/*
 * star_funcs.c -- Star and fixed-position object observation
 *
 * Takes J2000 catalog coordinates (RA in hours, Dec in degrees),
 * applies IAU 1976 precession to date of observation, computes
 * local hour angle, and converts to topocentric azimuth/elevation.
 *
 * Range and range_rate are zero -- stars are effectively at infinity.
 * For objects with known proper motion, apply it to (RA, Dec) before
 * calling star_observe.
 */

#include "postgres.h"
#include "fmgr.h"
#include "utils/timestamp.h"
#include "types.h"
#include "astro_math.h"

PG_FUNCTION_INFO_V1(star_observe);
PG_FUNCTION_INFO_V1(star_observe_safe);

/*
 * star_observe(ra_hours, dec_degrees, observer, timestamptz) -> topocentric
 *
 * Compute az/el of a fixed celestial object from an observer at a time.
 * Uses IAU 1976 precession (~1 arcsecond accuracy for centuries near J2000).
 */
Datum
star_observe(PG_FUNCTION_ARGS)
{
    double       ra_hours = PG_GETARG_FLOAT8(0);
    double       dec_deg  = PG_GETARG_FLOAT8(1);
    pg_observer *obs      = (pg_observer *) PG_GETARG_POINTER(2);
    int64        ts       = PG_GETARG_INT64(3);

    double          jd;
    double          ra_j2000, dec_j2000;
    double          ra_date, dec_date;
    double          gmst, lst, ha;
    double          az, el;
    pg_topocentric *result;

    if (ra_hours < 0.0 || ra_hours >= 24.0)
        ereport(ERROR,
                (errcode(ERRCODE_NUMERIC_VALUE_OUT_OF_RANGE),
                 errmsg("right ascension out of range: %.6f", ra_hours),
                 errhint("RA must be in [0, 24) hours.")));

    if (dec_deg < -90.0 || dec_deg > 90.0)
        ereport(ERROR,
                (errcode(ERRCODE_NUMERIC_VALUE_OUT_OF_RANGE),
                 errmsg("declination out of range: %.6f", dec_deg),
                 errhint("Declination must be between -90 and +90 degrees.")));

    jd = timestamptz_to_jd(ts);

    ra_j2000  = ra_hours * (M_PI / 12.0);
    dec_j2000 = dec_deg * DEG_TO_RAD;

    precess_j2000_to_date(jd, ra_j2000, dec_j2000, &ra_date, &dec_date);

    gmst = gmst_from_jd(jd);
    lst  = gmst + obs->lon;
    ha   = lst - ra_date;

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

    result = (pg_topocentric *) palloc(sizeof(pg_topocentric));
    result->azimuth    = az;
    result->elevation  = el;
    result->range_km   = 0.0;
    result->range_rate = 0.0;

    PG_RETURN_POINTER(result);
}


/*
 * star_observe_safe -- returns NULL if inputs are out of range.
 * For batch queries over star catalogs.
 */
Datum
star_observe_safe(PG_FUNCTION_ARGS)
{
    double       ra_hours = PG_GETARG_FLOAT8(0);
    double       dec_deg  = PG_GETARG_FLOAT8(1);
    pg_observer *obs      = (pg_observer *) PG_GETARG_POINTER(2);
    int64        ts       = PG_GETARG_INT64(3);

    double          jd;
    double          ra_j2000, dec_j2000;
    double          ra_date, dec_date;
    double          gmst, lst, ha;
    double          az, el;
    pg_topocentric *result;

    if (ra_hours < 0.0 || ra_hours >= 24.0)
        PG_RETURN_NULL();
    if (dec_deg < -90.0 || dec_deg > 90.0)
        PG_RETURN_NULL();

    jd = timestamptz_to_jd(ts);

    ra_j2000  = ra_hours * (M_PI / 12.0);
    dec_j2000 = dec_deg * DEG_TO_RAD;

    precess_j2000_to_date(jd, ra_j2000, dec_j2000, &ra_date, &dec_date);

    gmst = gmst_from_jd(jd);
    lst  = gmst + obs->lon;
    ha   = lst - ra_date;

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

    result = (pg_topocentric *) palloc(sizeof(pg_topocentric));
    result->azimuth    = az;
    result->elevation  = el;
    result->range_km   = 0.0;
    result->range_rate = 0.0;

    PG_RETURN_POINTER(result);
}