Unfinished attempt at converting duration strings to DateInterval objects

createDateIntervalFromDurationString.php

<?php

/**
 * Take duration string from a database - e.g. 00:21:15.2581 - and convert it to
 * a DateInterval object (PHP's built-in duration object). 
 * 
 * DateInterval does not support construction from these strings directly, which
 * is why this function is needed.
 * 
 * Supported units are years, months, days, hours, minutes, and seconds.
 * Weeks and microseconds are not currently supported.
 * 
 * @param string $duration_string The duration to convert from
 * @return DateInterval object of correct duration
 * 
 * @see https://www.php.net/manual/en/dateinterval.construct.php
 */
function createDateIntervalFromDurationString($duration_string) {
	$duration_array = explode(':', $duration_string); // e.g. 00:21:15.2581
	$array_size = count($duration_array);
	$construction_string = '';
	$operator_array = [
		'S', // seconds
		'M', // minutes
		'H', // hours
		'D', // days
		'M', // months
		'Y'  // years
	];

	$j = 0;
	for ($i = $array_size; $i >= 0; $i--) {
		$construction_string = (round($duration_array[$i]).$operator_array[$j]) . $construction_string;
		$j++;
	}
	$construction_string = 'P' . $construction_string;

	return new DateInterval($construction_string);
}