Convert between 6dp ISO8601-format dates and Unix epoch microseconds in Zapatos

iso8601us.ts

import { DateString, strict } from 'zapatos/db';

/**
 * Convert a `DateString` (to 6dp) to microseconds since 1 January 1970.
 * Nullability is preserved (e.g `DateString | null` becomes `number | null`)
 * using `strict`. Note: only dates before 5 June 2255 can be represented 
 * within `Number.MAX_SAFE_INTEGER` this way.
 */
export const toUnixMicroseconds = strict((d: DateString) => {
  const
    us = Date.parse(d) * 1000,
    uMatch = d.match(/[.]\d{3}(\d{3})([-+][\d:]+|Z|)$/),
    uAddition = uMatch ? parseInt(uMatch[1], 10) : 0;

  return us + uAddition;
});

/**
 * Convert microseconds since 1 January 1970 to a `DateString`. Nullability is
 * preserved (e.g `number | null` becomes `DateString | null`) using `strict`.
 * Note: only dates before 5 June 2255 can be represented within 
 * `Number.MAX_SAFE_INTEGER` this way.
 */
export const fromUnixMicroseconds = strict((microseconds: number) => {
  const
    us = Math.floor(microseconds),
    ms = Math.floor(us / 1000),
    uStr = String(us - ms * 1000),
    uPadded = '00'.slice(uStr.length - 1) + uStr,
    iso = new Date(ms).toISOString(),
    tz = iso.match(/[.]\d{3}(|Z|[-+][\d:]+)$/)![1];

  return iso.slice(0, iso.length - tz.length) + uPadded + tz as DateString;
});