use crate::vm::anp;

use super::{ee00a, gmst00};

///  Greenwich apparent sidereal time, IAU 2000A

///

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

///  resolutions).

///

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

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

///

///  Status:  canonical model.

///

///  Given:

///  ```

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

///     tta,ttb    double    TT as a 2-part Julian Date (Notes 1,2)

///  ```

///  Returned (function value):

///  ```

///                double    Greenwich apparent sidereal time (radians)

///  ```

///  Notes:

///

///  1) The UT1 and TT dates uta+utb and tta+ttb respectively, are both

///     Julian Dates, apportioned in any convenient way between the

///     argument pairs.  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 (in the case of UT;  the TT is not at all critical

///     in this respect).  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) Both UT1 and TT are required, UT1 to predict the Earth rotation

///     and TT to predict the effects of precession-nutation.  If UT1 is

///     used for both purposes, errors of order 100 microarcseconds

///     result.

///

///  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

///     iauEe00a     equation of the equinoxes, IAU 2000A

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

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

///

pub fn gst00a(uta: f64, utb: f64, tta: f64, ttb: f64) -> f64 {

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

    let ee00a = ee00a(tta, ttb);

    let gst = anp(gmst00 + ee00a);

    gst

}