use super::IauAstrom;

use crate::consts::{AULT, DAU, DAYSEC, DJ00, DJY};

use crate::vm::{cp, ir, pn};

///  Prepare for ICRS <−> CIRS, space, special

///

///  For an observer whose geocentric position and velocity are known,

///  prepare star-independent astrometry parameters for transformations

///  between ICRS and GCRS.  The Earth ephemeris is supplied by the

///  caller.

///

///  The parameters produced by this function are required in the space

///  motion, parallax, light deflection and aberration parts of the

///  astrometric transformation chain.

///

///  This function is part of the International Astronomical Union's

///  SOFA (Standards of Fundamental Astronomy) software collection.

///

///  Status:  support function.

///

///  Given:

///  ```

///     date1  double       TDB as a 2-part...

///     date2  double       ...Julian Date (Note 1)

///     pv     double[2][3] observer's geocentric pos/vel (m, m/s)

///     ebpv   double[2][3] Earth barycentric PV (au, au/day)

///     ehp    double[3]    Earth heliocentric P (au)

///  ```

///  Returned:

///  ```

///     astrom iauASTROM*   star-independent astrometry parameters:

///      pmt    double       PM time interval (SSB, Julian years)

///      eb     double[3]    SSB to observer (vector, au)

///      eh     double[3]    Sun to observer (unit vector)

///      em     double       distance from Sun to observer (au)

///      v      double[3]    barycentric observer velocity (vector, c)

///      bm1    double       sqrt(1-|v|^2): reciprocal of Lorenz factor

///      bpn    double[3][3] bias-precession-nutation matrix

///      along  double       unchanged

///      xpl    double       unchanged

///      ypl    double       unchanged

///      sphi   double       unchanged

///      cphi   double       unchanged

///      diurab double       unchanged

///      eral   double       unchanged

///      refa   double       unchanged

///      refb   double       unchanged

///  ```

///  Notes:

///

///  1) The TDB date date1+date2 is a Julian Date, apportioned in any

///     convenient way between the two arguments.  For example,

///     JD(TDB)=2450123.7 could be expressed in any of these ways, among

///     others:

///  ```

///            date1          date2

///

///         2450123.7           0.0       (JD method)

///         2451545.0       -1421.3       (J2000 method)

///         2400000.5       50123.2       (MJD method)

///         2450123.5           0.2       (date & time method)

///  ```

///     The JD method is the most natural and convenient to use in cases

///     where the loss of several decimal digits of resolution is

///     acceptable.  The J2000 method is best matched to the way the

///     argument is handled internally and will deliver the optimum

///     resolution.  The MJD method and the date & time methods are both

///     good compromises between resolution and convenience.  For most

///     applications of this function the choice will not be at all

///     critical.

///

///     TT can be used instead of TDB without any significant impact on

///     accuracy.

///

///  2) All the vectors are with respect to BCRS axes.

///

///  3) Providing separate arguments for (i) the observer's geocentric

///     position and velocity and (ii) the Earth ephemeris is done for

///     convenience in the geocentric, terrestrial and Earth orbit cases.

///     For deep space applications it maybe more convenient to specify

///     zero geocentric position and velocity and to supply the

///     observer's position and velocity information directly instead of

///     with respect to the Earth.  However, note the different units:

///     m and m/s for the geocentric vectors, au and au/day for the

///     heliocentric and barycentric vectors.

///

///  4) In cases where the caller does not wish to provide the Earth

///     ephemeris, the function iauApcs13 can be used instead of the

///     present function.  This computes the Earth ephemeris using the

///     SOFA function iauEpv00.

///

///  5) This is one of several functions that inserts into the astrom

///     structure star-independent parameters needed for the chain of

///     astrometric transformations ICRS <-> GCRS <-> CIRS <-> observed.

///

///     The various functions support different classes of observer and

///     portions of the transformation chain:

///  ```

///          functions         observer        transformation

///

///       iauApcg iauApcg13    geocentric      ICRS <-> GCRS

///       iauApci iauApci13    terrestrial     ICRS <-> CIRS

///       iauApco iauApco13    terrestrial     ICRS <-> observed

///       iauApcs iauApcs13    space           ICRS <-> GCRS

///       iauAper iauAper13    terrestrial     update Earth rotation

///       iauApio iauApio13    terrestrial     CIRS <-> observed

///  ```

///     Those with names ending in "13" use contemporary SOFA models to

///     compute the various ephemerides.  The others accept ephemerides

///     supplied by the caller.

///

///     The transformation from ICRS to GCRS covers space motion,

///     parallax, light deflection, and aberration.  From GCRS to CIRS

///     comprises frame bias and precession-nutation.  From CIRS to

///     observed takes account of Earth rotation, polar motion, diurnal

///     aberration and parallax (unless subsumed into the ICRS <-> GCRS

///     transformation), and atmospheric refraction.

///

///  6) The context structure astrom produced by this function is used by

///     iauAtciq* and iauAticq*.

///

///  Called:

///  ```

///     iauCp        copy p-vector

///     iauPm        modulus of p-vector

///     iauPn        decompose p-vector into modulus and direction

///     iauIr        initialize r-matrix to identity

///  ```

pub fn apcs(

    date1: f64,

    date2: f64,

    pv: &[[f64; 3]; 2],

    ebpv: &[[f64; 3]; 2],

    ehp: &[f64; 3],

    astrom: &mut IauAstrom,

) {

    // au/d to m/s

    let audms = DAU / DAYSEC;

    // Light time for 1 au (day)

    let cr = AULT / DAYSEC;

    let mut pb = [0.0; 3];

    let mut vb = [0.0; 3];

    let mut ph = [0.0; 3];

    // Time since reference epoch, years (for proper motion calculation).

    astrom.pmt = ((date1 - DJ00) + date2) / DJY;

    // Adjust Earth ephemeris to observer.

    for i in 0..3 {

        let dp = pv[0][i] / DAU;

        let dv = pv[1][i] / audms;

        pb[i] = ebpv[0][i] + dp;

        vb[i] = ebpv[1][i] + dv;

        ph[i] = ehp[i] + dp;

    }

    // Barycentric position of observer (au).

    cp(&pb, &mut astrom.eb);

    // Heliocentric direction and distance (unit vector and au).

    (astrom.em, astrom.eh) = pn(&ph);

    // Barycentric vel. in units of c, and reciprocal of Lorenz factor.

    let mut v2 = 0.0;

    for i in 0..3 {

        let w = vb[i] * cr;

        astrom.v[i] = w;

        v2 += w * w;

    }

    astrom.bm1 = (1.0 - v2).sqrt();

    // Reset the NPB matrix.

    ir(&mut astrom.bpn);

}