File RRule/LocalTime.php | PHP iCal Parser API

1:	<?php
2:	declare(strict_types=1);
3:
4:	namespace om\RRule;
5:
6:	use DateTime;
7:	use DateTimeZone;
8:
9:	/**
10:	* Converts a local (wall-clock) time to an instant as RFC 5545, section 3.3.5 requires:
11:	* an ambiguous time (DST fall-back) is the first occurrence, a nonexistent time (DST gap)
12:	* uses the UTC offset before the gap. PHP itself is not consistent in these cases.
13:	*/
14:	final class LocalTime {
15:	/**
16:	* @param int $local the wall-clock time as seconds since 1970-01-01 00:00 (as if it were UTC)
17:	*/
18:	public static function timestamp(DateTimeZone $timezone, int $local): int {
19:	static $probe;
20:	$probe ??= new DateTime('@0');
21:	$offsetAt = static fn(int $timestamp): int => $timezone->getOffset($probe->setTimestamp($timestamp));
22:
23:	// there is at most one transition within two days
24:	$before = $offsetAt($local - 2 * 86400);
25:	$after = $offsetAt($local + 2 * 86400);
26:	if ($before === $after && $offsetAt($local - $before) === $before) {
27:	return $local - $before;
28:	}
29:
30:	$valid = [];
31:	foreach ([$before, $after] as $offset) {
32:	$timestamp = $local - $offset;
33:	if ($offsetAt($timestamp) === $offset) {
34:	$valid[] = $timestamp;
35:	}
36:	}
37:	if ($valid !== []) {
38:	return min($valid); // the first of repeated times
39:	}
40:	// a nonexistent time is interpreted with the offset before the gap
41:	return $local - $before;
42:	}
43:	}
44: