use super::{IauAstrom, apci};

use crate::{

    eph::epv00,

    pnp::{bpn2xy, eors, pnm06a, s06},

};

///  Prepare for ICRS <−> CIRS, terrestrial

///

///  For a terrestrial observer, prepare star-independent astrometry

///  parameters for transformations between ICRS and geocentric CIRS

///  coordinates.  The caller supplies the date, and SOFA models are used

///  to predict the Earth ephemeris and CIP/CIO.

///

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

///  parallax, light deflection, aberration, and bias-precession-nutation

///  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)

///  ```

///  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

///     eo     double*     equation of the origins (ERA-GST, radians)

///  ```

///  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) In cases where the caller wishes to supply his own Earth

///     ephemeris and CIP/CIO, the function iauApci can be used instead

///     of the present function.

///

///  4) 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.

///

///  5) The context structure astrom produced by this function is used by

///     iauAtciq* and iauAticq*.

///

///  Called:

///  ```

///     iauEpv00     Earth position and velocity

///     iauPnm06a    classical NPB matrix, IAU 2006/2000A

///     iauBpn2xy    extract CIP X,Y coordinates from NPB matrix

///     iauS06       the CIO locator s, given X,Y, IAU 2006

///     iauApci      astrometry parameters, ICRS-CIRS

///     iauEors      equation of the origins, given NPB matrix and s

///  ```

pub fn apci13(date1: f64, date2: f64, astrom: &mut IauAstrom, eo: &mut f64) {

    /* Earth barycentric & heliocentric position/velocity (au, au/d). */

    let (ehpv, ebpv) = epv00(date1, date2).unwrap();

    /* Form the equinox based BPN matrix, IAU 2006/2000A. */

    let r = pnm06a(date1, date2);

    /* Extract CIP X,Y. */

    let (x, y) = bpn2xy(&r);

    /* Obtain CIO locator s. */

    let s = s06(date1, date2, x, y);

    /* Compute the star-independent astrometry parameters. */

    apci(date1, date2, &ebpv, &ehpv[0], x, y, s, astrom);

    /* Equation of the origins. */

    *eo = eors(&r, s);

}