#!/usr/bin/perl

# jd -- program to compute Julian day number from a Gregorian
#       calendar date and vice versa
#
# Leif.Harcke@jpl.nasa.gov
# March 1997

@days = ('Sun','Mon','Tue','Wed','Thu','Fri','Sat');
%months = ('Jan',1,'Feb',2,'Mar',3,'Apr',4,'May',5,'Jun',6,
	   'Jul',7,'Aug',8,'Sep',9,'Oct',10,'Nov',11,'Dec',12);
@months = ('Jan','Feb','Mar','Apr','May','Jun','Jul','Aug','Sep',
	   'Oct','Nov','Dec');

if (!((scalar(@ARGV) == 1) || (scalar(@ARGV) == 3))) {
    die "usage: jd JD | [-]YYYY MMM DD\n";
}

if (scalar(@ARGV) == 3) {
    $monthname = substr($ARGV[1],0,3);
    $monthname =~ tr/A-Z/a-z/;
    substr($monthname,0,1) =~ tr/a-z/A-Z/;

    $m = $months{$monthname} || die "Invalid month: $ARGV[1]\n";
    $y = $ARGV[0];
    $d = $ARGV[2];

    if ($m <= 2) {
	$y -= 1;
	$m += 12;
    }
    $a = int($y/100);
    $b = 2 - $a + int($a/4);

    $jd = int(365.25 * ($y + 4716)) + int(30.6001 * ($m + 1))
	+ $d + $b - 1524.5;

    $dow_m = (($jd + 1.5) % 7) + 1;
    print "Meeus:   JD$jd\n";

    $y = $ARGV[0];
    $m = $months{$monthname};
    $d = $ARGV[2];
    
    $jd = int((1461*($y+4800+int(($m-14)/12)))/4)
	+ int((367*($m-2-12*int(($m-14)/12)))/12)
	    -int((3*(int(($y+4900+int(($m-14)/12))/100)))/4)
		+ $d - 32075;

    $dow_f = $jd - 7*int(($jd+1)/7)+2;

    print "Fliegel: JD$jd\n";

    # Hatcher

    $Y = $ARGV[0];
    $M = $months{$monthname};
    $D = $ARGV[2];

    $J1 = 1721426;
    $y = 4716;
    $m = 3;
    $n = 12;
    $r = 4;
    $p = 1461;
    $q = 0;
    $v = 3;
    $u = 5;
    $s = 153;
    $t = 2;
    $w = 2;

    $Y_p = $Y + $y - int(($n + $m -1 -$M)/$n);

    $g = int(int(($Y_p + 184)/100) * 3/4) -38;
    $j = 1401 + $g;

    $M_p = ($M - $m) % $n;
    $D_p = $D - 1;
    $J = int(($p*$Y_p + $q)/$r) + int(($s*$M_p + $t)/$u) + $D_p - $j;

    print "Hatcher: JD$J\n";
    

    print "DOW Meeus:   $days[$dow_m-1]\n";
    print "DOW Fliegel: $days[$dow_f-1]\n";

} else {

    $jd = $ARGV[0];
    
    $z = int($jd + 0.5);
    $f = ($jd + 0.5) - $z;
    if ($z < 2299161) {
	$a = $z;
	$calendar = "Julian";
    } else {
	$alpha = int(($z - 1867216.25)/36524.25);
	$a = $z + 1 + $alpha - int($alpha/4);
	$calendar = "Gregorian";
    }
    $b = $a + 1524;
    $c = int(($b - 122.1)/365.25);
    $d = int(365.25*$c);
    $e = int(($b-$d)/30.6001);

    $d = $b - $d - int(30.6001*$e) + $f;
    if ($e < 14) {
	$m = $e -1;
    } else {
	$m = $e - 13;
    }
    if ($m > 2) {
	$y = $c - 4716;
    } else {
	$y = $c - 4715;
    }
    $sec = int(86400*$f);
    $sec_f = 86400*$f - $sec;
    $hour = int($sec/3600);
    $sec = $sec - 3600*$hour;
    $min = int($sec/60);
    $sec = int($sec - 60*$min);
    $time = sprintf("%02d:%02d:%02d",$hour,$min,$sec);
    print "Meeus:   $y $months[$m-1] $d $calendar\n";
    print "Meeus:   $time\n";

    $l = $jd + 68569;
    $n = int((4*$l)/146097);
    $l = $l - int((146097*$n + 3)/4);
    $i = int((4000*($l+1))/1461001);
    $l = $l - int((1461*$i)/4) + 31;
    $j = int((80*$l)/2447);
    $d = $l - int((2447*$j)/80);
    $l = int($j/11);
    $m = $j + 2 -12*$l;
    $y = 100*($n-49)+$i+$l;

    print "Fliegel: $y $months[$m-1] $d Gregorian\n";

    $J1 = 1721426;
    $y = 4716;
    $m = 3;
    $n = 12;
    $r = 4;
    $p = 1461;
    $q = 0;
    $v = 3;
    $u = 5;
    $s = 153;
    $t = 2;
    $w = 2;

    $J = $jd;

    $g = int(int(($J + 68569)/36524.5) * 3/4) - 38;
    $j = 1401 + $g;

    $J_p = $J + $j;
    $Y_p = int(($r*$J_p + $v)/$p);
    $T_p = int((($r*$J_p + $v) % $p)/$r);
    $M_p = int(($u*$T_p + $w)/$s);
    $D_p = int((($u*$T_p + $w) % $s)/$u);
    $D = $D_p + 1;
    $M = ($M_p + $m - 1) % $n + 1;
    $Y = $Y_p - $y + int(($n + $m - 1 - $M)/$n);

    print "Hatcher: $Y $months[$M-1] $D Gregorian\n";

    $j = $jd + 1402;
    $k = int(($j - 1)/1461);
    $l = $j - 1461 * $k;
    $n = int(($l-1)/365) - int($l/1461);
    $i = $l - 365*$n + 30;
    $j = int((80*$i)/2447);
    $d = $i - int((2447*$j)/80);
    $i = int($j/11);
    $m = $j + 2 -12*$i;
    $y = 4*$k + $n + $i - 4716;

    print "Fliegel: $y $months[$m-1] $d Julian\n";
    
}