use super::{bpn2xy, fw2m};

///  CIP X,Y given Fukushima-Williams bias-precession-nutation angles.

///

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

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

///

///  Status:  support function.

///

///  Given:

///     gamb     double    F-W angle gamma_bar (radians)

///     phib     double    F-W angle phi_bar (radians)

///     psi      double    F-W angle psi (radians)

///     eps      double    F-W angle epsilon (radians)

///

///  Returned (function value):

///     (x, y)   (f64, f64)  CIP unit vector X,Y

///

///  Notes:

///

///  1) Naming the following points:

///

///     ```text

///           e = J2000.0 ecliptic pole,

///           p = GCRS pole

///           E = ecliptic pole of date,

///     and   P = CIP,

///     ```

///

///     the four Fukushima-Williams angles are as follows:

///

///     ```text

///        gamb = gamma = epE

///        phib = phi = pE

///        psi = psi = pEP

///        eps = epsilon = EP

///     ```

///

///  2) The matrix representing the combined effects of frame bias,

///     precession and nutation is:

///

///        NxPxB = R_1(-epsA).R_3(-psi).R_1(phib).R_3(gamb)

///

///     The returned values x,y are elements [2][0] and [2][1] of the

///     matrix.  Near J2000.0, they are essentially angles in radians.

///

///  Called:

///     iauFw2m      F-W angles to r-matrix

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

///

///  Reference:

///

///     Hilton, J. et al., 2006, Celest.Mech.Dyn.Astron. 94, 351

pub fn fw2xy(gamb: f64, phib: f64, psi: f64, eps: f64) -> (f64, f64) {

    /* Form NxPxB matrix. */

    let r = fw2m(gamb, phib, psi, eps);

    /* Extract CIP X,Y. */

    bpn2xy(&r)

}