FALSE;
	time_t temptime;

	g_print ("1/1/1970 is %d and it is a %d\n", absolute_from_gregorian (1,1,1970), absolute_from_gregorian (1,1,1970) % 7);
	g_print ("07/19/622 is %d it is a %d\n", absolute_from_gregorian (7,19,622), absolute_from_gregorian (7,19,622) % 7);
	g_print ("4/6/2000 is %d\n", absolute_from_gregorian (4,6,2000));
	g_print ("4/13/2000 is %d\n", absolute_from_gregorian (4,13,2000));
	g_print ("Islamic date 1/1/1 is %d in absolute time_t\n", absolute_from_islamic (1,1,1));
	g_print ("Islamic date 1/2/1 is %d in absolute time_t\n", absolute_from_islamic (1,2,1));
	g_print ("Islamic date 1/1/1421 is %d in absolute time_t\n", absolute_from_islamic (1,1,1421));
	islamic_from_absolute (-492148,&month,&day,&year);
	g_print ("Given absolute -492148 the islam stuff is: %d %d %d\n",month,day,year);
	islamic_from_absolute(11053,&month,&day,&year);
	g_print ("Given absolute 11053 the islam stuff is: %d %d %d\n",month,day,year);
	islamic_from_absolute (-492147,&month,&day,&year);
        g_print ("Given absolute -492147 the islam stuff is: %d %d %d\n",month,day,year);
	islamic_from_absolute (11060,&month,&day,&year);
	g_print ("Given absolute 11060 the islam stuff is: %d %d %d\n",month,day,year);	
	islamic_from_absolute (-492149,&month,&day,&year);
        g_print ("Given absolute -492149 the islam stuff is: %d %d %d\n",month,day,year);

	temptime = time_from_islamic_date (1,1,1421);
	g_print ("time_from_islamic_date(1,1,1421) is %d\n", temptime);
	islamic_from_time (temptime, &month,&day, &year);
	g_print ("time_t %d in islamic is: %d %d %d\n",temptime,month,day,year);

	temptime = time_from_islamic_date (1,8,1421);
	g_print ("time_from_islamic_date(1,8,1421) is %d\n", temptime);
	islamic_from_time (temptime, &month,&day, &year);
	g_print ("time_t %d in islamic is: %d %d %d\n",temptime,month,day,year);
	islamic_from_time (time (NULL), &month,&day,&year);
	g_print ("time_t %d (RIGHT NOW!) in islamic is: %d %d %d\n",time(NULL),month,day,year);

		
/*	g_print ("Running Islamic Stress Test: ");
	for (x = -492148; x <= 492148; x++) {
		islamic_from_absolute(x, &month, &day, &year);
		if ((absolute_from_islamic (month,day,year)) != x)
			failed = TRUE;
	}
	if (failed)
		g_print ("FAILED");
	else
		g_print ("PASSED"); */
	return 0;
}