use crate::erst::era00;

use crate::pnp::{c2i00a, c2tcio, pom00, sp00};

///  Form the celestial to terrestrial matrix given the date, the UT1 and

///  the polar motion, using the IAU 2000A precession-nutation model.

///

///  Given:

///     tta,ttb  f64          TT as a 2-part Julian Date (Note 1)

///     uta,utb  f64          UT1 as a 2-part Julian Date (Note 1)

///     xp,yp    f64          CIP coordinates (radians, Note 2)

///

///  Returned (function value):

///                 [[f64; 3]; 3]   celestial-to-terrestrial matrix (Note 3)

///

///  Notes:

///

///  1) The TT and UT1 dates tta+ttb and uta+utb are Julian Dates,

///     apportioned in any convenient way between the arguments uta and

///     utb.  For example, JD(UT1)=2450123.7 could be expressed in any of

///     these ways, among others:

///

///             uta            utb

///

///         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 and MJD methods are good compromises

///     between resolution and convenience.  In the case of uta,utb, the

///     date & time method is best matched to the Earth rotation angle

///     algorithm used:  maximum precision is delivered when the uta

///     argument is for 0hrs UT1 on the day in question and the utb

///     argument lies in the range 0 to 1, or vice versa.

///

///  2) The arguments xp and yp are the coordinates (in radians) of the

///     Celestial Intermediate Pole with respect to the International

///     Terrestrial Reference System (see IERS Conventions 2003),

///     measured along the meridians 0 and 90 deg west respectively.

///

///  3) The matrix rc2t transforms from celestial to terrestrial

///     coordinates:

///

///        [TRS] = RPOM * R_3(ERA) * RC2I * [CRS]

///

///              = rc2t * [CRS]

///

///     where [CRS] is a vector in the Geocentric Celestial Reference

///     System and [TRS] is a vector in the International Terrestrial

///     Reference System (see IERS Conventions 2003), RC2I is the

///     celestial-to-intermediate matrix, ERA is the Earth rotation

///     angle and RPOM is the polar motion matrix.

///

///  4) A faster, but slightly less accurate, result (about 1 mas) can

///     be obtained by using instead the iauC2t00b function.

///

///  Called:

///     iauC2i00a    celestial-to-intermediate matrix, IAU 2000A

///     iauEra00     Earth rotation angle, IAU 2000

///     iauSp00      the TIO locator s', IERS 2000

///     iauPom00     polar motion matrix

///     iauC2tcio    form CIO-based celestial-to-terrestrial matrix

///

///  Reference:

///

///     McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003),

///     IERS Technical Note No. 32, BKG (2004)

pub fn c2t00a(tta: f64, ttb: f64, uta: f64, utb: f64, xp: f64, yp: f64) -> [[f64; 3]; 3] {

    /* Form the celestial-to-intermediate matrix for this TT (IAU 2000A). */

    let rc2i = c2i00a(tta, ttb);

    /* Predict the Earth rotation angle for this UT1. */

    let era = era00(uta, utb);

    /* Estimate s'. */

    let sp = sp00(tta, ttb);

    /* Form the polar motion matrix. */

    let rpom = pom00(xp, yp, sp);

    /* Combine to form the celestial-to-terrestrial matrix. */

    c2tcio(&rc2i, era, &rpom)

}