/*      $NetBSD: pom.c,v 1.21 2021/05/02 12:50:46 rillig Exp $  */

/*
 * 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.
 */

#include <sys/cdefs.h>
#ifndef lint
__COPYRIGHT("@(#) Copyright (c) 1989, 1993\
 The Regents of the University of California.  All rights reserved.");
#endif /* not lint */

#ifndef lint
#if 0
static char sccsid[] = "@(#)pom.c       8.1 (Berkeley) 5/31/93";
#else
__RCSID("$NetBSD: pom.c,v 1.21 2021/05/02 12:50:46 rillig Exp $");
#endif
#endif /* not lint */

/*
 * 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
 *
 * Updated to the Third Edition of Duffett-Smith's book, Paul Janzen, IX 1998
 *
 */

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

#ifndef PI
#define PI        3.14159265358979323846
#endif

/*
 * The EPOCH in the third edition of the book is 1990 Jan 0.0 TDT.
 * In this program, we do not bother to correct for the differences
 * between UTC (as shown by the UNIX clock) and TDT.  (TDT = TAI + 32.184s;
 * TAI-UTC = 32s in Jan 1999.)
 */
#define EPOCH_MINUS_1970        (20 * 365 + 5 - 1) /* 20 years, 5 leaps, back 1 day to Jan 0 */
#define EPSILONg  279.403303    /* solar ecliptic long at EPOCH */
#define RHOg      282.768422    /* solar ecliptic long of perigee at EPOCH */
#define ECCEN     0.016713      /* solar orbit eccentricity */
#define lzero     318.351648    /* lunar mean long at EPOCH */
#define Pzero     36.340410     /* lunar mean long of perigee at EPOCH */
#define Nzero     318.510107    /* lunar mean long of node at EPOCH */

int     main(int, char *[]);
static void adj360(double *);
static double dtor(double);
static double potm(double);
static time_t parsetime(char *);
static void badformat(void) __dead;

int
main(int argc, char *argv[])
{
        time_t tmpt, now;
        double days, today, tomorrow;
        char buf[1024];

        if (time(&now) == (time_t)-1)
                err(1, "time");
        if (argc > 1) {
                tmpt = parsetime(argv[1]);
                strftime(buf, sizeof(buf), "%a %Y %b %e %H:%M:%S (%Z)",
                        localtime(&tmpt));
                printf("%s:  ", buf);
        } else {
                tmpt = now;
        }
        days = (tmpt - EPOCH_MINUS_1970 * 86400) / 86400.0;
        today = potm(days) + .5;
        if (tmpt < now)
                (void)printf("The Moon was ");
        else if (tmpt == now)
                (void)printf("The Moon is ");
        else
                (void)printf("The Moon will be ");
        if ((int)today == 100)
                (void)printf("Full\n");
        else if (!(int)today)
                (void)printf("New\n");
        else {
                tomorrow = potm(days + 1);
                if ((int)today == 50)
                        (void)printf("%s\n", tomorrow > today ?
                            "at the First Quarter" : "at the Last Quarter");
                        /* today is 0.5 too big, but it doesn't matter here
                         * since the phase is changing fast enough
                         */
                else {
                        today -= 0.5;           /* Now it might matter */
                        (void)printf("%s ", tomorrow > today ?
                            "Waxing" : "Waning");
                        if (today > 50)
                                (void)printf("Gibbous (%1.0f%% of Full)\n",
                                    today);
                        else if (today < 50)
                                (void)printf("Crescent (%1.0f%% of Full)\n",
                                    today);
                }
        }

        return EXIT_SUCCESS;
}

/*
 * potm --
 *      return phase of the moon
 */
static double
potm(double days)
{
        double N, Msol, Ec, LambdaSol, l, Mm, Ev, Ac, A3, Mmprime;
        double A4, lprime, V, ldprime, D, Nm;

        N = 360 * days / 365.242191;                            /* sec 46 #3 */
        adj360(&N);
        Msol = N + EPSILONg - RHOg;                             /* sec 46 #4 */
        adj360(&Msol);
        Ec = 360 / PI * ECCEN * sin(dtor(Msol));                /* sec 46 #5 */
        LambdaSol = N + Ec + EPSILONg;                          /* sec 46 #6 */
        adj360(&LambdaSol);
        l = 13.1763966 * days + lzero;                          /* sec 65 #4 */
        adj360(&l);
        Mm = l - (0.1114041 * days) - Pzero;                    /* sec 65 #5 */
        adj360(&Mm);
        Nm = Nzero - (0.0529539 * days);                        /* sec 65 #6 */
        adj360(&Nm);
        Ev = 1.2739 * sin(dtor(2*(l - LambdaSol) - Mm));        /* sec 65 #7 */
        Ac = 0.1858 * sin(dtor(Msol));                          /* sec 65 #8 */
        A3 = 0.37 * sin(dtor(Msol));
        Mmprime = Mm + Ev - Ac - A3;                            /* sec 65 #9 */
        Ec = 6.2886 * sin(dtor(Mmprime));                       /* sec 65 #10 */
        A4 = 0.214 * sin(dtor(2 * Mmprime));                    /* sec 65 #11 */
        lprime = l + Ev + Ec - Ac + A4;                         /* sec 65 #12 */
        V = 0.6583 * sin(dtor(2 * (lprime - LambdaSol)));       /* sec 65 #13 */
        ldprime = lprime + V;                                   /* sec 65 #14 */
        D = ldprime - LambdaSol;                                /* sec 67 #2 */
        return(50.0 * (1 - cos(dtor(D))));                      /* sec 67 #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;
}

#define ATOI2(ar)       ((ar)[0] - '0') * 10 + ((ar)[1] - '0'); (ar) += 2;
static time_t
parsetime(char *p)
{
        struct tm *lt;
        int bigyear;
        int yearset = 0;
        time_t tval;
        char *t;

        for (t = p; *t; ++t) {
                if (isdigit((unsigned char) *t))
                        continue;
                badformat();
        }

        tval = time(NULL);
        lt = localtime(&tval);
        lt->tm_sec = 0;
        lt->tm_min = 0;

        switch (strlen(p)) {
        case 10:                                /* yyyy */
                bigyear = ATOI2(p);
                lt->tm_year = bigyear * 100 - 1900;
                yearset = 1;
                /* FALLTHROUGH */
        case 8:                                 /* yy */
                if (yearset) {
                        lt->tm_year += ATOI2(p);
                } else {
                        lt->tm_year = ATOI2(p);
                        if (lt->tm_year < 69)           /* hack for 2000 */
                                lt->tm_year += 100;
                }
                /* FALLTHROUGH */
        case 6:                                 /* mm */
                lt->tm_mon = ATOI2(p);
                if ((lt->tm_mon > 12) || !lt->tm_mon)
                        badformat();
                --lt->tm_mon;                   /* time struct is 0 - 11 */
                /* FALLTHROUGH */
        case 4:                                 /* dd */
                lt->tm_mday = ATOI2(p);
                if ((lt->tm_mday > 31) || !lt->tm_mday)
                        badformat();
                /* FALLTHROUGH */
        case 2:                                 /* HH */
                lt->tm_hour = ATOI2(p);
                if (lt->tm_hour > 23)
                        badformat();
                break;
        default:
                badformat();
        }
        /* The calling code needs a valid tm_ydays and this is the easiest
         * way to get one */
        if ((tval = mktime(lt)) == -1)
                errx(1, "specified date is outside allowed range");
        return (tval);
}

static void
badformat(void)
{
        warnx("illegal time format");
        (void)fprintf(stderr, "usage: %s [[[[[cc]yy]mm]dd]HH]\n",
            getprogname());
        exit(EXIT_FAILURE);
}