Function modifyDateBy

packages/localization/src/dates/modifyDateBy.ts:14–57

(date: CalendarDate, amount: number, unit: string, preserveDate = true, minDate?: CalendarDate, maxDate?: CalendarDate)

 * @param maxDate maximum date to enforce
 */
const modifyDateBy = (date: CalendarDate, amount: number, unit: string, preserveDate = true, minDate?: CalendarDate, maxDate?: CalendarDate) => {
	const newDate = new CalendarDate(date);

	switch (unit) {
	case "day":
		newDate.setDate(date.getDate() + amount);
		break;
	case "month":
		if (preserveDate) {
			newDate.setMonth(date.getMonth() + amount);
			const stillSameMonth = amount === -1 && newDate.getMonth() === date.getMonth(); // f.e. PageUp remained in the same month
			const monthSkipped = amount === 1 && newDate.getMonth() - date.getMonth() > 1; // f.e. PageDown skipped a whole month
			if (stillSameMonth || monthSkipped) { // Select the last day of the month in any of these 2 scenarios
				newDate.setDate(0);
			}
		} else {
			if (amount === 1) {
				newDate.setMonth(newDate.getMonth() + 1, 1);
			}
			if (amount === -1) {
				newDate.setDate(0);
			}
		}
		break;
	case "year":
		newDate.setYear(date.getYear() + amount);
		if (newDate.getMonth() !== date.getMonth()) { // f.e. 29th Feb to next/prev year
			newDate.setDate(0); // Select the last day of the month
		}
		break;
	default:
		break;
	}

	if (minDate && newDate.isBefore(minDate)) {
		return new CalendarDate(minDate);
	}

	if (maxDate && newDate.isAfter(maxDate)) {
		return new CalendarDate(maxDate);
	}

	return newDate;
};

export default modifyDateBy;