use std::ops::Rem;

use crate::consts::{D2PI, DAS2R, DJ00, DJC};

use crate::pnp::{nut80, obl80};

use crate::vm::anpm;

///  Equation of the equinoxes, IAU 1994 model.

///

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

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

///

///  Status:  canonical model.

///

///  Given:

///  ```

///     date1,date2   double     TDB date (Note 1)

///  ```

///  Returned (function value):

///  ```

///                   double     equation of the equinoxes (Note 2)

///  ```

///  Notes:

///

///  1) The date date1+date2 is a Julian Date, apportioned in any

///     convenient way between the two arguments.  For example,

///     JD(TT)=2450123.7 could be expressed in any of these ways,

///     among others:

///  ```

///            date1          date2

///

///         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 method is best matched to the way

///     the argument is handled internally and will deliver the

///     optimum resolution.  The MJD method and the date & time methods

///     are both good compromises between resolution and convenience.

///

///  2) The result, which is in radians, operates in the following sense:

///

///        Greenwich apparent ST = GMST + equation of the equinoxes

///

///  Called:

///  ```

///     iauAnpm      normalize angle into range +/- pi

///     iauNut80     nutation, IAU 1980

///     iauObl80     mean obliquity, IAU 1980

///  ```

///  References:

///

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

///

///     Capitaine, N. & Gontier, A.-M., 1993, Astron.Astrophys., 275,

///     645-650.

pub fn eqeq94(date1: f64, date2: f64) -> f64 {

    // double t,  om,  dpsi,  deps,  eps0, ee;

    /* Interval between fundamental epoch J2000.0 and given date (JC). */

    let t = ((date1 - DJ00) + date2) / DJC;

    /* Longitude of the mean ascending node of the lunar orbit on the */

    /* ecliptic, measured from the mean equinox of date. */

    let om = anpm(

        (450160.280 + (-482890.539 + (7.455 + 0.008 * t) * t) * t) * DAS2R

            + (-5.0 * t).rem(1.0) * D2PI,

    );

    /* Nutation components and mean obliquity. */

    let (dpsi, _) = nut80(date1, date2);

    let eps0 = obl80(date1, date2);

    /* Equation of the equinoxes. */

    let ee = dpsi * eps0.cos() + DAS2R * (0.00264 * om.sin() + 0.000063 * (om + om).sin());

    ee

}