/* mjd.c - Modified Julian Day number conversion utility
 *
 * Usage:
 *	mjd [-q] [-j|-g yyyy-mm-dd] [-a|-b] [-t hh:mm[:ss]] [-d|m ddd.ff]
 *
 * Copyright (C) 1996 R.M.O'Leary <robin@acm.org>
 *
 * 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.
 */

#include <stdio.h>
#include <getopt.h>


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

long julian_calendar_to_jd(int y, int m, int d)
{
	if(m<3) { y--; m+=12; }
	y+=4800;
	m-=3;
	return (y*365) +(y/4)
              +(30*m) +(m*3+2)/5
              +d
	      -32083
	;
}

long gregorian_calendar_to_jd(int y, int m, int d)
{
	if(m<3) { y--; m+=12; }
	y+=8000;
	/*return (y*365) +(y/4) -(y/100) +(y/400) -(y/4000)*/
	return (y*365) +(y/4) -(y/100) +(y/400)
              +(m*153+3)/5-92
              +d-1
	      -1200820
	;
}

void jd_to_calendar(long jd, long (*calendar_to_jd)(int y, int m, int d), int *yp, int *mp, int *dp)
{
        int y,m,d;
        for(y=jd/366-4715; (*calendar_to_jd)(y+1,1,1)<=jd; y++);
        for(m=1; (*calendar_to_jd)(y,m+1,1)<=jd; m++);
        for(d=1; (*calendar_to_jd)(y,m,d+1)<=jd; d++);
        *yp=y; *mp=m; *dp=d;
}


static void print_date(int y, int m, int d, int quiet, int qualify_ad_bc, const char *calendar)
{
    if(quiet)
	printf("%04d %02d %02d ",y,m,d);
    else
    {
	if(qualify_ad_bc)
	    printf("%s %04d", (y<1)?"BC":"AD", (y<1)?1-y:y);
	else
	    printf("%04d", y);
	printf("-%02d-%02d %s",m,d, calendar);
    }
}


int main(int argc, char *argv[])
{
	static struct option long_options[] =
	{
		{"ad",			0, 0, 'a'},
		{"bc",			0, 0, 'b'},
		{"gregorian_calendar",	1, 0, 'g'},
		{"julian_calendar",	1, 0, 'j'},
		{"julian_day",		1, 0, 'd'},
		{"modified_julian_day", 1, 0, 'm'},
		{"time",		1, 0, 't'},
		{"quiet",		0, 0, 'q'},
		{"help",		0, 0, 'h'},
		{0, 0, 0, 0}
	};
	int c;
	int is_bc=0;
	int is_julian_day=0;
	int is_gregorian_calendar=0;
	int is_julian_calendar=0;
	int is_modified_julian_day=0;
	int quiet=0;
	char *date=(char*)0;
	char *time=(char*)0;
	int bad=0;
	int help=0;
	long jd=0;
	double time_offset=0.0; /* Noon */

	while( (c=getopt_long(argc,argv,"abg:j:d:m:qt:h",long_options, NULL)) != -1 )
	{
	    switch (c)
	    {
		case 'a': is_bc=0; break;
		case 'b': is_bc=1; break;
		case 'd': is_julian_day=1; date=optarg; break;
		case 'g': is_gregorian_calendar=1; date=optarg; break;
		case 'j': is_julian_calendar=1; date=optarg; break;
		case 'm': is_modified_julian_day=1; date=optarg; break;
		case 't': time=optarg; break;
		case 'q': quiet=1; break;
		case 'h': help=1; break;

		case '?': bad++; break;

		default:
		    fprintf(stderr,"%s: BUG: option %c not handled!\n",
			argv[0],c);
	    }
	}

	if(argc!=optind)
	{
		fprintf(stderr,"%s: too many arguments (``%s'')\n",
		    argv[0],argv[optind+2]);
		bad++;
	}

	if(date)
	{
	    if(is_gregorian_calendar || is_julian_calendar)
	    {
		int y,m,d;
		if(sscanf(date,"%d-%d-%d",&y,&m,&d)!=3 )
		{
		    fprintf(stderr,"%s: ``%s'' is not a valid date.\n",
			argv[0],date);
		    bad++;
		}
		if(is_bc)
		    y=1-y;
		if(is_gregorian_calendar)
		    jd=gregorian_calendar_to_jd(y,m,d);
		else
		    jd=julian_calendar_to_jd(y,m,d);
		time_offset=-0.5; /* start from midnight */
	    }
	    else /* is_julian_day or is_modified_julian_day */
	    {
		double fjd;
		if(sscanf(date,"%lf",&fjd)!=1 )
		{
		    fprintf(stderr,"%s: ``%s'' is not a valid day number.\n",
			argv[0],date);
		    bad++;
		}
		if(is_modified_julian_day)
		    fjd+=2400000.5;
		jd=fjd;	/* fractional part truncated because jd is an int */
		time_offset=fjd-jd;
	    }
	}

	if(time)
	{
	    int h,m,s=0;
	    if(sscanf(time,"%d:%d:%d",&h,&m,&s)<2 )
	    {
		fprintf(stderr,"%s: ``%s'' is not a valid time hh:mm[:ss]\n",
		    argv[0],time);
		bad++;
	    }

	    /* Calendar dates and Modified Julian Day numbers start at
	     * midnight, as do conventional clock times, so no adjustment
	     * is needed.
	     * However, a Julian Day begins at noon (12:00) and continues
	     * through midnight (23:59, 00:00) up to the following noon
	     * (11:59).  So if we are given hours 00 to 11, they actually
	     * mean hours 12 to 23 after noon; but given 12 to 23 refers
	     * to hours 0 to 11 after noon.
	     */
	    if(is_julian_day)
	    {
		if(h<12) h+=12; else h-=12;
	    }
	    time_offset+=(double)((h*60+m)*60+s)/(24*60*60);
	}

	/* Paranoia.  I don't think this happens, but just in case... */
	if(time_offset<=-0.5)
	{
	    jd--;
	    time_offset+=1.0;
	}
	if(time_offset>=0.5)
	{
	    jd++;
	    time_offset-=1.0;
	}
	if(help)
	    printf(
"Modified Julian Day number conversion utility\n"
"Copyright (C) 1996 R.M.O'Leary <robin@acm.org>\n"
"\n"
"This program is free software; you can redistribute it and/or modify\n"
"it under the terms of the GNU General Public License as published by\n"
"the Free Software Foundation; either version 2 of the License, or\n"
"(at your option) any later version.\n"
"\n");

	if(bad || help)
	{
	    fprintf(help?stdout:stderr,
		"Usage: %s [-q] [-j|-g yyyy-mm-dd] [-a|-b] [-t hh:mm[:ss]] [-d|m ddd.ff]\n",
		argv[0]);
	    if(help)
		printf(
"    -h --help   display this message\n"
"    -q --quiet  makes output more computer-friendly (default off)\n"
"Converting from Julian or Gregorian calendars:\n"
"    -j --julian yyyy-mm-dd\n"
"                convert date specified in the Julian calendar\n"
"    -g --gregorian yyyy-mm-dd\n"
"                convert date specified in the Gregorian calendar\n"
"    -a --ad     indicates that year is AD (default)\n"
"    -b --bc     indicates that year is BC\n"
"    -t --time hh:mm[:ss]\n"
"                time of day (default 12:00 Noon)\n"
"Converting from Julian or Modified Julian Day numbers:\n"
"    -d --julian_day ddd.dd\n"
"                convert date and time specified as a Julian Day number\n"
"    -m --modified_julian_day ddd.dd\n"
"                convert date and time specified as a Modified Julian Day number\n"
);
	    else
		fprintf(stderr,
		    "       %s -h    for more information\n",
		    argv[0]);
	    return bad;
	}

	{
	    int y,m,d;
	    int hour,minute,second;
	    int s;

	    printf(
		quiet?"%.10g %.10g "
		     :"JD %.10g, MJD %.10g,\n",
		jd+time_offset,
		jd+time_offset-2400000.5);

	    s=(time_offset+0.5)*24*60*60;
	    second =  s%60;
	    minute = (s/60)%60;
	    hour   =  s/60/60;
	    printf(
		quiet?"%s %02d %02d %02d "
		     :"%s, %02d:%02d:%02d,\n",
		day_name[((long)jd%7+7)%7],
		hour,minute,second);
	    jd_to_calendar(jd,gregorian_calendar_to_jd,&y,&m,&d);
	    print_date(y, m, d, quiet, is_bc, "Gregorian calendar");
	    if(!quiet)printf(",\n");

	    jd_to_calendar(jd,julian_calendar_to_jd,&y,&m,&d);
	    print_date(y, m, d, quiet, is_bc, "Julian calendar");
	    if(!quiet)printf(".\n");
	}

	return 0;
}