Function durationBetween

packages/graph/src/TemporalTypes.ts:1637–1762

(start: TemporalValue, end: TemporalValue)

 * Compute the duration between two temporal values.
 */
export function durationBetween(start: TemporalValue, end: TemporalValue): DurationValue | null {
  // Handle dates
  if (start instanceof DateValue && end instanceof DateValue) {
    const _startDate = new Date(Date.UTC(start.year, start.month - 1, start.day));
    const endDate = new Date(Date.UTC(end.year, end.month - 1, end.day));

    // Calculate difference in months
    let months = (end.year - start.year) * 12 + (end.month - start.month);

    // Adjust for day difference
    if (end.day < start.day) {
      months--;
    }

    // Calculate remaining days
    const adjustedStart = new Date(Date.UTC(start.year, start.month - 1 + months, start.day));
    const days = Math.round((endDate.getTime() - adjustedStart.getTime()) / (24 * 60 * 60 * 1000));

    return new DurationValue(months, days, 0, 0);
  }

  // Handle local times
  if (start instanceof LocalTimeValue && end instanceof LocalTimeValue) {
    const startNanos =
      start.hour * 3_600_000_000_000 +
      start.minute * 60_000_000_000 +
      start.second * 1_000_000_000 +
      start.nanosecond;
    const endNanos =
      end.hour * 3_600_000_000_000 +
      end.minute * 60_000_000_000 +
      end.second * 1_000_000_000 +
      end.nanosecond;

    const diffNanos = endNanos - startNanos;
    const seconds = Math.trunc(diffNanos / 1_000_000_000);
    const nanoseconds = diffNanos % 1_000_000_000;

    return new DurationValue(0, 0, seconds, nanoseconds);
  }

  // Handle times with offset (convert to common reference)
  if (start instanceof TimeValue && end instanceof TimeValue) {
    const startNanos =
      (start.hour * 3600 + start.minute * 60 + start.second - start.offset) * 1_000_000_000 +
      start.nanosecond;
    const endNanos =
      (end.hour * 3600 + end.minute * 60 + end.second - end.offset) * 1_000_000_000 +
      end.nanosecond;

    const diffNanos = endNanos - startNanos;
    const seconds = Math.trunc(diffNanos / 1_000_000_000);
    const nanoseconds = diffNanos % 1_000_000_000;

    return new DurationValue(0, 0, seconds, nanoseconds);
  }

  // Handle local datetimes