use crate::astro::ld;

use crate::consts::{AULT, DAYSEC};

use crate::vm::{cp, pdp, pmp, pn, ppsp};

use super::IauLdBody;

///  Light deflection by multiple solar−system bodies

///

///  For a star, apply light deflection by multiple solar-system bodies,

///  as part of transforming coordinate direction into natural direction.

///

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

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

///

///  Status:  support function.

///

///  Given:

///  ```

///     n    int           number of bodies (note 1)

///     b    iauLDBODY[n]  data for each of the n bodies (Notes 1,2):

///      bm   double         mass of the body (solar masses, Note 3)

///      dl   double         deflection limiter (Note 4)

///      pv   [2][3]         barycentric PV of the body (au, au/day)

///     ob   double[3]     barycentric position of the observer (au)

///     sc   double[3]     observer to star coord direction (unit vector)

///  ```

///  Returned:

///  ```

///     sn    double[3]      observer to deflected star (unit vector)

///  ```

///  1) The array b contains n entries, one for each body to be

///     considered.  If n = 0, no gravitational light deflection will be

///     applied, not even for the Sun.

///

///  2) The array b should include an entry for the Sun as well as for

///     any planet or other body to be taken into account.  The entries

///     should be in the order in which the light passes the body.

///

///  3) In the entry in the b array for body i, the mass parameter

///     b[i].bm can, as required, be adjusted in order to allow for such

///     effects as quadrupole field.

///

///  4) The deflection limiter parameter b[i].dl is phi^2/2, where phi is

///     the angular separation (in radians) between star and body at

///     which limiting is applied.  As phi shrinks below the chosen

///     threshold, the deflection is artificially reduced, reaching zero

///     for phi = 0.   Example values suitable for a terrestrial

///     observer, together with masses, are as follows:

///  ```

///        body i     b[i].bm        b[i].dl

///

///        Sun        1.0            6e-6

///        Jupiter    0.00095435     3e-9

///        Saturn     0.00028574     3e-10

///  ```

///  5) For cases where the starlight passes the body before reaching the

///     observer, the body is placed back along its barycentric track by

///     the light time from that point to the observer.  For cases where

///     the body is "behind" the observer no such shift is applied.  If

///     a different treatment is preferred, the user has the option of

///     instead using the iauLd function.  Similarly, iauLd can be used

///     for cases where the source is nearby, not a star.

///

///  6) The returned vector sn is not normalized, but the consequential

///     departure from unit magnitude is always negligible.

///

///  7) The arguments sc and sn can be the same array.

///

///  8) For efficiency, validation is omitted.  The supplied masses must

///     be greater than zero, the position and velocity vectors must be

///     right, and the deflection limiter greater than zero.

///

///  Reference:

///

///     Urban, S. & Seidelmann, P. K. (eds), Explanatory Supplement to

///     the Astronomical Almanac, 3rd ed., University Science Books

///     (2013), Section 7.2.4.

///

///  Called:

///  ```

///     iauCp        copy p-vector

///     iauPdp       scalar product of two p-vectors

///     iauPmp       p-vector minus p-vector

///     iauPpsp      p-vector plus scaled p-vector

///     iauPn        decompose p-vector into modulus and direction

///     iauLd        light deflection by a solar-system body

///  ```

pub fn ldn(n: i32, b: &[IauLdBody], ob: &[f64; 3], sc: &[f64; 3]) -> [f64; 3] {

    let mut sn = [0.0; 3];

    /* Light time for 1 au (days) */

    const CR: f64 = AULT / DAYSEC;

    // int i;

    // double  v[3], dt, ev[3], em, e[3];

    /* Star direction prior to deflection. */

    cp(&sc, &mut sn);

    /* Body by body. */

    for i in 0..n {

        /* Body to observer vector at epoch of observation (au). */

        let v = pmp(ob, &b[i as usize].pv[0]);

        /* Minus the time since the light passed the body (days). */

        let dt = pdp(&mut sn, &v) * CR;

        /* Neutralize if the star is "behind" the observer. */

        let dt = dt.min(0.0);

        /* Backtrack the body to the time the light was passing the body. */

        let ev = ppsp(&v, -dt, &b[i as usize].pv[1]);

        /* Body to observer vector as magnitude and direction. */

        let (em, e) = pn(&ev);

        /* Apply light deflection for this body. */

        sn = ld(b[i as usize].bm, sn, sn, e, em, b[i as usize].dl);

        /* Next body. */

    }

    sn

}