use crate::erst::{ee00, gmst00};

use crate::pnp::{c2teqx, pn00, pom00, sp00};

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

///  the nutation and the polar motion.  IAU 2000.

///

///  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)

///     dpsi,deps  f64        nutation (Note 2)

///     xp,yp      f64        coordinates of the pole (radians, Note 3)

///

///  Returned:

///     rc2t       [[f64; 3]; 3]  celestial-to-terrestrial matrix (Note 4)

///

///  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:

///

///     ```text

///             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 caller is responsible for providing the nutation components;

///     they are in longitude and obliquity, in radians and are with

///     respect to the equinox and ecliptic of date.  For high-accuracy

///     applications, free core nutation should be included as well as

///     any other relevant corrections to the position of the CIP.

///

///  3) 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.

///

///  4) The matrix rc2t transforms from celestial to terrestrial

///     coordinates:

///

///        [TRS] = RPOM * R_3(GST) * RBPN * [CRS]

///

///        ```text

///              = 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), RBPN is the

///     bias-precession-nutation matrix, GST is the Greenwich (apparent)

///     Sidereal Time and RPOM is the polar motion matrix.

///

///  5) Although its name does not include "00", This function is in fact

///     specific to the IAU 2000 models.

///

///  Called:

///     iauPn00      bias/precession/nutation results, IAU 2000

///     iauGmst00    Greenwich mean sidereal time, IAU 2000

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

///     iauEe00      equation of the equinoxes, IAU 2000

///     iauPom00     polar motion matrix

///     iauC2teqx    form equinox-based celestial-to-terrestrial matrix

///

///  Reference:

///

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

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

pub fn c2tpe(

    tta: f64,

    ttb: f64,

    uta: f64,

    utb: f64,

    dpsi: f64,

    deps: f64,

    xp: f64,

    yp: f64,

) -> [[f64; 3]; 3] {

    /* Form the celestial-to-true matrix for this TT. */

    let (epsa, _, _, _, _, rbpn) = pn00(tta, ttb, dpsi, deps);

    /* Predict the Greenwich Mean Sidereal Time for this UT1 and TT. */

    let gmst = gmst00(uta, utb, tta, ttb);

    /* Predict the equation of the equinoxes given TT and nutation. */

    let ee = ee00(tta, ttb, epsa, dpsi);

    /* 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. */

    c2teqx(&rbpn, gmst + ee, &rpom)

}