CalendarHelper to calculate absolute interval between two dates

CalendarHelper.php

<?php
/**
 * @author Florent HAZARD <f.hazard@sowapps.com>
 * @license https://opensource.org/licenses/MIT
 */

use DateInterval;
use DateTime;
use DateTimeImmutable;
use DateTimeInterface;

/**
 * Class CalendarHelper
 * This class is a helper calendar manipulation
 * Very useful to get absolute interval between two dates using specific units
 *
 * @package App\Core\Calendar
 * @see https://www.php.net/manual/fr/class.dateinterval.php
 */
class CalendarHelper {
	
	const UNIT_YEAR = 'y';
	const UNIT_MONTH = 'm';
	const UNIT_DAY = 'd';
	const UNIT_HOUR = 'h';
	const UNIT_MINUTE = 'i';
	const UNIT_SECOND = 's';
	const UNIT_MICROSECOND = 'f';
	
	/**
	 * List of all units in order from tallest to smallest
	 */
	const UNITS = [
		// UNIT => X child units
		// X string get property's value in interval
		// X null stops process
		self::UNIT_YEAR        => 12,
		self::UNIT_MONTH       => 'days',
		self::UNIT_DAY         => 24,
		self::UNIT_HOUR        => 60,
		self::UNIT_MINUTE      => 60,
		self::UNIT_SECOND      => 1,// MS are a fraction of seconds, so MS are in seconds
		self::UNIT_MICROSECOND => null,
	];
	
	/**
	 * Get absolute interval between two date specifying the units to use.
	 * Example: Get only hours and minutes between $date1 and date2
	 * <code><?php $calendarHelper->getAbsoluteInterval($date1, $date2, [CalendarHelper::UNIT_HOUR, CalendarHelper::UNIT_MINUTE]) ?></code>
	 *
	 * @param $date1
	 * @param $date2
	 * @param array $units
	 * @return DateInterval
	 * @see convertToAbsolute
	 */
	public function getAbsoluteInterval($date1, $date2, array $units): DateInterval {
		$date1 = $this->formatToDatetime($date1);
		$date2 = $this->formatToDatetime($date2);
		
		return $this->convertToAbsolute(date_diff($date1, $date2), $units);
	}
	
	/**
	 * @param DateTimeInterface|string|int $date
	 * @return DateTime
	 */
	public function formatToDatetime($date): DateTime {
		if( $date instanceof DateTime ) {
			return $date;
		}
		if( $date instanceof DateTimeImmutable ) {
			return DateTime::createFromImmutable($date);
		}
		if( is_string($date) ) {
			return new DateTime($date);
		}
		
		// int
		return new DateTime('@' . $date);
	}
	
	/**
	 * Get absolute interval from any interval
	 *
	 * @param DateInterval $interval
	 * @param array $units
	 * @return DateInterval
	 */
	public function convertToAbsolute(DateInterval $interval, array $units): DateInterval {
		$absInterval = new DateInterval('PT0S');
		$absInterval->invert = $interval->invert;
		$parentCounter = 0;
		$abs = false;
		foreach( self::UNITS as $unit => $childCount ) {
			$unitValue = $parentCounter + ($abs ? 0 : $interval->$unit);
			if( in_array($unit, $units) ) {
				// Consume inheritance
				$absInterval->$unit = $unitValue;
				$parentCounter = 0;
				$abs = false;
			} elseif( $childCount !== null ) {
				// Transmit inheritance
				$abs = is_string($childCount);
				$parentCounter = $abs ? ($interval->$childCount ?: 0) : $unitValue * $childCount;
			}
		}
		
		return $absInterval;
	}
	
}