use crate::vm::anp;

use super::{ee00b, gmst00};

///  Greenwich apparent sidereal time, IAU 2000B

///

///  Greenwich apparent sidereal time (consistent with IAU 2000

///  resolutions but using the truncated nutation model IAU 2000B).

///

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

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

///

///  Status:  support function.

///

///  Given:

///  ```

///     uta,utb    double    UT1 as a 2-part Julian Date (Notes 1,2)

///  ```

///  Returned (function value):

///  ```

///                double    Greenwich apparent sidereal time (radians)

///  ```

///  Notes:

///

///  1) The UT1 date uta+utb is a Julian Date, apportioned in any

///     convenient way between the argument pair.  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.  For UT, the date & time

///     method is best matched to the algorithm that is used by the Earth

///     Rotation Angle function, called internally:  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 result is compatible with the IAU 2000 resolutions, except

///     that accuracy has been compromised for the sake of speed and

///     convenience in two respects:

///

///     . UT is used instead of TDB (or TT) to compute the precession

///       component of GMST and the equation of the equinoxes.  This

///       results in errors of order 0.1 mas at present.

///

///     . The IAU 2000B abridged nutation model (McCarthy & Luzum, 2003)

///       is used, introducing errors of up to 1 mas.

///

///  3) This GAST is compatible with the IAU 2000 resolutions and must be

///     used only in conjunction with other IAU 2000 compatible

///     components such as precession-nutation.

///

///  4) The result is returned in the range 0 to 2pi.

///

///  5) The algorithm is from Capitaine et al. (2003) and IERS

///     Conventions 2003.

///

///  Called:

///  ```

///     iauGmst00    Greenwich mean sidereal time, IAU 2000

///     iauEe00b     equation of the equinoxes, IAU 2000B

///     iauAnp       normalize angle into range 0 to 2pi

///  ```

///  References:

///

///     Capitaine, N., Wallace, P.T. and McCarthy, D.D., "Expressions to

///     implement the IAU 2000 definition of UT1", Astronomy &

///     Astrophysics, 406, 1135-1149 (2003)

///

///     McCarthy, D.D. & Luzum, B.J., "An abridged model of the

///     precession-nutation of the celestial pole", Celestial Mechanics &

///     Dynamical Astronomy, 85, 37-49 (2003)

///

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

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

///

pub fn gst00b(uta: f64, utb: f64) -> f64 {

    let gmst00 = gmst00(uta, utb, uta, utb);

    let ee00b = ee00b(uta, utb);

    let gst = anp(gmst00 + ee00b);

    gst

}