Repository: adobe/react-spectrum
File: packages/@react-stately/datepicker/src/IncompleteDate.ts (TypeScript)

Code before:
        // Allow incrementing up to the maximum number of days in any month.
        res.day = cycleValue(res.day ?? 1, amount, 1, this.calendar.getMaximumDaysInMonth());
        break;
      case 'hour': {
        // if date is fully defined and we have a time zone, use ZonedDateTime to cycle so DST fallback is properly handled
        if ('timeZone' in placeholder && res.year != null && res.month != null && res.day != null) {
          let hour = res.hour ?? 0;
          hour = fromHourCycle(hour, res.dayPeriod ?? 0, this.hourCycle);
          // get the offset of the current date time in case we don't have a offset stored already (can't just use placeholder offset since that is a different datetime).
          if (res.offset == null) {
            let calendarDateTime = new CalendarDateTime(
              this.calendar,
              res.era ?? placeholder.era,
              res.year,
              res.month,
              res.day,
              hour,
              res.minute ?? placeholder.minute,
              res.second ?? placeholder.second,
              res.millisecond ?? placeholder.millisecond
            );

            res.offset = toZoned(calendarDateTime, placeholder.timeZone).offset;
          }

          let date = new ZonedDateTime(this.calendar, res.era ?? placeholder.era, res.year, res.month, res.day, placeholder.timeZone, res.offset, hour, res.minute ?? placeholder.minute, res.second ?? placeholder.second ?? 0, res.millisecond ?? placeholder.millisecond ?? 0);
          date = date.cycle('hour', amount, {hourCycle: this.hourCycle === 'h12' ? 12 : 24, round: false});
          let [dayPeriod, adjustedHour] = toHourCycle(date.hour, this.hourCycle);
          res.hour = adjustedHour;
          res.dayPeriod = dayPeriod;
          res.offset = date.offset;
        } else {
          let hours = res.hour ?? 0;
          let limits = this.getSegmentLimits('hour')!;
          res.hour = cycleValue(hours, amount, limits.minValue, limits.maxValue);
          if (res.dayPeriod == null && 'hour' in placeholder) {
            res.dayPeriod = toHourCycle(placeholder.hour, this.hourCycle)[0];
          }
        }
        break;
      }
      case 'dayPeriod':
        res.dayPeriod = cycleValue(res.dayPeriod ?? 0, amount, 0, 1);
        break;
      case 'minute':
        res.minute = cycleValue(res.minute ?? 0, amount, 0, 59, true);
        break;
      case 'second':
        res.second = cycleValue(res.second ?? 0, amount, 0, 59, true);
        break;
    }

Review comment (refactor):
I think we could simplify the above (including the if statement) to this:

```tsx
let date = this.toValue(placeholder) as ZonedDateTime;
```

If `offset` is null, then this will fall back to the value calculated by `value.set` inside `toValue`.

Code after:
        // Allow incrementing up to the maximum number of days in any month.
        res.day = cycleValue(res.day ?? 1, amount, 1, this.calendar.getMaximumDaysInMonth());
        break;
      case 'hour': {
        // if date is fully defined or it is just a time field, and we have a time zone, use toValue to get a ZonedDateTime to cycle
        // so DST fallback is properly handled
        let hasDateSegements = displaySegments.some(s => ['year', 'month', 'day'].includes(s));
        if ('timeZone' in placeholder && (!hasDateSegements || (res.year != null && res.month != null && res.day != null))) {
          let date = this.toValue(placeholder) as ZonedDateTime;
          date = date.cycle('hour', amount, {hourCycle: this.hourCycle === 'h12' ? 12 : 24, round: false});
          let [dayPeriod, adjustedHour] = toHourCycle(date.hour, this.hourCycle);
          res.hour = adjustedHour;
          res.dayPeriod = dayPeriod;
          res.offset = date.offset;
        } else {
          let hours = res.hour ?? 0;
          let limits = this.getSegmentLimits('hour')!;
          res.hour = cycleValue(hours, amount, limits.minValue, limits.maxValue);
          if (res.dayPeriod == null && 'hour' in placeholder) {
            res.dayPeriod = toHourCycle(placeholder.hour, this.hourCycle)[0];
          }
        }
        break;
      }
      case 'dayPeriod':
        res.dayPeriod = cycleValue(res.dayPeriod ?? 0, amount, 0, 1);
        break;
      case 'minute':
        res.minute = cycleValue(res.minute ?? 0, amount, 0, 59, true);
        break;
      case 'second':
        res.second = cycleValue(res.second ?? 0, amount, 0, 59, true);
        break;
    }

    return res;
  }

  /** Converts the incomplete date to a full date value, using the provided value for any unset fields. */
  toValue(value: DateValue): DateValue {
    if ('hour' in value) {
      let hour = this.hour;
      if (hour != null) {
        hour = fromHourCycle(hour, this.dayPeriod ?? 0, this.hourCycle);
      } else if (this.hourCycle === 'h12' || this.hourCycle === 'h11') {
        hour = this.dayPeriod === 1 ? 12 : 0;
      }

      let res = value.set({
        era: this.era ?? value.era,
        year: this.year ?? value.year,