use crate::consts::{DAYSEC, DJM0, DJM77, ELB, TDB0, TTMTAI};

///  Time scale transformation:  Barycentric Coordinate Time, TCB, to

///  Barycentric Dynamical Time, TDB.

///

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

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

///

///  Status:  canonical.

///

///  Given:

///     tcb1,tcb2  double    TCB as a 2-part Julian Date

///

///  Returned:

///     tdb1,tdb2  double    TDB as a 2-part Julian Date

///

///  Returned (function value):

///                int       status:  0 = OK

///

pub fn tcbtdb(tcb1: f64, tcb2: f64) -> Result<(f64, f64), i32> {

    /* 1977 Jan 1 00:00:32.184 TT, as two-part JD */

    const T77TD: f64 = DJM0 + DJM77;

    let t77tf: f64 = TTMTAI / DAYSEC;

    /* TDB (days) at TAI 1977 Jan 1.0 */

    let tdb0_val: f64 = TDB0 / DAYSEC;

    let d;

    let (tdb1, tdb2);

    /* Result, safeguarding precision. */

    if tcb1.abs() > tcb2.abs() {

        d = tcb1 - T77TD;

        tdb1 = tcb1;

        tdb2 = tcb2 + tdb0_val - (d + (tcb2 - t77tf)) * ELB;

    } else {

        d = tcb2 - T77TD;

        tdb1 = tcb1 + tdb0_val - (d + (tcb1 - t77tf)) * ELB;

        tdb2 = tcb2;

    }

    Ok((tdb1, tdb2))

}