3 files changed, 832 insertions, 499 deletions

diff --git a/apps/dav/lib/CalDAV/EventComparisonService.php b/apps/dav/lib/CalDAV/EventComparisonService.php
new file mode 100644
index 00000000000..0fd4d08e83e
--- /dev/null
+++ b/apps/dav/lib/CalDAV/EventComparisonService.php
@@ -0,0 +1,123 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * @copyright 2022 Anna Larch <anna.larch@gmx.net>
+ *
+ * @author 2022 Anna Larch <anna.larch@gmx.net>
+ *
+ * @license GNU AGPL version 3 or any later version
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+namespace OCA\DAV\CalDAV;
+
+use OCA\DAV\AppInfo\Application;
+use OCA\DAV\CalDAV\Schedule\IMipService;
+use OCP\AppFramework\Utility\ITimeFactory;
+use OCP\IConfig;
+use Sabre\VObject\Component\VCalendar;
+use Sabre\VObject\Component\VEvent;
+use Sabre\VObject\Component\VTimeZone;
+use Sabre\VObject\Component\VTodo;
+use function max;
+
+class EventComparisonService {
+
+	/** @var string[] */
+	private const EVENT_DIFF = [
+		'RECURRENCE-ID',
+		'RRULE',
+		'SEQUENCE',
+		'LAST-MODIFIED'
+	];
+
+
+	/**
+	 * If found, remove the event from $eventsToFilter that
+	 * is identical to the passed $filterEvent
+	 * and return whether an identical event was found
+	 *
+	 * This function takes into account the SEQUENCE,
+	 * RRULE, RECURRENCE-ID and LAST-MODIFIED parameters
+	 *
+	 * @param VEvent $filterEvent
+	 * @param array $eventsToFilter
+	 * @return bool true if there was an identical event found and removed, false if there wasn't
+	 */
+	private function removeIfUnchanged(VEvent $filterEvent, array &$eventsToFilter): bool {
+		$filterEventData = [];
+		foreach(self::EVENT_DIFF as $eventDiff) {
+			$filterEventData[] = IMipService::readPropertyWithDefault($filterEvent, $eventDiff, '');
+		}
+
+		/** @var VEvent $component */
+		foreach ($eventsToFilter as $k => $eventToFilter) {
+			$eventToFilterData = [];
+			foreach(self::EVENT_DIFF as $eventDiff) {
+				$eventToFilterData[] = IMipService::readPropertyWithDefault($eventToFilter, $eventDiff, '');
+			}
+			// events are identical and can be removed
+			if (empty(array_diff($filterEventData, $eventToFilterData))) {
+				unset($eventsToFilter[$k]);
+				return true;
+			}
+		}
+		return false;
+	}
+
+	/**
+	 * Compare two VCalendars with each other and find all changed elements
+	 *
+	 * Returns an array of old and new events
+	 *
+	 * Old events are only detected if they are also changed
+	 * If there is no corresponding old event for a VEvent, it
+	 * has been newly created
+	 *
+	 * @param VCalendar $new
+	 * @param VCalendar|null $old
+	 * @return array<string, VEvent[]>
+	 */
+	public function findModified(VCalendar $new, ?VCalendar $old): array {
+		$newEventComponents = $new->getComponents();
+
+		foreach ($newEventComponents as $k => $event) {
+			if(!$event instanceof VEvent) {
+				unset($newEventComponents[$k]);
+			}
+		}
+
+		if(empty($old)) {
+			return ['old' => null, 'new' => $newEventComponents];
+		}
+
+		$oldEventComponents = $old->getComponents();
+		if(is_array($oldEventComponents) && !empty($oldEventComponents)) {
+			foreach ($oldEventComponents as $k => $event) {
+				if(!$event instanceof VEvent) {
+					unset($oldEventComponents[$k]);
+					continue;
+				}
+				if($this->removeIfUnchanged($event, $newEventComponents)) {
+					unset($oldEventComponents[$k]);
+				}
+			}
+		}
+
+		return ['old' => array_values($oldEventComponents), 'new' => array_values($newEventComponents)];
+	}
+}
diff --git a/apps/dav/lib/CalDAV/Schedule/IMipPlugin.php b/apps/dav/lib/CalDAV/Schedule/IMipPlugin.php
index 50390549570..d4c2976fc1a 100644
--- a/apps/dav/lib/CalDAV/Schedule/IMipPlugin.php
+++ b/apps/dav/lib/CalDAV/Schedule/IMipPlugin.php
@@ -4,6 +4,7 @@
  * @copyright Copyright (c) 2017, Georg Ehrke
  * @copyright Copyright (C) 2007-2015 fruux GmbH (https://fruux.com/).
  * @copyright Copyright (C) 2007-2015 fruux GmbH (https://fruux.com/).
+ * @copyright 2022 Anna Larch <anna.larch@gmx.net>
  *
  * @author brad2014 <brad2014@users.noreply.github.com>
  * @author Brad Rubenstein <brad@wbr.tech>
@@ -16,6 +17,7 @@
  * @author Roeland Jago Douma <roeland@famdouma.nl>
  * @author Thomas Citharel <nextcloud@tcit.fr>
  * @author Thomas Müller <thomas.mueller@tmit.eu>
+ * @author Anna Larch <anna.larch@gmx.net>
  *
  * @license AGPL-3.0
  *
@@ -34,6 +36,8 @@
  */
 namespace OCA\DAV\CalDAV\Schedule;
 
+use OCA\DAV\CalDAV\CalendarObject;
+use OCA\DAV\CalDAV\EventComparisonService;
 use OCP\AppFramework\Utility\ITimeFactory;
 use OCP\Defaults;
 use OCP\IConfig;
@@ -48,12 +52,16 @@ use OCP\Security\ISecureRandom;
 use OCP\Util;
 use Psr\Log\LoggerInterface;
 use Sabre\CalDAV\Schedule\IMipPlugin as SabreIMipPlugin;
+use Sabre\DAV;
+use Sabre\DAV\INode;
 use Sabre\VObject\Component\VCalendar;
 use Sabre\VObject\Component\VEvent;
+use Sabre\VObject\Component\VTimeZone;
 use Sabre\VObject\DateTimeParser;
 use Sabre\VObject\ITip\Message;
 use Sabre\VObject\Parameter;
 use Sabre\VObject\Property;
+use Sabre\VObject\Reader;
 use Sabre\VObject\Recur\EventIterator;
 
 /**
@@ -71,63 +79,63 @@ use Sabre\VObject\Recur\EventIterator;
  * @license http://sabre.io/license/ Modified BSD License
  */
 class IMipPlugin extends SabreIMipPlugin {
-	/** @var string */
-	private $userId;
-
-	/** @var IConfig */
-	private $config;
-
-	/** @var IMailer */
-	private $mailer;
-
+	private ?string $userId;
+	private IConfig $config;
+	private IMailer $mailer;
 	private LoggerInterface $logger;
-
-	/** @var ITimeFactory */
-	private $timeFactory;
-
-	/** @var L10NFactory */
-	private $l10nFactory;
-
-	/** @var IURLGenerator */
-	private $urlGenerator;
-
-	/** @var ISecureRandom */
-	private $random;
-
-	/** @var IDBConnection */
-	private $db;
-
-	/** @var Defaults */
-	private $defaults;
-
-	/** @var IUserManager */
-	private $userManager;
-
+	private ITimeFactory $timeFactory;
+	private Defaults $defaults;
+	private IUserManager $userManager;
+	private ?VCalendar $vCalendar = null;
+	private IMipService $imipService;
 	public const MAX_DATE = '2038-01-01';
-
 	public const METHOD_REQUEST = 'request';
 	public const METHOD_REPLY = 'reply';
 	public const METHOD_CANCEL = 'cancel';
 	public const IMIP_INDENT = 15; // Enough for the length of all body bullet items, in all languages
+	private EventComparisonService $eventComparisonService;
 
-	public function __construct(IConfig $config, IMailer $mailer,
+	public function __construct(IConfig $config,
+								IMailer $mailer,
 								LoggerInterface $logger,
-								ITimeFactory $timeFactory, L10NFactory $l10nFactory,
-								IURLGenerator $urlGenerator, Defaults $defaults,
-								ISecureRandom $random, IDBConnection $db, IUserManager $userManager,
-								$userId) {
+								ITimeFactory $timeFactory,
+								Defaults $defaults,
+								IUserManager $userManager,
+								$userId,
+								IMipService $imipService,
+								EventComparisonService $eventComparisonService) {
 		parent::__construct('');
 		$this->userId = $userId;
 		$this->config = $config;
 		$this->mailer = $mailer;
 		$this->logger = $logger;
 		$this->timeFactory = $timeFactory;
-		$this->l10nFactory = $l10nFactory;
-		$this->urlGenerator = $urlGenerator;
-		$this->random = $random;
-		$this->db = $db;
 		$this->defaults = $defaults;
 		$this->userManager = $userManager;
+		$this->imipService = $imipService;
+		$this->eventComparisonService = $eventComparisonService;
+	}
+
+	public function initialize(DAV\Server $server): void {
+		parent::initialize($server);
+		$server->on('beforeWriteContent', [$this, 'beforeWriteContent'], 10);
+	}
+
+	/**
+	 * Check quota before writing content
+	 *
+	 * @param string $uri target file URI
+	 * @param INode $node Sabre Node
+	 * @param resource $data data
+	 * @param bool $modified modified
+	 */
+	public function beforeWriteContent($uri, INode $node, $data, $modified): void {
+		if(!$node instanceof CalendarObject) {
+			return;
+		}
+		/** @var VCalendar $vCalendar */
+		$vCalendar = Reader::read($node->get());
+		$this->setVCalendar($vCalendar);
 	}
 
 	/**
@@ -146,34 +154,55 @@ class IMipPlugin extends SabreIMipPlugin {
 			return;
 		}
 
-		$summary = $iTipMessage->message->VEVENT->SUMMARY;
-
-		if (parse_url($iTipMessage->sender, PHP_URL_SCHEME) !== 'mailto') {
-			return;
-		}
-
-		if (parse_url($iTipMessage->recipient, PHP_URL_SCHEME) !== 'mailto') {
+		if (parse_url($iTipMessage->sender, PHP_URL_SCHEME) !== 'mailto'
+			|| parse_url($iTipMessage->recipient, PHP_URL_SCHEME) !== 'mailto') {
 			return;
 		}
 
 		// don't send out mails for events that already took place
-		$lastOccurrence = $this->getLastOccurrence($iTipMessage->message);
+		$lastOccurrence = $this->imipService->getLastOccurrence($iTipMessage->message);
 		$currentTime = $this->timeFactory->getTime();
 		if ($lastOccurrence < $currentTime) {
 			return;
 		}
 
 		// Strip off mailto:
-		$sender = substr($iTipMessage->sender, 7);
 		$recipient = substr($iTipMessage->recipient, 7);
 		if (!$this->mailer->validateMailAddress($recipient)) {
 			// Nothing to send if the recipient doesn't have a valid email address
 			$iTipMessage->scheduleStatus = '5.0; EMail delivery failed';
 			return;
 		}
-
 		$recipientName = $iTipMessage->recipientName ?: null;
 
+		$newEvents = $iTipMessage->message;
+		$oldEvents = $this->getVCalendar();
+
+		$modified = $this->eventComparisonService->findModified($newEvents, $oldEvents);
+		/** @var VEvent $vEvent */
+		$vEvent = array_pop($modified['new']);
+		/** @var VEvent $oldVevent */
+		$oldVevent = !empty($modified['old']) && is_array($modified['old']) ? array_pop($modified['old']) : null;
+
+		// No changed events after all - this shouldn't happen if there is significant change yet here we are
+		// The scheduling status is debatable
+		if(empty($vEvent)) {
+			$this->logger->warning('iTip message said the change was significant but comparison did not detect any updated VEvents');
+			$iTipMessage->scheduleStatus = '1.0;We got the message, but it\'s not significant enough to warrant an email';
+			return;
+		}
+
+		// we (should) have one event component left
+		// as the ITip\Broker creates one iTip message per change
+		// and triggers the "schedule" event once per message
+		// we also might not have an old event as this could be a new
+		// invitation, or a new recurrence exception
+		$attendee = $this->imipService->getCurrentAttendee($iTipMessage);
+		$this->imipService->setL10n($attendee);
+
+		// Build the sender name.
+		// Due to a bug in sabre, the senderName property for an iTIP message
+		// can actually also be a VObject Property
 		/** @var Parameter|string|null $senderName */
 		$senderName = $iTipMessage->senderName ?: null;
 		if($senderName instanceof Parameter) {
@@ -183,47 +212,29 @@ class IMipPlugin extends SabreIMipPlugin {
 		if ($senderName === null || empty(trim($senderName))) {
 			$senderName = $this->userManager->getDisplayName($this->userId);
 		}
+		$sender = substr($iTipMessage->sender, 7);
 
-		/** @var VEvent $vevent */
-		$vevent = $iTipMessage->message->VEVENT;
-
-		$attendee = $this->getCurrentAttendee($iTipMessage);
-		$defaultLang = $this->l10nFactory->findGenericLanguage();
-		$lang = $this->getAttendeeLangOrDefault($defaultLang, $attendee);
-		$l10n = $this->l10nFactory->get('dav', $lang);
-
-		$meetingAttendeeName = $recipientName ?: $recipient;
-		$meetingInviteeName = $senderName ?: $sender;
-
-		$meetingTitle = $vevent->SUMMARY;
-		$meetingDescription = $vevent->DESCRIPTION;
-
-
-		$meetingUrl = $vevent->URL;
-		$meetingLocation = $vevent->LOCATION;
-
-		$defaultVal = '--';
-
-		$method = self::METHOD_REQUEST;
 		switch (strtolower($iTipMessage->method)) {
 			case self::METHOD_REPLY:
 				$method = self::METHOD_REPLY;
+				$data = $this->imipService->buildBodyData($vEvent, $oldVevent);
 				break;
 			case self::METHOD_CANCEL:
 				$method = self::METHOD_CANCEL;
+				$data = $this->imipService->buildCancelledBodyData($vEvent);
+				break;
+			default:
+				$method = self::METHOD_REQUEST;
+				$data = $this->imipService->buildBodyData($vEvent, $oldVevent);
 				break;
 		}
 
-		$data = [
-			'attendee_name' => (string)$meetingAttendeeName ?: $defaultVal,
-			'invitee_name' => (string)$meetingInviteeName ?: $defaultVal,
-			'meeting_title' => (string)$meetingTitle ?: $defaultVal,
-			'meeting_description' => (string)$meetingDescription ?: $defaultVal,
-			'meeting_url' => (string)$meetingUrl ?: $defaultVal,
-		];
+
+		$data['attendee_name'] = ($recipientName ?: $recipient);
+		$data['invitee_name'] = ($senderName ?: $sender);
 
 		$fromEMail = Util::getDefaultEmailAddress('invitations-noreply');
-		$fromName = $l10n->t('%1$s via %2$s', [$senderName ?? $this->userId, $this->defaults->getName()]);
+		$fromName = $this->imipService->getFrom($senderName, $this->defaults->getName());
 
 		$message = $this->mailer->createMessage()
 			->setFrom([$fromEMail => $fromName])
@@ -233,13 +244,12 @@ class IMipPlugin extends SabreIMipPlugin {
 		$template = $this->mailer->createEMailTemplate('dav.calendarInvite.' . $method, $data);
 		$template->addHeader();
 
-		$summary = ((string) $summary !== '') ? (string) $summary : $l10n->t('Untitled event');
-
-		$this->addSubjectAndHeading($template, $l10n, $method, $summary);
-		$this->addBulletList($template, $l10n, $vevent);
+		$this->imipService->addSubjectAndHeading($template, $method, $data['invitee_name'], $data['meeting_title']);
+		$this->imipService->addBulletList($template, $vEvent, $data);
 
 		// Only add response buttons to invitation requests: Fix Issue #11230
-		if (($method == self::METHOD_REQUEST) && $this->getAttendeeRsvpOrReqForParticipant($attendee)) {
+		if (strcasecmp($method, self::METHOD_REQUEST) === 0 && $this->imipService->getAttendeeRsvpOrReqForParticipant($attendee)) {
+
 			/*
 			** Only offer invitation accept/reject buttons, which link back to the
 			** nextcloud server, to recipients who can access the nextcloud server via
@@ -259,13 +269,15 @@ class IMipPlugin extends SabreIMipPlugin {
 			** To suppress URLs entirely, set invitation_link_recipients to boolean "no".
 			*/
 
-			$recipientDomain = substr(strrchr($recipient, "@"), 1);
+			$recipientDomain = substr(strrchr($recipient, '@'), 1);
 			$invitationLinkRecipients = explode(',', preg_replace('/\s+/', '', strtolower($this->config->getAppValue('dav', 'invitation_link_recipients', 'yes'))));
 
 			if (strcmp('yes', $invitationLinkRecipients[0]) === 0
-				 || in_array(strtolower($recipient), $invitationLinkRecipients)
-				 || in_array(strtolower($recipientDomain), $invitationLinkRecipients)) {
-				$this->addResponseButtons($template, $l10n, $iTipMessage, $lastOccurrence);
+				|| in_array(strtolower($recipient), $invitationLinkRecipients)
+				|| in_array(strtolower($recipientDomain), $invitationLinkRecipients)) {
+				$token = $this->imipService->createInvitationToken($iTipMessage, $vEvent, $lastOccurrence);
+				$this->imipService->addResponseButtons($template, $token);
+				$this->imipService->addMoreOptionsButton($template, $token);
 			}
 		}
 
@@ -273,9 +285,11 @@ class IMipPlugin extends SabreIMipPlugin {
 
 		$message->useTemplate($template);
 
+		$vCalendar = $this->imipService->generateVCalendar($iTipMessage, $vEvent);
+
 		$attachment = $this->mailer->createAttachment(
-			$iTipMessage->message->serialize(),
-			'event.ics',// TODO(leon): Make file name unique, e.g. add event id
+			$vCalendar->serialize(),
+			'event.ics',
 			'text/calendar; method=' . $iTipMessage->method
 		);
 		$message->attach($attachment);
@@ -283,7 +297,7 @@ class IMipPlugin extends SabreIMipPlugin {
 		try {
 			$failed = $this->mailer->send($message);
 			$iTipMessage->scheduleStatus = '1.1; Scheduling message is sent via iMip';
-			if ($failed) {
+			if (!empty($failed)) {
 				$this->logger->error('Unable to deliver message to {failed}', ['app' => 'dav', 'failed' => implode(', ', $failed)]);
 				$iTipMessage->scheduleStatus = '5.0; EMail delivery failed';
 			}
@@ -294,418 +308,17 @@ class IMipPlugin extends SabreIMipPlugin {
 	}
 
 	/**
-	 * check if event took place in the past already
-	 * @param VCalendar $vObject
-	 * @return int
-	 */
-	private function getLastOccurrence(VCalendar $vObject) {
-		/** @var VEvent $component */
-		$component = $vObject->VEVENT;
-
-		$firstOccurrence = $component->DTSTART->getDateTime()->getTimeStamp();
-		// Finding the last occurrence is a bit harder
-		if (!isset($component->RRULE)) {
-			if (isset($component->DTEND)) {
-				$lastOccurrence = $component->DTEND->getDateTime()->getTimeStamp();
-			} elseif (isset($component->DURATION)) {
-				/** @var \DateTime $endDate */
-				$endDate = clone $component->DTSTART->getDateTime();
-				// $component->DTEND->getDateTime() returns DateTimeImmutable
-				$endDate = $endDate->add(DateTimeParser::parse($component->DURATION->getValue()));
-				$lastOccurrence = $endDate->getTimestamp();
-			} elseif (!$component->DTSTART->hasTime()) {
-				/** @var \DateTime $endDate */
-				$endDate = clone $component->DTSTART->getDateTime();
-				// $component->DTSTART->getDateTime() returns DateTimeImmutable
-				$endDate = $endDate->modify('+1 day');
-				$lastOccurrence = $endDate->getTimestamp();
-			} else {
-				$lastOccurrence = $firstOccurrence;
-			}
-		} else {
-			$it = new EventIterator($vObject, (string)$component->UID);
-			$maxDate = new \DateTime(self::MAX_DATE);
-			if ($it->isInfinite()) {
-				$lastOccurrence = $maxDate->getTimestamp();
-			} else {
-				$end = $it->getDtEnd();
-				while ($it->valid() && $end < $maxDate) {
-					$end = $it->getDtEnd();
-					$it->next();
-				}
-				$lastOccurrence = $end->getTimestamp();
-			}
-		}
-
-		return $lastOccurrence;
-	}
-
-	/**
-	 * @param Message $iTipMessage
-	 * @return null|Property
-	 */
-	private function getCurrentAttendee(Message $iTipMessage) {
-		/** @var VEvent $vevent */
-		$vevent = $iTipMessage->message->VEVENT;
-		$attendees = $vevent->select('ATTENDEE');
-		foreach ($attendees as $attendee) {
-			/** @var Property $attendee */
-			if (strcasecmp($attendee->getValue(), $iTipMessage->recipient) === 0) {
-				return $attendee;
-			}
-		}
-		return null;
-	}
-
-	/**
-	 * @param string $default
-	 * @param Property|null $attendee
-	 * @return string
+	 * @return ?VCalendar
 	 */
-	private function getAttendeeLangOrDefault($default, Property $attendee = null) {
-		if ($attendee !== null) {
-			$lang = $attendee->offsetGet('LANGUAGE');
-			if ($lang instanceof Parameter) {
-				return $lang->getValue();
-			}
-		}
-		return $default;
+	public function getVCalendar(): ?VCalendar {
+		return $this->vCalendar;
 	}
 
 	/**
-	 * @param Property|null $attendee
-	 * @return bool
+	 * @param ?VCalendar $vCalendar
 	 */
-	private function getAttendeeRsvpOrReqForParticipant(Property $attendee = null) {
-		if ($attendee !== null) {
-			$rsvp = $attendee->offsetGet('RSVP');
-			if (($rsvp instanceof Parameter) && (strcasecmp($rsvp->getValue(), 'TRUE') === 0)) {
-				return true;
-			}
-			$role = $attendee->offsetGet('ROLE');
-			// @see https://datatracker.ietf.org/doc/html/rfc5545#section-3.2.16
-			// Attendees without a role are assumed required and should receive an invitation link even if they have no RSVP set
-			if ($role === null
-				|| (($role instanceof Parameter) && (strcasecmp($role->getValue(), 'REQ-PARTICIPANT') === 0))
-				|| (($role instanceof Parameter) && (strcasecmp($role->getValue(), 'OPT-PARTICIPANT') === 0))
-			) {
-				return true;
-			}
-		}
-		// RFC 5545 3.2.17: default RSVP is false
-		return false;
+	public function setVCalendar(?VCalendar $vCalendar): void {
+		$this->vCalendar = $vCalendar;
 	}
 
-	/**
-	 * @param IL10N $l10n
-	 * @param VEvent $vevent
-	 */
-	private function generateWhenString(IL10N $l10n, VEvent $vevent) {
-		$dtstart = $vevent->DTSTART;
-		if (isset($vevent->DTEND)) {
-			$dtend = $vevent->DTEND;
-		} elseif (isset($vevent->DURATION)) {
-			$isFloating = $vevent->DTSTART->isFloating();
-			$dtend = clone $vevent->DTSTART;
-			$endDateTime = $dtend->getDateTime();
-			$endDateTime = $endDateTime->add(DateTimeParser::parse($vevent->DURATION->getValue()));
-			$dtend->setDateTime($endDateTime, $isFloating);
-		} elseif (!$vevent->DTSTART->hasTime()) {
-			$isFloating = $vevent->DTSTART->isFloating();
-			$dtend = clone $vevent->DTSTART;
-			$endDateTime = $dtend->getDateTime();
-			$endDateTime = $endDateTime->modify('+1 day');
-			$dtend->setDateTime($endDateTime, $isFloating);
-		} else {
-			$dtend = clone $vevent->DTSTART;
-		}
-
-		$isAllDay = $dtstart instanceof Property\ICalendar\Date;
-
-		/** @var Property\ICalendar\Date | Property\ICalendar\DateTime $dtstart */
-		/** @var Property\ICalendar\Date | Property\ICalendar\DateTime $dtend */
-		/** @var \DateTimeImmutable $dtstartDt */
-		$dtstartDt = $dtstart->getDateTime();
-		/** @var \DateTimeImmutable $dtendDt */
-		$dtendDt = $dtend->getDateTime();
-
-		$diff = $dtstartDt->diff($dtendDt);
-
-		$dtstartDt = new \DateTime($dtstartDt->format(\DateTimeInterface::ATOM));
-		$dtendDt = new \DateTime($dtendDt->format(\DateTimeInterface::ATOM));
-
-		if ($isAllDay) {
-			// One day event
-			if ($diff->days === 1) {
-				return $l10n->l('date', $dtstartDt, ['width' => 'medium']);
-			}
-
-			// DTEND is exclusive, so if the ics data says 2020-01-01 to 2020-01-05,
-			// the email should show 2020-01-01 to 2020-01-04.
-			$dtendDt->modify('-1 day');
-
-			//event that spans over multiple days
-			$localeStart = $l10n->l('date', $dtstartDt, ['width' => 'medium']);
-			$localeEnd = $l10n->l('date', $dtendDt, ['width' => 'medium']);
-
-			return $localeStart . ' - ' . $localeEnd;
-		}
-
-		/** @var Property\ICalendar\DateTime $dtstart */
-		/** @var Property\ICalendar\DateTime $dtend */
-		$isFloating = $dtstart->isFloating();
-		$startTimezone = $endTimezone = null;
-		if (!$isFloating) {
-			$prop = $dtstart->offsetGet('TZID');
-			if ($prop instanceof Parameter) {
-				$startTimezone = $prop->getValue();
-			}
-
-			$prop = $dtend->offsetGet('TZID');
-			if ($prop instanceof Parameter) {
-				$endTimezone = $prop->getValue();
-			}
-		}
-
-		$localeStart = $l10n->l('weekdayName', $dtstartDt, ['width' => 'abbreviated']) . ', ' .
-			$l10n->l('datetime', $dtstartDt, ['width' => 'medium|short']);
-
-		// always show full date with timezone if timezones are different
-		if ($startTimezone !== $endTimezone) {
-			$localeEnd = $l10n->l('datetime', $dtendDt, ['width' => 'medium|short']);
-
-			return $localeStart . ' (' . $startTimezone . ') - ' .
-				$localeEnd . ' (' . $endTimezone . ')';
-		}
-
-		// show only end time if date is the same
-		if ($this->isDayEqual($dtstartDt, $dtendDt)) {
-			$localeEnd = $l10n->l('time', $dtendDt, ['width' => 'short']);
-		} else {
-			$localeEnd = $l10n->l('weekdayName', $dtendDt, ['width' => 'abbreviated']) . ', ' .
-				$l10n->l('datetime', $dtendDt, ['width' => 'medium|short']);
-		}
-
-		return  $localeStart . ' - ' . $localeEnd . ' (' . $startTimezone . ')';
-	}
-
-	/**
-	 * @param \DateTime $dtStart
-	 * @param \DateTime $dtEnd
-	 * @return bool
-	 */
-	private function isDayEqual(\DateTime $dtStart, \DateTime $dtEnd) {
-		return $dtStart->format('Y-m-d') === $dtEnd->format('Y-m-d');
-	}
-
-	/**
-	 * @param IEMailTemplate $template
-	 * @param IL10N $l10n
-	 * @param string $method
-	 * @param string $summary
-	 */
-	private function addSubjectAndHeading(IEMailTemplate $template, IL10N $l10n,
-										  $method, $summary) {
-		if ($method === self::METHOD_CANCEL) {
-			// TRANSLATORS Subject for email, when an invitation is cancelled. Ex: "Cancelled: {{Event Name}}"
-			$template->setSubject($l10n->t('Cancelled: %1$s', [$summary]));
-			$template->addHeading($l10n->t('Invitation canceled'));
-		} elseif ($method === self::METHOD_REPLY) {
-			// TRANSLATORS Subject for email, when an invitation is updated. Ex: "Re: {{Event Name}}"
-			$template->setSubject($l10n->t('Re: %1$s', [$summary]));
-			$template->addHeading($l10n->t('Invitation updated'));
-		} else {
-			// TRANSLATORS Subject for email, when an invitation is sent. Ex: "Invitation: {{Event Name}}"
-			$template->setSubject($l10n->t('Invitation: %1$s', [$summary]));
-			$template->addHeading($l10n->t('Invitation'));
-		}
-	}
-
-	/**
-	 * @param IEMailTemplate $template
-	 * @param IL10N $l10n
-	 * @param VEVENT $vevent
-	 */
-	private function addBulletList(IEMailTemplate $template, IL10N $l10n, $vevent) {
-		if ($vevent->SUMMARY) {
-			$template->addBodyListItem($vevent->SUMMARY, $l10n->t('Title:'),
-				$this->getAbsoluteImagePath('caldav/title.png'), '', '', self::IMIP_INDENT);
-		}
-		$meetingWhen = $this->generateWhenString($l10n, $vevent);
-		if ($meetingWhen) {
-			$template->addBodyListItem($meetingWhen, $l10n->t('Time:'),
-				$this->getAbsoluteImagePath('caldav/time.png'), '', '', self::IMIP_INDENT);
-		}
-		if ($vevent->LOCATION) {
-			$template->addBodyListItem($vevent->LOCATION, $l10n->t('Location:'),
-				$this->getAbsoluteImagePath('caldav/location.png'), '', '', self::IMIP_INDENT);
-		}
-		if ($vevent->URL) {
-			$url = $vevent->URL->getValue();
-			$template->addBodyListItem(sprintf('<a href="%s">%s</a>',
-				htmlspecialchars($url),
-				htmlspecialchars($url)),
-				$l10n->t('Link:'),
-				$this->getAbsoluteImagePath('caldav/link.png'),
-				$url, '', self::IMIP_INDENT);
-		}
-
-		$this->addAttendees($template, $l10n, $vevent);
-
-		/* Put description last, like an email body, since it can be arbitrarily long */
-		if ($vevent->DESCRIPTION) {
-			$template->addBodyListItem($vevent->DESCRIPTION->getValue(), $l10n->t('Description:'),
-				$this->getAbsoluteImagePath('caldav/description.png'), '', '', self::IMIP_INDENT);
-		}
-	}
-
-	/**
-	 * addAttendees: add organizer and attendee names/emails to iMip mail.
-	 *
-	 * Enable with DAV setting: invitation_list_attendees (default: no)
-	 *
-	 * The default is 'no', which matches old behavior, and is privacy preserving.
-	 *
-	 * To enable including attendees in invitation emails:
-	 *   % php occ config:app:set dav invitation_list_attendees --value yes
-	 *
-	 * @param IEMailTemplate $template
-	 * @param IL10N $l10n
-	 * @param Message $iTipMessage
-	 * @param int $lastOccurrence
-	 * @author brad2014 on github.com
-	 */
-
-	private function addAttendees(IEMailTemplate $template, IL10N $l10n, VEvent $vevent) {
-		if ($this->config->getAppValue('dav', 'invitation_list_attendees', 'no') === 'no') {
-			return;
-		}
-
-		if (isset($vevent->ORGANIZER)) {
-			/** @var Property\ICalendar\CalAddress $organizer */
-			$organizer = $vevent->ORGANIZER;
-			$organizerURI = $organizer->getNormalizedValue();
-			[$scheme,$organizerEmail] = explode(':', $organizerURI, 2); # strip off scheme mailto:
-			/** @var string|null $organizerName */
-			$organizerName = isset($organizer['CN']) ? $organizer['CN'] : null;
-			$organizerHTML = sprintf('<a href="%s">%s</a>',
-				htmlspecialchars($organizerURI),
-				htmlspecialchars($organizerName ?: $organizerEmail));
-			$organizerText = sprintf('%s <%s>', $organizerName, $organizerEmail);
-			if (isset($organizer['PARTSTAT'])) {
-				/** @var Parameter $partstat */
-				$partstat = $organizer['PARTSTAT'];
-				if (strcasecmp($partstat->getValue(), 'ACCEPTED') === 0) {
-					$organizerHTML .= ' ✔︎';
-					$organizerText .= ' ✔︎';
-				}
-			}
-			$template->addBodyListItem($organizerHTML, $l10n->t('Organizer:'),
-				$this->getAbsoluteImagePath('caldav/organizer.png'),
-				$organizerText, '', self::IMIP_INDENT);
-		}
-
-		$attendees = $vevent->select('ATTENDEE');
-		if (count($attendees) === 0) {
-			return;
-		}
-
-		$attendeesHTML = [];
-		$attendeesText = [];
-		foreach ($attendees as $attendee) {
-			$attendeeURI = $attendee->getNormalizedValue();
-			[$scheme,$attendeeEmail] = explode(':', $attendeeURI, 2); # strip off scheme mailto:
-			$attendeeName = isset($attendee['CN']) ? $attendee['CN'] : null;
-			$attendeeHTML = sprintf('<a href="%s">%s</a>',
-				htmlspecialchars($attendeeURI),
-				htmlspecialchars($attendeeName ?: $attendeeEmail));
-			$attendeeText = sprintf('%s <%s>', $attendeeName, $attendeeEmail);
-			if (isset($attendee['PARTSTAT'])
-				&& strcasecmp($attendee['PARTSTAT'], 'ACCEPTED') === 0) {
-				$attendeeHTML .= ' ✔︎';
-				$attendeeText .= ' ✔︎';
-			}
-			array_push($attendeesHTML, $attendeeHTML);
-			array_push($attendeesText, $attendeeText);
-		}
-
-		$template->addBodyListItem(implode('<br/>', $attendeesHTML), $l10n->t('Attendees:'),
-			$this->getAbsoluteImagePath('caldav/attendees.png'),
-			implode("\n", $attendeesText), '', self::IMIP_INDENT);
-	}
-
-	/**
-	 * @param IEMailTemplate $template
-	 * @param IL10N $l10n
-	 * @param Message $iTipMessage
-	 * @param int $lastOccurrence
-	 */
-	private function addResponseButtons(IEMailTemplate $template, IL10N $l10n,
-										Message $iTipMessage, $lastOccurrence) {
-		$token = $this->createInvitationToken($iTipMessage, $lastOccurrence);
-
-		$template->addBodyButtonGroup(
-			$l10n->t('Accept'),
-			$this->urlGenerator->linkToRouteAbsolute('dav.invitation_response.accept', [
-				'token' => $token,
-			]),
-			$l10n->t('Decline'),
-			$this->urlGenerator->linkToRouteAbsolute('dav.invitation_response.decline', [
-				'token' => $token,
-			])
-		);
-
-		$moreOptionsURL = $this->urlGenerator->linkToRouteAbsolute('dav.invitation_response.options', [
-			'token' => $token,
-		]);
-		$html = vsprintf('<small><a href="%s">%s</a></small>', [
-			$moreOptionsURL, $l10n->t('More options …')
-		]);
-		$text = $l10n->t('More options at %s', [$moreOptionsURL]);
-
-		$template->addBodyText($html, $text);
-	}
-
-	/**
-	 * @param string $path
-	 * @return string
-	 */
-	private function getAbsoluteImagePath($path) {
-		return $this->urlGenerator->getAbsoluteURL(
-			$this->urlGenerator->imagePath('core', $path)
-		);
-	}
-
-	/**
-	 * @param Message $iTipMessage
-	 * @param int $lastOccurrence
-	 * @return string
-	 */
-	private function createInvitationToken(Message $iTipMessage, $lastOccurrence):string {
-		$token = $this->random->generate(60, ISecureRandom::CHAR_ALPHANUMERIC);
-
-		/** @var VEvent $vevent */
-		$vevent = $iTipMessage->message->VEVENT;
-		$attendee = $iTipMessage->recipient;
-		$organizer = $iTipMessage->sender;
-		$sequence = $iTipMessage->sequence;
-		$recurrenceId = isset($vevent->{'RECURRENCE-ID'}) ?
-			$vevent->{'RECURRENCE-ID'}->serialize() : null;
-		$uid = $vevent->{'UID'};
-
-		$query = $this->db->getQueryBuilder();
-		$query->insert('calendar_invitations')
-			->values([
-				'token' => $query->createNamedParameter($token),
-				'attendee' => $query->createNamedParameter($attendee),
-				'organizer' => $query->createNamedParameter($organizer),
-				'sequence' => $query->createNamedParameter($sequence),
-				'recurrenceid' => $query->createNamedParameter($recurrenceId),
-				'expiration' => $query->createNamedParameter($lastOccurrence),
-				'uid' => $query->createNamedParameter($uid)
-			])
-			->execute();
-
-		return $token;
-	}
 }
diff --git a/apps/dav/lib/CalDAV/Schedule/IMipService.php b/apps/dav/lib/CalDAV/Schedule/IMipService.php
new file mode 100644
index 00000000000..88f8bb8f54e
--- /dev/null
+++ b/apps/dav/lib/CalDAV/Schedule/IMipService.php
@@ -0,0 +1,597 @@
+<?php
+declare(strict_types=1);
+/*
+ * DAV App
+ *
+ * @copyright 2022 Anna Larch <anna.larch@gmx.net>
+ *
+ * @author Anna Larch <anna.larch@gmx.net>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU AFFERO GENERAL PUBLIC LICENSE
+ * License as published by the Free Software Foundation; either
+ * version 3 of the License, or any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU AFFERO GENERAL PUBLIC LICENSE for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public
+ * License along with this library.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+namespace OCA\DAV\CalDAV\Schedule;
+
+use OC\URLGenerator;
+use OCP\IConfig;
+use OCP\IDBConnection;
+use OCP\IL10N;
+use OCP\L10N\IFactory as L10NFactory;
+use OCP\Mail\IEMailTemplate;
+use OCP\Security\ISecureRandom;
+use Sabre\VObject\Component\VCalendar;
+use Sabre\VObject\Component\VEvent;
+use Sabre\VObject\DateTimeParser;
+use Sabre\VObject\ITip\Message;
+use Sabre\VObject\Parameter;
+use Sabre\VObject\Property;
+use Sabre\VObject\Recur\EventIterator;
+
+class IMipService {
+
+	private URLGenerator $urlGenerator;
+	private IConfig $config;
+	private IDBConnection $db;
+	private ISecureRandom $random;
+	private L10NFactory $l10nFactory;
+	private IL10N $l10n;
+
+	/** @var string[] */
+	private const STRING_DIFF = [
+		'meeting_title' => 'SUMMARY',
+		'meeting_description' => 'DESCRIPTION',
+		'meeting_url' => 'URL',
+		'meeting_location' => 'LOCATION'
+	];
+
+	public function __construct(URLGenerator $urlGenerator,
+								IConfig $config,
+								IDBConnection $db,
+								ISecureRandom $random,
+								L10NFactory $l10nFactory) {
+		$this->urlGenerator = $urlGenerator;
+		$this->config = $config;
+		$this->db = $db;
+		$this->random = $random;
+		$this->l10nFactory = $l10nFactory;
+		$default = $this->l10nFactory->findGenericLanguage();
+		$this->l10n = $this->l10nFactory->get('dav', $default);
+	}
+
+	/**
+	 * @param string $senderName
+	 * @param $default
+	 * @return string
+	 */
+	public function getFrom(string $senderName, $default): string {
+		return $this->l10n->t('%1$s via %2$s', [$senderName, $default]);
+	}
+
+	public static function readPropertyWithDefault(VEvent $vevent, string $property, string $default) {
+		if (isset($vevent->$property)) {
+			$value = $vevent->$property->getValue();
+			if (!empty($value)) {
+				return $value;
+			}
+		}
+		return $default;
+	}
+
+	private function generateDiffString(VEvent $vevent, VEvent $oldVEvent, string $property, string $default): ?string {
+		$strikethrough = "<span style='text-decoration: line-through'>%s</span><br />%s";
+		if (!isset($vevent->$property)) {
+			return $default;
+		}
+		$newstring = $vevent->$property->getValue();
+		if(isset($oldVEvent->$property)) {
+			$oldstring = $oldVEvent->$property->getValue();
+			return sprintf($strikethrough, $oldstring, $newstring);
+		}
+		return $newstring;
+	}
+
+	/**
+	 * @param VEvent $vEvent
+	 * @param VEvent|null $oldVEvent
+	 * @return array
+	 */
+	public function buildBodyData(VEvent $vEvent, ?VEvent $oldVEvent): array {
+		$defaultVal = '';
+		$data = [];
+		$data['meeting_when'] = $this->generateWhenString($vEvent);
+
+		foreach(self::STRING_DIFF as $key => $property) {
+			$data[$key] = self::readPropertyWithDefault($vEvent, $property, $defaultVal);
+		}
+
+		$data['meeting_url_html'] = self::readPropertyWithDefault($vEvent, 'URL', $defaultVal);
+
+		if(!empty($oldVEvent)) {
+			$oldMeetingWhen = $this->generateWhenString($oldVEvent);
+			$data['meeting_title_html']	= $this->generateDiffString($vEvent, $oldVEvent, 'SUMMARY', $data['meeting_title']);
+			$data['meeting_description_html'] = $this->generateDiffString($vEvent, $oldVEvent, 'DESCRIPTION', $data['meeting_description']);
+			$data['meeting_location_html'] = $this->generateDiffString($vEvent, $oldVEvent, 'LOCATION', $data['meeting_location']);
+
+			$oldUrl = self::readPropertyWithDefault($oldVEvent, 'URL', $defaultVal);
+			$data['meeting_url_html'] = !empty($oldUrl) ? sprintf('<a href="%1$s">%1$s</a>', $oldUrl) : $data['meeting_url'];
+
+			$data['meeting_when_html'] =
+				($oldMeetingWhen !== $data['meeting_when'] && $oldMeetingWhen !== null)
+					? sprintf("<span style='text-decoration: line-through'>%s</span><br />%s", $oldMeetingWhen, $data['meeting_when'])
+					: $data['meeting_when'];
+		}
+		return $data;
+	}
+
+	/**
+	 * @param IL10N $this->l10n
+	 * @param VEvent $vevent
+	 * @return false|int|string
+	 */
+	public function generateWhenString(VEvent $vevent) {
+		/** @var Property\ICalendar\DateTime $dtstart */
+		$dtstart = $vevent->DTSTART;
+		if (isset($vevent->DTEND)) {
+			/** @var Property\ICalendar\DateTime $dtend */
+			$dtend = $vevent->DTEND;
+		} elseif (isset($vevent->DURATION)) {
+			$isFloating = $dtstart->isFloating();
+			$dtend = clone $dtstart;
+			$endDateTime = $dtend->getDateTime();
+			$endDateTime = $endDateTime->add(DateTimeParser::parse($vevent->DURATION->getValue()));
+			$dtend->setDateTime($endDateTime, $isFloating);
+		} elseif (!$dtstart->hasTime()) {
+			$isFloating = $dtstart->isFloating();
+			$dtend = clone $dtstart;
+			$endDateTime = $dtend->getDateTime();
+			$endDateTime = $endDateTime->modify('+1 day');
+			$dtend->setDateTime($endDateTime, $isFloating);
+		} else {
+			$dtend = clone $dtstart;
+		}
+
+		/** @var Property\ICalendar\Date | Property\ICalendar\DateTime $dtstart */
+		/** @var \DateTimeImmutable $dtstartDt */
+		$dtstartDt = $dtstart->getDateTime();
+
+		/** @var Property\ICalendar\Date | Property\ICalendar\DateTime $dtend */
+		/** @var \DateTimeImmutable $dtendDt */
+		$dtendDt = $dtend->getDateTime();
+
+		$diff = $dtstartDt->diff($dtendDt);
+
+		$dtstartDt = new \DateTime($dtstartDt->format(\DateTimeInterface::ATOM));
+		$dtendDt = new \DateTime($dtendDt->format(\DateTimeInterface::ATOM));
+
+		if ($dtstart instanceof Property\ICalendar\Date) {
+			// One day event
+			if ($diff->days === 1) {
+				return $this->l10n->l('date', $dtstartDt, ['width' => 'medium']);
+			}
+
+			// DTEND is exclusive, so if the ics data says 2020-01-01 to 2020-01-05,
+			// the email should show 2020-01-01 to 2020-01-04.
+			$dtendDt->modify('-1 day');
+
+			//event that spans over multiple days
+			$localeStart = $this->l10n->l('date', $dtstartDt, ['width' => 'medium']);
+			$localeEnd = $this->l10n->l('date', $dtendDt, ['width' => 'medium']);
+
+			return $localeStart . ' - ' . $localeEnd;
+		}
+
+		/** @var Property\ICalendar\DateTime $dtstart */
+		/** @var Property\ICalendar\DateTime $dtend */
+		$isFloating = $dtstart->isFloating();
+		$startTimezone = $endTimezone = null;
+		if (!$isFloating) {
+			$prop = $dtstart->offsetGet('TZID');
+			if ($prop instanceof Parameter) {
+				$startTimezone = $prop->getValue();
+			}
+
+			$prop = $dtend->offsetGet('TZID');
+			if ($prop instanceof Parameter) {
+				$endTimezone = $prop->getValue();
+			}
+		}
+
+		$localeStart = $this->l10n->l('weekdayName', $dtstartDt, ['width' => 'abbreviated']) . ', ' .
+			$this->l10n->l('datetime', $dtstartDt, ['width' => 'medium|short']);
+
+		// always show full date with timezone if timezones are different
+		if ($startTimezone !== $endTimezone) {
+			$localeEnd = $this->l10n->l('datetime', $dtendDt, ['width' => 'medium|short']);
+
+			return $localeStart . ' (' . $startTimezone . ') - ' .
+				$localeEnd . ' (' . $endTimezone . ')';
+		}
+
+		// show only end time if date is the same
+		if ($dtstartDt->format('Y-m-d') === $dtendDt->format('Y-m-d')) {
+			$localeEnd = $this->l10n->l('time', $dtendDt, ['width' => 'short']);
+		} else {
+			$localeEnd = $this->l10n->l('weekdayName', $dtendDt, ['width' => 'abbreviated']) . ', ' .
+				$this->l10n->l('datetime', $dtendDt, ['width' => 'medium|short']);
+		}
+
+		return $localeStart . ' - ' . $localeEnd . ' (' . $startTimezone . ')';
+	}
+
+	/**
+	 * @param VEvent $vEvent
+	 * @return array
+	 */
+	public function buildCancelledBodyData(VEvent $vEvent): array {
+		$defaultVal = '';
+		$strikethrough = "<span style='text-decoration: line-through'>%s</span>";
+
+		$newMeetingWhen = $this->generateWhenString($vEvent);
+		$newSummary = isset($vEvent->SUMMARY) && (string)$vEvent->SUMMARY !== '' ? (string)$vEvent->SUMMARY : $this->l10n->t('Untitled event');;
+		$newDescription = isset($vEvent->DESCRIPTION) && (string)$vEvent->DESCRIPTION !== '' ? (string)$vEvent->DESCRIPTION : $defaultVal;
+		$newUrl = isset($vEvent->URL) && (string)$vEvent->URL !== '' ? sprintf('<a href="%1$s">%1$s</a>', $vEvent->URL) : $defaultVal;
+		$newLocation = isset($vEvent->LOCATION) && (string)$vEvent->LOCATION !== '' ? (string)$vEvent->LOCATION : $defaultVal;
+
+		$data = [];
+		$data['meeting_when_html'] = $newMeetingWhen === '' ?: sprintf($strikethrough, $newMeetingWhen);
+		$data['meeting_when'] = $newMeetingWhen;
+		$data['meeting_title_html'] = sprintf($strikethrough, $newSummary);
+		$data['meeting_title'] = $newSummary !== '' ? $newSummary: $this->l10n->t('Untitled event');
+		$data['meeting_description_html'] = $newDescription !== '' ? sprintf($strikethrough, $newDescription) : '';
+		$data['meeting_description'] = $newDescription;
+		$data['meeting_url_html'] = $newUrl !== '' ? sprintf($strikethrough, $newUrl) : '';
+		$data['meeting_url'] = isset($vEvent->URL) ? (string)$vEvent->URL : '';
+		$data['meeting_location_html'] = $newLocation !== '' ? sprintf($strikethrough, $newLocation) : '';
+		$data['meeting_location'] = $newLocation;
+		return $data;
+	}
+
+	/**
+	 * Check if event took place in the past
+	 *
+	 * @param VCalendar $vObject
+	 * @return int
+	 */
+	public function getLastOccurrence(VCalendar $vObject) {
+		/** @var VEvent $component */
+		$component = $vObject->VEVENT;
+
+		if (isset($component->RRULE)) {
+			$it = new EventIterator($vObject, (string)$component->UID);
+			$maxDate = new \DateTime(IMipPlugin::MAX_DATE);
+			if ($it->isInfinite()) {
+				return $maxDate->getTimestamp();
+			}
+
+			$end = $it->getDtEnd();
+			while ($it->valid() && $end < $maxDate) {
+				$end = $it->getDtEnd();
+				$it->next();
+			}
+			return $end->getTimestamp();
+		}
+
+		/** @var Property\ICalendar\DateTime $dtStart */
+		$dtStart = $component->DTSTART;
+
+		if (isset($component->DTEND)) {
+			/** @var Property\ICalendar\DateTime $dtEnd */
+			$dtEnd = $component->DTEND;
+			return $dtEnd->getDateTime()->getTimeStamp();
+		}
+
+		if(isset($component->DURATION)) {
+			/** @var \DateTime $endDate */
+			$endDate = clone $dtStart->getDateTime();
+			// $component->DTEND->getDateTime() returns DateTimeImmutable
+			$endDate = $endDate->add(DateTimeParser::parse($component->DURATION->getValue()));
+			return $endDate->getTimestamp();
+		}
+
+		if(!$dtStart->hasTime()) {
+			/** @var \DateTime $endDate */
+			// $component->DTSTART->getDateTime() returns DateTimeImmutable
+			$endDate = clone $dtStart->getDateTime();
+			$endDate = $endDate->modify('+1 day');
+			return $endDate->getTimestamp();
+		}
+
+		// No computation of end time possible - return start date
+		return $dtStart->getDateTime()->getTimeStamp();
+	}
+
+	/**
+	 * @param Property|null $attendee
+	 */
+	public function setL10n(?Property $attendee = null) {
+		if($attendee === null) {
+			return;
+		}
+
+		$lang = $attendee->offsetGet('LANGUAGE');
+		if ($lang instanceof Parameter) {
+			$lang = $lang->getValue();
+			$this->l10n = $this->l10nFactory->get('dav', $lang);
+		}
+	}
+
+	/**
+	 * @param Property|null $attendee
+	 * @return bool
+	 */
+	public function getAttendeeRsvpOrReqForParticipant(?Property $attendee = null) {
+		if($attendee === null) {
+			return false;
+		}
+
+		$rsvp = $attendee->offsetGet('RSVP');
+		if (($rsvp instanceof Parameter) && (strcasecmp($rsvp->getValue(), 'TRUE') === 0)) {
+			return true;
+		}
+		$role = $attendee->offsetGet('ROLE');
+		// @see https://datatracker.ietf.org/doc/html/rfc5545#section-3.2.16
+		// Attendees without a role are assumed required and should receive an invitation link even if they have no RSVP set
+		if ($role === null
+			|| (($role instanceof Parameter) && (strcasecmp($role->getValue(), 'REQ-PARTICIPANT') === 0))
+			|| (($role instanceof Parameter) && (strcasecmp($role->getValue(), 'OPT-PARTICIPANT') === 0))
+		) {
+			return true;
+		}
+
+		// RFC 5545 3.2.17: default RSVP is false
+		return false;
+	}
+
+	/**
+	 * @param IEMailTemplate $template
+	 * @param string $method
+	 * @param string $sender
+	 * @param string $summary
+	 * @param string|null $partstat
+	 */
+	public function addSubjectAndHeading(IEMailTemplate $template,
+		string $method, string $sender, string $summary): void {
+		if ($method === IMipPlugin::METHOD_CANCEL) {
+			// TRANSLATORS Subject for email, when an invitation is cancelled. Ex: "Cancelled: {{Event Name}}"
+			$template->setSubject($this->l10n->t('Cancelled: %1$s', [$summary]));
+			$template->addHeading($this->l10n->t('"%1$s" has been canceled', [$summary]));
+		} elseif ($method === IMipPlugin::METHOD_REPLY) {
+			// TRANSLATORS Subject for email, when an invitation is replied to. Ex: "Re: {{Event Name}}"
+			$template->setSubject($this->l10n->t('Re: %1$s', [$summary]));
+			$template->addHeading($this->l10n->t('%1$s has responded your invitation', [$sender]));
+		} else {
+			// TRANSLATORS Subject for email, when an invitation is sent. Ex: "Invitation: {{Event Name}}"
+			$template->setSubject($this->l10n->t('Invitation: %1$s', [$summary]));
+			$template->addHeading($this->l10n->t('%1$s would like to invite you to "%2$s"', [$sender, $summary]));
+		}
+	}
+
+	/**
+	 * @param string $path
+	 * @return string
+	 */
+	public function getAbsoluteImagePath($path): string {
+		return $this->urlGenerator->getAbsoluteURL(
+			$this->urlGenerator->imagePath('core', $path)
+		);
+	}
+
+	/**
+	 * addAttendees: add organizer and attendee names/emails to iMip mail.
+	 *
+	 * Enable with DAV setting: invitation_list_attendees (default: no)
+	 *
+	 * The default is 'no', which matches old behavior, and is privacy preserving.
+	 *
+	 * To enable including attendees in invitation emails:
+	 *   % php occ config:app:set dav invitation_list_attendees --value yes
+	 *
+	 * @param IEMailTemplate $template
+	 * @param IL10N $this->l10n
+	 * @param VEvent $vevent
+	 * @author brad2014 on github.com
+	 */
+	public function addAttendees(IEMailTemplate $template, VEvent $vevent) {
+		if ($this->config->getAppValue('dav', 'invitation_list_attendees', 'no') === 'no') {
+			return;
+		}
+
+		if (isset($vevent->ORGANIZER)) {
+			/** @var Property | Property\ICalendar\CalAddress $organizer */
+			$organizer = $vevent->ORGANIZER;
+			$organizerEmail = substr($organizer->getNormalizedValue(), 7);
+			/** @var string|null $organizerName */
+			$organizerName = isset($organizer->CN) ? $organizer->CN->getValue() : null;
+			$organizerHTML = sprintf('<a href="%s">%s</a>',
+				htmlspecialchars($organizer->getNormalizedValue()),
+				htmlspecialchars($organizerName ?: $organizerEmail));
+			$organizerText = sprintf('%s <%s>', $organizerName, $organizerEmail);
+			if(isset($organizer['PARTSTAT']) ) {
+				/** @var Parameter $partstat */
+				$partstat = $organizer['PARTSTAT'];
+				if(strcasecmp($partstat->getValue(), 'ACCEPTED') === 0) {
+					$organizerHTML .= ' ✔︎';
+					$organizerText .= ' ✔︎';
+				}
+			}
+			$template->addBodyListItem($organizerHTML, $this->l10n->t('Organizer:'),
+				$this->getAbsoluteImagePath('caldav/organizer.png'),
+				$organizerText, '', IMipPlugin::IMIP_INDENT);
+		}
+
+		$attendees = $vevent->select('ATTENDEE');
+		if (count($attendees) === 0) {
+			return;
+		}
+
+		$attendeesHTML = [];
+		$attendeesText = [];
+		foreach ($attendees as $attendee) {
+			$attendeeEmail = substr($attendee->getNormalizedValue(), 7);
+			$attendeeName = isset($attendee['CN']) ? $attendee['CN']->getValue() : null;
+			$attendeeHTML = sprintf('<a href="%s">%s</a>',
+				htmlspecialchars($attendee->getNormalizedValue()),
+				htmlspecialchars($attendeeName ?: $attendeeEmail));
+			$attendeeText = sprintf('%s <%s>', $attendeeName, $attendeeEmail);
+			if (isset($attendee['PARTSTAT'])) {
+				/** @var Parameter $partstat */
+				$partstat = $attendee['PARTSTAT'];
+				if (strcasecmp($partstat->getValue(), 'ACCEPTED') === 0) {
+					$attendeeHTML .= ' ✔︎';
+					$attendeeText .= ' ✔︎';
+				}
+			}
+			$attendeesHTML[] = $attendeeHTML;
+			$attendeesText[] = $attendeeText;
+		}
+
+		$template->addBodyListItem(implode('<br/>', $attendeesHTML), $this->l10n->t('Attendees:'),
+			$this->getAbsoluteImagePath('caldav/attendees.png'),
+			implode("\n", $attendeesText), '', IMipPlugin::IMIP_INDENT);
+	}
+
+	/**
+	 * @param IEMailTemplate $template
+	 * @param VEVENT $vevent
+	 * @param $data
+	 */
+	public function addBulletList(IEMailTemplate $template, VEvent $vevent, $data) {
+		$template->addBodyListItem(
+			$data['meeting_title'], $this->l10n->t('Title:'),
+			$this->getAbsoluteImagePath('caldav/title.png'), $data['meeting_title'], '', IMipPlugin::IMIP_INDENT);
+		if ($data['meeting_when'] !== '') {
+			$template->addBodyListItem($data['meeting_when_html'] ?? $data['meeting_when'], $this->l10n->t('Time:'),
+				$this->getAbsoluteImagePath('caldav/time.png'), $data['meeting_when'], '', IMipPlugin::IMIP_INDENT);
+		}
+		if ($data['meeting_location'] !== '') {
+			$template->addBodyListItem($data['meeting_location_html'] ?? $data['meeting_location'], $this->l10n->t('Location:'),
+				$this->getAbsoluteImagePath('caldav/location.png'), $data['meeting_location'], '', IMipPlugin::IMIP_INDENT);
+		}
+		if ($data['meeting_url'] !== '') {
+			$template->addBodyListItem($data['meeting_url_html'] ?? $data['meeting_url'], $this->l10n->t('Link:'),
+				$this->getAbsoluteImagePath('caldav/link.png'), $data['meeting_url'], '', IMipPlugin::IMIP_INDENT);
+		}
+
+		$this->addAttendees($template, $vevent);
+
+		/* Put description last, like an email body, since it can be arbitrarily long */
+		if ($data['meeting_description']) {
+			$template->addBodyListItem($data['meeting_description_html'] ?? $data['meeting_description'], $this->l10n->t('Description:'),
+				$this->getAbsoluteImagePath('caldav/description.png'), $data['meeting_description'], '', IMipPlugin::IMIP_INDENT);
+		}
+	}
+
+	/**
+	 * @param Message $iTipMessage
+	 * @return null|Property
+	 */
+	public function getCurrentAttendee(Message $iTipMessage): ?Property {
+		/** @var VEvent $vevent */
+		$vevent = $iTipMessage->message->VEVENT;
+		$attendees = $vevent->select('ATTENDEE');
+		foreach ($attendees as $attendee) {
+			/** @var Property $attendee */
+			if (strcasecmp($attendee->getValue(), $iTipMessage->recipient) === 0) {
+				return $attendee;
+			}
+		}
+		return null;
+	}
+
+	/**
+	 * @param Message $iTipMessage
+	 * @param VEvent $vevent
+	 * @param int $lastOccurrence
+	 * @return string
+	 */
+	public function createInvitationToken(Message $iTipMessage, VEvent $vevent, int $lastOccurrence): string {
+		$token = $this->random->generate(60, ISecureRandom::CHAR_ALPHANUMERIC);
+
+		$attendee = $iTipMessage->recipient;
+		$organizer = $iTipMessage->sender;
+		$sequence = $iTipMessage->sequence;
+		$recurrenceId = isset($vevent->{'RECURRENCE-ID'}) ?
+			$vevent->{'RECURRENCE-ID'}->serialize() : null;
+		$uid = $vevent->{'UID'};
+
+		$query = $this->db->getQueryBuilder();
+		$query->insert('calendar_invitations')
+			->values([
+				'token' => $query->createNamedParameter($token),
+				'attendee' => $query->createNamedParameter($attendee),
+				'organizer' => $query->createNamedParameter($organizer),
+				'sequence' => $query->createNamedParameter($sequence),
+				'recurrenceid' => $query->createNamedParameter($recurrenceId),
+				'expiration' => $query->createNamedParameter($lastOccurrence),
+				'uid' => $query->createNamedParameter($uid)
+			])
+			->execute();
+
+		return $token;
+	}
+
+	/**
+	 * Create a valid VCalendar object out of the details of
+	 * a VEvent and its associated iTip Message
+	 *
+	 * We do this to filter out all unchanged VEvents
+	 * This is especially important in iTip Messages with recurrences
+	 * and recurrence exceptions
+	 *
+	 * @param Message $iTipMessage
+	 * @param VEvent $vEvent
+	 * @return VCalendar
+	 */
+	public function generateVCalendar(Message $iTipMessage, VEvent $vEvent): VCalendar {
+		$vCalendar = new VCalendar();
+		$vCalendar->add('METHOD', $iTipMessage->method);
+		foreach ($iTipMessage->message->getComponents() as $component) {
+			if ($component instanceof VEvent) {
+				continue;
+			}
+			$vCalendar->add(clone $component);
+		}
+		$vCalendar->add($vEvent);
+		return $vCalendar;
+	}
+
+	/**
+	 * @param IEMailTemplate $template
+	 * @param $token
+	 */
+	public function addResponseButtons(IEMailTemplate $template, $token) {
+		$template->addBodyButtonGroup(
+			$this->l10n->t('Accept'),
+			$this->urlGenerator->linkToRouteAbsolute('dav.invitation_response.accept', [
+				'token' => $token,
+			]),
+			$this->l10n->t('Decline'),
+			$this->urlGenerator->linkToRouteAbsolute('dav.invitation_response.decline', [
+				'token' => $token,
+			])
+		);
+	}
+
+	public function addMoreOptionsButton(IEMailTemplate $template, $token) {
+		$moreOptionsURL = $this->urlGenerator->linkToRouteAbsolute('dav.invitation_response.options', [
+			'token' => $token,
+		]);
+		$html = vsprintf('<small><a href="%s">%s</a></small>', [
+			$moreOptionsURL, $this->l10n->t('More options …')
+		]);
+		$text = $this->l10n->t('More options at %s', [$moreOptionsURL]);
+
+		$template->addBodyText($html, $text);
+	}
+}