DateTime: constructor and modify() correctly handle the relative time even if the daylight saving time is changed

Author: dg

src/Utils/DateTime.php

@@ -110,14 +110,13 @@ public static function createFromFormat(
 
 	public function __construct(string $datetime = 'now', ?\DateTimeZone $timezone = null)
 	{
-		parent::__construct($datetime, $timezone);
-		$this->handleErrors($datetime);
+		$this->apply($datetime, $timezone, true);
 	}
 
 
 	public function modify(string $modifier): static
 	{
-		parent::modify($modifier) && $this->handleErrors($modifier);
+		$this->apply($modifier);
 		return $this;
 	}
 
@@ -155,6 +154,34 @@ public static function relativeToSeconds(string $relativeTime): int
 	}
 
 
+	private function apply(string $datetime, $timezone = null, bool $ctr = false): void
+	{
+		$relPart = '';
+		$absPart = preg_replace_callback(
+			'/[+-]?\s*\d+\s+((microsecond|millisecond|[mµu]sec)s?|[mµ]s|sec(ond)?s?|min(ute)?s?|hours?)\b/iu',
+			function ($m) use (&$relPart) {
+				$relPart .= $m[0] . ' ';
+				return '';
+			},
+			$datetime,
+		);
+
+		if ($ctr) {
+			parent::__construct($absPart, $timezone);
+			$this->handleErrors($datetime);
+		} elseif (trim($absPart)) {
+			parent::modify($absPart) && $this->handleErrors($datetime);
+		}
+
+		if ($relPart) {
+			$timezone ??= $this->getTimezone();
+			$this->setTimezone(new \DateTimeZone('UTC'));
+			parent::modify($relPart) && $this->handleErrors($datetime);
+			$this->setTimezone($timezone);
+		}
+	}
+
+
 	/**
 	 * Returns JSON representation in ISO 8601 (used by JavaScript).
 	 */

tests/Utils/DateTime.modify.phpt

@@ -14,7 +14,7 @@ require __DIR__ . '/../bootstrap.php';
 date_default_timezone_set('Europe/Prague');
 
 
-test('Basic operations', function () {
+test('Basic operations (no DST involved)', function () {
 	$base = new DateTime('2024-07-15 10:00:00'); // Summer time (CEST)
 
 	$dt = clone $base;
@@ -35,6 +35,68 @@ test('Basic operations', function () {
 });
 
 
+test('Spring DST transition (2025-03-30 02:00 -> 03:00)', function () {
+	$startSpring = new DateTime('2025-03-30 01:45:00'); // Before the jump (CET +01:00)
+
+	// Modification ending BEFORE the jump
+	$dt = clone $startSpring;
+	$dt->modify('+10 minutes');
+	Assert::same('2025-03-30 01:55:00 CET (+01:00)', $dt->format('Y-m-d H:i:s T (P)'), '+10 min (ends before jump)');
+
+	// Modification crossing the jump (duration logic thanks to Nette fix)
+	$dt = clone $startSpring;
+	$dt->modify('+30 minutes'); // 01:45 CET + 30 min duration = 01:15 UTC = 03:15 CEST
+	Assert::same('2025-03-30 03:15:00 CEST (+02:00)', $dt->format('Y-m-d H:i:s T (P)'), '+30 min (crosses jump)');
+
+	$dt = clone $startSpring;
+	$dt->modify('+90 minutes'); // 01:45 CET + 90 min duration = 02:15 UTC = 04:15 CEST (Key test!)
+	Assert::same('2025-03-30 04:15:00 CEST (+02:00)', $dt->format('Y-m-d H:i:s T (P)'), '+90 min (crosses jump)');
+
+	// Adding a day across the jump (day has only 23 hours)
+	$dt = clone $startSpring;
+	$dt->modify('+1 day');
+	Assert::same('2025-03-31 01:45:00 CEST (+02:00)', $dt->format('Y-m-d H:i:s T (P)'), '+1 day');
+
+	// Combination of day + hours across the jump
+	$dt = clone $startSpring;
+	$dt->modify('+1 day +1 hour');
+	Assert::same('2025-03-31 02:45:00 CEST (+02:00)', $dt->format('Y-m-d H:i:s T (P)'), '+1 day + 1 hour');
+
+	$dt = clone $startSpring;
+	$dt->modify('+2 hours'); // 01:45 CET + 2h duration = 02:45 UTC = 04:45 CEST
+	Assert::same('2025-03-30 04:45:00 CEST (+02:00)', $dt->format('Y-m-d H:i:s T (P)'), '+2 hours (crosses jump)');
+});
+
+
+test('Autumn DST transition (2024-10-27 03:00 -> 02:00)', function () {
+	$startAutumn = new DateTime('2024-10-27 01:45:00'); // Before the fallback (CEST +02:00)
+
+	// Modification ending BEFORE the fallback (still CEST)
+	$dt = clone $startAutumn;
+	$dt->modify('+30 minutes');
+	Assert::same('2024-10-27 02:15:00 CEST (+02:00)', $dt->format('Y-m-d H:i:s T (P)'), '+30 min (ends before fallback)');
+
+	// Modification crossing the fallback (lands in the second 2:xx hour - CET)
+	$dt = clone $startAutumn;
+	$dt->modify('+90 minutes'); // 01:45 CEST + 90 min duration = 01:15 UTC = 02:15 CET
+	Assert::same('2024-10-27 02:15:00 CET (+01:00)', $dt->format('Y-m-d H:i:s T (P)'), '+90 min (crosses fallback, lands in CET)');
+
+	$dt = clone $startAutumn;
+	$dt->modify('+1 hour + 30 minutes'); // Same as +90 minutes
+	Assert::same('2024-10-27 02:15:00 CET (+01:00)', $dt->format('Y-m-d H:i:s T (P)'), '+1 hour + 30 minutes (crosses fallback)');
+
+	// Adding a day across the fallback (day has 25 hours)
+	$dt = clone $startAutumn;
+	$dt->modify('+1 day');
+	Assert::same('2024-10-28 01:45:00 CET (+01:00)', $dt->format('Y-m-d H:i:s T (P)'), '+1 day');
+
+	// Combination of day + hours across the fallback
+	$dt = clone $startAutumn;
+	$dt->modify('+1 day +2 hours');
+	Assert::same('2024-10-28 03:45:00 CET (+01:00)', $dt->format('Y-m-d H:i:s T (P)'), '+1 day + 2 hours');
+});
+
+
 test('Complex and varied format strings', function () {
 	$dt = new DateTime('2024-04-10 12:00:00'); // CEST
 	// Expected: -2m -> 2024-02-10 12:00 CET | +7d -> 2024-02-17 12:00 CET | +23h 59m 59s -> 2024-02-18 11:59:59 CET