Add a trashbin for calendars and calendar objects

Signed-off-by: Christoph Wurst <christoph@winzerhof-wurst.at>

14 files changed, 1120 insertions, 59 deletions

diff --git a/apps/dav/lib/CalDAV/Activity/Backend.php b/apps/dav/lib/CalDAV/Activity/Backend.php
index 16f581db872..4b896de3b89 100644
--- a/apps/dav/lib/CalDAV/Activity/Backend.php
+++ b/apps/dav/lib/CalDAV/Activity/Backend.php
@@ -85,12 +85,32 @@ class Backend {
 	}
 
 	/**
+	 * Creates activities when a calendar was moved to trash
+	 *
+	 * @param array $calendarData
+	 * @param array $shares
+	 */
+	public function onCalendarMovedToTrash(array $calendarData, array $shares): void {
+		$this->triggerCalendarActivity(Calendar::SUBJECT_MOVE_TO_TRASH, $calendarData, $shares);
+	}
+
+	/**
+	 * Creates activities when a calendar was restored
+	 *
+	 * @param array $calendarData
+	 * @param array $shares
+	 */
+	public function onCalendarRestored(array $calendarData, array $shares): void {
+		$this->triggerCalendarActivity(Calendar::SUBJECT_RESTORE, $calendarData, $shares);
+	}
+
+	/**
 	 * Creates activities when a calendar was deleted
 	 *
 	 * @param array $calendarData
 	 * @param array $shares
 	 */
-	public function onCalendarDelete(array $calendarData, array $shares) {
+	public function onCalendarDelete(array $calendarData, array $shares): void {
 		$this->triggerCalendarActivity(Calendar::SUBJECT_DELETE, $calendarData, $shares);
 	}
 
diff --git a/apps/dav/lib/CalDAV/Activity/Provider/Calendar.php b/apps/dav/lib/CalDAV/Activity/Provider/Calendar.php
index 382825d8955..a30c628a3ad 100644
--- a/apps/dav/lib/CalDAV/Activity/Provider/Calendar.php
+++ b/apps/dav/lib/CalDAV/Activity/Provider/Calendar.php
@@ -39,6 +39,8 @@ use OCP\L10N\IFactory;
 class Calendar extends Base {
 	public const SUBJECT_ADD = 'calendar_add';
 	public const SUBJECT_UPDATE = 'calendar_update';
+	public const SUBJECT_MOVE_TO_TRASH = 'calendar_move_to_trash';
+	public const SUBJECT_RESTORE = 'calendar_restore';
 	public const SUBJECT_DELETE = 'calendar_delete';
 	public const SUBJECT_PUBLISH = 'calendar_publish';
 	public const SUBJECT_UNPUBLISH = 'calendar_unpublish';
@@ -107,6 +109,14 @@ class Calendar extends Base {
 			$subject = $this->l->t('{actor} updated calendar {calendar}');
 		} elseif ($event->getSubject() === self::SUBJECT_UPDATE . '_self') {
 			$subject = $this->l->t('You updated calendar {calendar}');
+		} elseif ($event->getSubject() === self::SUBJECT_MOVE_TO_TRASH) {
+			$subject = $this->l->t('{actor} deleted calendar {calendar}');
+		} elseif ($event->getSubject() === self::SUBJECT_MOVE_TO_TRASH . '_self') {
+			$subject = $this->l->t('You deleted calendar {calendar}');
+		} elseif ($event->getSubject() === self::SUBJECT_RESTORE) {
+			$subject = $this->l->t('{actor} restored calendar {calendar}');
+		} elseif ($event->getSubject() === self::SUBJECT_RESTORE . '_self') {
+			$subject = $this->l->t('You restored calendar {calendar}');
 		} elseif ($event->getSubject() === self::SUBJECT_PUBLISH . '_self') {
 			$subject = $this->l->t('You shared calendar {calendar} as public link');
 		} elseif ($event->getSubject() === self::SUBJECT_UNPUBLISH . '_self') {
@@ -172,6 +182,10 @@ class Calendar extends Base {
 				case self::SUBJECT_DELETE . '_self':
 				case self::SUBJECT_UPDATE:
 				case self::SUBJECT_UPDATE . '_self':
+				case self::SUBJECT_MOVE_TO_TRASH:
+				case self::SUBJECT_MOVE_TO_TRASH . '_self':
+				case self::SUBJECT_RESTORE:
+				case self::SUBJECT_RESTORE . '_self':
 				case self::SUBJECT_PUBLISH . '_self':
 				case self::SUBJECT_UNPUBLISH . '_self':
 				case self::SUBJECT_SHARE_USER:
diff --git a/apps/dav/lib/CalDAV/Activity/Provider/Event.php b/apps/dav/lib/CalDAV/Activity/Provider/Event.php
index 8850715a1c5..03845cc4d87 100644
--- a/apps/dav/lib/CalDAV/Activity/Provider/Event.php
+++ b/apps/dav/lib/CalDAV/Activity/Provider/Event.php
@@ -40,6 +40,8 @@ use OCP\L10N\IFactory;
 class Event extends Base {
 	public const SUBJECT_OBJECT_ADD = 'object_add';
 	public const SUBJECT_OBJECT_UPDATE = 'object_update';
+	public const SUBJECT_OBJECT_MOVE_TO_TRASH = 'object_move_to_trash';
+	public const SUBJECT_OBJECT_RESTORE = 'object_restore';
 	public const SUBJECT_OBJECT_DELETE = 'object_delete';
 
 	/** @var IFactory */
@@ -143,6 +145,14 @@ class Event extends Base {
 			$subject = $this->l->t('{actor} updated event {event} in calendar {calendar}');
 		} elseif ($event->getSubject() === self::SUBJECT_OBJECT_UPDATE . '_event_self') {
 			$subject = $this->l->t('You updated event {event} in calendar {calendar}');
+		} elseif ($event->getSubject() === self::SUBJECT_OBJECT_MOVE_TO_TRASH . '_event') {
+			$subject = $this->l->t('{actor} deleted event {event} from calendar {calendar}');
+		} elseif ($event->getSubject() === self::SUBJECT_OBJECT_MOVE_TO_TRASH . '_event_self') {
+			$subject = $this->l->t('You deleted event {event} from calendar {calendar}');
+		} elseif ($event->getSubject() === self::SUBJECT_OBJECT_RESTORE . '_event') {
+			$subject = $this->l->t('{actor} restored event {event} of calendar {calendar}');
+		} elseif ($event->getSubject() === self::SUBJECT_OBJECT_RESTORE . '_event_self') {
+			$subject = $this->l->t('You restored event {event} of calendar {calendar}');
 		} else {
 			throw new \InvalidArgumentException();
 		}
@@ -169,6 +179,8 @@ class Event extends Base {
 				case self::SUBJECT_OBJECT_ADD . '_event':
 				case self::SUBJECT_OBJECT_DELETE . '_event':
 				case self::SUBJECT_OBJECT_UPDATE . '_event':
+				case self::SUBJECT_OBJECT_MOVE_TO_TRASH . '_event':
+				case self::SUBJECT_OBJECT_RESTORE . '_event':
 					return [
 						'actor' => $this->generateUserParameter($parameters['actor']),
 						'calendar' => $this->generateCalendarParameter($parameters['calendar'], $this->l),
@@ -177,6 +189,8 @@ class Event extends Base {
 				case self::SUBJECT_OBJECT_ADD . '_event_self':
 				case self::SUBJECT_OBJECT_DELETE . '_event_self':
 				case self::SUBJECT_OBJECT_UPDATE . '_event_self':
+				case self::SUBJECT_OBJECT_MOVE_TO_TRASH . '_event_self':
+				case self::SUBJECT_OBJECT_RESTORE . '_event_self':
 					return [
 						'calendar' => $this->generateCalendarParameter($parameters['calendar'], $this->l),
 						'event' => $this->generateClassifiedObjectParameter($parameters['object']),
diff --git a/apps/dav/lib/CalDAV/CalDavBackend.php b/apps/dav/lib/CalDAV/CalDavBackend.php
index 2daa03843de..53749855b8c 100644
--- a/apps/dav/lib/CalDAV/CalDavBackend.php
+++ b/apps/dav/lib/CalDAV/CalDavBackend.php
@@ -39,6 +39,7 @@
 namespace OCA\DAV\CalDAV;
 
 use DateTime;
+use OCA\DAV\AppInfo\Application;
 use OCA\DAV\Connector\Sabre\Principal;
 use OCA\DAV\DAV\Sharing\Backend;
 use OCA\DAV\DAV\Sharing\IShareable;
@@ -47,10 +48,14 @@ use OCA\DAV\Events\CachedCalendarObjectDeletedEvent;
 use OCA\DAV\Events\CachedCalendarObjectUpdatedEvent;
 use OCA\DAV\Events\CalendarCreatedEvent;
 use OCA\DAV\Events\CalendarDeletedEvent;
+use OCA\DAV\Events\CalendarMovedToTrashEvent;
 use OCA\DAV\Events\CalendarObjectCreatedEvent;
 use OCA\DAV\Events\CalendarObjectDeletedEvent;
+use OCA\DAV\Events\CalendarObjectMovedToTrashEvent;
+use OCA\DAV\Events\CalendarObjectRestoredEvent;
 use OCA\DAV\Events\CalendarObjectUpdatedEvent;
 use OCA\DAV\Events\CalendarPublishedEvent;
+use OCA\DAV\Events\CalendarRestoredEvent;
 use OCA\DAV\Events\CalendarShareUpdatedEvent;
 use OCA\DAV\Events\CalendarUnpublishedEvent;
 use OCA\DAV\Events\CalendarUpdatedEvent;
@@ -59,12 +64,14 @@ use OCA\DAV\Events\SubscriptionDeletedEvent;
 use OCA\DAV\Events\SubscriptionUpdatedEvent;
 use OCP\DB\QueryBuilder\IQueryBuilder;
 use OCP\EventDispatcher\IEventDispatcher;
+use OCP\IConfig;
 use OCP\IDBConnection;
 use OCP\IGroupManager;
 use OCP\ILogger;
 use OCP\IUser;
 use OCP\IUserManager;
 use OCP\Security\ISecureRandom;
+use RuntimeException;
 use Sabre\CalDAV\Backend\AbstractBackend;
 use Sabre\CalDAV\Backend\SchedulingSupport;
 use Sabre\CalDAV\Backend\SubscriptionSupport;
@@ -72,6 +79,7 @@ use Sabre\CalDAV\Backend\SyncSupport;
 use Sabre\CalDAV\Xml\Property\ScheduleCalendarTransp;
 use Sabre\CalDAV\Xml\Property\SupportedCalendarComponentSet;
 use Sabre\DAV;
+use Sabre\DAV\Exception\BadRequest;
 use Sabre\DAV\Exception\Forbidden;
 use Sabre\DAV\Exception\NotFound;
 use Sabre\DAV\PropPatch;
@@ -87,6 +95,15 @@ use Sabre\VObject\Reader;
 use Sabre\VObject\Recur\EventIterator;
 use Symfony\Component\EventDispatcher\EventDispatcherInterface;
 use Symfony\Component\EventDispatcher\GenericEvent;
+use function array_merge;
+use function array_values;
+use function explode;
+use function is_array;
+use function pathinfo;
+use function sprintf;
+use function str_replace;
+use function strtolower;
+use function time;
 
 /**
  * Class CalDavBackend
@@ -134,6 +151,7 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 		'{urn:ietf:params:xml:ns:caldav}calendar-timezone' => 'timezone',
 		'{http://apple.com/ns/ical/}calendar-order' => 'calendarorder',
 		'{http://apple.com/ns/ical/}calendar-color' => 'calendarcolor',
+		'{' . \OCA\DAV\DAV\Sharing\Plugin::NS_NEXTCLOUD . '}deleted-at' => 'deleted_at',
 	];
 
 	/**
@@ -191,6 +209,9 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 	/** @var EventDispatcherInterface */
 	private $legacyDispatcher;
 
+	/** @var IConfig */
+	private $config;
+
 	/** @var bool */
 	private $legacyEndpoint;
 
@@ -218,6 +239,7 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 								ILogger $logger,
 								IEventDispatcher $dispatcher,
 								EventDispatcherInterface $legacyDispatcher,
+								IConfig $config,
 								bool $legacyEndpoint = false) {
 		$this->db = $db;
 		$this->principalBackend = $principalBackend;
@@ -227,6 +249,7 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 		$this->logger = $logger;
 		$this->dispatcher = $dispatcher;
 		$this->legacyDispatcher = $legacyDispatcher;
+		$this->config = $config;
 		$this->legacyEndpoint = $legacyEndpoint;
 	}
 
@@ -262,6 +285,26 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 	}
 
 	/**
+	 * @return array{id: int, deleted_at: int}[]
+	 */
+	public function getDeletedCalendars(int $deletedBefore): array {
+		$qb = $this->db->getQueryBuilder();
+		$qb->select(['id', 'deleted_at'])
+			->from('calendars')
+			->where($qb->expr()->isNotNull('deleted_at'))
+			->andWhere($qb->expr()->lt('deleted_at', $qb->createNamedParameter($deletedBefore)));
+		$result = $qb->executeQuery();
+		$raw = $result->fetchAll();
+		$result->closeCursor();
+		return array_map(function ($row) {
+			return [
+				'id' => (int) $row['id'],
+				'deleted_at' => (int) $row['deleted_at'],
+			];
+		}, $raw);
+	}
+
+	/**
 	 * Returns a list of calendars for a principal.
 	 *
 	 * Every project is an array with the following keys:
@@ -334,7 +377,8 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 				$calendar[$xmlName] = $row[$dbName];
 			}
 
-			$this->addOwnerPrincipal($calendar);
+			$calendar = $this->addOwnerPrincipalToCalendar($calendar);
+			$calendar = $this->addResourceTypeToCalendar($row, $calendar);
 
 			if (!isset($calendars[$calendar['id']])) {
 				$calendars[$calendar['id']] = $calendar;
@@ -410,7 +454,8 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 				$calendar[$xmlName] = $row[$dbName];
 			}
 
-			$this->addOwnerPrincipal($calendar);
+			$calendar = $this->addOwnerPrincipalToCalendar($calendar);
+			$calendar = $this->addResourceTypeToCalendar($row, $calendar);
 
 			$calendars[$calendar['id']] = $calendar;
 		}
@@ -458,7 +503,8 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 				$calendar[$xmlName] = $row[$dbName];
 			}
 
-			$this->addOwnerPrincipal($calendar);
+			$calendar = $this->addOwnerPrincipalToCalendar($calendar);
+			$calendar = $this->addResourceTypeToCalendar($row, $calendar);
 
 			if (!isset($calendars[$calendar['id']])) {
 				$calendars[$calendar['id']] = $calendar;
@@ -534,7 +580,8 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 				$calendar[$xmlName] = $row[$dbName];
 			}
 
-			$this->addOwnerPrincipal($calendar);
+			$calendar = $this->addOwnerPrincipalToCalendar($calendar);
+			$calendar = $this->addResourceTypeToCalendar($row, $calendar);
 
 			if (!isset($calendars[$calendar['id']])) {
 				$calendars[$calendar['id']] = $calendar;
@@ -601,7 +648,8 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 			$calendar[$xmlName] = $row[$dbName];
 		}
 
-		$this->addOwnerPrincipal($calendar);
+		$calendar = $this->addOwnerPrincipalToCalendar($calendar);
+		$calendar = $this->addResourceTypeToCalendar($row, $calendar);
 
 		return $calendar;
 	}
@@ -654,7 +702,8 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 			$calendar[$xmlName] = $row[$dbName];
 		}
 
-		$this->addOwnerPrincipal($calendar);
+		$calendar = $this->addOwnerPrincipalToCalendar($calendar);
+		$calendar = $this->addResourceTypeToCalendar($row, $calendar);
 
 		return $calendar;
 	}
@@ -705,7 +754,8 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 			$calendar[$xmlName] = $row[$dbName];
 		}
 
-		$this->addOwnerPrincipal($calendar);
+		$calendar = $this->addOwnerPrincipalToCalendar($calendar);
+		$calendar = $this->addResourceTypeToCalendar($row, $calendar);
 
 		return $calendar;
 	}
@@ -872,33 +922,84 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 	 * @param mixed $calendarId
 	 * @return void
 	 */
-	public function deleteCalendar($calendarId) {
+	public function deleteCalendar($calendarId, bool $forceDeletePermanently = false) {
+		// The calendar is deleted right away if this is either enforced by the caller
+		// or the special contacts birthday calendar or when the preference of an empty
+		// retention (0 seconds) is set, which signals a disabled trashbin.
 		$calendarData = $this->getCalendarById($calendarId);
-		$shares = $this->getShares($calendarId);
+		$isBirthdayCalendar = isset($calendarData['uri']) && $calendarData['uri'] === BirthdayService::BIRTHDAY_CALENDAR_URI;
+		$trashbinDisabled = $this->config->getAppValue(Application::APP_ID, RetentionService::RETENTION_CONFIG_KEY) === '0';
+		if ($forceDeletePermanently || $isBirthdayCalendar || $trashbinDisabled) {
+			$calendarData = $this->getCalendarById($calendarId);
+			$shares = $this->getShares($calendarId);
 
-		$stmt = $this->db->prepare('DELETE FROM `*PREFIX*calendarobjects` WHERE `calendarid` = ? AND `calendartype` = ?');
-		$stmt->execute([$calendarId, self::CALENDAR_TYPE_CALENDAR]);
+			$qbDeleteCalendarObjectProps = $this->db->getQueryBuilder();
+			$qbDeleteCalendarObjectProps->delete($this->dbObjectPropertiesTable)
+				->where($qbDeleteCalendarObjectProps->expr()->eq('calendarid', $qbDeleteCalendarObjectProps->createNamedParameter($calendarId)))
+				->andWhere($qbDeleteCalendarObjectProps->expr()->eq('calendartype', $qbDeleteCalendarObjectProps->createNamedParameter(self::CALENDAR_TYPE_CALENDAR)))
+				->executeStatement();
 
-		$stmt = $this->db->prepare('DELETE FROM `*PREFIX*calendars` WHERE `id` = ?');
-		$stmt->execute([$calendarId]);
+			$qbDeleteCalendarObjects = $this->db->getQueryBuilder();
+			$qbDeleteCalendarObjects->delete('calendarobjects')
+				->where($qbDeleteCalendarObjects->expr()->eq('calendarid', $qbDeleteCalendarObjects->createNamedParameter($calendarId)))
+				->andWhere($qbDeleteCalendarObjects->expr()->eq('calendartype', $qbDeleteCalendarObjects->createNamedParameter(self::CALENDAR_TYPE_CALENDAR)))
+				->executeStatement();
 
-		$stmt = $this->db->prepare('DELETE FROM `*PREFIX*calendarchanges` WHERE `calendarid` = ? AND `calendartype` = ?');
-		$stmt->execute([$calendarId, self::CALENDAR_TYPE_CALENDAR]);
+			$qbDeleteCalendarChanges = $this->db->getQueryBuilder();
+			$qbDeleteCalendarObjects->delete('calendarchanges')
+				->where($qbDeleteCalendarChanges->expr()->eq('calendarid', $qbDeleteCalendarChanges->createNamedParameter($calendarId)))
+				->andWhere($qbDeleteCalendarChanges->expr()->eq('calendartype', $qbDeleteCalendarChanges->createNamedParameter(self::CALENDAR_TYPE_CALENDAR)))
+				->executeStatement();
 
-		$this->calendarSharingBackend->deleteAllShares($calendarId);
+			$this->calendarSharingBackend->deleteAllShares($calendarId);
 
-		$query = $this->db->getQueryBuilder();
-		$query->delete($this->dbObjectPropertiesTable)
-			->where($query->expr()->eq('calendarid', $query->createNamedParameter($calendarId)))
-			->andWhere($query->expr()->eq('calendartype', $query->createNamedParameter(self::CALENDAR_TYPE_CALENDAR)))
-			->executeStatement();
+			$qbDeleteCalendar = $this->db->getQueryBuilder();
+			$qbDeleteCalendarObjects->delete('calendars')
+				->where($qbDeleteCalendar->expr()->eq('id', $qbDeleteCalendar->createNamedParameter($calendarId)))
+				->executeStatement();
+
+			// Only dispatch if we actually deleted anything
+			if ($calendarData) {
+				$this->dispatcher->dispatchTyped(new CalendarDeletedEvent((int)$calendarId, $calendarData, $shares));
+			}
+		} else {
+			$qbMarkCalendarDeleted = $this->db->getQueryBuilder();
+			$qbMarkCalendarDeleted->update('calendars')
+				->set('deleted_at', $qbMarkCalendarDeleted->createNamedParameter(time()))
+				->where($qbMarkCalendarDeleted->expr()->eq('id', $qbMarkCalendarDeleted->createNamedParameter($calendarId)))
+				->executeStatement();
 
-		// Only dispatch if we actually deleted anything
-		if ($calendarData) {
-			$this->dispatcher->dispatchTyped(new CalendarDeletedEvent((int)$calendarId, $calendarData, $shares));
+			$calendarData = $this->getCalendarById($calendarId);
+			$shares = $this->getShares($calendarId);
+			if ($calendarData) {
+				$this->dispatcher->dispatchTyped(new CalendarMovedToTrashEvent(
+					(int)$calendarId,
+					$calendarData,
+					$shares
+				));
+			}
 		}
 	}
 
+	public function restoreCalendar(int $id): void {
+		$qb = $this->db->getQueryBuilder();
+		$update = $qb->update('calendars')
+			->set('deleted_at', $qb->createNamedParameter(null))
+			->where($qb->expr()->eq('id', $qb->createNamedParameter($id, IQueryBuilder::PARAM_INT), IQueryBuilder::PARAM_INT));
+		$update->executeStatement();
+
+		$calendarData = $this->getCalendarById($id);
+		$shares = $this->getShares($id);
+		if ($calendarData === null) {
+			throw new RuntimeException('Calendar data that was just written can\'t be read back. Check your database configuration.');
+		}
+		$this->dispatcher->dispatchTyped(new CalendarRestoredEvent(
+			$id,
+			$calendarData,
+			$shares
+		));
+	}
+
 	/**
 	 * Delete all of an user's shares
 	 *
@@ -946,7 +1047,8 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 		$query->select(['id', 'uri', 'lastmodified', 'etag', 'calendarid', 'size', 'componenttype', 'classification'])
 			->from('calendarobjects')
 			->where($query->expr()->eq('calendarid', $query->createNamedParameter($calendarId)))
-			->andWhere($query->expr()->eq('calendartype', $query->createNamedParameter($calendarType)));
+			->andWhere($query->expr()->eq('calendartype', $query->createNamedParameter($calendarType)))
+			->andWhere($query->expr()->isNull('deleted_at'));
 		$stmt = $query->executeQuery();
 
 		$result = [];
@@ -967,6 +1069,63 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 		return $result;
 	}
 
+	public function getDeletedCalendarObjects(int $deletedBefore): array {
+		$query = $this->db->getQueryBuilder();
+		$query->select(['co.id', 'co.uri', 'co.lastmodified', 'co.etag', 'co.calendarid', 'co.calendartype', 'co.size', 'co.componenttype', 'co.classification', 'co.deleted_at'])
+			->from('calendarobjects', 'co')
+			->join('co', 'calendars', 'c', $query->expr()->eq('c.id', 'co.calendarid', IQueryBuilder::PARAM_INT))
+			->where($query->expr()->isNotNull('co.deleted_at'))
+			->andWhere($query->expr()->lt('co.deleted_at', $query->createNamedParameter($deletedBefore)));
+		$stmt = $query->executeQuery();
+
+		$result = [];
+		foreach ($stmt->fetchAll() as $row) {
+			$result[] = [
+				'id' => $row['id'],
+				'uri' => $row['uri'],
+				'lastmodified' => $row['lastmodified'],
+				'etag' => '"' . $row['etag'] . '"',
+				'calendarid' => (int) $row['calendarid'],
+				'calendartype' => (int) $row['calendartype'],
+				'size' => (int) $row['size'],
+				'component' => strtolower($row['componenttype']),
+				'classification' => (int) $row['classification'],
+				'{' . \OCA\DAV\DAV\Sharing\Plugin::NS_NEXTCLOUD . '}deleted-at' => $row['deleted_at'],
+			];
+		}
+		$stmt->closeCursor();
+
+		return $result;
+	}
+
+	public function getDeletedCalendarObjectsByPrincipal(string $principalUri): array {
+		$query = $this->db->getQueryBuilder();
+		$query->select(['co.id', 'co.uri', 'co.lastmodified', 'co.etag', 'co.calendarid', 'co.size', 'co.componenttype', 'co.classification', 'co.deleted_at'])
+			->from('calendarobjects', 'co')
+			->join('co', 'calendars', 'c', $query->expr()->eq('c.id', 'co.calendarid', IQueryBuilder::PARAM_INT))
+			->where($query->expr()->eq('principaluri', $query->createNamedParameter($principalUri)))
+			->andWhere($query->expr()->isNotNull('co.deleted_at'));
+		$stmt = $query->executeQuery();
+
+		$result = [];
+		while ($row = $stmt->fetch()) {
+			$result[] = [
+				'id' => $row['id'],
+				'uri' => $row['uri'],
+				'lastmodified' => $row['lastmodified'],
+				'etag' => '"' . $row['etag'] . '"',
+				'calendarid' => $row['calendarid'],
+				'size' => (int)$row['size'],
+				'component' => strtolower($row['componenttype']),
+				'classification' => (int)$row['classification'],
+				'{' . \OCA\DAV\DAV\Sharing\Plugin::NS_NEXTCLOUD . '}deleted-at' => $row['deleted_at'],
+			];
+		}
+		$stmt->closeCursor();
+
+		return $result;
+	}
+
 	/**
 	 * Returns information from a single calendar object, based on it's object
 	 * uri.
@@ -984,7 +1143,7 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 	 * @param int $calendarType
 	 * @return array|null
 	 */
-	public function getCalendarObject($calendarId, $objectUri, $calendarType = self::CALENDAR_TYPE_CALENDAR) {
+	public function getCalendarObject($calendarId, $objectUri, int $calendarType = self::CALENDAR_TYPE_CALENDAR) {
 		$query = $this->db->getQueryBuilder();
 		$query->select(['id', 'uri', 'lastmodified', 'etag', 'calendarid', 'size', 'calendardata', 'componenttype', 'classification'])
 			->from('calendarobjects')
@@ -1038,7 +1197,8 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 			->from('calendarobjects')
 			->where($query->expr()->eq('calendarid', $query->createNamedParameter($calendarId)))
 			->andWhere($query->expr()->in('uri', $query->createParameter('uri')))
-			->andWhere($query->expr()->eq('calendartype', $query->createNamedParameter($calendarType)));
+			->andWhere($query->expr()->eq('calendartype', $query->createNamedParameter($calendarType)))
+			->andWhere($query->expr()->isNull('deleted_at'));
 
 		foreach ($chunks as $uris) {
 			$query->setParameter('uri', $uris, IQueryBuilder::PARAM_STR_ARRAY);
@@ -1085,19 +1245,34 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 	public function createCalendarObject($calendarId, $objectUri, $calendarData, $calendarType = self::CALENDAR_TYPE_CALENDAR) {
 		$extraData = $this->getDenormalizedData($calendarData);
 
-		$q = $this->db->getQueryBuilder();
-		$q->select($q->func()->count('*'))
+		// Try to detect duplicates
+		$qb = $this->db->getQueryBuilder();
+		$qb->select($qb->func()->count('*'))
 			->from('calendarobjects')
-			->where($q->expr()->eq('calendarid', $q->createNamedParameter($calendarId)))
-			->andWhere($q->expr()->eq('uid', $q->createNamedParameter($extraData['uid'])))
-			->andWhere($q->expr()->eq('calendartype', $q->createNamedParameter($calendarType)));
-
-		$result = $q->executeQuery();
+			->where($qb->expr()->eq('calendarid', $qb->createNamedParameter($calendarId)))
+			->andWhere($qb->expr()->eq('uid', $qb->createNamedParameter($extraData['uid'])))
+			->andWhere($qb->expr()->eq('calendartype', $qb->createNamedParameter($calendarType)))
+			->andWhere($qb->expr()->isNull('deleted_at'));
+		$result = $qb->executeQuery();
 		$count = (int) $result->fetchOne();
 		$result->closeCursor();
 
 		if ($count !== 0) {
-			throw new \Sabre\DAV\Exception\BadRequest('Calendar object with uid already exists in this calendar collection.');
+			throw new BadRequest('Calendar object with uid already exists in this calendar collection.');
+		}
+		// For a more specific error message we also try to explicitly look up the UID but as a deleted entry
+		$qbDel = $this->db->getQueryBuilder();
+		$qbDel->select($qb->func()->count('*'))
+			->from('calendarobjects')
+			->where($qbDel->expr()->eq('calendarid', $qbDel->createNamedParameter($calendarId)))
+			->andWhere($qbDel->expr()->eq('uid', $qbDel->createNamedParameter($extraData['uid'])))
+			->andWhere($qbDel->expr()->eq('calendartype', $qbDel->createNamedParameter($calendarType)))
+			->andWhere($qbDel->expr()->isNotNull('deleted_at'));
+		$result = $qbDel->executeQuery();
+		$count = (int) $result->fetchOne();
+		$result->closeCursor();
+		if ($count !== 0) {
+			throw new BadRequest('Deleted calendar object with uid already exists in this calendar collection.');
 		}
 
 		$query = $this->db->getQueryBuilder();
@@ -1236,11 +1411,23 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 	 * @param mixed $calendarId
 	 * @param string $objectUri
 	 * @param int $calendarType
+	 * @param bool $forceDeletePermanently
 	 * @return void
 	 */
-	public function deleteCalendarObject($calendarId, $objectUri, $calendarType = self::CALENDAR_TYPE_CALENDAR) {
+	public function deleteCalendarObject($calendarId, $objectUri, $calendarType = self::CALENDAR_TYPE_CALENDAR, bool $forceDeletePermanently = false) {
 		$data = $this->getCalendarObject($calendarId, $objectUri, $calendarType);
-		if (is_array($data)) {
+
+		if ($data === null) {
+			// Nothing to delete
+			return;
+		}
+
+		if ($forceDeletePermanently || $this->config->getAppValue(Application::APP_ID, RetentionService::RETENTION_CONFIG_KEY) === '0') {
+			$stmt = $this->db->prepare('DELETE FROM `*PREFIX*calendarobjects` WHERE `calendarid` = ? AND `uri` = ? AND `calendartype` = ?');
+			$stmt->execute([$calendarId, $objectUri, $calendarType]);
+
+			$this->purgeProperties($calendarId, $data['id']);
+
 			if ($calendarType === self::CALENDAR_TYPE_CALENDAR) {
 				$calendarRow = $this->getCalendarById($calendarId);
 				$shares = $this->getShares($calendarId);
@@ -1260,19 +1447,108 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 					]
 				));
 			}
-		}
+		} else {
+			$pathInfo = pathinfo($data['uri']);
+			if (!empty($pathInfo['extension'])) {
+				// Append a suffix to "free" the old URI for recreation
+				$newUri = sprintf(
+					"%s-deleted.%s",
+					$pathInfo['filename'],
+					$pathInfo['extension']
+				);
+			} else {
+				$newUri = sprintf(
+					"%s-deleted",
+					$pathInfo['filename']
+				);
+			}
 
-		$stmt = $this->db->prepare('DELETE FROM `*PREFIX*calendarobjects` WHERE `calendarid` = ? AND `uri` = ? AND `calendartype` = ?');
-		$stmt->execute([$calendarId, $objectUri, $calendarType]);
+			// Try to detect conflicts before the DB does
+			// As unlikely as it seems, this can happen when the user imports, then deletes, imports and deletes again
+			$newObject = $this->getCalendarObject($calendarId, $newUri, $calendarType);
+			if ($newObject !== null) {
+				throw new Forbidden("A calendar object with URI $newUri already exists in calendar $calendarId, therefore this object can't be moved into the trashbin");
+			}
+
+			$qb = $this->db->getQueryBuilder();
+			$markObjectDeletedQuery = $qb->update('calendarobjects')
+				->set('deleted_at', $qb->createNamedParameter(time(), IQueryBuilder::PARAM_INT))
+				->set('uri', $qb->createNamedParameter($newUri))
+				->where(
+					$qb->expr()->eq('calendarid', $qb->createNamedParameter($calendarId)),
+					$qb->expr()->eq('calendartype', $qb->createNamedParameter($calendarType, IQueryBuilder::PARAM_INT), IQueryBuilder::PARAM_INT),
+					$qb->expr()->eq('uri', $qb->createNamedParameter($objectUri))
+				);
+			$markObjectDeletedQuery->executeStatement();
 
-		if (is_array($data)) {
-			$this->purgeProperties($calendarId, $data['id'], $calendarType);
+			$calendarData = $this->getCalendarById($calendarId);
+			if ($calendarData !== null) {
+				$this->dispatcher->dispatchTyped(
+					new CalendarObjectMovedToTrashEvent(
+						(int)$calendarId,
+						$calendarData,
+						$this->getShares($calendarId),
+						$data
+					)
+				);
+			}
 		}
 
 		$this->addChange($calendarId, $objectUri, 3, $calendarType);
 	}
 
 	/**
+	 * @param mixed $objectData
+	 *
+	 * @throws Forbidden
+	 */
+	public function restoreCalendarObject(array $objectData): void {
+		$id = (int) $objectData['id'];
+		$restoreUri = str_replace("-deleted.ics", ".ics", $objectData['uri']);
+		$targetObject = $this->getCalendarObject(
+			$objectData['calendarid'],
+			$restoreUri
+		);
+		if ($targetObject !== null) {
+			throw new Forbidden("Can not restore calendar $id because a calendar object with the URI $restoreUri already exists");
+		}
+
+		$qb = $this->db->getQueryBuilder();
+		$update = $qb->update('calendarobjects')
+			->set('uri', $qb->createNamedParameter($restoreUri))
+			->set('deleted_at', $qb->createNamedParameter(null))
+			->where($qb->expr()->eq('id', $qb->createNamedParameter($id, IQueryBuilder::PARAM_INT), IQueryBuilder::PARAM_INT));
+		$update->executeStatement();
+
+		// Make sure this change is tracked in the changes table
+		$qb2 = $this->db->getQueryBuilder();
+		$selectObject = $qb2->select('calendardata', 'uri', 'calendarid', 'calendartype')
+			->from('calendarobjects')
+			->where($qb2->expr()->eq('id', $qb2->createNamedParameter($id, IQueryBuilder::PARAM_INT), IQueryBuilder::PARAM_INT));
+		$result = $selectObject->executeQuery();
+		$row = $result->fetch();
+		$result->closeCursor();
+		if ($row === false) {
+			// Welp, this should possibly not have happened, but let's ignore
+			return;
+		}
+		$this->addChange($row['calendarid'], $row['uri'], 1, (int) $row['calendartype']);
+
+		$calendarRow = $this->getCalendarById((int) $row['calendarid']);
+		if ($calendarRow === null) {
+			throw new RuntimeException('Calendar object data that was just written can\'t be read back. Check your database configuration.');
+		}
+		$this->dispatcher->dispatchTyped(
+			new CalendarObjectRestoredEvent(
+				(int) $objectData['calendarid'],
+				$calendarRow,
+				$this->getShares((int) $row['calendarid']),
+				$row
+			)
+		);
+	}
+
+	/**
 	 * Performs a calendar-query on the contents of this calendar.
 	 *
 	 * The calendar-query is defined in RFC4791 : CalDAV. Using the
@@ -1359,7 +1635,8 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 		$query->select($columns)
 			->from('calendarobjects')
 			->where($query->expr()->eq('calendarid', $query->createNamedParameter($calendarId)))
-			->andWhere($query->expr()->eq('calendartype', $query->createNamedParameter($calendarType)));
+			->andWhere($query->expr()->eq('calendartype', $query->createNamedParameter($calendarType)))
+			->andWhere($query->expr()->isNull('deleted_at'));
 
 		if ($componentType) {
 			$query->andWhere($query->expr()->eq('componenttype', $query->createNamedParameter($componentType)));
@@ -1508,7 +1785,8 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 			->andWhere($compExpr)
 			->andWhere($propParamExpr)
 			->andWhere($query->expr()->iLike('i.value',
-				$query->createNamedParameter('%'.$this->db->escapeLikeParameter($filters['search-term']).'%')));
+				$query->createNamedParameter('%'.$this->db->escapeLikeParameter($filters['search-term']).'%')))
+			->andWhere($query->expr()->isNull('deleted_at'));
 
 		if ($offset) {
 			$query->setFirstResult($offset);
@@ -1574,7 +1852,8 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 		}
 
 		$outerQuery->select('c.id', 'c.calendardata', 'c.componenttype', 'c.uid', 'c.uri')
-			->from('calendarobjects', 'c');
+			->from('calendarobjects', 'c')
+			->where($outerQuery->expr()->isNull('deleted_at'));
 
 		if (isset($options['timerange'])) {
 			if (isset($options['timerange']['start']) && $options['timerange']['start'] instanceof DateTime) {
@@ -1776,7 +2055,8 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 			->leftJoin('cob', 'calendarobjects', 'co', $calendarObjectIdQuery->expr()->eq('co.id', 'cob.objectid'))
 			->andWhere($calendarObjectIdQuery->expr()->in('co.componenttype', $calendarObjectIdQuery->createNamedParameter($componentTypes, IQueryBuilder::PARAM_STR_ARRAY)))
 			->andWhere($calendarOr)
-			->andWhere($searchOr);
+			->andWhere($searchOr)
+			->andWhere($calendarObjectIdQuery->expr()->isNull('deleted_at'));
 
 		if ('' !== $pattern) {
 			if (!$escapePattern) {
@@ -1843,8 +2123,8 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 			->from('calendarobjects', 'co')
 			->leftJoin('co', 'calendars', 'c', $query->expr()->eq('co.calendarid', 'c.id'))
 			->where($query->expr()->eq('c.principaluri', $query->createNamedParameter($principalUri)))
-			->andWhere($query->expr()->eq('co.uid', $query->createNamedParameter($uid)));
-
+			->andWhere($query->expr()->eq('co.uid', $query->createNamedParameter($uid)))
+			->andWhere($query->expr()->isNull('co.deleted_at'));
 		$stmt = $query->executeQuery();
 		$row = $stmt->fetch();
 		$stmt->closeCursor();
@@ -1855,6 +2135,35 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 		return null;
 	}
 
+	public function getCalendarObjectById(string $principalUri, int $id): ?array {
+		$query = $this->db->getQueryBuilder();
+		$query->select(['co.id', 'co.uri', 'co.lastmodified', 'co.etag', 'co.calendarid', 'co.size', 'co.calendardata', 'co.componenttype', 'co.classification', 'co.deleted_at'])
+			->from('calendarobjects', 'co')
+			->join('co', 'calendars', 'c', $query->expr()->eq('c.id', 'co.calendarid', IQueryBuilder::PARAM_INT))
+			->where($query->expr()->eq('c.principaluri', $query->createNamedParameter($principalUri)))
+			->andWhere($query->expr()->eq('co.id', $query->createNamedParameter($id, IQueryBuilder::PARAM_INT), IQueryBuilder::PARAM_INT));
+		$stmt = $query->executeQuery();
+		$row = $stmt->fetch();
+		$stmt->closeCursor();
+
+		if (!$row) {
+			return null;
+		}
+
+		return [
+			'id' => $row['id'],
+			'uri' => $row['uri'],
+			'lastmodified' => $row['lastmodified'],
+			'etag' => '"' . $row['etag'] . '"',
+			'calendarid' => $row['calendarid'],
+			'size' => (int)$row['size'],
+			'calendardata' => $this->readBlob($row['calendardata']),
+			'component' => strtolower($row['componenttype']),
+			'classification' => (int)$row['classification'],
+			'deleted_at' => isset($row['deleted_at']) ? ((int) $row['deleted_at']) : null,
+		];
+	}
+
 	/**
 	 * The getChanges method returns all the changes that have happened, since
 	 * the specified syncToken in the specified calendar.
@@ -2410,7 +2719,7 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 			}
 		}
 		if (!$componentType) {
-			throw new \Sabre\DAV\Exception\BadRequest('Calendar objects must have a VJOURNAL, VEVENT or VTODO component');
+			throw new BadRequest('Calendar objects must have a VJOURNAL, VEVENT or VTODO component');
 		}
 
 		if ($hasDTSTART) {
@@ -2670,7 +2979,10 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 
 		$ids = $result->fetchAll();
 		foreach ($ids as $id) {
-			$this->deleteCalendar($id['id']);
+			$this->deleteCalendar(
+				$id['id'],
+				true // No data to keep in the trashbin, if the user re-enables then we regenerate
+			);
 		}
 	}
 
@@ -2802,9 +3114,8 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 	/**
 	 * adds information about an owner to the calendar data
 	 *
-	 * @param $calendarInfo
 	 */
-	private function addOwnerPrincipal(&$calendarInfo) {
+	private function addOwnerPrincipalToCalendar(array $calendarInfo): array {
 		$ownerPrincipalKey = '{' . \OCA\DAV\DAV\Sharing\Plugin::NS_OWNCLOUD . '}owner-principal';
 		$displaynameKey = '{' . \OCA\DAV\DAV\Sharing\Plugin::NS_NEXTCLOUD . '}owner-displayname';
 		if (isset($calendarInfo[$ownerPrincipalKey])) {
@@ -2817,5 +3128,20 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 		if (isset($principalInformation['{DAV:}displayname'])) {
 			$calendarInfo[$displaynameKey] = $principalInformation['{DAV:}displayname'];
 		}
+		return $calendarInfo;
+	}
+
+	private function addResourceTypeToCalendar(array $row, array $calendar): array {
+		if (isset($row['deleted_at'])) {
+			// Columns is set and not null -> this is a deleted calendar
+			// we send a custom resourcetype to hide the deleted calendar
+			// from ordinary DAV clients, but the Calendar app will know
+			// how to handle this special resource.
+			$calendar['{DAV:}resourcetype'] = new DAV\Xml\Property\ResourceType([
+				'{DAV:}collection',
+				sprintf('{%s}deleted-calendar', \OCA\DAV\DAV\Sharing\Plugin::NS_NEXTCLOUD),
+			]);
+		}
+		return $calendar;
 	}
 }
diff --git a/apps/dav/lib/CalDAV/Calendar.php b/apps/dav/lib/CalDAV/Calendar.php
index abddf2b706f..191ac384e72 100644
--- a/apps/dav/lib/CalDAV/Calendar.php
+++ b/apps/dav/lib/CalDAV/Calendar.php
@@ -42,9 +42,9 @@ use Sabre\DAV\PropPatch;
  * Class Calendar
  *
  * @package OCA\DAV\CalDAV
- * @property BackendInterface|CalDavBackend $caldavBackend
+ * @property CalDavBackend $caldavBackend
  */
-class Calendar extends \Sabre\CalDAV\Calendar implements IShareable {
+class Calendar extends \Sabre\CalDAV\Calendar implements IRestorable, IShareable {
 
 	/** @var IConfig */
 	private $config;
@@ -52,6 +52,9 @@ class Calendar extends \Sabre\CalDAV\Calendar implements IShareable {
 	/** @var IL10N */
 	protected $l10n;
 
+	/** @var bool */
+	private $useTrashbin = true;
+
 	/**
 	 * Calendar constructor.
 	 *
@@ -269,7 +272,10 @@ class Calendar extends \Sabre\CalDAV\Calendar implements IShareable {
 			$this->config->setUserValue($userId, 'dav', 'generateBirthdayCalendar', 'no');
 		}
 
-		parent::delete();
+		$this->caldavBackend->deleteCalendar(
+			$this->calendarInfo['id'],
+			!$this->useTrashbin
+		);
 	}
 
 	public function propPatch(PropPatch $propPatch) {
@@ -399,4 +405,12 @@ class Calendar extends \Sabre\CalDAV\Calendar implements IShareable {
 
 		return parent::getChanges($syncToken, $syncLevel, $limit);
 	}
+
+	public function restore(): void {
+		$this->caldavBackend->restoreCalendar((int) $this->calendarInfo['id']);
+	}
+
+	public function disableTrashbin(): void {
+		$this->useTrashbin = false;
+	}
 }
diff --git a/apps/dav/lib/CalDAV/CalendarHome.php b/apps/dav/lib/CalDAV/CalendarHome.php
index c746ab04112..c418ff049c1 100644
--- a/apps/dav/lib/CalDAV/CalendarHome.php
+++ b/apps/dav/lib/CalDAV/CalendarHome.php
@@ -30,6 +30,7 @@ namespace OCA\DAV\CalDAV;
 use OCA\DAV\AppInfo\PluginManager;
 use OCA\DAV\CalDAV\Integration\ExternalCalendar;
 use OCA\DAV\CalDAV\Integration\ICalendarProvider;
+use OCA\DAV\CalDAV\Trashbin\TrashbinHome;
 use Sabre\CalDAV\Backend\BackendInterface;
 use Sabre\CalDAV\Backend\NotificationSupport;
 use Sabre\CalDAV\Backend\SchedulingSupport;
@@ -38,6 +39,7 @@ use Sabre\CalDAV\Schedule\Inbox;
 use Sabre\CalDAV\Subscriptions\Subscription;
 use Sabre\DAV\Exception\MethodNotAllowed;
 use Sabre\DAV\Exception\NotFound;
+use Sabre\DAV\INode;
 use Sabre\DAV\MkCol;
 
 class CalendarHome extends \Sabre\CalDAV\CalendarHome {
@@ -74,8 +76,11 @@ class CalendarHome extends \Sabre\CalDAV\CalendarHome {
 	/**
 	 * @inheritdoc
 	 */
-	public function createExtendedCollection($name, MkCol $mkCol) {
-		$reservedNames = [BirthdayService::BIRTHDAY_CALENDAR_URI];
+	public function createExtendedCollection($name, MkCol $mkCol): void {
+		$reservedNames = [
+			BirthdayService::BIRTHDAY_CALENDAR_URI,
+			TrashbinHome::NAME,
+		];
 
 		if (\in_array($name, $reservedNames, true) || ExternalCalendar::doesViolateReservedName($name)) {
 			throw new MethodNotAllowed('The resource you tried to create has a reserved name');
@@ -104,6 +109,10 @@ class CalendarHome extends \Sabre\CalDAV\CalendarHome {
 			$objects[] = new \Sabre\CalDAV\Notifications\Collection($this->caldavBackend, $this->principalInfo['uri']);
 		}
 
+		if ($this->caldavBackend instanceof CalDavBackend) {
+			$objects[] = new TrashbinHome($this->caldavBackend, $this->principalInfo);
+		}
+
 		// If the backend supports subscriptions, we'll add those as well,
 		if ($this->caldavBackend instanceof SubscriptionSupport) {
 			foreach ($this->caldavBackend->getSubscriptionsForUser($this->principalInfo['uri']) as $subscription) {
@@ -127,7 +136,9 @@ class CalendarHome extends \Sabre\CalDAV\CalendarHome {
 	}
 
 	/**
-	 * @inheritdoc
+	 * @param string $name
+	 *
+	 * @return INode
 	 */
 	public function getChild($name) {
 		// Special nodes
@@ -140,6 +151,9 @@ class CalendarHome extends \Sabre\CalDAV\CalendarHome {
 		if ($name === 'notifications' && $this->caldavBackend instanceof NotificationSupport) {
 			return new \Sabre\CalDAV\Notifications\Collection($this->caldavBackend, $this->principalInfo['uri']);
 		}
+		if ($name === TrashbinHome::NAME && $this->caldavBackend instanceof CalDavBackend) {
+			return new TrashbinHome($this->caldavBackend, $this->principalInfo);
+		}
 
 		// Calendars
 		foreach ($this->caldavBackend->getCalendarsForUser($this->principalInfo['uri']) as $calendar) {
diff --git a/apps/dav/lib/CalDAV/CalendarObject.php b/apps/dav/lib/CalDAV/CalendarObject.php
index 766062ffdf1..0e42d9522ab 100644
--- a/apps/dav/lib/CalDAV/CalendarObject.php
+++ b/apps/dav/lib/CalDAV/CalendarObject.php
@@ -82,6 +82,10 @@ class CalendarObject extends \Sabre\CalDAV\CalendarObject {
 		return $vObject->serialize();
 	}
 
+	public function getId(): int {
+		return (int) $this->objectData['id'];
+	}
+
 	protected function isShared() {
 		if (!isset($this->calendarInfo['{http://owncloud.org/ns}owner-principal'])) {
 			return false;
diff --git a/apps/dav/lib/CalDAV/IRestorable.php b/apps/dav/lib/CalDAV/IRestorable.php
new file mode 100644
index 00000000000..438098b5a0e
--- /dev/null
+++ b/apps/dav/lib/CalDAV/IRestorable.php
@@ -0,0 +1,41 @@
+<?php
+
+declare(strict_types=1);
+
+/*
+ * @copyright 2021 Christoph Wurst <christoph@winzerhof-wurst.at>
+ *
+ * @author 2021 Christoph Wurst <christoph@winzerhof-wurst.at>
+ *
+ * @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 Sabre\DAV\Exception;
+
+/**
+ * Interface for nodes that can be restored from the trashbin
+ */
+interface IRestorable {
+
+	/**
+	 * Restore this node
+	 *
+	 * @throws Exception
+	 */
+	public function restore(): void;
+}
diff --git a/apps/dav/lib/CalDAV/RetentionService.php b/apps/dav/lib/CalDAV/RetentionService.php
new file mode 100644
index 00000000000..934e6f71530
--- /dev/null
+++ b/apps/dav/lib/CalDAV/RetentionService.php
@@ -0,0 +1,80 @@
+<?php
+
+declare(strict_types=1);
+
+/*
+ * @copyright 2021 Christoph Wurst <christoph@winzerhof-wurst.at>
+ *
+ * @author 2021 Christoph Wurst <christoph@winzerhof-wurst.at>
+ *
+ * @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 OCP\AppFramework\Utility\ITimeFactory;
+use OCP\IConfig;
+use function max;
+
+class RetentionService {
+	public const RETENTION_CONFIG_KEY = 'calendarRetentionObligation';
+	private const DEFAULT_RETENTION_SECONDS = 30 * 24 * 60 * 60;
+
+	/** @var IConfig */
+	private $config;
+
+	/** @var ITimeFactory */
+	private $time;
+
+	/** @var CalDavBackend */
+	private $calDavBackend;
+
+	public function __construct(IConfig $config,
+								ITimeFactory $time,
+								CalDavBackend $calDavBackend) {
+		$this->config = $config;
+		$this->time = $time;
+		$this->calDavBackend = $calDavBackend;
+	}
+
+	public function cleanUp(): void {
+		$retentionTime = max(
+			(int) $this->config->getAppValue(
+				Application::APP_ID,
+				self::RETENTION_CONFIG_KEY,
+				(string) self::DEFAULT_RETENTION_SECONDS
+			),
+			0 // Just making sure we don't delete things in the future when a negative number is passed
+		);
+		$now = $this->time->getTime();
+
+		$calendars = $this->calDavBackend->getDeletedCalendars($now - $retentionTime);
+		foreach ($calendars as $calendar) {
+			$this->calDavBackend->deleteCalendar($calendar['id'], true);
+		}
+
+		$objects = $this->calDavBackend->getDeletedCalendarObjects($now - $retentionTime);
+		foreach ($objects as $object) {
+			$this->calDavBackend->deleteCalendarObject(
+				$object['calendarid'],
+				$object['uri'],
+				$object['calendartype'],
+				true
+			);
+		}
+	}
+}
diff --git a/apps/dav/lib/CalDAV/Trashbin/DeletedCalendarObject.php b/apps/dav/lib/CalDAV/Trashbin/DeletedCalendarObject.php
new file mode 100644
index 00000000000..43d96b52efd
--- /dev/null
+++ b/apps/dav/lib/CalDAV/Trashbin/DeletedCalendarObject.php
@@ -0,0 +1,96 @@
+<?php
+
+declare(strict_types=1);
+
+/*
+ * @copyright 2021 Christoph Wurst <christoph@winzerhof-wurst.at>
+ *
+ * @author 2021 Christoph Wurst <christoph@winzerhof-wurst.at>
+ *
+ * @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\Trashbin;
+
+use OCA\DAV\CalDAV\CalDavBackend;
+use OCA\DAV\CalDAV\IRestorable;
+use Sabre\CalDAV\ICalendarObject;
+use Sabre\DAV\Exception\Forbidden;
+
+class DeletedCalendarObject implements ICalendarObject, IRestorable {
+
+	/** @var string */
+	private $name;
+
+	/** @var mixed[] */
+	private $objectData;
+
+	/** @var CalDavBackend */
+	private $calDavBackend;
+
+	public function __construct(string $name,
+								array $objectData,
+								CalDavBackend $calDavBackend) {
+		$this->name = $name;
+		$this->objectData = $objectData;
+		$this->calDavBackend = $calDavBackend;
+	}
+
+	public function delete() {
+		throw new Forbidden();
+	}
+
+	public function getName() {
+		return $this->name;
+	}
+
+	public function setName($name) {
+		throw new Forbidden();
+	}
+
+	public function getLastModified() {
+		return 0;
+	}
+
+	public function put($data) {
+		throw new Forbidden();
+	}
+
+	public function get() {
+		return $this->objectData['calendardata'];
+	}
+
+	public function getContentType() {
+		$mime = 'text/calendar; charset=utf-8';
+		if (isset($this->objectData['component']) && $this->objectData['component']) {
+			$mime .= '; component='.$this->objectData['component'];
+		}
+
+		return $mime;
+	}
+
+	public function getETag() {
+		return $this->objectData['etag'];
+	}
+
+	public function getSize() {
+		return (int) $this->objectData['size'];
+	}
+
+	public function restore(): void {
+		$this->calDavBackend->restoreCalendarObject($this->objectData);
+	}
+}
diff --git a/apps/dav/lib/CalDAV/Trashbin/DeletedCalendarObjectsCollection.php b/apps/dav/lib/CalDAV/Trashbin/DeletedCalendarObjectsCollection.php
new file mode 100644
index 00000000000..2d79db03bce
--- /dev/null
+++ b/apps/dav/lib/CalDAV/Trashbin/DeletedCalendarObjectsCollection.php
@@ -0,0 +1,131 @@
+<?php
+
+declare(strict_types=1);
+
+/*
+ * @copyright 2021 Christoph Wurst <christoph@winzerhof-wurst.at>
+ *
+ * @author 2021 Christoph Wurst <christoph@winzerhof-wurst.at>
+ *
+ * @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\Trashbin;
+
+use OCA\DAV\CalDAV\CalDavBackend;
+use Sabre\CalDAV\ICalendarObjectContainer;
+use Sabre\DAV\Exception\BadRequest;
+use Sabre\DAV\Exception\Forbidden;
+use Sabre\DAV\Exception\NotFound;
+use Sabre\DAV\Exception\NotImplemented;
+use function array_map;
+use function implode;
+use function preg_match;
+
+class DeletedCalendarObjectsCollection implements ICalendarObjectContainer {
+	public const NAME = 'objects';
+
+	/** @var CalDavBackend */
+	protected $caldavBackend;
+
+	/** @var mixed[] */
+	private $principalInfo;
+
+	public function __construct(CalDavBackend $caldavBackend,
+								array $principalInfo) {
+		$this->caldavBackend = $caldavBackend;
+		$this->principalInfo = $principalInfo;
+	}
+
+	/**
+	 * @see \OCA\DAV\CalDAV\Trashbin\DeletedCalendarObjectsCollection::calendarQuery
+	 */
+	public function getChildren() {
+		throw new NotImplemented();
+	}
+
+	public function getChild($name) {
+		if (!preg_match("/(\d+)\\.ics/", $name, $matches)) {
+			throw new NotFound();
+		}
+
+		$data = $this->caldavBackend->getCalendarObjectById(
+			$this->principalInfo['uri'],
+			(int) $matches[1],
+		);
+
+		// If the object hasn't been deleted yet then we don't want to find it here
+		if ($data === null) {
+			throw new NotFound();
+		}
+		if (!isset($data['deleted_at'])) {
+			throw new BadRequest('The calendar object you\'re trying to restore is not marked as deleted');
+		}
+
+		return new DeletedCalendarObject(
+			$this->getRelativeObjectPath($data),
+			$data,
+			$this->caldavBackend
+		);
+	}
+
+	public function createFile($name, $data = null) {
+		throw new Forbidden();
+	}
+
+	public function createDirectory($name) {
+		throw new Forbidden();
+	}
+
+	public function childExists($name) {
+		try {
+			$this->getChild($name);
+		} catch (NotFound $e) {
+			return false;
+		}
+
+		return true;
+	}
+
+	public function delete() {
+		throw new Forbidden();
+	}
+
+	public function getName(): string {
+		return self::NAME;
+	}
+
+	public function setName($name) {
+		throw new Forbidden();
+	}
+
+	public function getLastModified(): int {
+		return 0;
+	}
+
+	public function calendarQuery(array $filters) {
+		return array_map(function (array $calendarInfo) {
+			return $this->getRelativeObjectPath($calendarInfo);
+		}, $this->caldavBackend->getDeletedCalendarObjectsByPrincipal($this->principalInfo['uri']));
+	}
+
+	private function getRelativeObjectPath(array $calendarInfo): string {
+		return implode(
+			'.',
+			[$calendarInfo['id'], 'ics'],
+		);
+	}
+}
diff --git a/apps/dav/lib/CalDAV/Trashbin/Plugin.php b/apps/dav/lib/CalDAV/Trashbin/Plugin.php
new file mode 100644
index 00000000000..d42a09f1c0d
--- /dev/null
+++ b/apps/dav/lib/CalDAV/Trashbin/Plugin.php
@@ -0,0 +1,96 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * @copyright 2021 Christoph Wurst <christoph@winzerhof-wurst.at>
+ *
+ * @author 2021 Christoph Wurst <christoph@winzerhof-wurst.at>
+ *
+ * @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\Trashbin;
+
+use OCA\DAV\CalDAV\Calendar;
+use OCP\IRequest;
+use Sabre\DAV\Exception\NotFound;
+use Sabre\DAV\Server;
+use Sabre\DAV\ServerPlugin;
+use Sabre\HTTP\RequestInterface;
+use Sabre\HTTP\ResponseInterface;
+use function array_slice;
+use function implode;
+
+/**
+ * Conditional logic to bypass the calendar trashbin
+ */
+class Plugin extends ServerPlugin {
+
+	/** @var bool */
+	private $disableTrashbin;
+
+	/** @var Server */
+	private $server;
+
+	public function __construct(IRequest $request) {
+		$this->disableTrashbin = $request->getHeader('X-NC-CalDAV-No-Trashbin') === '1';
+	}
+
+	public function initialize(Server $server): void {
+		$this->server = $server;
+		$server->on('beforeMethod:*', [$this, 'beforeMethod']);
+	}
+
+	public function beforeMethod(RequestInterface $request, ResponseInterface $response): void {
+		if (!$this->disableTrashbin) {
+			return;
+		}
+
+		$path = $request->getPath();
+		$pathParts = explode('/', ltrim($path, '/'));
+		if (\count($pathParts) < 3) {
+			// We are looking for a path like calendars/username/calendarname
+			return;
+		}
+
+		// $calendarPath will look like calendars/username/calendarname
+		$calendarPath = implode(
+			'/',
+			array_slice($pathParts, 0, 3)
+		);
+		try {
+			$calendar = $this->server->tree->getNodeForPath($calendarPath);
+			if (!($calendar instanceof Calendar)) {
+				// This is odd
+				return;
+			}
+
+			/** @var Calendar $calendar */
+			$calendar->disableTrashbin();
+		} catch (NotFound $ex) {
+			return;
+		}
+	}
+
+	public function getFeatures(): array {
+		return ['nc-calendar-trashbin'];
+	}
+
+	public function getPluginName(): string {
+		return 'nc-calendar-trashbin';
+	}
+}
diff --git a/apps/dav/lib/CalDAV/Trashbin/RestoreTarget.php b/apps/dav/lib/CalDAV/Trashbin/RestoreTarget.php
new file mode 100644
index 00000000000..0175168e8d2
--- /dev/null
+++ b/apps/dav/lib/CalDAV/Trashbin/RestoreTarget.php
@@ -0,0 +1,82 @@
+<?php
+
+declare(strict_types=1);
+
+/*
+ * @copyright 2021 Christoph Wurst <christoph@winzerhof-wurst.at>
+ *
+ * @author 2021 Christoph Wurst <christoph@winzerhof-wurst.at>
+ *
+ * @license GNU AGPL version 3 or any later version
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+namespace OCA\DAV\CalDAV\Trashbin;
+
+use OCA\DAV\CalDAV\IRestorable;
+use Sabre\DAV\Exception\Forbidden;
+use Sabre\DAV\Exception\NotFound;
+use Sabre\DAV\ICollection;
+use Sabre\DAV\IMoveTarget;
+use Sabre\DAV\INode;
+
+class RestoreTarget implements ICollection, IMoveTarget {
+	public const NAME = 'restore';
+
+	public function createFile($name, $data = null) {
+		throw new Forbidden();
+	}
+
+	public function createDirectory($name) {
+		throw new Forbidden();
+	}
+
+	public function getChild($name) {
+		throw new NotFound();
+	}
+
+	public function getChildren(): array {
+		return [];
+	}
+
+	public function childExists($name): bool {
+		return false;
+	}
+
+	public function moveInto($targetName, $sourcePath, INode $sourceNode): bool {
+		if ($sourceNode instanceof IRestorable) {
+			$sourceNode->restore();
+			return true;
+		}
+
+		return false;
+	}
+
+	public function delete() {
+		throw new Forbidden();
+	}
+
+	public function getName(): string {
+		return 'restore';
+	}
+
+	public function setName($name) {
+		throw new Forbidden();
+	}
+
+	public function getLastModified() {
+		return 0;
+	}
+}
diff --git a/apps/dav/lib/CalDAV/Trashbin/TrashbinHome.php b/apps/dav/lib/CalDAV/Trashbin/TrashbinHome.php
new file mode 100644
index 00000000000..87f1f24aaab
--- /dev/null
+++ b/apps/dav/lib/CalDAV/Trashbin/TrashbinHome.php
@@ -0,0 +1,129 @@
+<?php
+
+declare(strict_types=1);
+
+/*
+ * @copyright 2021 Christoph Wurst <christoph@winzerhof-wurst.at>
+ *
+ * @author 2021 Christoph Wurst <christoph@winzerhof-wurst.at>
+ *
+ * @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\Trashbin;
+
+use OCA\DAV\CalDAV\CalDavBackend;
+use Sabre\DAV\Exception\Forbidden;
+use Sabre\DAV\Exception\NotFound;
+use Sabre\DAV\ICollection;
+use Sabre\DAV\INode;
+use Sabre\DAV\IProperties;
+use Sabre\DAV\PropPatch;
+use Sabre\DAV\Xml\Property\ResourceType;
+use Sabre\DAVACL\ACLTrait;
+use Sabre\DAVACL\IACL;
+use function in_array;
+use function sprintf;
+
+class TrashbinHome implements IACL, ICollection, IProperties {
+	use ACLTrait;
+
+	public const NAME = 'trashbin';
+
+	/** @var CalDavBackend */
+	private $caldavBackend;
+
+	/** @var array */
+	private $principalInfo;
+
+	public function __construct(CalDavBackend $caldavBackend,
+								array $principalInfo) {
+		$this->caldavBackend = $caldavBackend;
+		$this->principalInfo = $principalInfo;
+	}
+
+	public function getOwner(): string {
+		return $this->principalInfo['uri'];
+	}
+
+	public function createFile($name, $data = null) {
+		throw new Forbidden('Permission denied to create files in the trashbin');
+	}
+
+	public function createDirectory($name) {
+		throw new Forbidden('Permission denied to create a directory in the trashbin');
+	}
+
+	public function getChild($name): INode {
+		switch ($name) {
+			case RestoreTarget::NAME:
+				return new RestoreTarget();
+			case DeletedCalendarObjectsCollection::NAME:
+				return new DeletedCalendarObjectsCollection(
+					$this->caldavBackend,
+					$this->principalInfo
+				);
+		}
+
+		throw new NotFound();
+	}
+
+	public function getChildren(): array {
+		return [
+			new RestoreTarget(),
+			new DeletedCalendarObjectsCollection(
+				$this->caldavBackend,
+				$this->principalInfo
+			),
+		];
+	}
+
+	public function childExists($name): bool {
+		return in_array($name, [
+			RestoreTarget::NAME,
+			DeletedCalendarObjectsCollection::NAME,
+		], true);
+	}
+
+	public function delete() {
+		throw new Forbidden('Permission denied to delete the trashbin');
+	}
+
+	public function getName(): string {
+		return self::NAME;
+	}
+
+	public function setName($name) {
+		throw new Forbidden('Permission denied to rename the trashbin');
+	}
+
+	public function getLastModified(): int {
+		return 0;
+	}
+
+	public function propPatch(PropPatch $propPatch): void {
+		throw new Forbidden('not implemented');
+	}
+
+	public function getProperties($properties): array {
+		return [
+			'{DAV:}resourcetype' => new ResourceType([
+				'{DAV:}collection',
+				sprintf('{%s}trash-bin', \OCA\DAV\DAV\Sharing\Plugin::NS_NEXTCLOUD),
+			]),
+		];
+	}
+}