'use strict';

Object.defineProperty(exports, '__esModule', { value: true });

var base = require('./base.cjs');

/**
 * @copyright 2013 Sonia Keys
 * @copyright 2016 commenthol
 * @license MIT
 * @module binary
 */
const { atan, atan2, cos, sqrt, tan } = Math;

/**
 * computes mean anomaly for the given date.
 *
 * @param {Number} year - is a decimal year specifying the date
 * @param {Number} T - is time of periastron, as a decimal year
 * @param {Number} P - is period of revolution in mean solar years
 * @returns {Number} mean anomaly in radians.
 */
function meanAnomaly (year, T, P) { // (year, T, P float64)  float64
  const n = 2 * Math.PI / P;
  return base["default"].pmod(n * (year - T), 2 * Math.PI)
}

/**
 * Position computes apparent position angle and angular distance of
 * components of a binary star.
 *
 * @param {Number} a - is apparent semimajor axis in arc seconds
 * @param {Number} e - is eccentricity of the true orbit
 * @param {Number} i - is inclination relative to the line of sight
 * @param {Number} Ω - is position angle of the ascending node
 * @param {Number} ω - is longitude of periastron
 * @param {Number} E - is eccentric anomaly, computed for example with package kepler
 *  and the mean anomaly as returned by function M in this package.
 * @returns {Number[]} [θ, ρ]
 *  {Number} θ -is the apparent position angle in radians,
 *  {Number} ρ is the angular distance in arc seconds.
 */
function position (a, e, i, Ω, ω, E) { // (a, e, i, Ω, ω, E float64)  (θ, ρ float64)
  const r = a * (1 - e * cos(E));
  const ν = 2 * atan(sqrt((1 + e) / (1 - e)) * tan(E / 2));
  const [sinνω, cosνω] = base["default"].sincos(ν + ω);
  const cosi = cos(i);
  const num = sinνω * cosi;
  let θ = atan2(num, cosνω) + Ω;
  if (θ < 0) {
    θ += 2 * Math.PI;
  }
  const ρ = r * sqrt(num * num + cosνω * cosνω);
  return [θ, ρ]
}

/**
 * ApparentEccentricity returns apparent eccenticity of a binary star
 * given true orbital elements.
 *
 * @param {Number} e - is eccentricity of the true orbit
 * @param {Number} i - is inclination relative to the line of sight
 * @param {Number} ω - is longitude of periastron
 * @returns {Number} apparent eccenticity of a binary star
 */
function apparentEccentricity (e, i, ω) { // (e, i, ω float64)  float64
  const cosi = cos(i);
  const [sinω, cosω] = base["default"].sincos(ω);
  const A = (1 - e * e * cosω * cosω) * cosi * cosi;
  const B = e * e * sinω * cosω * cosi;
  const C = 1 - e * e * sinω * sinω;
  const d = A - C;
  const sqrtD = sqrt(d * d + 4 * B * B);
  return sqrt(2 * sqrtD / (A + C + sqrtD))
}

var binary = {
  meanAnomaly,
  position,
  apparentEccentricity
};

exports.apparentEccentricity = apparentEccentricity;
exports["default"] = binary;
exports.meanAnomaly = meanAnomaly;
exports.position = position;