/*
 * planet_funcs.c -- VSOP87 planet and ELP82B Moon observation
 *
 * SQL functions for planetary/Sun/Moon position and observation.
 * Wraps VSOP87 (Bretagnon & Francou) for 8 planets + Sun, and
 * ELP2000-82B (Chapront-Touze) for the Moon.
 *
 * The observation pipeline:
 *   1. Heliocentric ecliptic J2000 position (VSOP87 or ELP82B)
 *   2. Geocentric ecliptic (subtract Earth's heliocentric)
 *   3. Ecliptic -> equatorial J2000 (obliquity rotation)
 *   4. Spherical coordinates (RA, Dec, distance)
 *   5. Precession J2000 -> date (IAU 1976, Lieske)
 *   6. Sidereal time -> hour angle -> az/el
 *   7. Return topocentric result
 */

#include "postgres.h"
#include "fmgr.h"
#include "funcapi.h"
#include "utils/timestamp.h"
#include "types.h"
#include "astro_math.h"
#include "vsop87.h"
#include "elp82b.h"
#include <math.h>

PG_FUNCTION_INFO_V1(planet_heliocentric);
PG_FUNCTION_INFO_V1(planet_observe);
PG_FUNCTION_INFO_V1(sun_observe);
PG_FUNCTION_INFO_V1(moon_observe);


/* ================================================================
 * Internal: geocentric observation pipeline
 *
 * Takes geocentric ecliptic J2000 position, observer location,
 * and Julian date.  Converts through equatorial, precesses to
 * date, and computes topocentric az/el.
 *
 * geo_ecl_au[3] = geocentric ecliptic J2000 position in AU
 * ================================================================
 */
static void
observe_from_geocentric(const double geo_ecl_au[3], double jd,
                        const pg_observer *obs, pg_topocentric *result)
{
    double geo_equ[3];
    double ra_j2000, dec_j2000, geo_dist;
    double ra_date, dec_date;
    double gmst_val, lst, ha;
    double az, el;

    /* Ecliptic J2000 -> equatorial J2000 */
    ecliptic_to_equatorial(geo_ecl_au, geo_equ);

    /* Cartesian -> spherical */
    cartesian_to_spherical(geo_equ, &ra_j2000, &dec_j2000, &geo_dist);

    /* Precess J2000 -> date */
    precess_j2000_to_date(jd, ra_j2000, dec_j2000, &ra_date, &dec_date);

    /* Hour angle and az/el */
    gmst_val = gmst_from_jd(jd);
    lst = gmst_val + obs->lon;
    ha  = lst - ra_date;

    equatorial_to_horizontal(ha, dec_date, obs->lat, &az, &el);

    result->azimuth   = az;
    result->elevation = el;
    result->range_km  = geo_dist * AU_KM;
    result->range_rate = 0.0;  /* no velocity computation yet */
}


/* ================================================================
 * planet_heliocentric(body_id int, timestamptz) -> heliocentric
 *
 * Returns the heliocentric ecliptic J2000 position of a planet
 * (or the Sun, as the barycenter proxy at (0,0,0)).
 *
 * Body IDs: 0=Sun, 1=Mercury, ..., 8=Neptune
 * ================================================================
 */
Datum
planet_heliocentric(PG_FUNCTION_ARGS)
{
    int32            body_id = PG_GETARG_INT32(0);
    int64            ts      = PG_GETARG_INT64(1);
    double           jd;
    double           xyz[6];
    int              vsop_body;
    pg_heliocentric *result;

    if (body_id == BODY_SUN)
    {
        /* Sun is at the origin of heliocentric coordinates */
        result = (pg_heliocentric *) palloc(sizeof(pg_heliocentric));
        result->x = 0.0;
        result->y = 0.0;
        result->z = 0.0;
        PG_RETURN_POINTER(result);
    }

    if (body_id < BODY_MERCURY || body_id > BODY_NEPTUNE)
        ereport(ERROR,
                (errcode(ERRCODE_NUMERIC_VALUE_OUT_OF_RANGE),
                 errmsg("invalid body_id %d: must be 0 (Sun) or 1-8 (Mercury-Neptune)",
                        body_id)));

    jd = timestamptz_to_jd(ts);
    vsop_body = body_id - 1;  /* pg_orbit 1-based -> VSOP87 0-based */
    GetVsop87Coor(jd, vsop_body, xyz);

    result = (pg_heliocentric *) palloc(sizeof(pg_heliocentric));
    result->x = xyz[0];
    result->y = xyz[1];
    result->z = xyz[2];

    PG_RETURN_POINTER(result);
}


/* ================================================================
 * planet_observe(body_id int, observer, timestamptz) -> topocentric
 *
 * Full pipeline: VSOP87 position -> geocentric -> equatorial ->
 * precession -> topocentric az/el.
 *
 * Body IDs: 1=Mercury, ..., 8=Neptune (not Sun or Moon)
 * ================================================================
 */
Datum
planet_observe(PG_FUNCTION_ARGS)
{
    int32           body_id = PG_GETARG_INT32(0);
    pg_observer    *obs     = (pg_observer *) PG_GETARG_POINTER(1);
    int64           ts      = PG_GETARG_INT64(2);
    double          jd;
    double          earth_xyz[6];
    double          planet_xyz[6];
    double          geo_ecl[3];
    int             vsop_body;
    pg_topocentric *result;

    if (body_id < BODY_MERCURY || body_id > BODY_NEPTUNE)
        ereport(ERROR,
                (errcode(ERRCODE_NUMERIC_VALUE_OUT_OF_RANGE),
                 errmsg("planet_observe: body_id %d must be 1-8 (Mercury-Neptune)",
                        body_id)));

    if (body_id == BODY_EARTH)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("cannot observe Earth from Earth")));

    jd = timestamptz_to_jd(ts);

    /* Earth's heliocentric position */
    GetVsop87Coor(jd, 2, earth_xyz);  /* VSOP87 body 2 = Earth */

    /* Target planet heliocentric position */
    vsop_body = body_id - 1;
    GetVsop87Coor(jd, vsop_body, planet_xyz);

    /* Geocentric ecliptic = planet - Earth */
    geo_ecl[0] = planet_xyz[0] - earth_xyz[0];
    geo_ecl[1] = planet_xyz[1] - earth_xyz[1];
    geo_ecl[2] = planet_xyz[2] - earth_xyz[2];

    result = (pg_topocentric *) palloc(sizeof(pg_topocentric));
    observe_from_geocentric(geo_ecl, jd, obs, result);

    PG_RETURN_POINTER(result);
}


/* ================================================================
 * sun_observe(observer, timestamptz) -> topocentric
 *
 * The Sun's geocentric position is the negation of Earth's
 * heliocentric VSOP87 position.
 * ================================================================
 */
Datum
sun_observe(PG_FUNCTION_ARGS)
{
    pg_observer    *obs = (pg_observer *) PG_GETARG_POINTER(0);
    int64           ts  = PG_GETARG_INT64(1);
    double          jd;
    double          earth_xyz[6];
    double          geo_ecl[3];
    pg_topocentric *result;

    jd = timestamptz_to_jd(ts);

    /* Earth heliocentric -> Sun geocentric by negation */
    GetVsop87Coor(jd, 2, earth_xyz);
    geo_ecl[0] = -earth_xyz[0];
    geo_ecl[1] = -earth_xyz[1];
    geo_ecl[2] = -earth_xyz[2];

    result = (pg_topocentric *) palloc(sizeof(pg_topocentric));
    observe_from_geocentric(geo_ecl, jd, obs, result);

    PG_RETURN_POINTER(result);
}


/* ================================================================
 * moon_observe(observer, timestamptz) -> topocentric
 *
 * ELP2000-82B returns geocentric ecliptic J2000 Moon position.
 * No Earth subtraction needed.
 * ================================================================
 */
Datum
moon_observe(PG_FUNCTION_ARGS)
{
    pg_observer    *obs = (pg_observer *) PG_GETARG_POINTER(0);
    int64           ts  = PG_GETARG_INT64(1);
    double          jd;
    double          moon_ecl[3];
    pg_topocentric *result;

    jd = timestamptz_to_jd(ts);

    /* Moon geocentric ecliptic J2000 in AU */
    GetElp82bCoor(jd, moon_ecl);

    result = (pg_topocentric *) palloc(sizeof(pg_topocentric));
    observe_from_geocentric(moon_ecl, jd, obs, result);

    PG_RETURN_POINTER(result);
}