numfmt/lib/toYMD.js

Full Excel style number formatting

import { EPOCH_1317, EPOCH_1904 } from './constants.js';
const floor = Math.floor;

// https://www.codeproject.com/Articles/2750/Excel-Serial-Date-to-Day-Month-Year-and-Vice-Versa
export function toYMD_1900 (ord, leap1900 = true) {
  if (leap1900 && ord >= 0) {
    if (ord === 0) {
      return [ 1900, 1, 0 ];
    }
    if (ord === 60) {
      return [ 1900, 2, 29 ];
    }
    if (ord < 60) {
      return [ 1900, (ord < 32 ? 1 : 2), ((ord - 1) % 31) + 1 ];
    }
  }
  let l = ord + 68569 + 2415019;
  const n = floor((4 * l) / 146097);
  l = l - floor((146097 * n + 3) / 4);
  const i = floor((4000 * (l + 1)) / 1461001);
  l = l - floor((1461 * i) / 4) + 31;
  const j = floor((80 * l) / 2447);
  const nDay = l - floor((2447 * j) / 80);
  l = floor(j / 11);
  const nMonth = j + 2 - (12 * l);
  const nYear = 100 * (n - 49) + i + l;
  return [ nYear | 0, nMonth | 0, nDay | 0 ];
}

export function toYMD_1904 (ord) {
  return toYMD_1900(ord + 1462);
}

// https://web.archive.org/web/20080209173858/https://www.microsoft.com/globaldev/DrIntl/columns/002/default.mspx
// > [algorithm] is used in many Microsoft products, including all
// > operating systems that support Arabic locales, Microsoft Office,
// > COM, Visual Basic, VBA, and SQL Server 2000.
export function toYMD_1317 (ord) {
  if (ord === 60) {
    throw new Error('#VALUE!');
  }
  if (ord <= 1) {
    return [ 1317, 8, 29 ];
  }
  if (ord < 60) {
    return [ 1317, (ord < 32 ? 9 : 10), 1 + ((ord - 2) % 30) ];
  }
  const y = 10631 / 30;
  const shift1 = 8.01 / 60;
  let z = ord + 466935;
  const cyc = floor(z / 10631);
  z = z - 10631 * cyc;
  const j = floor((z - shift1) / y);
  z = z - floor(j * y + shift1);
  const m = floor((z + 28.5001) / 29.5);
  if (m === 13) {
    return [ 30 * cyc + j, 12, 30 ];
  }
  return [ 30 * cyc + j, m, z - floor(29.5001 * m - 29) ];
}

export function toYMD (ord, system = 0, leap1900 = true) {
  const int = floor(ord);
  if (system === EPOCH_1317) {
    return toYMD_1317(int);
  }
  if (system === EPOCH_1904) {
    return toYMD_1904(int);
  }
  return toYMD_1900(int, leap1900);
}