/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * Copyright (c) 1989, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software posted to USENET.
 *
 * 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.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS 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 REGENTS 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.
 */

/*
 * Phase of the Moon.  Calculates the current phase of the moon.
 * Based on routines from `Practical Astronomy with Your Calculator',
 * by Duffett-Smith.  Comments give the section from the book that
 * particular piece of code was adapted from.
 *
 * -- Keith E. Brandt  VIII 1984
 *
 */

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <string.h>
#include <sysexits.h>
#include <time.h>
#include <unistd.h> 

#include "calendar.h"

#ifndef PI
#define PI        3.14159265358979323846
#endif
#define EPOCH     85
#define EPSILONg  279.611371    /* solar ecliptic long at EPOCH */
#define RHOg      282.680403    /* solar ecliptic long of perigee at EPOCH */
#define ECCEN     0.01671542    /* solar orbit eccentricity */
#define lzero     18.251907     /* lunar mean long at EPOCH */
#define Pzero     192.917585    /* lunar mean long of perigee at EPOCH */
#define Nzero     55.204723     /* lunar mean long of node at EPOCH */
#define isleap(y) ((((y) % 4) == 0 && ((y) % 100) != 0) || ((y) % 400) == 0)

static void     adj360(double *);
static double   dtor(double);
static double   potm(double onday);
static double   potm_minute(double onday, int olddir);

void
pom(int year, double utcoffset, int *fms, int *nms)
{
        double ffms[MAXMOONS];
        double fnms[MAXMOONS];
        int i, j;

        fpom(year, utcoffset, ffms, fnms);

        j = 0;
        for (i = 0; ffms[i] != 0; i++)
                fms[j++] = round(ffms[i]);
        fms[i] = -1;
        for (i = 0; fnms[i] != 0; i++)
                nms[i] = round(fnms[i]);
        nms[i] = -1;
}

void
fpom(int year, double utcoffset, double *ffms, double *fnms)
{
        time_t tt;
        struct tm GMT, tmd_today, tmd_tomorrow;
        double days_today, days_tomorrow, today, tomorrow;
        int cnt, d;
        int yeardays;
        int olddir, newdir;
        double *pfnms, *pffms, t;

        pfnms = fnms;
        pffms = ffms;

        /*
         * We take the phase of the moon one second before and one second
         * after midnight.
         */
        memset(&tmd_today, 0, sizeof(tmd_today));
        tmd_today.tm_year = year - 1900;
        tmd_today.tm_mon = 0;
        tmd_today.tm_mday = -1;         /* 31 December */
        tmd_today.tm_hour = 23;
        tmd_today.tm_min = 59;
        tmd_today.tm_sec = 59;
        memset(&tmd_tomorrow, 0, sizeof(tmd_tomorrow));
        tmd_tomorrow.tm_year = year - 1900;
        tmd_tomorrow.tm_mon = 0;
        tmd_tomorrow.tm_mday = 0;       /* 01 January */
        tmd_tomorrow.tm_hour = 0;
        tmd_tomorrow.tm_min = 0;
        tmd_tomorrow.tm_sec = 1;

        tt = mktime(&tmd_today);
        gmtime_r(&tt, &GMT);
        yeardays = 0;
        for (cnt = EPOCH; cnt < GMT.tm_year; ++cnt)
                yeardays += isleap(1900 + cnt) ? DAYSPERLEAPYEAR : DAYSPERYEAR;
        days_today = (GMT.tm_yday + 1) + ((GMT.tm_hour +
            (GMT.tm_min / FSECSPERMINUTE) + (GMT.tm_sec / FSECSPERHOUR)) /
            FHOURSPERDAY);
        days_today += yeardays;

        tt = mktime(&tmd_tomorrow);
        gmtime_r(&tt, &GMT);
        yeardays = 0;
        for (cnt = EPOCH; cnt < GMT.tm_year; ++cnt)
                yeardays += isleap(1900 + cnt) ? DAYSPERLEAPYEAR : DAYSPERYEAR;
        days_tomorrow = (GMT.tm_yday + 1) + ((GMT.tm_hour +
            (GMT.tm_min / FSECSPERMINUTE) + (GMT.tm_sec / FSECSPERHOUR)) /
            FHOURSPERDAY);
        days_tomorrow += yeardays;

        today = potm(days_today);               /* 30 December 23:59:59 */
        tomorrow = potm(days_tomorrow);         /* 31 December 00:00:01 */
        olddir = today > tomorrow ? -1 : +1;

        yeardays = 1 + (isleap(year) ? DAYSPERLEAPYEAR : DAYSPERYEAR); /* reuse */
        for (d = 0; d <= yeardays; d++) {
                today = potm(days_today);
                tomorrow = potm(days_tomorrow);
                newdir = today > tomorrow ? -1 : +1;
                if (olddir != newdir) {
                        t = potm_minute(days_today - 1, olddir) +
                             utcoffset / FHOURSPERDAY;
                        if (olddir == -1 && newdir == +1) {
                                *pfnms = d - 1 + t;
                                pfnms++;
                        } else if (olddir == +1 && newdir == -1) {
                                *pffms = d - 1 + t;
                                pffms++;
                        }
                }
                olddir = newdir;
                days_today++;
                days_tomorrow++;
        }
        *pffms = -1;
        *pfnms = -1;
}

static double
potm_minute(double onday, int olddir) {
        double period = FSECSPERDAY / 2.0;
        double p1, p2;
        double before, after;
        int newdir;

//      printf("---> days:%g olddir:%d\n", days, olddir);

        p1 = onday + (period / SECSPERDAY);
        period /= 2;

        while (period > 30) {   /* half a minute */
//              printf("period:%g - p1:%g - ", period, p1);
                p2 = p1 + (2.0 / SECSPERDAY);
                before = potm(p1);
                after = potm(p2);
//              printf("before:%10.10g - after:%10.10g\n", before, after);
                newdir = before < after ? -1 : +1;
                if (olddir != newdir)
                        p1 += (period / SECSPERDAY);
                else
                        p1 -= (period / SECSPERDAY);
                period /= 2;
//              printf("newdir:%d - p1:%10.10f - period:%g\n",
//                  newdir, p1, period);
        }
        p1 -= floor(p1);
        //exit(0);
        return (p1);
}

/*
 * potm --
 *      return phase of the moon, as a percentage [0 ... 100]
 */
static double
potm(double onday)
{
        double N, Msol, Ec, LambdaSol, l, Mm, Ev, Ac, A3, Mmprime;
        double A4, lprime, V, ldprime, D, Nm;

        N = 360 * onday / 365.2422;                             /* sec 42 #3 */
        adj360(&N);
        Msol = N + EPSILONg - RHOg;                             /* sec 42 #4 */
        adj360(&Msol);
        Ec = 360 / PI * ECCEN * sin(dtor(Msol));                /* sec 42 #5 */
        LambdaSol = N + Ec + EPSILONg;                          /* sec 42 #6 */
        adj360(&LambdaSol);
        l = 13.1763966 * onday + lzero;                         /* sec 61 #4 */
        adj360(&l);
        Mm = l - (0.1114041 * onday) - Pzero;                   /* sec 61 #5 */
        adj360(&Mm);
        Nm = Nzero - (0.0529539 * onday);                       /* sec 61 #6 */
        adj360(&Nm);
        Ev = 1.2739 * sin(dtor(2*(l - LambdaSol) - Mm));        /* sec 61 #7 */
        Ac = 0.1858 * sin(dtor(Msol));                          /* sec 61 #8 */
        A3 = 0.37 * sin(dtor(Msol));
        Mmprime = Mm + Ev - Ac - A3;                            /* sec 61 #9 */
        Ec = 6.2886 * sin(dtor(Mmprime));                       /* sec 61 #10 */
        A4 = 0.214 * sin(dtor(2 * Mmprime));                    /* sec 61 #11 */
        lprime = l + Ev + Ec - Ac + A4;                         /* sec 61 #12 */
        V = 0.6583 * sin(dtor(2 * (lprime - LambdaSol)));       /* sec 61 #13 */
        ldprime = lprime + V;                                   /* sec 61 #14 */
        D = ldprime - LambdaSol;                                /* sec 63 #2 */
        return(50 * (1 - cos(dtor(D))));                        /* sec 63 #3 */
}

/*
 * dtor --
 *      convert degrees to radians
 */
static double
dtor(double deg)
{

        return(deg * PI / 180);
}

/*
 * adj360 --
 *      adjust value so 0 <= deg <= 360
 */
static void
adj360(double *deg)
{

        for (;;)
                if (*deg < 0)
                        *deg += 360;
                else if (*deg > 360)
                        *deg -= 360;
                else
                        break;
}