parsedate.js

import { JulianOffset } from "./constants";
import { ERRORTYPES as error } from "./error";
import isNaN from "./isnan";
import isDate from "./isdate";

export default function parsedate(val) {
  /* *******************
  Extracted from Social Calc

  convert_date_julian_to_gregorian(juliandate)

  ymd->{}
  .year
  .month
  .day

  From: http://aa.usno.navy.mil/faq/docs/JD_Formula.html
  Uses: Fliegel, H. F. and van Flandern, T. C. (1968). Communications of the ACM, Vol. 11, No. 10 (October, 1968).
  Translated from the FORTRAN

  ************************* */
  function convert_date_julian_to_gregorian(juliandate) {
    var L, N, I, J, K;

    L = juliandate + 68569;
    N = Math.floor(4 * L / 146097);
    L = L - Math.floor((146097 * N + 3) / 4);
    I = Math.floor(4000 * (L + 1) / 1461001);
    L = L - Math.floor(1461 * I / 4) + 31;
    J = Math.floor(80 * L / 2447);
    K = L - Math.floor(2447 * J / 80);
    L = Math.floor(J / 11);
    J = J + 2 - 12 * L;
    I = 100 * (N - 49) + I + L;

    return new Date(I, J - 1, K);
  }

  if (val instanceof Error) {
    return val;
  } else if (isDate(val)) {
    return val;
  } else if (typeof val === "number") {

    return convert_date_julian_to_gregorian(Math.floor(val + JulianOffset));
  } else if (typeof val === "string") {
    var timestamp = Date.parse(val);
    if (isNaN(timestamp)) {
      return error.value;
    }
    return new Date(timestamp);
  }

  return error.value;
}