Timestamp duration conversion

index.ts

// {second}.{millisecond}
// {minute}:{second}.{millisecond}
// {hour}:{...}

const unitScale = [
  1000 /* millsecond -> second */,
  60 /* second -> minute */,
  60 /* minute -> hour */,
  24 /* hour -> day */,
  7 /* day -> week */
];

const REGEX = /(?:\d+|-):*\d+\.\d+/;

function getScale(index: number): [number, number] {
  if (index < 0) return [NaN, NaN];

  let acc = 1;

  for (let t = 0; t < index; t++) {
    acc *= unitScale[t];

    if (t + 1 > unitScale.length) break;
  }

  return [unitScale[index], acc];
}

function floorBy(amount: number, factor: number): number {
  return Math.floor(amount * factor) / factor;
}

function parse(input: string): number {
  if (!REGEX.test(input)) {
    return NaN;
  }

  let result = 0;

  const segments = input.split(":").reverse();

  for (const [index, segment] of segments.entries()) {
    // if (segment === '-') continue;

    const [, scale] = getScale(index + 1);

    result += parseFloat(segment) * scale;
  }

  return result;
}

function generate(input: number): string {
  let result: number[] = [];

  for (let index = 0; unitScale.length > index && input >= 0; index++) {

    const [unit, scale] = getScale(index + 1);

    const remainder = (input / scale) % unit;

    if (~~remainder === 0) break;

    result.push(floorBy(remainder, index === 0 ? 1000 : 1));
  }

  return result.reverse().join(':');
}

parse("01:42:39.385")
generate(6159385)