use crate::consts::{DAYSEC, DJM0, DJM77, ELG, TTMTAI};

///  Time scale transformation:  Geocentric Coordinate Time, TCG, to

///  Terrestrial Time, TT.

///

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

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

///

///  Status:  canonical.

///

///  Given:

///     tcg1,tcg2  double    TCG as a 2-part Julian Date

///

///  Returned:

///     tt1,tt2    double    TT as a 2-part Julian Date

///

///  Returned (function value):

///                int       status:  0 = OK

///

pub fn tcgtt(tcg1: f64, tcg2: f64) -> Result<(f64, f64), i32> {

    /* 1977 Jan 1 00:00:32.184 TT, as MJD */

    let t77t: f64 = DJM77 + TTMTAI / DAYSEC;

    let (tt1, tt2);

    /* Result, safeguarding precision. */

    if tcg1.abs() > tcg2.abs() {

        tt1 = tcg1;

        tt2 = tcg2 - ((tcg1 - DJM0) + (tcg2 - t77t)) * ELG;

    } else {

        tt1 = tcg1 - ((tcg2 - DJM0) + (tcg1 - t77t)) * ELG;

        tt2 = tcg2;

    }

    Ok((tt1, tt2))

}