From 5c74c2e66798eae154866106e1bfbbc47e18745f Mon Sep 17 00:00:00 2001
From: luxick <git@luxick.de>
Date: Fri, 3 Apr 2026 15:40:06 +0200
Subject: [PATCH] Fix timezone parsing for calendars

---
 src/CalendarService.php | 59 +++++++++++++++++++++++++++++++++++++----
 1 file changed, 54 insertions(+), 5 deletions(-)

diff --git a/src/CalendarService.php b/src/CalendarService.php
index e7b9a9d..5abd9d4 100644
--- a/src/CalendarService.php
+++ b/src/CalendarService.php
@@ -138,12 +138,13 @@ class CalendarService
             if ($calendar === null) continue;
 
             try {
+                $uidTimezones = self::buildUidTimezoneMap($calendar);
                 $expanded = $calendar->expand($rangeStart, $rangeEnd);
                 if (!($expanded instanceof VCalendar)) continue;
 
                 for ($day = 1; $day <= $daysInMonth; $day++) {
                     $dateIso = sprintf('%04d-%02d-%02d', $year, $month, $day);
-                    $events = self::collectFromCalendar($expanded, $slot->getKey(), $dateIso);
+                    $events = self::collectFromCalendar($expanded, $slot->getKey(), $dateIso, $uidTimezones);
                     $cacheKey = $slot->getKey() . '|' . $dateIso;
                     self::$dayCache[$cacheKey] = $events;
 
@@ -222,6 +223,28 @@ class CalendarService
         }
     }
 
+    /**
+     * Build a UID → TZID map from the original (non-expanded) calendar.
+     *
+     * VCalendar::expand() normalizes all timezone-aware datetimes to UTC, losing
+     * the original TZID. This map lets us restore the correct timezone afterwards.
+     *
+     * @param VCalendar $calendar
+     * @return array<string,string> uid => tzid
+     */
+    protected static function buildUidTimezoneMap(VCalendar $calendar): array
+    {
+        $map = [];
+        foreach ($calendar->select('VEVENT') as $vevent) {
+            if (!isset($vevent->DTSTART)) continue;
+            $uid = trim((string)($vevent->UID ?? ''));
+            if ($uid === '' || isset($map[$uid])) continue;
+            $tzid = (string)($vevent->DTSTART['TZID'] ?? '');
+            if ($tzid !== '') $map[$uid] = $tzid;
+        }
+        return $map;
+    }
+
     /**
      * Parse events from a local ICS file for a specific date.
      *
@@ -236,6 +259,8 @@ class CalendarService
         if ($calendar === null) return [];
 
         try {
+            $uidTimezones = self::buildUidTimezoneMap($calendar);
+
             $utc = new DateTimeZone('UTC');
             $rangeStart = new DateTimeImmutable($dateIso . ' 00:00:00', $utc);
             $rangeStart = $rangeStart->sub(new DateInterval('P1D'));
@@ -244,7 +269,7 @@ class CalendarService
             $expanded = $calendar->expand($rangeStart, $rangeEnd);
             if (!($expanded instanceof VCalendar)) return [];
 
-            return self::collectFromCalendar($expanded, $slotKey, $dateIso);
+            return self::collectFromCalendar($expanded, $slotKey, $dateIso, $uidTimezones);
         } catch (Throwable $e) {
             return [];
         }
@@ -256,9 +281,10 @@ class CalendarService
      * @param VCalendar $calendar
      * @param string $slotKey
      * @param string $dateIso
+     * @param array<string,string> $uidTimezones uid => tzid, for restoring timezone after expand()
      * @return CalendarEvent[]
      */
-    protected static function collectFromCalendar(VCalendar $calendar, string $slotKey, string $dateIso): array
+    protected static function collectFromCalendar(VCalendar $calendar, string $slotKey, string $dateIso, array $uidTimezones = []): array
     {
         $result = [];
         $seen = [];
@@ -266,7 +292,7 @@ class CalendarService
         // VEVENTs
         foreach ($calendar->select('VEVENT') as $vevent) {
             if (!($vevent instanceof VEvent)) continue;
-            $event = self::normalizeVEventForDay($vevent, $slotKey, $dateIso);
+            $event = self::normalizeVEventForDay($vevent, $slotKey, $dateIso, $uidTimezones);
             if ($event === null) continue;
 
             $dedupeKey = $event->uid . '|' . $event->recurrenceId . '|' . $event->startIso . '|' . $event->summary;
@@ -285,9 +311,10 @@ class CalendarService
      * @param VEvent $vevent
      * @param string $slotKey
      * @param string $dateIso
+     * @param array<string,string> $uidTimezones uid => tzid, for restoring timezone after expand()
      * @return CalendarEvent|null
      */
-    protected static function normalizeVEventForDay(VEvent $vevent, string $slotKey, string $dateIso): ?CalendarEvent
+    protected static function normalizeVEventForDay(VEvent $vevent, string $slotKey, string $dateIso, array $uidTimezones = []): ?CalendarEvent
     {
         if (!isset($vevent->DTSTART)) return null;
 
@@ -295,8 +322,30 @@ class CalendarService
         $start = self::toImmutable($vevent->DTSTART->getDateTime());
         if ($start === null) return null;
 
+        // VCalendar::expand() normalizes all timezone-aware datetimes to UTC, losing
+        // the original TZID. Restore it using the pre-expansion UID→TZID map so that
+        // display times and day-boundary checks use the event's original timezone.
+        $restoredTz = null;
+        if (!$isAllDay && $uidTimezones !== [] && $start->getTimezone()->getName() === 'UTC') {
+            $uid = trim((string)($vevent->UID ?? ''));
+            $tzid = $uidTimezones[$uid] ?? '';
+            if ($tzid !== '') {
+                try {
+                    $restoredTz = new DateTimeZone($tzid);
+                    $start = $start->setTimezone($restoredTz);
+                } catch (Throwable $e) {
+                    $restoredTz = null;
+                }
+            }
+        }
+
         $end = self::resolveEnd($vevent, $start, $isAllDay);
 
+        // Apply the same timezone restoration to the end datetime.
+        if ($restoredTz !== null && $end->getTimezone()->getName() === 'UTC') {
+            $end = $end->setTimezone($restoredTz);
+        }
+
         if (!self::intersectsDay($start, $end, $isAllDay, $dateIso)) return null;
 
         $event = new CalendarEvent();