nextcloud / server

apps/dav/lib/CalDAV/Reminder/ReminderService.php

Indentation +828 added lines, -828 removed lines

@@ -55,832 +55,832 @@
 
 class ReminderService {
 
-	/** @var Backend */
-	private $backend;
-
-	/** @var NotificationProviderManager */
-	private $notificationProviderManager;
-
-	/** @var IUserManager */
-	private $userManager;
-
-	/** @var IGroupManager */
-	private $groupManager;
-
-	/** @var CalDavBackend */
-	private $caldavBackend;
-
-	/** @var ITimeFactory */
-	private $timeFactory;
-
-	/** @var IConfig */
-	private $config;
-
-	/** @var LoggerInterface */
-	private $logger;
-
-	/** @var Principal */
-	private $principalConnector;
-
-	public const REMINDER_TYPE_EMAIL = 'EMAIL';
-	public const REMINDER_TYPE_DISPLAY = 'DISPLAY';
-	public const REMINDER_TYPE_AUDIO = 'AUDIO';
-
-	/**
-	 * @var String[]
-	 *
-	 * Official RFC5545 reminder types
-	 */
-	public const REMINDER_TYPES = [
-		self::REMINDER_TYPE_EMAIL,
-		self::REMINDER_TYPE_DISPLAY,
-		self::REMINDER_TYPE_AUDIO
-	];
-
-	public function __construct(Backend $backend,
-								NotificationProviderManager $notificationProviderManager,
-								IUserManager $userManager,
-								IGroupManager $groupManager,
-								CalDavBackend $caldavBackend,
-								ITimeFactory $timeFactory,
-								IConfig $config,
-								LoggerInterface $logger,
-								Principal $principalConnector) {
-		$this->backend = $backend;
-		$this->notificationProviderManager = $notificationProviderManager;
-		$this->userManager = $userManager;
-		$this->groupManager = $groupManager;
-		$this->caldavBackend = $caldavBackend;
-		$this->timeFactory = $timeFactory;
-		$this->config = $config;
-		$this->logger = $logger;
-		$this->principalConnector = $principalConnector;
-	}
-
-	/**
-	 * Process reminders to activate
-	 *
-	 * @throws NotificationProvider\ProviderNotAvailableException
-	 * @throws NotificationTypeDoesNotExistException
-	 */
-	public function processReminders() :void {
-		$reminders = $this->backend->getRemindersToProcess();
-		$this->logger->debug('{numReminders} reminders to process', [
-			'numReminders' => count($reminders),
-		]);
-
-		foreach ($reminders as $reminder) {
-			$calendarData = is_resource($reminder['calendardata'])
-				? stream_get_contents($reminder['calendardata'])
-				: $reminder['calendardata'];
-
-			if (!$calendarData) {
-				continue;
-			}
-
-			$vcalendar = $this->parseCalendarData($calendarData);
-			if (!$vcalendar) {
-				$this->logger->debug('Reminder {id} does not belong to a valid calendar', [
-					'id' => $reminder['id'],
-				]);
-				$this->backend->removeReminder($reminder['id']);
-				continue;
-			}
-
-			try {
-				$vevent = $this->getVEventByRecurrenceId($vcalendar, $reminder['recurrence_id'], $reminder['is_recurrence_exception']);
-			} catch (MaxInstancesExceededException $e) {
-				$this->logger->debug('Recurrence with too many instances detected, skipping VEVENT', ['exception' => $e]);
-				$this->backend->removeReminder($reminder['id']);
-				continue;
-			}
-
-			if (!$vevent) {
-				$this->logger->debug('Reminder {id} does not belong to a valid event', [
-					'id' => $reminder['id'],
-				]);
-				$this->backend->removeReminder($reminder['id']);
-				continue;
-			}
-
-			if ($this->wasEventCancelled($vevent)) {
-				$this->logger->debug('Reminder {id} belongs to a cancelled event', [
-					'id' => $reminder['id'],
-				]);
-				$this->deleteOrProcessNext($reminder, $vevent);
-				continue;
-			}
-
-			if (!$this->notificationProviderManager->hasProvider($reminder['type'])) {
-				$this->logger->debug('Reminder {id} does not belong to a valid notification provider', [
-					'id' => $reminder['id'],
-				]);
-				$this->deleteOrProcessNext($reminder, $vevent);
-				continue;
-			}
-
-			if ($this->config->getAppValue('dav', 'sendEventRemindersToSharedUsers', 'yes') === 'no') {
-				$users = $this->getAllUsersWithWriteAccessToCalendar($reminder['calendar_id']);
-			} else {
-				$users = [];
-			}
-
-			$user = $this->getUserFromPrincipalURI($reminder['principaluri']);
-			if ($user) {
-				$users[] = $user;
-			}
-
-			$userPrincipalEmailAddresses = [];
-			$userPrincipal = $this->principalConnector->getPrincipalByPath($reminder['principaluri']);
-			if ($userPrincipal) {
-				$userPrincipalEmailAddresses = $this->principalConnector->getEmailAddressesOfPrincipal($userPrincipal);
-			}
-
-			$this->logger->debug('Reminder {id} will be sent to {numUsers} users', [
-				'id' => $reminder['id'],
-				'numUsers' => count($users),
-			]);
-			$notificationProvider = $this->notificationProviderManager->getProvider($reminder['type']);
-			$notificationProvider->send($vevent, $reminder['displayname'], $userPrincipalEmailAddresses, $users);
-
-			$this->deleteOrProcessNext($reminder, $vevent);
-		}
-	}
-
-	/**
-	 * @param array $objectData
-	 * @throws VObject\InvalidDataException
-	 */
-	public function onCalendarObjectCreate(array $objectData):void {
-		// We only support VEvents for now
-		if (strcasecmp($objectData['component'], 'vevent') !== 0) {
-			return;
-		}
-
-		$calendarData = is_resource($objectData['calendardata'])
-			? stream_get_contents($objectData['calendardata'])
-			: $objectData['calendardata'];
-
-		if (!$calendarData) {
-			return;
-		}
-
-		$vcalendar = $this->parseCalendarData($calendarData);
-		if (!$vcalendar) {
-			return;
-		}
-		$calendarTimeZone = $this->getCalendarTimeZone((int) $objectData['calendarid']);
-
-		$vevents = $this->getAllVEventsFromVCalendar($vcalendar);
-		if (count($vevents) === 0) {
-			return;
-		}
-
-		$uid = (string) $vevents[0]->UID;
-		$recurrenceExceptions = $this->getRecurrenceExceptionFromListOfVEvents($vevents);
-		$masterItem = $this->getMasterItemFromListOfVEvents($vevents);
-		$now = $this->timeFactory->getDateTime();
-		$isRecurring = $masterItem ? $this->isRecurring($masterItem) : false;
-
-		foreach ($recurrenceExceptions as $recurrenceException) {
-			$eventHash = $this->getEventHash($recurrenceException);
-
-			if (!isset($recurrenceException->VALARM)) {
-				continue;
-			}
-
-			foreach ($recurrenceException->VALARM as $valarm) {
-				/** @var VAlarm $valarm */
-				$alarmHash = $this->getAlarmHash($valarm);
-				$triggerTime = $valarm->getEffectiveTriggerTime();
-				$diff = $now->diff($triggerTime);
-				if ($diff->invert === 1) {
-					continue;
-				}
-
-				$alarms = $this->getRemindersForVAlarm($valarm, $objectData, $calendarTimeZone,
-					$eventHash, $alarmHash, true, true);
-				$this->writeRemindersToDatabase($alarms);
-			}
-		}
-
-		if ($masterItem) {
-			$processedAlarms = [];
-			$masterAlarms = [];
-			$masterHash = $this->getEventHash($masterItem);
-
-			if (!isset($masterItem->VALARM)) {
-				return;
-			}
-
-			foreach ($masterItem->VALARM as $valarm) {
-				$masterAlarms[] = $this->getAlarmHash($valarm);
-			}
-
-			try {
-				$iterator = new EventIterator($vevents, $uid);
-			} catch (NoInstancesException $e) {
-				// This event is recurring, but it doesn't have a single
-				// instance. We are skipping this event from the output
-				// entirely.
-				return;
-			} catch (MaxInstancesExceededException $e) {
-				// The event has more than 3500 recurring-instances
-				// so we can ignore it
-				return;
-			}
-
-			while ($iterator->valid() && count($processedAlarms) < count($masterAlarms)) {
-				$event = $iterator->getEventObject();
-
-				// Recurrence-exceptions are handled separately, so just ignore them here
-				if (\in_array($event, $recurrenceExceptions, true)) {
-					$iterator->next();
-					continue;
-				}
-
-				foreach ($event->VALARM as $valarm) {
-					/** @var VAlarm $valarm */
-					$alarmHash = $this->getAlarmHash($valarm);
-					if (\in_array($alarmHash, $processedAlarms, true)) {
-						continue;
-					}
-
-					if (!\in_array((string) $valarm->ACTION, self::REMINDER_TYPES, true)) {
-						// Action allows x-name, we don't insert reminders
-						// into the database if they are not standard
-						$processedAlarms[] = $alarmHash;
-						continue;
-					}
-
-					try {
-						$triggerTime = $valarm->getEffectiveTriggerTime();
-						/**
-						 * @psalm-suppress DocblockTypeContradiction
-						 *   https://github.com/vimeo/psalm/issues/9244
-						 */
-						if ($triggerTime->getTimezone() === false || $triggerTime->getTimezone()->getName() === 'UTC') {
-							$triggerTime = new DateTimeImmutable(
-								$triggerTime->format('Y-m-d H:i:s'),
-								$calendarTimeZone
-							);
-						}
-					} catch (InvalidDataException $e) {
-						continue;
-					}
-
-					// If effective trigger time is in the past
-					// just skip and generate for next event
-					$diff = $now->diff($triggerTime);
-					if ($diff->invert === 1) {
-						// If an absolute alarm is in the past,
-						// just add it to processedAlarms, so
-						// we don't extend till eternity
-						if (!$this->isAlarmRelative($valarm)) {
-							$processedAlarms[] = $alarmHash;
-						}
-
-						continue;
-					}
-
-					$alarms = $this->getRemindersForVAlarm($valarm, $objectData, $calendarTimeZone, $masterHash, $alarmHash, $isRecurring, false);
-					$this->writeRemindersToDatabase($alarms);
-					$processedAlarms[] = $alarmHash;
-				}
-
-				$iterator->next();
-			}
-		}
-	}
-
-	/**
-	 * @param array $objectData
-	 * @throws VObject\InvalidDataException
-	 */
-	public function onCalendarObjectEdit(array $objectData):void {
-		// TODO - this can be vastly improved
-		//  - get cached reminders
-		//  - ...
-
-		$this->onCalendarObjectDelete($objectData);
-		$this->onCalendarObjectCreate($objectData);
-	}
-
-	/**
-	 * @param array $objectData
-	 * @throws VObject\InvalidDataException
-	 */
-	public function onCalendarObjectDelete(array $objectData):void {
-		// We only support VEvents for now
-		if (strcasecmp($objectData['component'], 'vevent') !== 0) {
-			return;
-		}
-
-		$this->backend->cleanRemindersForEvent((int) $objectData['id']);
-	}
-
-	/**
-	 * @param VAlarm $valarm
-	 * @param array $objectData
-	 * @param DateTimeZone $calendarTimeZone
-	 * @param string|null $eventHash
-	 * @param string|null $alarmHash
-	 * @param bool $isRecurring
-	 * @param bool $isRecurrenceException
-	 * @return array
-	 */
-	private function getRemindersForVAlarm(VAlarm $valarm,
-										   array $objectData,
-										   DateTimeZone $calendarTimeZone,
-										   string $eventHash = null,
-										   string $alarmHash = null,
-										   bool $isRecurring = false,
-										   bool $isRecurrenceException = false):array {
-		if ($eventHash === null) {
-			$eventHash = $this->getEventHash($valarm->parent);
-		}
-		if ($alarmHash === null) {
-			$alarmHash = $this->getAlarmHash($valarm);
-		}
-
-		$recurrenceId = $this->getEffectiveRecurrenceIdOfVEvent($valarm->parent);
-		$isRelative = $this->isAlarmRelative($valarm);
-		/** @var DateTimeImmutable $notificationDate */
-		$notificationDate = $valarm->getEffectiveTriggerTime();
-		/**
-		 * @psalm-suppress DocblockTypeContradiction
-		 *   https://github.com/vimeo/psalm/issues/9244
-		 */
-		if ($notificationDate->getTimezone() === false || $notificationDate->getTimezone()->getName() === 'UTC') {
-			$notificationDate = new DateTimeImmutable(
-				$notificationDate->format('Y-m-d H:i:s'),
-				$calendarTimeZone
-			);
-		}
-		$clonedNotificationDate = new \DateTime('now', $notificationDate->getTimezone());
-		$clonedNotificationDate->setTimestamp($notificationDate->getTimestamp());
-
-		$alarms = [];
-
-		$alarms[] = [
-			'calendar_id' => $objectData['calendarid'],
-			'object_id' => $objectData['id'],
-			'uid' => (string) $valarm->parent->UID,
-			'is_recurring' => $isRecurring,
-			'recurrence_id' => $recurrenceId,
-			'is_recurrence_exception' => $isRecurrenceException,
-			'event_hash' => $eventHash,
-			'alarm_hash' => $alarmHash,
-			'type' => (string) $valarm->ACTION,
-			'is_relative' => $isRelative,
-			'notification_date' => $notificationDate->getTimestamp(),
-			'is_repeat_based' => false,
-		];
-
-		$repeat = isset($valarm->REPEAT) ? (int) $valarm->REPEAT->getValue() : 0;
-		for ($i = 0; $i < $repeat; $i++) {
-			if ($valarm->DURATION === null) {
-				continue;
-			}
-
-			$clonedNotificationDate->add($valarm->DURATION->getDateInterval());
-			$alarms[] = [
-				'calendar_id' => $objectData['calendarid'],
-				'object_id' => $objectData['id'],
-				'uid' => (string) $valarm->parent->UID,
-				'is_recurring' => $isRecurring,
-				'recurrence_id' => $recurrenceId,
-				'is_recurrence_exception' => $isRecurrenceException,
-				'event_hash' => $eventHash,
-				'alarm_hash' => $alarmHash,
-				'type' => (string) $valarm->ACTION,
-				'is_relative' => $isRelative,
-				'notification_date' => $clonedNotificationDate->getTimestamp(),
-				'is_repeat_based' => true,
-			];
-		}
-
-		return $alarms;
-	}
-
-	/**
-	 * @param array $reminders
-	 */
-	private function writeRemindersToDatabase(array $reminders): void {
-		foreach ($reminders as $reminder) {
-			$this->backend->insertReminder(
-				(int) $reminder['calendar_id'],
-				(int) $reminder['object_id'],
-				$reminder['uid'],
-				$reminder['is_recurring'],
-				(int) $reminder['recurrence_id'],
-				$reminder['is_recurrence_exception'],
-				$reminder['event_hash'],
-				$reminder['alarm_hash'],
-				$reminder['type'],
-				$reminder['is_relative'],
-				(int) $reminder['notification_date'],
-				$reminder['is_repeat_based']
-			);
-		}
-	}
-
-	/**
-	 * @param array $reminder
-	 * @param VEvent $vevent
-	 */
-	private function deleteOrProcessNext(array $reminder,
-										 VObject\Component\VEvent $vevent):void {
-		if ($reminder['is_repeat_based'] ||
-			!$reminder['is_recurring'] ||
-			!$reminder['is_relative'] ||
-			$reminder['is_recurrence_exception']) {
-			$this->backend->removeReminder($reminder['id']);
-			return;
-		}
-
-		$vevents = $this->getAllVEventsFromVCalendar($vevent->parent);
-		$recurrenceExceptions = $this->getRecurrenceExceptionFromListOfVEvents($vevents);
-		$now = $this->timeFactory->getDateTime();
-		$calendarTimeZone = $this->getCalendarTimeZone((int) $reminder['calendar_id']);
-
-		try {
-			$iterator = new EventIterator($vevents, $reminder['uid']);
-		} catch (NoInstancesException $e) {
-			// This event is recurring, but it doesn't have a single
-			// instance. We are skipping this event from the output
-			// entirely.
-			return;
-		}
-
-		try {
-			while ($iterator->valid()) {
-				$event = $iterator->getEventObject();
-
-				// Recurrence-exceptions are handled separately, so just ignore them here
-				if (\in_array($event, $recurrenceExceptions, true)) {
-					$iterator->next();
-					continue;
-				}
-
-				$recurrenceId = $this->getEffectiveRecurrenceIdOfVEvent($event);
-				if ($reminder['recurrence_id'] >= $recurrenceId) {
-					$iterator->next();
-					continue;
-				}
-
-				foreach ($event->VALARM as $valarm) {
-					/** @var VAlarm $valarm */
-					$alarmHash = $this->getAlarmHash($valarm);
-					if ($alarmHash !== $reminder['alarm_hash']) {
-						continue;
-					}
-
-					$triggerTime = $valarm->getEffectiveTriggerTime();
-
-					// If effective trigger time is in the past
-					// just skip and generate for next event
-					$diff = $now->diff($triggerTime);
-					if ($diff->invert === 1) {
-						continue;
-					}
-
-					$this->backend->removeReminder($reminder['id']);
-					$alarms = $this->getRemindersForVAlarm($valarm, [
-						'calendarid' => $reminder['calendar_id'],
-						'id' => $reminder['object_id'],
-					], $calendarTimeZone, $reminder['event_hash'], $alarmHash, true, false);
-					$this->writeRemindersToDatabase($alarms);
-
-					// Abort generating reminders after creating one successfully
-					return;
-				}
-
-				$iterator->next();
-			}
-		} catch (MaxInstancesExceededException $e) {
-			// Using debug logger as this isn't really an error
-			$this->logger->debug('Recurrence with too many instances detected, skipping VEVENT', ['exception' => $e]);
-		}
-
-		$this->backend->removeReminder($reminder['id']);
-	}
-
-	/**
-	 * @param int $calendarId
-	 * @return IUser[]
-	 */
-	private function getAllUsersWithWriteAccessToCalendar(int $calendarId):array {
-		$shares = $this->caldavBackend->getShares($calendarId);
-
-		$users = [];
-		$userIds = [];
-		$groups = [];
-		foreach ($shares as $share) {
-			// Only consider writable shares
-			if ($share['readOnly']) {
-				continue;
-			}
-
-			$principal = explode('/', $share['{http://owncloud.org/ns}principal']);
-			if ($principal[1] === 'users') {
-				$user = $this->userManager->get($principal[2]);
-				if ($user) {
-					$users[] = $user;
-					$userIds[] = $principal[2];
-				}
-			} elseif ($principal[1] === 'groups') {
-				$groups[] = $principal[2];
-			}
-		}
-
-		foreach ($groups as $gid) {
-			$group = $this->groupManager->get($gid);
-			if ($group instanceof IGroup) {
-				foreach ($group->getUsers() as $user) {
-					if (!\in_array($user->getUID(), $userIds, true)) {
-						$users[] = $user;
-						$userIds[] = $user->getUID();
-					}
-				}
-			}
-		}
-
-		return $users;
-	}
-
-	/**
-	 * Gets a hash of the event.
-	 * If the hash changes, we have to update all relative alarms.
-	 *
-	 * @param VEvent $vevent
-	 * @return string
-	 */
-	private function getEventHash(VEvent $vevent):string {
-		$properties = [
-			(string) $vevent->DTSTART->serialize(),
-		];
-
-		if ($vevent->DTEND) {
-			$properties[] = (string) $vevent->DTEND->serialize();
-		}
-		if ($vevent->DURATION) {
-			$properties[] = (string) $vevent->DURATION->serialize();
-		}
-		if ($vevent->{'RECURRENCE-ID'}) {
-			$properties[] = (string) $vevent->{'RECURRENCE-ID'}->serialize();
-		}
-		if ($vevent->RRULE) {
-			$properties[] = (string) $vevent->RRULE->serialize();
-		}
-		if ($vevent->EXDATE) {
-			$properties[] = (string) $vevent->EXDATE->serialize();
-		}
-		if ($vevent->RDATE) {
-			$properties[] = (string) $vevent->RDATE->serialize();
-		}
-
-		return md5(implode('::', $properties));
-	}
-
-	/**
-	 * Gets a hash of the alarm.
-	 * If the hash changes, we have to update oc_dav_reminders.
-	 *
-	 * @param VAlarm $valarm
-	 * @return string
-	 */
-	private function getAlarmHash(VAlarm $valarm):string {
-		$properties = [
-			(string) $valarm->ACTION->serialize(),
-			(string) $valarm->TRIGGER->serialize(),
-		];
-
-		if ($valarm->DURATION) {
-			$properties[] = (string) $valarm->DURATION->serialize();
-		}
-		if ($valarm->REPEAT) {
-			$properties[] = (string) $valarm->REPEAT->serialize();
-		}
-
-		return md5(implode('::', $properties));
-	}
-
-	/**
-	 * @param VObject\Component\VCalendar $vcalendar
-	 * @param int $recurrenceId
-	 * @param bool $isRecurrenceException
-	 * @return VEvent|null
-	 */
-	private function getVEventByRecurrenceId(VObject\Component\VCalendar $vcalendar,
-											 int $recurrenceId,
-											 bool $isRecurrenceException):?VEvent {
-		$vevents = $this->getAllVEventsFromVCalendar($vcalendar);
-		if (count($vevents) === 0) {
-			return null;
-		}
-
-		$uid = (string) $vevents[0]->UID;
-		$recurrenceExceptions = $this->getRecurrenceExceptionFromListOfVEvents($vevents);
-		$masterItem = $this->getMasterItemFromListOfVEvents($vevents);
-
-		// Handle recurrence-exceptions first, because recurrence-expansion is expensive
-		if ($isRecurrenceException) {
-			foreach ($recurrenceExceptions as $recurrenceException) {
-				if ($this->getEffectiveRecurrenceIdOfVEvent($recurrenceException) === $recurrenceId) {
-					return $recurrenceException;
-				}
-			}
-
-			return null;
-		}
-
-		if ($masterItem) {
-			try {
-				$iterator = new EventIterator($vevents, $uid);
-			} catch (NoInstancesException $e) {
-				// This event is recurring, but it doesn't have a single
-				// instance. We are skipping this event from the output
-				// entirely.
-				return null;
-			}
-
-			while ($iterator->valid()) {
-				$event = $iterator->getEventObject();
-
-				// Recurrence-exceptions are handled separately, so just ignore them here
-				if (\in_array($event, $recurrenceExceptions, true)) {
-					$iterator->next();
-					continue;
-				}
-
-				if ($this->getEffectiveRecurrenceIdOfVEvent($event) === $recurrenceId) {
-					return $event;
-				}
-
-				$iterator->next();
-			}
-		}
-
-		return null;
-	}
-
-	/**
-	 * @param VEvent $vevent
-	 * @return string
-	 */
-	private function getStatusOfEvent(VEvent $vevent):string {
-		if ($vevent->STATUS) {
-			return (string) $vevent->STATUS;
-		}
-
-		// Doesn't say so in the standard,
-		// but we consider events without a status
-		// to be confirmed
-		return 'CONFIRMED';
-	}
-
-	/**
-	 * @param VObject\Component\VEvent $vevent
-	 * @return bool
-	 */
-	private function wasEventCancelled(VObject\Component\VEvent $vevent):bool {
-		return $this->getStatusOfEvent($vevent) === 'CANCELLED';
-	}
-
-	/**
-	 * @param string $calendarData
-	 * @return VObject\Component\VCalendar|null
-	 */
-	private function parseCalendarData(string $calendarData):?VObject\Component\VCalendar {
-		try {
-			return VObject\Reader::read($calendarData,
-				VObject\Reader::OPTION_FORGIVING);
-		} catch (ParseException $ex) {
-			return null;
-		}
-	}
-
-	/**
-	 * @param string $principalUri
-	 * @return IUser|null
-	 */
-	private function getUserFromPrincipalURI(string $principalUri):?IUser {
-		if (!$principalUri) {
-			return null;
-		}
-
-		if (stripos($principalUri, 'principals/users/') !== 0) {
-			return null;
-		}
-
-		$userId = substr($principalUri, 17);
-		return $this->userManager->get($userId);
-	}
-
-	/**
-	 * @param VObject\Component\VCalendar $vcalendar
-	 * @return VObject\Component\VEvent[]
-	 */
-	private function getAllVEventsFromVCalendar(VObject\Component\VCalendar $vcalendar):array {
-		$vevents = [];
-
-		foreach ($vcalendar->children() as $child) {
-			if (!($child instanceof VObject\Component)) {
-				continue;
-			}
-
-			if ($child->name !== 'VEVENT') {
-				continue;
-			}
-			// Ignore invalid events with no DTSTART
-			if ($child->DTSTART === null) {
-				continue;
-			}
-
-			$vevents[] = $child;
-		}
-
-		return $vevents;
-	}
-
-	/**
-	 * @param array $vevents
-	 * @return VObject\Component\VEvent[]
-	 */
-	private function getRecurrenceExceptionFromListOfVEvents(array $vevents):array {
-		return array_values(array_filter($vevents, function (VEvent $vevent) {
-			return $vevent->{'RECURRENCE-ID'} !== null;
-		}));
-	}
-
-	/**
-	 * @param array $vevents
-	 * @return VEvent|null
-	 */
-	private function getMasterItemFromListOfVEvents(array $vevents):?VEvent {
-		$elements = array_values(array_filter($vevents, function (VEvent $vevent) {
-			return $vevent->{'RECURRENCE-ID'} === null;
-		}));
-
-		if (count($elements) === 0) {
-			return null;
-		}
-		if (count($elements) > 1) {
-			throw new \TypeError('Multiple master objects');
-		}
-
-		return $elements[0];
-	}
-
-	/**
-	 * @param VAlarm $valarm
-	 * @return bool
-	 */
-	private function isAlarmRelative(VAlarm $valarm):bool {
-		$trigger = $valarm->TRIGGER;
-		return $trigger instanceof VObject\Property\ICalendar\Duration;
-	}
-
-	/**
-	 * @param VEvent $vevent
-	 * @return int
-	 */
-	private function getEffectiveRecurrenceIdOfVEvent(VEvent $vevent):int {
-		if (isset($vevent->{'RECURRENCE-ID'})) {
-			return $vevent->{'RECURRENCE-ID'}->getDateTime()->getTimestamp();
-		}
-
-		return $vevent->DTSTART->getDateTime()->getTimestamp();
-	}
-
-	/**
-	 * @param VEvent $vevent
-	 * @return bool
-	 */
-	private function isRecurring(VEvent $vevent):bool {
-		return isset($vevent->RRULE) || isset($vevent->RDATE);
-	}
-
-	/**
-	 * @param int $calendarid
-	 *
-	 * @return DateTimeZone
-	 */
-	private function getCalendarTimeZone(int $calendarid): DateTimeZone {
-		$calendarInfo = $this->caldavBackend->getCalendarById($calendarid);
-		$tzProp = '{urn:ietf:params:xml:ns:caldav}calendar-timezone';
-		if (!isset($calendarInfo[$tzProp])) {
-			// Defaulting to UTC
-			return new DateTimeZone('UTC');
-		}
-		// This property contains a VCALENDAR with a single VTIMEZONE
-		/** @var string $timezoneProp */
-		$timezoneProp = $calendarInfo[$tzProp];
-		/** @var VObject\Component\VCalendar $vtimezoneObj */
-		$vtimezoneObj = VObject\Reader::read($timezoneProp);
-		/** @var VObject\Component\VTimeZone $vtimezone */
-		$vtimezone = $vtimezoneObj->VTIMEZONE;
-		return $vtimezone->getTimeZone();
-	}
+    /** @var Backend */
+    private $backend;
+
+    /** @var NotificationProviderManager */
+    private $notificationProviderManager;
+
+    /** @var IUserManager */
+    private $userManager;
+
+    /** @var IGroupManager */
+    private $groupManager;
+
+    /** @var CalDavBackend */
+    private $caldavBackend;
+
+    /** @var ITimeFactory */
+    private $timeFactory;
+
+    /** @var IConfig */
+    private $config;
+
+    /** @var LoggerInterface */
+    private $logger;
+
+    /** @var Principal */
+    private $principalConnector;
+
+    public const REMINDER_TYPE_EMAIL = 'EMAIL';
+    public const REMINDER_TYPE_DISPLAY = 'DISPLAY';
+    public const REMINDER_TYPE_AUDIO = 'AUDIO';
+
+    /**
+     * @var String[]
+     *
+     * Official RFC5545 reminder types
+     */
+    public const REMINDER_TYPES = [
+        self::REMINDER_TYPE_EMAIL,
+        self::REMINDER_TYPE_DISPLAY,
+        self::REMINDER_TYPE_AUDIO
+    ];
+
+    public function __construct(Backend $backend,
+                                NotificationProviderManager $notificationProviderManager,
+                                IUserManager $userManager,
+                                IGroupManager $groupManager,
+                                CalDavBackend $caldavBackend,
+                                ITimeFactory $timeFactory,
+                                IConfig $config,
+                                LoggerInterface $logger,
+                                Principal $principalConnector) {
+        $this->backend = $backend;
+        $this->notificationProviderManager = $notificationProviderManager;
+        $this->userManager = $userManager;
+        $this->groupManager = $groupManager;
+        $this->caldavBackend = $caldavBackend;
+        $this->timeFactory = $timeFactory;
+        $this->config = $config;
+        $this->logger = $logger;
+        $this->principalConnector = $principalConnector;
+    }
+
+    /**
+     * Process reminders to activate
+     *
+     * @throws NotificationProvider\ProviderNotAvailableException
+     * @throws NotificationTypeDoesNotExistException
+     */
+    public function processReminders() :void {
+        $reminders = $this->backend->getRemindersToProcess();
+        $this->logger->debug('{numReminders} reminders to process', [
+            'numReminders' => count($reminders),
+        ]);
+
+        foreach ($reminders as $reminder) {
+            $calendarData = is_resource($reminder['calendardata'])
+                ? stream_get_contents($reminder['calendardata'])
+                : $reminder['calendardata'];
+
+            if (!$calendarData) {
+                continue;
+            }
+
+            $vcalendar = $this->parseCalendarData($calendarData);
+            if (!$vcalendar) {
+                $this->logger->debug('Reminder {id} does not belong to a valid calendar', [
+                    'id' => $reminder['id'],
+                ]);
+                $this->backend->removeReminder($reminder['id']);
+                continue;
+            }
+
+            try {
+                $vevent = $this->getVEventByRecurrenceId($vcalendar, $reminder['recurrence_id'], $reminder['is_recurrence_exception']);
+            } catch (MaxInstancesExceededException $e) {
+                $this->logger->debug('Recurrence with too many instances detected, skipping VEVENT', ['exception' => $e]);
+                $this->backend->removeReminder($reminder['id']);
+                continue;
+            }
+
+            if (!$vevent) {
+                $this->logger->debug('Reminder {id} does not belong to a valid event', [
+                    'id' => $reminder['id'],
+                ]);
+                $this->backend->removeReminder($reminder['id']);
+                continue;
+            }
+
+            if ($this->wasEventCancelled($vevent)) {
+                $this->logger->debug('Reminder {id} belongs to a cancelled event', [
+                    'id' => $reminder['id'],
+                ]);
+                $this->deleteOrProcessNext($reminder, $vevent);
+                continue;
+            }
+
+            if (!$this->notificationProviderManager->hasProvider($reminder['type'])) {
+                $this->logger->debug('Reminder {id} does not belong to a valid notification provider', [
+                    'id' => $reminder['id'],
+                ]);
+                $this->deleteOrProcessNext($reminder, $vevent);
+                continue;
+            }
+
+            if ($this->config->getAppValue('dav', 'sendEventRemindersToSharedUsers', 'yes') === 'no') {
+                $users = $this->getAllUsersWithWriteAccessToCalendar($reminder['calendar_id']);
+            } else {
+                $users = [];
+            }
+
+            $user = $this->getUserFromPrincipalURI($reminder['principaluri']);
+            if ($user) {
+                $users[] = $user;
+            }
+
+            $userPrincipalEmailAddresses = [];
+            $userPrincipal = $this->principalConnector->getPrincipalByPath($reminder['principaluri']);
+            if ($userPrincipal) {
+                $userPrincipalEmailAddresses = $this->principalConnector->getEmailAddressesOfPrincipal($userPrincipal);
+            }
+
+            $this->logger->debug('Reminder {id} will be sent to {numUsers} users', [
+                'id' => $reminder['id'],
+                'numUsers' => count($users),
+            ]);
+            $notificationProvider = $this->notificationProviderManager->getProvider($reminder['type']);
+            $notificationProvider->send($vevent, $reminder['displayname'], $userPrincipalEmailAddresses, $users);
+
+            $this->deleteOrProcessNext($reminder, $vevent);
+        }
+    }
+
+    /**
+     * @param array $objectData
+     * @throws VObject\InvalidDataException
+     */
+    public function onCalendarObjectCreate(array $objectData):void {
+        // We only support VEvents for now
+        if (strcasecmp($objectData['component'], 'vevent') !== 0) {
+            return;
+        }
+
+        $calendarData = is_resource($objectData['calendardata'])
+            ? stream_get_contents($objectData['calendardata'])
+            : $objectData['calendardata'];
+
+        if (!$calendarData) {
+            return;
+        }
+
+        $vcalendar = $this->parseCalendarData($calendarData);
+        if (!$vcalendar) {
+            return;
+        }
+        $calendarTimeZone = $this->getCalendarTimeZone((int) $objectData['calendarid']);
+
+        $vevents = $this->getAllVEventsFromVCalendar($vcalendar);
+        if (count($vevents) === 0) {
+            return;
+        }
+
+        $uid = (string) $vevents[0]->UID;
+        $recurrenceExceptions = $this->getRecurrenceExceptionFromListOfVEvents($vevents);
+        $masterItem = $this->getMasterItemFromListOfVEvents($vevents);
+        $now = $this->timeFactory->getDateTime();
+        $isRecurring = $masterItem ? $this->isRecurring($masterItem) : false;
+
+        foreach ($recurrenceExceptions as $recurrenceException) {
+            $eventHash = $this->getEventHash($recurrenceException);
+
+            if (!isset($recurrenceException->VALARM)) {
+                continue;
+            }
+
+            foreach ($recurrenceException->VALARM as $valarm) {
+                /** @var VAlarm $valarm */
+                $alarmHash = $this->getAlarmHash($valarm);
+                $triggerTime = $valarm->getEffectiveTriggerTime();
+                $diff = $now->diff($triggerTime);
+                if ($diff->invert === 1) {
+                    continue;
+                }
+
+                $alarms = $this->getRemindersForVAlarm($valarm, $objectData, $calendarTimeZone,
+                    $eventHash, $alarmHash, true, true);
+                $this->writeRemindersToDatabase($alarms);
+            }
+        }
+
+        if ($masterItem) {
+            $processedAlarms = [];
+            $masterAlarms = [];
+            $masterHash = $this->getEventHash($masterItem);
+
+            if (!isset($masterItem->VALARM)) {
+                return;
+            }
+
+            foreach ($masterItem->VALARM as $valarm) {
+                $masterAlarms[] = $this->getAlarmHash($valarm);
+            }
+
+            try {
+                $iterator = new EventIterator($vevents, $uid);
+            } catch (NoInstancesException $e) {
+                // This event is recurring, but it doesn't have a single
+                // instance. We are skipping this event from the output
+                // entirely.
+                return;
+            } catch (MaxInstancesExceededException $e) {
+                // The event has more than 3500 recurring-instances
+                // so we can ignore it
+                return;
+            }
+
+            while ($iterator->valid() && count($processedAlarms) < count($masterAlarms)) {
+                $event = $iterator->getEventObject();
+
+                // Recurrence-exceptions are handled separately, so just ignore them here
+                if (\in_array($event, $recurrenceExceptions, true)) {
+                    $iterator->next();
+                    continue;
+                }
+
+                foreach ($event->VALARM as $valarm) {
+                    /** @var VAlarm $valarm */
+                    $alarmHash = $this->getAlarmHash($valarm);
+                    if (\in_array($alarmHash, $processedAlarms, true)) {
+                        continue;
+                    }
+
+                    if (!\in_array((string) $valarm->ACTION, self::REMINDER_TYPES, true)) {
+                        // Action allows x-name, we don't insert reminders
+                        // into the database if they are not standard
+                        $processedAlarms[] = $alarmHash;
+                        continue;
+                    }
+
+                    try {
+                        $triggerTime = $valarm->getEffectiveTriggerTime();
+                        /**
+                         * @psalm-suppress DocblockTypeContradiction
+                         *   https://github.com/vimeo/psalm/issues/9244
+                         */
+                        if ($triggerTime->getTimezone() === false || $triggerTime->getTimezone()->getName() === 'UTC') {
+                            $triggerTime = new DateTimeImmutable(
+                                $triggerTime->format('Y-m-d H:i:s'),
+                                $calendarTimeZone
+                            );
+                        }
+                    } catch (InvalidDataException $e) {
+                        continue;
+                    }
+
+                    // If effective trigger time is in the past
+                    // just skip and generate for next event
+                    $diff = $now->diff($triggerTime);
+                    if ($diff->invert === 1) {
+                        // If an absolute alarm is in the past,
+                        // just add it to processedAlarms, so
+                        // we don't extend till eternity
+                        if (!$this->isAlarmRelative($valarm)) {
+                            $processedAlarms[] = $alarmHash;
+                        }
+
+                        continue;
+                    }
+
+                    $alarms = $this->getRemindersForVAlarm($valarm, $objectData, $calendarTimeZone, $masterHash, $alarmHash, $isRecurring, false);
+                    $this->writeRemindersToDatabase($alarms);
+                    $processedAlarms[] = $alarmHash;
+                }
+
+                $iterator->next();
+            }
+        }
+    }
+
+    /**
+     * @param array $objectData
+     * @throws VObject\InvalidDataException
+     */
+    public function onCalendarObjectEdit(array $objectData):void {
+        // TODO - this can be vastly improved
+        //  - get cached reminders
+        //  - ...
+
+        $this->onCalendarObjectDelete($objectData);
+        $this->onCalendarObjectCreate($objectData);
+    }
+
+    /**
+     * @param array $objectData
+     * @throws VObject\InvalidDataException
+     */
+    public function onCalendarObjectDelete(array $objectData):void {
+        // We only support VEvents for now
+        if (strcasecmp($objectData['component'], 'vevent') !== 0) {
+            return;
+        }
+
+        $this->backend->cleanRemindersForEvent((int) $objectData['id']);
+    }
+
+    /**
+     * @param VAlarm $valarm
+     * @param array $objectData
+     * @param DateTimeZone $calendarTimeZone
+     * @param string|null $eventHash
+     * @param string|null $alarmHash
+     * @param bool $isRecurring
+     * @param bool $isRecurrenceException
+     * @return array
+     */
+    private function getRemindersForVAlarm(VAlarm $valarm,
+                                            array $objectData,
+                                            DateTimeZone $calendarTimeZone,
+                                            string $eventHash = null,
+                                            string $alarmHash = null,
+                                            bool $isRecurring = false,
+                                            bool $isRecurrenceException = false):array {
+        if ($eventHash === null) {
+            $eventHash = $this->getEventHash($valarm->parent);
+        }
+        if ($alarmHash === null) {
+            $alarmHash = $this->getAlarmHash($valarm);
+        }
+
+        $recurrenceId = $this->getEffectiveRecurrenceIdOfVEvent($valarm->parent);
+        $isRelative = $this->isAlarmRelative($valarm);
+        /** @var DateTimeImmutable $notificationDate */
+        $notificationDate = $valarm->getEffectiveTriggerTime();
+        /**
+         * @psalm-suppress DocblockTypeContradiction
+         *   https://github.com/vimeo/psalm/issues/9244
+         */
+        if ($notificationDate->getTimezone() === false || $notificationDate->getTimezone()->getName() === 'UTC') {
+            $notificationDate = new DateTimeImmutable(
+                $notificationDate->format('Y-m-d H:i:s'),
+                $calendarTimeZone
+            );
+        }
+        $clonedNotificationDate = new \DateTime('now', $notificationDate->getTimezone());
+        $clonedNotificationDate->setTimestamp($notificationDate->getTimestamp());
+
+        $alarms = [];
+
+        $alarms[] = [
+            'calendar_id' => $objectData['calendarid'],
+            'object_id' => $objectData['id'],
+            'uid' => (string) $valarm->parent->UID,
+            'is_recurring' => $isRecurring,
+            'recurrence_id' => $recurrenceId,
+            'is_recurrence_exception' => $isRecurrenceException,
+            'event_hash' => $eventHash,
+            'alarm_hash' => $alarmHash,
+            'type' => (string) $valarm->ACTION,
+            'is_relative' => $isRelative,
+            'notification_date' => $notificationDate->getTimestamp(),
+            'is_repeat_based' => false,
+        ];
+
+        $repeat = isset($valarm->REPEAT) ? (int) $valarm->REPEAT->getValue() : 0;
+        for ($i = 0; $i < $repeat; $i++) {
+            if ($valarm->DURATION === null) {
+                continue;
+            }
+
+            $clonedNotificationDate->add($valarm->DURATION->getDateInterval());
+            $alarms[] = [
+                'calendar_id' => $objectData['calendarid'],
+                'object_id' => $objectData['id'],
+                'uid' => (string) $valarm->parent->UID,
+                'is_recurring' => $isRecurring,
+                'recurrence_id' => $recurrenceId,
+                'is_recurrence_exception' => $isRecurrenceException,
+                'event_hash' => $eventHash,
+                'alarm_hash' => $alarmHash,
+                'type' => (string) $valarm->ACTION,
+                'is_relative' => $isRelative,
+                'notification_date' => $clonedNotificationDate->getTimestamp(),
+                'is_repeat_based' => true,
+            ];
+        }
+
+        return $alarms;
+    }
+
+    /**
+     * @param array $reminders
+     */
+    private function writeRemindersToDatabase(array $reminders): void {
+        foreach ($reminders as $reminder) {
+            $this->backend->insertReminder(
+                (int) $reminder['calendar_id'],
+                (int) $reminder['object_id'],
+                $reminder['uid'],
+                $reminder['is_recurring'],
+                (int) $reminder['recurrence_id'],
+                $reminder['is_recurrence_exception'],
+                $reminder['event_hash'],
+                $reminder['alarm_hash'],
+                $reminder['type'],
+                $reminder['is_relative'],
+                (int) $reminder['notification_date'],
+                $reminder['is_repeat_based']
+            );
+        }
+    }
+
+    /**
+     * @param array $reminder
+     * @param VEvent $vevent
+     */
+    private function deleteOrProcessNext(array $reminder,
+                                            VObject\Component\VEvent $vevent):void {
+        if ($reminder['is_repeat_based'] ||
+            !$reminder['is_recurring'] ||
+            !$reminder['is_relative'] ||
+            $reminder['is_recurrence_exception']) {
+            $this->backend->removeReminder($reminder['id']);
+            return;
+        }
+
+        $vevents = $this->getAllVEventsFromVCalendar($vevent->parent);
+        $recurrenceExceptions = $this->getRecurrenceExceptionFromListOfVEvents($vevents);
+        $now = $this->timeFactory->getDateTime();
+        $calendarTimeZone = $this->getCalendarTimeZone((int) $reminder['calendar_id']);
+
+        try {
+            $iterator = new EventIterator($vevents, $reminder['uid']);
+        } catch (NoInstancesException $e) {
+            // This event is recurring, but it doesn't have a single
+            // instance. We are skipping this event from the output
+            // entirely.
+            return;
+        }
+
+        try {
+            while ($iterator->valid()) {
+                $event = $iterator->getEventObject();
+
+                // Recurrence-exceptions are handled separately, so just ignore them here
+                if (\in_array($event, $recurrenceExceptions, true)) {
+                    $iterator->next();
+                    continue;
+                }
+
+                $recurrenceId = $this->getEffectiveRecurrenceIdOfVEvent($event);
+                if ($reminder['recurrence_id'] >= $recurrenceId) {
+                    $iterator->next();
+                    continue;
+                }
+
+                foreach ($event->VALARM as $valarm) {
+                    /** @var VAlarm $valarm */
+                    $alarmHash = $this->getAlarmHash($valarm);
+                    if ($alarmHash !== $reminder['alarm_hash']) {
+                        continue;
+                    }
+
+                    $triggerTime = $valarm->getEffectiveTriggerTime();
+
+                    // If effective trigger time is in the past
+                    // just skip and generate for next event
+                    $diff = $now->diff($triggerTime);
+                    if ($diff->invert === 1) {
+                        continue;
+                    }
+
+                    $this->backend->removeReminder($reminder['id']);
+                    $alarms = $this->getRemindersForVAlarm($valarm, [
+                        'calendarid' => $reminder['calendar_id'],
+                        'id' => $reminder['object_id'],
+                    ], $calendarTimeZone, $reminder['event_hash'], $alarmHash, true, false);
+                    $this->writeRemindersToDatabase($alarms);
+
+                    // Abort generating reminders after creating one successfully
+                    return;
+                }
+
+                $iterator->next();
+            }
+        } catch (MaxInstancesExceededException $e) {
+            // Using debug logger as this isn't really an error
+            $this->logger->debug('Recurrence with too many instances detected, skipping VEVENT', ['exception' => $e]);
+        }
+
+        $this->backend->removeReminder($reminder['id']);
+    }
+
+    /**
+     * @param int $calendarId
+     * @return IUser[]
+     */
+    private function getAllUsersWithWriteAccessToCalendar(int $calendarId):array {
+        $shares = $this->caldavBackend->getShares($calendarId);
+
+        $users = [];
+        $userIds = [];
+        $groups = [];
+        foreach ($shares as $share) {
+            // Only consider writable shares
+            if ($share['readOnly']) {
+                continue;
+            }
+
+            $principal = explode('/', $share['{http://owncloud.org/ns}principal']);
+            if ($principal[1] === 'users') {
+                $user = $this->userManager->get($principal[2]);
+                if ($user) {
+                    $users[] = $user;
+                    $userIds[] = $principal[2];
+                }
+            } elseif ($principal[1] === 'groups') {
+                $groups[] = $principal[2];
+            }
+        }
+
+        foreach ($groups as $gid) {
+            $group = $this->groupManager->get($gid);
+            if ($group instanceof IGroup) {
+                foreach ($group->getUsers() as $user) {
+                    if (!\in_array($user->getUID(), $userIds, true)) {
+                        $users[] = $user;
+                        $userIds[] = $user->getUID();
+                    }
+                }
+            }
+        }
+
+        return $users;
+    }
+
+    /**
+     * Gets a hash of the event.
+     * If the hash changes, we have to update all relative alarms.
+     *
+     * @param VEvent $vevent
+     * @return string
+     */
+    private function getEventHash(VEvent $vevent):string {
+        $properties = [
+            (string) $vevent->DTSTART->serialize(),
+        ];
+
+        if ($vevent->DTEND) {
+            $properties[] = (string) $vevent->DTEND->serialize();
+        }
+        if ($vevent->DURATION) {
+            $properties[] = (string) $vevent->DURATION->serialize();
+        }
+        if ($vevent->{'RECURRENCE-ID'}) {
+            $properties[] = (string) $vevent->{'RECURRENCE-ID'}->serialize();
+        }
+        if ($vevent->RRULE) {
+            $properties[] = (string) $vevent->RRULE->serialize();
+        }
+        if ($vevent->EXDATE) {
+            $properties[] = (string) $vevent->EXDATE->serialize();
+        }
+        if ($vevent->RDATE) {
+            $properties[] = (string) $vevent->RDATE->serialize();
+        }
+
+        return md5(implode('::', $properties));
+    }
+
+    /**
+     * Gets a hash of the alarm.
+     * If the hash changes, we have to update oc_dav_reminders.
+     *
+     * @param VAlarm $valarm
+     * @return string
+     */
+    private function getAlarmHash(VAlarm $valarm):string {
+        $properties = [
+            (string) $valarm->ACTION->serialize(),
+            (string) $valarm->TRIGGER->serialize(),
+        ];
+
+        if ($valarm->DURATION) {
+            $properties[] = (string) $valarm->DURATION->serialize();
+        }
+        if ($valarm->REPEAT) {
+            $properties[] = (string) $valarm->REPEAT->serialize();
+        }
+
+        return md5(implode('::', $properties));
+    }
+
+    /**
+     * @param VObject\Component\VCalendar $vcalendar
+     * @param int $recurrenceId
+     * @param bool $isRecurrenceException
+     * @return VEvent|null
+     */
+    private function getVEventByRecurrenceId(VObject\Component\VCalendar $vcalendar,
+                                                int $recurrenceId,
+                                                bool $isRecurrenceException):?VEvent {
+        $vevents = $this->getAllVEventsFromVCalendar($vcalendar);
+        if (count($vevents) === 0) {
+            return null;
+        }
+
+        $uid = (string) $vevents[0]->UID;
+        $recurrenceExceptions = $this->getRecurrenceExceptionFromListOfVEvents($vevents);
+        $masterItem = $this->getMasterItemFromListOfVEvents($vevents);
+
+        // Handle recurrence-exceptions first, because recurrence-expansion is expensive
+        if ($isRecurrenceException) {
+            foreach ($recurrenceExceptions as $recurrenceException) {
+                if ($this->getEffectiveRecurrenceIdOfVEvent($recurrenceException) === $recurrenceId) {
+                    return $recurrenceException;
+                }
+            }
+
+            return null;
+        }
+
+        if ($masterItem) {
+            try {
+                $iterator = new EventIterator($vevents, $uid);
+            } catch (NoInstancesException $e) {
+                // This event is recurring, but it doesn't have a single
+                // instance. We are skipping this event from the output
+                // entirely.
+                return null;
+            }
+
+            while ($iterator->valid()) {
+                $event = $iterator->getEventObject();
+
+                // Recurrence-exceptions are handled separately, so just ignore them here
+                if (\in_array($event, $recurrenceExceptions, true)) {
+                    $iterator->next();
+                    continue;
+                }
+
+                if ($this->getEffectiveRecurrenceIdOfVEvent($event) === $recurrenceId) {
+                    return $event;
+                }
+
+                $iterator->next();
+            }
+        }
+
+        return null;
+    }
+
+    /**
+     * @param VEvent $vevent
+     * @return string
+     */
+    private function getStatusOfEvent(VEvent $vevent):string {
+        if ($vevent->STATUS) {
+            return (string) $vevent->STATUS;
+        }
+
+        // Doesn't say so in the standard,
+        // but we consider events without a status
+        // to be confirmed
+        return 'CONFIRMED';
+    }
+
+    /**
+     * @param VObject\Component\VEvent $vevent
+     * @return bool
+     */
+    private function wasEventCancelled(VObject\Component\VEvent $vevent):bool {
+        return $this->getStatusOfEvent($vevent) === 'CANCELLED';
+    }
+
+    /**
+     * @param string $calendarData
+     * @return VObject\Component\VCalendar|null
+     */
+    private function parseCalendarData(string $calendarData):?VObject\Component\VCalendar {
+        try {
+            return VObject\Reader::read($calendarData,
+                VObject\Reader::OPTION_FORGIVING);
+        } catch (ParseException $ex) {
+            return null;
+        }
+    }
+
+    /**
+     * @param string $principalUri
+     * @return IUser|null
+     */
+    private function getUserFromPrincipalURI(string $principalUri):?IUser {
+        if (!$principalUri) {
+            return null;
+        }
+
+        if (stripos($principalUri, 'principals/users/') !== 0) {
+            return null;
+        }
+
+        $userId = substr($principalUri, 17);
+        return $this->userManager->get($userId);
+    }
+
+    /**
+     * @param VObject\Component\VCalendar $vcalendar
+     * @return VObject\Component\VEvent[]
+     */
+    private function getAllVEventsFromVCalendar(VObject\Component\VCalendar $vcalendar):array {
+        $vevents = [];
+
+        foreach ($vcalendar->children() as $child) {
+            if (!($child instanceof VObject\Component)) {
+                continue;
+            }
+
+            if ($child->name !== 'VEVENT') {
+                continue;
+            }
+            // Ignore invalid events with no DTSTART
+            if ($child->DTSTART === null) {
+                continue;
+            }
+
+            $vevents[] = $child;
+        }
+
+        return $vevents;
+    }
+
+    /**
+     * @param array $vevents
+     * @return VObject\Component\VEvent[]
+     */
+    private function getRecurrenceExceptionFromListOfVEvents(array $vevents):array {
+        return array_values(array_filter($vevents, function (VEvent $vevent) {
+            return $vevent->{'RECURRENCE-ID'} !== null;
+        }));
+    }
+
+    /**
+     * @param array $vevents
+     * @return VEvent|null
+     */
+    private function getMasterItemFromListOfVEvents(array $vevents):?VEvent {
+        $elements = array_values(array_filter($vevents, function (VEvent $vevent) {
+            return $vevent->{'RECURRENCE-ID'} === null;
+        }));
+
+        if (count($elements) === 0) {
+            return null;
+        }
+        if (count($elements) > 1) {
+            throw new \TypeError('Multiple master objects');
+        }
+
+        return $elements[0];
+    }
+
+    /**
+     * @param VAlarm $valarm
+     * @return bool
+     */
+    private function isAlarmRelative(VAlarm $valarm):bool {
+        $trigger = $valarm->TRIGGER;
+        return $trigger instanceof VObject\Property\ICalendar\Duration;
+    }
+
+    /**
+     * @param VEvent $vevent
+     * @return int
+     */
+    private function getEffectiveRecurrenceIdOfVEvent(VEvent $vevent):int {
+        if (isset($vevent->{'RECURRENCE-ID'})) {
+            return $vevent->{'RECURRENCE-ID'}->getDateTime()->getTimestamp();
+        }
+
+        return $vevent->DTSTART->getDateTime()->getTimestamp();
+    }
+
+    /**
+     * @param VEvent $vevent
+     * @return bool
+     */
+    private function isRecurring(VEvent $vevent):bool {
+        return isset($vevent->RRULE) || isset($vevent->RDATE);
+    }
+
+    /**
+     * @param int $calendarid
+     *
+     * @return DateTimeZone
+     */
+    private function getCalendarTimeZone(int $calendarid): DateTimeZone {
+        $calendarInfo = $this->caldavBackend->getCalendarById($calendarid);
+        $tzProp = '{urn:ietf:params:xml:ns:caldav}calendar-timezone';
+        if (!isset($calendarInfo[$tzProp])) {
+            // Defaulting to UTC
+            return new DateTimeZone('UTC');
+        }
+        // This property contains a VCALENDAR with a single VTIMEZONE
+        /** @var string $timezoneProp */
+        $timezoneProp = $calendarInfo[$tzProp];
+        /** @var VObject\Component\VCalendar $vtimezoneObj */
+        $vtimezoneObj = VObject\Reader::read($timezoneProp);
+        /** @var VObject\Component\VTimeZone $vtimezone */
+        $vtimezone = $vtimezoneObj->VTIMEZONE;
+        return $vtimezone->getTimeZone();
+    }
 }