use crate::vm::anp;

use super::{eqeq94, gmst82};

///  Greenwich apparent sidereal time, IAU 1994

///

///  Greenwich apparent sidereal time (consistent with IAU 1982/94

///  resolutions).

///

///  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 1982 and 1994 resolutions,

///     except that accuracy has been compromised for the sake of

///     convenience in that UT is used instead of TDB (or TT) to compute

///     the equation of the equinoxes.

///

///  3) This GAST must be used only in conjunction with contemporaneous

///     IAU standards such as 1976 precession, 1980 obliquity and 1982

///     nutation.  It is not compatible with the IAU 2000 resolutions.

///

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

///

///  Called:

///  ```

///     iauGmst82    Greenwich mean sidereal time, IAU 1982

///     iauEqeq94    equation of the equinoxes, IAU 1994

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

///  ```

///  References:

///

///     Explanatory Supplement to the Astronomical Almanac,

///     P. Kenneth Seidelmann (ed), University Science Books (1992)

///

///     IAU Resolution C7, Recommendation 3 (1994)

///

pub fn gst94(uta: f64, utb: f64) -> f64 {

    let gmst82 = gmst82(uta, utb);

    let eqeq94 = eqeq94(uta, utb);

    let gst = anp(gmst82 + eqeq94);

    gst

}