// Phase - phase of the moon calculations
//
// Adapted from "moontool.c" by John Walker, Release 2.0.
//
// Copyright (C)1996,1998 by Jef Poskanzer <jef@acme.com>.  All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions
// are met:
// 1. Redistributions of source code must retain the above copyright
//    notice, this list of conditions and the following disclaimer.
// 2. Redistributions in binary form must reproduce the above copyright
//    notice, this list of conditions and the following disclaimer in the
//    documentation and/or other materials provided with the distribution.
//
// THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
// ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
// ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
// FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
// OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
// HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
// LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
// OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
// SUCH DAMAGE.
//
// Visit the ACME Labs Java page for up-to-date versions of this and other
// fine Java utilities: http://www.acme.com/java/

package Acme;

import java.util.*;

/// Phase - phase of the moon calculations
// <P>
// Adapted from "moontool.c" by John Walker, Release 2.0.
// <P>
// <A HREF="/resources/classes/Acme/Phase.java">Fetch the software.</A><BR>
// <A HREF="/resources/classes/Acme.tar.gz">Fetch the entire Acme package.</A>

public class Phase
    {

    // Astronomical constants.

    // 1980 January 0.0
    private static final double epoch = 2444238.5D;

    // Constants defining the Sun's apparent orbit.

    // ecliptic longitude of the Sun at epoch 1980.0
    private static final double elonge = 278.833540D;

    // ecliptic longitude of the Sun at perigee
    private static final double elongp = 282.596403D;

    // eccentricity of Earth's orbit
    private static final double eccent = 0.016718D;

    // semi-major axis of Earth's orbit, km
    private static final double sunsmax = 1.495985e8D;

    // sun's angular size, degrees, at semi-major axis distance
    private static final double sunangsiz = 0.533128D;

    // Elements of the Moon's orbit, epoch 1980.0.

    // moon's mean lonigitude at the epoch
    private static final double mmlong = 64.975464D;

    // mean longitude of the perigee at the epoch
    private static final double mmlongp = 349.383063D;

    // mean longitude of the node at the epoch
    private static final double mlnode = 151.950429D;

    // inclination of the Moon's orbit
    private static final double minc = 5.145396D;

    // eccentricity of the Moon's orbit
    private static final double mecc = 0.054900D;

    // moon's angular size at distance a from Earth
    private static final double mangsiz = 0.5181D;

    // semi-major axis of Moon's orbit in km
    private static final double msmax = 384401.0D;

    // parallax at distance a from Earth
    private static final double mparallax = 0.9507D;

    // synodic month (new Moon to new Moon)
    private static final double synmonth = 29.53058868D;

    // base date for E. W. Brown's numbered series of lunations (1923 Jan 16)
    private static final double lunatbase = 2423436.0D;

    // Properties of the Earth.

    // radius of Earth in kilometres
    private static final double earthrad = 6378.16D;

    // Mathematical constants.
    private static final double EPSILON = 1E-6D;

    // Handy mathematical functions.

    // Fix angle.
    private static double fixangle( double a )
	{
	double b = a - 360.0 * Math.floor( a / 360.0D );
	// Can't use Math.IEEEremainder here because remainder differs
	// from modulus for negative numbers.
	return b;
	}

    // Degrees to radians.
    private static double torad( double d )
	{
	return d * Math.PI / 180.0D;
	}

    // Radians to degrees.
    private static double todeg( double r )
	{
	return r * 180.0D / Math.PI;
	}

    // Sin from degrees.
    private static double dsin( double d )
	{
	return Math.sin( torad( d ) );
	}

    // Cos from degrees.
    private static double dcos( double d )
	{
	return Math.cos( torad( d ) );
	}

    // jdate - convert internal GMT date to Julian day.
    private static long jdate( Date t )
	{
	long c, m, y;

	Calendar cal = new GregorianCalendar();
	cal.setTime( t );
	y = cal.get( Calendar.YEAR ) + 1900;
	m = cal.get( Calendar.MONTH ) + 1;
	if ( m > 2 )
	    m = m - 3;
	else
	    {
	    m = m + 9;
	    --y;
	    }
	c = y / 100L;		// compute century
	y -= 100L * c;
	return cal.get( Calendar.DATE ) +
	  ( c * 146097L ) / 4 + ( y * 1461L ) / 4 +
	  ( m * 153L + 2 ) / 5 + 1721119L;
	}

    /// Convert internal date and time to astronomical Julian
    // time (i.e. Julian date plus day fraction, expressed as
    // a double).
    public static double jtime( Date t )
	{
	int c;

	Calendar cal = new GregorianCalendar();
	cal.setTime( t );
	c = - cal.get( Calendar.ZONE_OFFSET );	// !!! should this be negative?
	return ( jdate( t ) - 0.5 ) + 
	    ( cal.get( Calendar.SECOND ) + 60 * ( cal.get( Calendar.MINUTE ) + c + 60 * cal.get( Calendar.HOUR_OF_DAY ) ) ) / 86400.0;
	}

    // jyear - convert Julian date to year, month, day, which are
    //     returned via integer pointers to integers
    private static void jyear( double td, RefInt yy, RefInt mm, RefInt dd )
	{
	double j, d, y, m;

	td += 0.5;	// astronomical to civil
	j = Math.floor(td);
	j = j - 1721119.0;
	y = Math.floor(((4 * j) - 1) / 146097.0);
	j = (j * 4.0) - (1.0 + (146097.0 * y));
	d = Math.floor(j / 4.0);
	j = Math.floor(((4.0 * d) + 3.0) / 1461.0);
	d = ((4.0 * d) + 3.0) - (1461.0 * j);
	d = Math.floor((d + 4.0) / 4.0);
	m = Math.floor(((5.0 * d) - 3) / 153.0);
	d = (5.0 * d) - (3.0 + (153.0 * m));
	d = Math.floor((d + 5.0) / 5.0);
	y = (100.0 * y) + j;
	if (m < 10.0)
	    m = m + 3;
	else
	    {
	    m = m - 9;
	    y = y + 1;
	    }
	yy.val = (int) y;
	mm.val = (int) m;
	dd.val = (int) d;
	}

    // meanphase - calculates mean phase of the Moon for a given base date
    //     and desired phase:
    //         0.0   New Moon
    //         0.25  First quarter
    //         0.5   Full moon
    //         0.75  Last quarter
    // Beware!!!  This routine returns meaningless results for any other
    // phase arguments.  Don't attempt to generalise it without understanding
    // that the motion of the moon is far more complicated that this
    // calculation reveals.
    private static double meanphase( double sdate, double phase, RefDouble usek )
	{
	RefInt yy = new RefInt();
	RefInt mm = new RefInt();
	RefInt dd = new RefInt();
	double k, t, t2, t3, nt1;

	jyear( sdate, yy, mm, dd );

	k = (yy.val + ((mm.val - 1) * (1.0 / 12.0)) - 1900) * 12.3685;

	// Time in Julian centuries from 1900 January 0.5.
	t = (sdate - 2415020.0) / 36525;
	t2 = t * t;		   // square for frequent use
	t3 = t2 * t;		   // cube for frequent use

	usek.val = k = Math.floor(k) + phase;
	nt1 = 2415020.75933 + synmonth * k
	      + 0.0001178 * t2
	      - 0.000000155 * t3
	      + 0.00033 * dsin(166.56 + 132.87 * t - 0.009173 * t2);

	return nt1;
	}

    // truephase - given a K value used to determine the mean phase of the
    //     new moon, and a phase selector (0.0, 0.25, 0.5, 0.75),
    //     obtain the true, corrected phase time
    private static double truephase( double k, double phase )
	{
	double t, t2, t3, pt, m, mprime, f;
	boolean apcor = false;

	k += phase;		   /* add phase to new moon time */
	t = k / 1236.85;	   /* time in Julian centuries from
				        1900 January 0.5 */
	t2 = t * t;		   /* square for frequent use */
	t3 = t2 * t;		   /* cube for frequent use */
	pt = 2415020.75933	   /* mean time of phase */
	     + synmonth * k
	     + 0.0001178 * t2
	     - 0.000000155 * t3
	     + 0.00033 * dsin(166.56 + 132.87 * t - 0.009173 * t2);

        m = 359.2242               /* Sun's mean anomaly */
	    + 29.10535608 * k
	    - 0.0000333 * t2
	    - 0.00000347 * t3;
        mprime = 306.0253          /* Moon's mean anomaly */
	    + 385.81691806 * k
	    + 0.0107306 * t2
	    + 0.00001236 * t3;
        f = 21.2964                /* Moon's argument of latitude */
	    + 390.67050646 * k
	    - 0.0016528 * t2
	    - 0.00000239 * t3;
	if ((phase < 0.01) || (Math.abs(phase - 0.5) < 0.01))
	    {
	    /* Corrections for New and Full Moon. */
	    pt +=     (0.1734 - 0.000393 * t) * dsin(m)
		     + 0.0021 * dsin(2 * m)
		     - 0.4068 * dsin(mprime)
		     + 0.0161 * dsin(2 * mprime)
		     - 0.0004 * dsin(3 * mprime)
		     + 0.0104 * dsin(2 * f)
		     - 0.0051 * dsin(m + mprime)
		     - 0.0074 * dsin(m - mprime)
		     + 0.0004 * dsin(2 * f + m)
		     - 0.0004 * dsin(2 * f - m)
		     - 0.0006 * dsin(2 * f + mprime)
		     + 0.0010 * dsin(2 * f - mprime)
		     + 0.0005 * dsin(m + 2 * mprime);
	    apcor = true;
	    }
	else if ((Math.abs(phase - 0.25) < 0.01 || (Math.abs(phase - 0.75) < 0.01)))
	    {
	    pt +=     (0.1721 - 0.0004 * t) * dsin(m)
		     + 0.0021 * dsin(2 * m)
		     - 0.6280 * dsin(mprime)
		     + 0.0089 * dsin(2 * mprime)
		     - 0.0004 * dsin(3 * mprime)
		     + 0.0079 * dsin(2 * f)
		     - 0.0119 * dsin(m + mprime)
		     - 0.0047 * dsin(m - mprime)
		     + 0.0003 * dsin(2 * f + m)
		     - 0.0004 * dsin(2 * f - m)
		     - 0.0006 * dsin(2 * f + mprime)
		     + 0.0021 * dsin(2 * f - mprime)
		     + 0.0003 * dsin(m + 2 * mprime)
		     + 0.0004 * dsin(m - 2 * mprime)
		     - 0.0003 * dsin(2 * m + mprime);
	    if (phase < 0.5)
	        /* First quarter correction. */
	        pt += 0.0028 - 0.0004 * dcos(m) + 0.0003 * dcos(mprime);
	    else
	        /* Last quarter correction. */
	        pt += -0.0028 + 0.0004 * dcos(m) - 0.0003 * dcos(mprime);
	    apcor = true;
	    }
	if (!apcor)
            throw new InternalError( "Acme.Phase.truephase() called with invalid phase selector" );
	return pt;
	}

    /// Find time of phases of the moon which surround the current
    // date.  Five phases are found, starting and ending with the
    // new moons which bound the current lunation.
    public static void phasehunt5( double sdate, double[] phases )
	{
	double adate, nt1, nt2;
	RefDouble k1 = new RefDouble();
	RefDouble k2 = new RefDouble();

	adate = sdate - 45;
	nt1 = meanphase(adate, 0.0, k1);
	for (;;)
	    {
	    adate += synmonth;
	    nt2 = meanphase(adate, 0.0, k2);
	    if (nt1 <= sdate && nt2 > sdate)
	        break;
	    nt1 = nt2;
	    k1.val = k2.val;
	    }
	phases[0] = truephase(k1.val, 0.0);
	phases[1] = truephase(k1.val, 0.25);
	phases[2] = truephase(k1.val, 0.5);
	phases[3] = truephase(k1.val, 0.75);
	phases[4] = truephase(k2.val, 0.0);
	}

    // phasehunt2 - find time of phases of the moon which surround the current
    //     date.  Two phases are found.
    void phasehunt2( double sdate, double[] phases, double[] which )
	{
	double adate, nt1, nt2;
	RefDouble k1 = new RefDouble();
	RefDouble k2 = new RefDouble();

	adate = sdate - 45;
	nt1 = meanphase(adate, 0.0, k1);
	for (;;)
	    {
	    adate += synmonth;
	    nt2 = meanphase(adate, 0.0, k2);
	    if (nt1 <= sdate && nt2 > sdate)
	        break;
	    nt1 = nt2;
	    k1.val = k2.val;
	    }
	phases[0] = truephase(k1.val, 0.0);
	which[0] = 0.0;
	phases[1] = truephase(k1.val, 0.25);
	which[1] = 0.25;
	if ( phases[1] <= sdate )
	    {
	    phases[0] = phases[1];
	    which[0] = which[1];
	    phases[1] = truephase(k1.val, 0.5);
	    which[1] = 0.5;
	    if ( phases[1] <= sdate )
		{
	        phases[0] = phases[1];
	        which[0] = which[1];
	        phases[1] = truephase(k1.val, 0.75);
	        which[1] = 0.75;
	        if ( phases[1] <= sdate )
		    {
		    phases[0] = phases[1];
		    which[0] = which[1];
		    phases[1] = truephase(k2.val, 0.0);
		    which[1] = 0.0;
		    }
		}
	    }
	}

    // kepler - solve the equation of Kepler
    private static double kepler( double m,  double ecc )
	{
	double e, delta;

	e = m = torad(m);
	do
	    {
	    delta = e - ecc * Math.sin(e) - m;
	    e -= delta / (1 - ecc * Math.cos(e));
	    }
	while (Math.abs(delta) > EPSILON);
	return e;
	}

    /// Calculate phase of moon as a fraction.
    // <P>
    // @param pdate time for which the phase is requested, as from jtime()
    // @param pphaseR Ref for illuminated fraction of Moon's disk
    // @param mageR Ref for age of moon in days
    // @param distR Ref for distance in km from center of Earth
    // @param angdiaR Ref for angular diameter in degrees as seen from Earth
    // @param sudistR Ref for distance in km to Sun
    // @param suangdiaR Ref for Sun's angular diameter
    // @return terminator phase angle as a fraction of a full circle (i.e., 0 to 1)
    // 
    public static double phase(
	double pdate, RefDouble pphaseR, RefDouble mageR, RefDouble distR,
	RefDouble angdiaR, RefDouble sudistR, RefDouble suangdiaR )
	{
	double Day, N, M, Ec, Lambdasun, ml, MM, Ev, Ae, A3, MmP,
	       mEc, A4, lP, V, lPP,
	       MoonAge, MoonPhase,
	       MoonDist, MoonDFrac, MoonAng,
	       F, SunDist, SunAng;

        // Calculation of the Sun's position.

	Day = pdate - epoch;			// date within epoch
	N = fixangle((360 / 365.2422) * Day);	// mean anomaly of the Sun
	M = fixangle(N + elonge - elongp);	// convert from perigee co-ordinates to epoch 1980.0
	Ec = kepler(M, eccent);			// solve equation of Kepler
	Ec = Math.sqrt((1 + eccent) / (1 - eccent)) * Math.tan(Ec / 2);
	Ec = 2 * todeg(Math.atan(Ec));		// true anomaly
        Lambdasun = fixangle(Ec + elongp);	// Sun's geocentric ecliptic longitude
	// Orbital distance factor.
	F = ((1 + eccent * Math.cos(torad(Ec))) / (1 - eccent * eccent));
	SunDist = sunsmax / F;			// distance to Sun in km
        SunAng = F * sunangsiz;			// Sun's angular size in degrees

        // Calculation of the Moon's position.

        // Moon's mean longitude.
	ml = fixangle(13.1763966 * Day + mmlong);

        // Moon's mean anomaly.
	MM = fixangle(ml - 0.1114041 * Day - mmlongp);

	// Evection.
	Ev = 1.2739 * Math.sin(torad(2 * (ml - Lambdasun) - MM));

	// Annual equation.
	Ae = 0.1858 * Math.sin(torad(M));

	// Correction term.
	A3 = 0.37 * Math.sin(torad(M));

	// Corrected anomaly.
	MmP = MM + Ev - Ae - A3;

	// Correction for the equation of the centre.
	mEc = 6.2886 * Math.sin(torad(MmP));

	// Another correction term.
	A4 = 0.214 * Math.sin(torad(2 * MmP));

	// Corrected longitude.
	lP = ml + Ev + mEc - Ae + A4;

	// Variation.
	V = 0.6583 * Math.sin(torad(2 * (lP - Lambdasun)));

	// True longitude.
	lPP = lP + V;

	// Calculation of the phase of the Moon.

	// Age of the Moon in degrees.
	MoonAge = lPP - Lambdasun;

	// Phase of the Moon.
	MoonPhase = (1 - Math.cos(torad(MoonAge))) / 2;

	// Calculate distance of moon from the centre of the Earth.

	MoonDist = (msmax * (1 - mecc * mecc)) /
	   (1 + mecc * Math.cos(torad(MmP + mEc)));

        // Calculate Moon's angular diameter.

	MoonDFrac = MoonDist / msmax;
	MoonAng = mangsiz / MoonDFrac;

	pphaseR.val = MoonPhase;
	mageR.val = synmonth * (fixangle(MoonAge) / 360.0);
	distR.val = MoonDist;
	angdiaR.val = MoonAng;
	sudistR.val = SunDist;
	suangdiaR.val = SunAng;
	return torad(fixangle(MoonAge));
	}

    }
