fixup! feat: calendar federationfeat/federated-calendar-sharing

28 files changed, 447 insertions, 239 deletions

diff --git a/apps/dav/appinfo/v1/caldav.php b/apps/dav/appinfo/v1/caldav.php
index 2cee1866a36..bd8dd5bf606 100644
--- a/apps/dav/appinfo/v1/caldav.php
+++ b/apps/dav/appinfo/v1/caldav.php
@@ -10,6 +10,7 @@ use OC\KnownUser\KnownUserService;
 use OCA\DAV\CalDAV\CalDavBackend;
 use OCA\DAV\CalDAV\CalendarRoot;
 use OCA\DAV\CalDAV\DefaultCalendarValidator;
+use OCA\DAV\CalDAV\Federation\FederatedCalendarMapper;
 use OCA\DAV\CalDAV\Proxy\ProxyMapper;
 use OCA\DAV\CalDAV\Schedule\IMipPlugin;
 use OCA\DAV\CalDAV\Security\RateLimitingPlugin;
@@ -71,6 +72,7 @@ $calDavBackend = new CalDavBackend(
 	$dispatcher,
 	$config,
 	Server::get(\OCA\DAV\CalDAV\Sharing\Backend::class),
+	Server::get(FederatedCalendarMapper::class),
 	true
 );
 
diff --git a/apps/dav/composer/composer/autoload_classmap.php b/apps/dav/composer/composer/autoload_classmap.php
index a3bd18b55bf..9220bc41428 100644
--- a/apps/dav/composer/composer/autoload_classmap.php
+++ b/apps/dav/composer/composer/autoload_classmap.php
@@ -69,11 +69,11 @@ return array(
     'OCA\\DAV\\CalDAV\\Federation\\FederatedCalendar' => $baseDir . '/../lib/CalDAV/Federation/FederatedCalendar.php',
     'OCA\\DAV\\CalDAV\\Federation\\FederatedCalendarAuth' => $baseDir . '/../lib/CalDAV/Federation/FederatedCalendarAuth.php',
     'OCA\\DAV\\CalDAV\\Federation\\FederatedCalendarEntity' => $baseDir . '/../lib/CalDAV/Federation/FederatedCalendarEntity.php',
+    'OCA\\DAV\\CalDAV\\Federation\\FederatedCalendarImpl' => $baseDir . '/../lib/CalDAV/Federation/FederatedCalendarImpl.php',
     'OCA\\DAV\\CalDAV\\Federation\\FederatedCalendarMapper' => $baseDir . '/../lib/CalDAV/Federation/FederatedCalendarMapper.php',
     'OCA\\DAV\\CalDAV\\Federation\\FederatedCalendarProvider' => $baseDir . '/../lib/CalDAV/Federation/FederatedCalendarProvider.php',
     'OCA\\DAV\\CalDAV\\Federation\\FederatedCalendarService' => $baseDir . '/../lib/CalDAV/Federation/FederatedCalendarService.php',
     'OCA\\DAV\\CalDAV\\Federation\\FederatedCalendarSyncService' => $baseDir . '/../lib/CalDAV/Federation/FederatedCalendarSyncService.php',
-    'OCA\\DAV\\CalDAV\\Federation\\FederatedCalendar_actual' => $baseDir . '/../lib/CalDAV/Federation/FederatedCalendar_actual.php',
     'OCA\\DAV\\CalDAV\\Federation\\FederatedCalendar_old' => $baseDir . '/../lib/CalDAV/Federation/FederatedCalendar_old.php',
     'OCA\\DAV\\CalDAV\\Federation\\FederationSharingPlugin' => $baseDir . '/../lib/CalDAV/Federation/FederationSharingPlugin.php',
     'OCA\\DAV\\CalDAV\\Federation\\FederationSharingService' => $baseDir . '/../lib/CalDAV/Federation/FederationSharingService.php',
@@ -81,6 +81,7 @@ return array(
     'OCA\\DAV\\CalDAV\\Federation\\Protocol\\CalendarProtocolParseException' => $baseDir . '/../lib/CalDAV/Federation/Protocol/CalendarProtocolParseException.php',
     'OCA\\DAV\\CalDAV\\Federation\\Protocol\\ICalendarFederationProtocol' => $baseDir . '/../lib/CalDAV/Federation/Protocol/ICalendarFederationProtocol.php',
     'OCA\\DAV\\CalDAV\\Federation\\RemoteUserCalendarHome' => $baseDir . '/../lib/CalDAV/Federation/RemoteUserCalendarHome.php',
+    'OCA\\DAV\\CalDAV\\Federation\\RemoteUserPrincipalParser' => $baseDir . '/../lib/CalDAV/Federation/RemoteUserPrincipalParser.php',
     'OCA\\DAV\\CalDAV\\FreeBusy\\FreeBusyGenerator' => $baseDir . '/../lib/CalDAV/FreeBusy/FreeBusyGenerator.php',
     'OCA\\DAV\\CalDAV\\ICSExportPlugin\\ICSExportPlugin' => $baseDir . '/../lib/CalDAV/ICSExportPlugin/ICSExportPlugin.php',
     'OCA\\DAV\\CalDAV\\IRestorable' => $baseDir . '/../lib/CalDAV/IRestorable.php',
diff --git a/apps/dav/composer/composer/autoload_static.php b/apps/dav/composer/composer/autoload_static.php
index e6831f14345..ca971179eab 100644
--- a/apps/dav/composer/composer/autoload_static.php
+++ b/apps/dav/composer/composer/autoload_static.php
@@ -84,11 +84,11 @@ class ComposerStaticInitDAV
         'OCA\\DAV\\CalDAV\\Federation\\FederatedCalendar' => __DIR__ . '/..' . '/../lib/CalDAV/Federation/FederatedCalendar.php',
         'OCA\\DAV\\CalDAV\\Federation\\FederatedCalendarAuth' => __DIR__ . '/..' . '/../lib/CalDAV/Federation/FederatedCalendarAuth.php',
         'OCA\\DAV\\CalDAV\\Federation\\FederatedCalendarEntity' => __DIR__ . '/..' . '/../lib/CalDAV/Federation/FederatedCalendarEntity.php',
+        'OCA\\DAV\\CalDAV\\Federation\\FederatedCalendarImpl' => __DIR__ . '/..' . '/../lib/CalDAV/Federation/FederatedCalendarImpl.php',
         'OCA\\DAV\\CalDAV\\Federation\\FederatedCalendarMapper' => __DIR__ . '/..' . '/../lib/CalDAV/Federation/FederatedCalendarMapper.php',
         'OCA\\DAV\\CalDAV\\Federation\\FederatedCalendarProvider' => __DIR__ . '/..' . '/../lib/CalDAV/Federation/FederatedCalendarProvider.php',
         'OCA\\DAV\\CalDAV\\Federation\\FederatedCalendarService' => __DIR__ . '/..' . '/../lib/CalDAV/Federation/FederatedCalendarService.php',
         'OCA\\DAV\\CalDAV\\Federation\\FederatedCalendarSyncService' => __DIR__ . '/..' . '/../lib/CalDAV/Federation/FederatedCalendarSyncService.php',
-        'OCA\\DAV\\CalDAV\\Federation\\FederatedCalendar_actual' => __DIR__ . '/..' . '/../lib/CalDAV/Federation/FederatedCalendar_actual.php',
         'OCA\\DAV\\CalDAV\\Federation\\FederatedCalendar_old' => __DIR__ . '/..' . '/../lib/CalDAV/Federation/FederatedCalendar_old.php',
         'OCA\\DAV\\CalDAV\\Federation\\FederationSharingPlugin' => __DIR__ . '/..' . '/../lib/CalDAV/Federation/FederationSharingPlugin.php',
         'OCA\\DAV\\CalDAV\\Federation\\FederationSharingService' => __DIR__ . '/..' . '/../lib/CalDAV/Federation/FederationSharingService.php',
@@ -96,6 +96,7 @@ class ComposerStaticInitDAV
         'OCA\\DAV\\CalDAV\\Federation\\Protocol\\CalendarProtocolParseException' => __DIR__ . '/..' . '/../lib/CalDAV/Federation/Protocol/CalendarProtocolParseException.php',
         'OCA\\DAV\\CalDAV\\Federation\\Protocol\\ICalendarFederationProtocol' => __DIR__ . '/..' . '/../lib/CalDAV/Federation/Protocol/ICalendarFederationProtocol.php',
         'OCA\\DAV\\CalDAV\\Federation\\RemoteUserCalendarHome' => __DIR__ . '/..' . '/../lib/CalDAV/Federation/RemoteUserCalendarHome.php',
+        'OCA\\DAV\\CalDAV\\Federation\\RemoteUserPrincipalParser' => __DIR__ . '/..' . '/../lib/CalDAV/Federation/RemoteUserPrincipalParser.php',
         'OCA\\DAV\\CalDAV\\FreeBusy\\FreeBusyGenerator' => __DIR__ . '/..' . '/../lib/CalDAV/FreeBusy/FreeBusyGenerator.php',
         'OCA\\DAV\\CalDAV\\ICSExportPlugin\\ICSExportPlugin' => __DIR__ . '/..' . '/../lib/CalDAV/ICSExportPlugin/ICSExportPlugin.php',
         'OCA\\DAV\\CalDAV\\IRestorable' => __DIR__ . '/..' . '/../lib/CalDAV/IRestorable.php',
diff --git a/apps/dav/lib/CalDAV/CalDavBackend.php b/apps/dav/lib/CalDAV/CalDavBackend.php
index 838674136ef..4d1b24e654f 100644
--- a/apps/dav/lib/CalDAV/CalDavBackend.php
+++ b/apps/dav/lib/CalDAV/CalDavBackend.php
@@ -11,6 +11,8 @@ use DateTimeImmutable;
 use DateTimeInterface;
 use Generator;
 use OCA\DAV\AppInfo\Application;
+use OCA\DAV\CalDAV\Federation\FederatedCalendarEntity;
+use OCA\DAV\CalDAV\Federation\FederatedCalendarMapper;
 use OCA\DAV\CalDAV\Sharing\Backend;
 use OCA\DAV\Connector\Sabre\Principal;
 use OCA\DAV\DAV\Sharing\IShareable;
@@ -210,6 +212,7 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 		private IEventDispatcher $dispatcher,
 		private IConfig $config,
 		private Sharing\Backend $calendarSharingBackend,
+		private FederatedCalendarMapper $federatedCalendarMapper,
 		private bool $legacyEndpoint = false,
 	) {
 	}
@@ -3750,4 +3753,21 @@ class CalDavBackend extends AbstractBackend implements SyncSupport, Subscription
 			}
 		}, $this->db);
 	}
+
+	public function getFederatedCalendarsForUser(string $principalUri): array {
+		return $this->atomic(function () use ($principalUri) {
+			$federatedCalendars = $this->federatedCalendarMapper->findByPrincipalUri($principalUri);
+			return array_map(
+				static fn (FederatedCalendarEntity $entity) => $entity->toCalendarInfo(),
+				$federatedCalendars,
+			);
+		}, $this->db);
+	}
+
+	public function getFederatedCalendarByUri(string $principalUri, string $uri): ?array {
+		return $this->atomic(function () use ($principalUri, $uri) {
+			$federatedCalendar = $this->federatedCalendarMapper->findByUri($principalUri, $uri);
+			return $federatedCalendar?->toCalendarInfo();
+		}, $this->db);
+	}
 }
diff --git a/apps/dav/lib/CalDAV/CalendarHome.php b/apps/dav/lib/CalDAV/CalendarHome.php
index ef36705fdd1..ffdebcf9072 100644
--- a/apps/dav/lib/CalDAV/CalendarHome.php
+++ b/apps/dav/lib/CalDAV/CalendarHome.php
@@ -8,12 +8,11 @@
 namespace OCA\DAV\CalDAV;
 
 use OCA\DAV\AppInfo\PluginManager;
-use OCA\DAV\CalDAV\Federation\FederatedCalendar_actual;
+use OCA\DAV\CalDAV\Federation\FederatedCalendar;
 use OCA\DAV\CalDAV\Federation\FederatedCalendarMapper;
 use OCA\DAV\CalDAV\Integration\ExternalCalendar;
 use OCA\DAV\CalDAV\Integration\ICalendarProvider;
 use OCA\DAV\CalDAV\Trashbin\TrashbinHome;
-use OCA\DAV\DAV\Sharing\Backend;
 use OCP\App\IAppManager;
 use OCP\IConfig;
 use OCP\IL10N;
@@ -25,7 +24,6 @@ use Sabre\CalDAV\Backend\SchedulingSupport;
 use Sabre\CalDAV\Backend\SubscriptionSupport;
 use Sabre\CalDAV\Schedule\Inbox;
 use Sabre\CalDAV\Subscriptions\Subscription;
-use Sabre\CalDAV\Xml\Property\SupportedCalendarComponentSet;
 use Sabre\DAV\Exception\MethodNotAllowed;
 use Sabre\DAV\Exception\NotFound;
 use Sabre\DAV\INode;
@@ -42,7 +40,7 @@ class CalendarHome extends \Sabre\CalDAV\CalendarHome {
 	/** @var PluginManager */
 	private $pluginManager;
 
-	private FederatedCalendarMapper $federatedCalendarMapper;
+	private readonly FederatedCalendarMapper $federatedCalendarMapper;
 	private ?array $cachedChildren = null;
 
 	public function __construct(
@@ -97,27 +95,6 @@ class CalendarHome extends \Sabre\CalDAV\CalendarHome {
 			$objects[] = new Calendar($this->caldavBackend, $calendar, $this->l10n, $this->config, $this->logger);
 		}
 
-		$federatedCalendars = $this->federatedCalendarMapper->findByPrincipalUri($this->principalInfo['uri']);
-		foreach ($federatedCalendars as $federatedCalendar) {
-			// TODO: move this to CalDavBackend? -> Ref subscriptions (rowToSubscription)
-			// TODO: move this to the the entity?
-			$calendarInfo = [
-				'id' => $federatedCalendar->getId(),
-				'uri' => $federatedCalendar->getUri(),
-				'principaluri' => $federatedCalendar->getPrincipaluri(),
-				'federated' => true,
-
-				'{DAV:}displayname' => $federatedCalendar->getDisplayName(),
-				// TODO: load from remote
-				'{' . Plugin::NS_CALDAV . '}supported-calendar-component-set' => new SupportedCalendarComponentSet(['VTODO', 'VEVENT']),
-				'{http://sabredav.org/ns}sync-token' => $federatedCalendar->getSyncToken(),
-				'{' . Plugin::NS_CALENDARSERVER . '}getctag' => $federatedCalendar->getSyncTokenForSabre(),
-				'{' . \OCA\DAV\DAV\Sharing\Plugin::NS_OWNCLOUD . '}owner-principal' => $federatedCalendar->getSharedByPrincipal(),
-				'{' . \OCA\DAV\DAV\Sharing\Plugin::NS_OWNCLOUD . '}read-only' => $federatedCalendar->getPermissions() === Backend::ACCESS_READ,
-			];
-			$objects[] = new FederatedCalendar_actual($this->caldavBackend, $calendarInfo, $this->l10n, $this->config, $this->logger, $this->federatedCalendarMapper);
-		}
-
 		if ($this->caldavBackend instanceof SchedulingSupport) {
 			$objects[] = new Inbox($this->caldavBackend, $this->principalInfo['uri']);
 			$objects[] = new Outbox($this->config, $this->principalInfo['uri']);
@@ -130,6 +107,20 @@ class CalendarHome extends \Sabre\CalDAV\CalendarHome {
 
 		if ($this->caldavBackend instanceof CalDavBackend) {
 			$objects[] = new TrashbinHome($this->caldavBackend, $this->principalInfo);
+
+			$federatedCalendars = $this->caldavBackend->getFederatedCalendarsForUser(
+				$this->principalInfo['uri'],
+			);
+			foreach ($federatedCalendars as $federatedCalendarInfo) {
+				$objects[] = new FederatedCalendar(
+					$this->caldavBackend,
+					$federatedCalendarInfo,
+					$this->l10n,
+					$this->config,
+					$this->logger,
+					$this->federatedCalendarMapper,
+				);
+			}
 		}
 
 		// If the backend supports subscriptions, we'll add those as well,
@@ -175,13 +166,29 @@ class CalendarHome extends \Sabre\CalDAV\CalendarHome {
 			return new TrashbinHome($this->caldavBackend, $this->principalInfo);
 		}
 
-		// Calendar - this covers all "regular" calendars, but not shared
-		// only check if the method is available
+		// Only check if the methods are available
 		if ($this->caldavBackend instanceof CalDavBackend) {
+			// Calendar - this covers all "regular" calendars, but not shared
 			$calendar = $this->caldavBackend->getCalendarByUri($this->principalInfo['uri'], $name);
 			if (!empty($calendar)) {
 				return new Calendar($this->caldavBackend, $calendar, $this->l10n, $this->config, $this->logger);
 			}
+
+			// Federated calendar
+			$federatedCalendar = $this->caldavBackend->getFederatedCalendarByUri(
+				$this->principalInfo['uri'],
+				$name,
+			);
+			if ($federatedCalendar !== null) {
+				return new FederatedCalendar(
+					$this->caldavBackend,
+					$federatedCalendar,
+					$this->l10n,
+					$this->config,
+					$this->logger,
+					$this->federatedCalendarMapper,
+				);
+			}
 		}
 
 		// Fallback to cover shared calendars
@@ -203,26 +210,6 @@ class CalendarHome extends \Sabre\CalDAV\CalendarHome {
 			}
 		}
 
-		$federatedCalendar = $this->federatedCalendarMapper->findByUri($this->principalInfo['uri'], $name);
-		if ($federatedCalendar) {
-			// TODO: merge with above
-			$calendarInfo = [
-				'id' => $federatedCalendar->getId(),
-				'uri' => $federatedCalendar->getUri(),
-				'principaluri' => $federatedCalendar->getPrincipaluri(),
-				'federated' => true,
-
-				'{DAV:}displayname' => $federatedCalendar->getDisplayName(),
-				// TODO: load from remote
-				'{' . Plugin::NS_CALDAV . '}supported-calendar-component-set' => new SupportedCalendarComponentSet(['VTODO', 'VEVENT']),
-				'{http://sabredav.org/ns}sync-token' => $federatedCalendar->getSyncToken(),
-				'{' . Plugin::NS_CALENDARSERVER . '}getctag' => $federatedCalendar->getSyncTokenForSabre(),
-				'{' . \OCA\DAV\DAV\Sharing\Plugin::NS_OWNCLOUD . '}owner-principal' => $federatedCalendar->getSharedByPrincipal(),
-				'{' . \OCA\DAV\DAV\Sharing\Plugin::NS_OWNCLOUD . '}read-only' => $federatedCalendar->getPermissions() === Backend::ACCESS_READ,
-			];
-			return new FederatedCalendar_actual($this->caldavBackend, $calendarInfo, $this->l10n, $this->config, $this->logger, $this->federatedCalendarMapper);
-		}
-
 		if (ExternalCalendar::isAppGeneratedCalendar($name)) {
 			[$appId, $calendarUri] = ExternalCalendar::splitAppGeneratedCalendarUri($name);
 
diff --git a/apps/dav/lib/CalDAV/CalendarProvider.php b/apps/dav/lib/CalDAV/CalendarProvider.php
index 3cc4039ed36..0f6ce928d38 100644
--- a/apps/dav/lib/CalDAV/CalendarProvider.php
+++ b/apps/dav/lib/CalDAV/CalendarProvider.php
@@ -8,6 +8,9 @@ declare(strict_types=1);
  */
 namespace OCA\DAV\CalDAV;
 
+use OCA\DAV\CalDAV\Federation\FederatedCalendar;
+use OCA\DAV\CalDAV\Federation\FederatedCalendarImpl;
+use OCA\DAV\CalDAV\Federation\FederatedCalendarMapper;
 use OCA\DAV\Db\Property;
 use OCA\DAV\Db\PropertyMapper;
 use OCP\Calendar\ICalendarProvider;
@@ -23,20 +26,27 @@ class CalendarProvider implements ICalendarProvider {
 		private IConfig $config,
 		private LoggerInterface $logger,
 		private PropertyMapper $propertyMapper,
+		private FederatedCalendarMapper $federatedCalendarMapper,
 	) {
 	}
 
 	public function getCalendars(string $principalUri, array $calendarUris = []): array {
 
 		$calendarInfos = $this->calDavBackend->getCalendarsForUser($principalUri) ?? [];
+		$federatedCalendarInfos = $this->calDavBackend->getFederatedCalendarsForUser($principalUri);
 
 		if (!empty($calendarUris)) {
 			$calendarInfos = array_filter($calendarInfos, function ($calendar) use ($calendarUris) {
 				return in_array($calendar['uri'], $calendarUris);
 			});
+
+			$federatedCalendarInfos = array_filter($federatedCalendarInfos, function ($federatedCalendar) use ($calendarUris) {
+				return in_array($federatedCalendar['uri'], $calendarUris);
+			});
 		}
 
 		$iCalendars = [];
+
 		foreach ($calendarInfos as $calendarInfo) {
 			$calendarInfo = array_merge($calendarInfo, $this->getAdditionalProperties($calendarInfo['principaluri'], $calendarInfo['uri']));
 			$calendar = new Calendar($this->calDavBackend, $calendarInfo, $this->l10n, $this->config, $this->logger);
@@ -46,6 +56,24 @@ class CalendarProvider implements ICalendarProvider {
 				$this->calDavBackend,
 			);
 		}
+
+		foreach ($federatedCalendarInfos as $calendarInfo) {
+			$calendarInfo = array_merge($calendarInfo, $this->getAdditionalProperties($calendarInfo['principaluri'], $calendarInfo['uri']));
+			$calendar = new FederatedCalendar(
+				$this->calDavBackend,
+				$calendarInfo,
+				$this->l10n,
+				$this->config,
+				$this->logger,
+				$this->federatedCalendarMapper,
+			);
+			$iCalendars[] = new FederatedCalendarImpl(
+				$calendar,
+				$calendarInfo,
+				$this->calDavBackend,
+			);
+		}
+
 		return $iCalendars;
 	}
 
diff --git a/apps/dav/lib/CalDAV/Federation/CalendarFederationProvider.php b/apps/dav/lib/CalDAV/Federation/CalendarFederationProvider.php
index da011edb564..98a8eb60f4e 100644
--- a/apps/dav/lib/CalDAV/Federation/CalendarFederationProvider.php
+++ b/apps/dav/lib/CalDAV/Federation/CalendarFederationProvider.php
@@ -9,14 +9,12 @@ declare(strict_types=1);
 
 namespace OCA\DAV\CalDAV\Federation;
 
-use OCA\DAV\CalDAV\CalDavBackend;
 use OCA\DAV\CalDAV\Federation\Protocol\CalendarFederationProtocolV1;
 use OCA\DAV\CalDAV\Federation\Protocol\ICalendarFederationProtocol;
 use OCP\AppFramework\Http;
 use OCP\Federation\Exceptions\ProviderCouldNotAddShareException;
 use OCP\Federation\ICloudFederationProvider;
 use OCP\Federation\ICloudFederationShare;
-use OCP\Federation\ICloudIdManager;
 use Psr\Log\LoggerInterface;
 
 class CalendarFederationProvider implements ICloudFederationProvider {
@@ -24,9 +22,7 @@ class CalendarFederationProvider implements ICloudFederationProvider {
 	public const CALENDAR_RESOURCE = 'calendar';
 
 	public function __construct(
-		private readonly CalDavBackend $calDavBackend,
 		private readonly LoggerInterface $logger,
-		private readonly ICloudIdManager $cloudIdManager,
 		private readonly FederatedCalendarMapper $federatedCalendarMapper,
 	) {
 	}
@@ -38,11 +34,20 @@ class CalendarFederationProvider implements ICloudFederationProvider {
 	public function shareReceived(ICloudFederationShare $share): string {
 		if (!$this->isFederationEnabled()) {
 			$this->logger->debug('Received a federation invite but federation is disabled');
-			throw new ProviderCouldNotAddShareException('Server does not support talk federation', '', Http::STATUS_SERVICE_UNAVAILABLE);
+			throw new ProviderCouldNotAddShareException(
+				'Server does not support talk federation',
+				'',
+				Http::STATUS_SERVICE_UNAVAILABLE,
+			);
 		}
+
 		if (!in_array($share->getShareType(), $this->getSupportedShareTypes(), true)) {
 			$this->logger->debug('Received a federation invite for invalid share type');
-			throw new ProviderCouldNotAddShareException('Support for sharing with non-users not implemented yet', '', Http::STATUS_NOT_IMPLEMENTED);
+			throw new ProviderCouldNotAddShareException(
+				'Support for sharing with non-users not implemented yet',
+				'',
+				Http::STATUS_NOT_IMPLEMENTED,
+			);
 			// TODO: Implement group shares
 		}
 
@@ -50,7 +55,15 @@ class CalendarFederationProvider implements ICloudFederationProvider {
 		// TODO: test what happens if no version in protocol
 		switch ($rawProtocol[ICalendarFederationProtocol::PROP_VERSION]) {
 			case CalendarFederationProtocolV1::VERSION:
-				$protocol = CalendarFederationProtocolV1::parse($rawProtocol);
+				try {
+					$protocol = CalendarFederationProtocolV1::parse($rawProtocol);
+				} catch (Protocol\CalendarProtocolParseException $e) {
+					throw new ProviderCouldNotAddShareException(
+						'Invalid protocol data (v1)',
+						'',
+						Http::STATUS_BAD_REQUEST,
+					);
+				}
 				$calendarUrl = $protocol->getUrl();
 				$displayName = $protocol->getDisplayName();
 				$color = $protocol->getColor();
@@ -72,8 +85,9 @@ class CalendarFederationProvider implements ICloudFederationProvider {
 			);
 		}
 
-		//$sharedBy = $this->cloudIdManager->resolveCloudId($share->getSharedBy());
-
+		// The calendar uri is the local name of the calendar. As such it must not contain slashes.
+		// Just use the hashed url for simplicity here.
+		// Example: calendars/foo-bar-user/<calendar-uri>
 		$calendarUri = hash('md5', $calendarUrl);
 
 		$sharedWithPrincipal = 'principals/users/' . $share->getShareWith();
@@ -95,7 +109,6 @@ class CalendarFederationProvider implements ICloudFederationProvider {
 		$calendar->setRemoteUrl($calendarUrl);
 		$calendar->setDisplayName($displayName);
 		$calendar->setColor($color);
-		$calendar->setPermissions(1); // TODO: handle permissions
 		$calendar->setToken($share->getShareSecret());
 		$calendar->setSharedBy($share->getSharedBy());
 		$calendar->setSharedByDisplayName($share->getSharedByDisplayName());
@@ -105,7 +118,6 @@ class CalendarFederationProvider implements ICloudFederationProvider {
 	}
 
 	public function notificationReceived($notificationType, $providerId, array $notification) {
-		// TODO: Implement notificationReceived() method.
 	}
 
 	/**
diff --git a/apps/dav/lib/CalDAV/Federation/FederatedCalendar.php b/apps/dav/lib/CalDAV/Federation/FederatedCalendar.php
index 8f87debdefa..34367e0e88e 100644
--- a/apps/dav/lib/CalDAV/Federation/FederatedCalendar.php
+++ b/apps/dav/lib/CalDAV/Federation/FederatedCalendar.php
@@ -10,82 +10,29 @@ declare(strict_types=1);
 namespace OCA\DAV\CalDAV\Federation;
 
 use OCA\DAV\CalDAV\CalDavBackend;
-use OCA\DAV\DAV\Sharing\Backend;
-use OCP\Calendar\ICalendar;
-use OCP\Calendar\ICalendarIsShared;
-use OCP\Calendar\ICalendarIsWritable;
-use OCP\Calendar\IDeleteable;
-use OCP\Constants;
-use OCP\Server;
+use OCA\DAV\CalDAV\Calendar;
+use OCP\IConfig;
+use OCP\IL10N;
+use Psr\Log\LoggerInterface;
+use Sabre\CalDAV\Backend;
 
-class FederatedCalendar implements ICalendar, ICalendarIsShared, ICalendarIsWritable, IDeleteable {
+class FederatedCalendar extends Calendar {
 	public function __construct(
-		private int $id,
-		private string $uri,
-		private string $displayName,
-		private ?string $color,
-		private int $permissions,
-		private string $principalUri,
+		Backend\BackendInterface $caldavBackend,
+		$calendarInfo,
+		IL10N $l10n,
+		IConfig $config,
+		LoggerInterface $logger,
+		private readonly FederatedCalendarMapper $federatedCalendarMapper,
 	) {
+		parent::__construct($caldavBackend, $calendarInfo, $l10n, $config, $logger);
 	}
 
-	public function getKey(): string {
-		return (string)$this->id;
+	public function delete() {
+		$this->federatedCalendarMapper->deleteById($this->getResourceId());
 	}
 
-	public function getUri(): string {
-		return $this->uri;
-	}
-
-	public function getDisplayName(): ?string {
-		return $this->displayName;
-	}
-
-	public function getDisplayColor(): ?string {
-		return $this->color;
-	}
-
-	public function search(string $pattern, array $searchProperties = [], array $options = [], ?int $limit = null, ?int $offset = null): array {
-		// TODO: Implement search() method.
-		//return [];
-		$calDavBackend = Server::get(CalDavBackend::class);
-		$calendarInfo = [
-			'id' => $this->id,
-			'principaluri' => $this->principalUri,
-			'federated' => true,
-			'{http://owncloud.org/ns}owner-principal' => $this->principalUri,
-		];
-		$result = $calDavBackend->search($calendarInfo, $pattern, $searchProperties, $options, $limit, $offset);
-
-		foreach ($result as $object) {
-			assert(count($object['objects']) === 1);
-		}
-
-		$objects = array_map(static fn ($result) => $result['objects'][0], $result);
-		//$objects = array_map(static fn ($result) => ['VEVENT' => $result['objects'][0]], $result);
-		//return array_merge(...$objects);
-		return $objects;
-	}
-
-	public function getPermissions(): int {
-		// TODO: implement this properly via ACLs?
-		return Constants::PERMISSION_READ;
-	}
-
-	public function isDeleted(): bool {
-		return false;
-	}
-
-	public function isShared(): bool {
-		return true;
-	}
-
-	public function isWritable(): bool {
-		return false;
-	}
-
-	public function delete(): void {
-		$federatedCalendarMapper = Server::get(FederatedCalendarMapper::class);
-		$federatedCalendarMapper->deleteById($this->id);
+	protected function getCalendarType(): int {
+		return CalDavBackend::CALENDAR_TYPE_FEDERATED;
 	}
 }
diff --git a/apps/dav/lib/CalDAV/Federation/FederatedCalendarEntity.php b/apps/dav/lib/CalDAV/Federation/FederatedCalendarEntity.php
index 89ddfbfbe63..146d4b05d95 100644
--- a/apps/dav/lib/CalDAV/Federation/FederatedCalendarEntity.php
+++ b/apps/dav/lib/CalDAV/Federation/FederatedCalendarEntity.php
@@ -11,6 +11,7 @@ namespace OCA\DAV\CalDAV\Federation;
 
 use OCP\AppFramework\Db\Entity;
 use OCP\DB\Types;
+use Sabre\CalDAV\Xml\Property\SupportedCalendarComponentSet;
 
 // TODO: write a migration for this entity
 
@@ -37,6 +38,8 @@ use OCP\DB\Types;
  * @method void setSharedBy(string $sharedBy)
  * @method string getSharedByDisplayName()
  * @method void setSharedByDisplayName(string $sharedByDisplayName)
+ * @method string getComponents()
+ * @method void setComponents(string $components)
  */
 class FederatedCalendarEntity extends Entity {
 	protected string $principaluri = '';
@@ -50,6 +53,7 @@ class FederatedCalendarEntity extends Entity {
 	protected ?int $lastSync = null;
 	protected string $sharedBy = '';
 	protected string $sharedByDisplayName = '';
+	protected string $components = '';
 
 	public function __construct() {
 		$this->addType('principaluri', Types::STRING);
@@ -63,17 +67,7 @@ class FederatedCalendarEntity extends Entity {
 		$this->addType('lastSync', Types::INTEGER);
 		$this->addType('sharedBy', Types::STRING);
 		$this->addType('sharedByDisplayName', Types::STRING);
-	}
-
-	public function toFederatedCalendar(): FederatedCalendar {
-		return new FederatedCalendar(
-			$this->getId(),
-			$this->getUri(),
-			$this->getDisplayName(),
-			$this->getColor(),
-			$this->getPermissions(),
-			$this->getPrincipaluri(),
-		);
+		$this->addType('components', Types::STRING);
 	}
 
 	public function getSyncTokenForSabre(): string {
@@ -83,4 +77,26 @@ class FederatedCalendarEntity extends Entity {
 	public function getSharedByPrincipal(): string {
 		return 'principals/remote-users/' . base64_encode($this->getSharedBy());
 	}
+
+	public function getSupportedCalendarComponentSet(): SupportedCalendarComponentSet {
+		$components = explode(',', $this->getComponents());
+		return new SupportedCalendarComponentSet($components);
+	}
+
+	public function toCalendarInfo(): array {
+		return [
+			'id' => $this->getId(),
+			'uri' => $this->getUri(),
+			'principaluri' => $this->getPrincipaluri(),
+			//'federated' => true,
+
+			'{DAV:}displayname' => $this->getDisplayName(),
+			'{http://sabredav.org/ns}sync-token' => $this->getSyncToken(),
+			'{' . \Sabre\CalDAV\Plugin::NS_CALENDARSERVER . '}getctag' => $this->getSyncTokenForSabre(),
+			'{' . \Sabre\CalDAV\Plugin::NS_CALDAV . '}supported-calendar-component-set' => $this->getSupportedCalendarComponentSet(),
+			'{' . \OCA\DAV\DAV\Sharing\Plugin::NS_OWNCLOUD . '}owner-principal' => $this->getSharedByPrincipal(),
+			// TODO: implement read-write sharing
+			'{' . \OCA\DAV\DAV\Sharing\Plugin::NS_OWNCLOUD . '}read-only' => 1
+		];
+	}
 }
diff --git a/apps/dav/lib/CalDAV/Federation/FederatedCalendarImpl.php b/apps/dav/lib/CalDAV/Federation/FederatedCalendarImpl.php
new file mode 100644
index 00000000000..20c238944d6
--- /dev/null
+++ b/apps/dav/lib/CalDAV/Federation/FederatedCalendarImpl.php
@@ -0,0 +1,79 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * SPDX-FileCopyrightText: 2025 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace OCA\DAV\CalDAV\Federation;
+
+use OCA\DAV\CalDAV\CalDavBackend;
+use OCP\Calendar\ICalendar;
+use OCP\Calendar\ICalendarIsEnabled;
+use OCP\Calendar\ICalendarIsShared;
+use OCP\Calendar\ICalendarIsWritable;
+use OCP\Calendar\IDeleteable;
+use OCP\Constants;
+
+class FederatedCalendarImpl implements ICalendar, ICalendarIsShared, IDeleteable, ICalendarIsWritable, ICalendarIsEnabled {
+	public function __construct(
+		private readonly FederatedCalendar $federatedCalendar,
+		private readonly array $calendarInfo,
+		private readonly CalDavBackend $calDavBackend,
+	) {
+	}
+
+	public function getKey(): string {
+		return (string)$this->calendarInfo['id'];
+	}
+
+	public function getUri(): string {
+		return $this->calendarInfo['uri'];
+	}
+
+	public function getDisplayName(): ?string {
+		return $this->calendarInfo['{DAV:}displayname'];
+	}
+
+	public function getDisplayColor(): ?string {
+		return $this->calendarInfo['{http://apple.com/ns/ical/}calendar-color'];
+	}
+
+	public function search(string $pattern, array $searchProperties = [], array $options = [], ?int $limit = null, ?int $offset = null): array {
+		return $this->calDavBackend->search(
+			$this->calendarInfo,
+			$pattern,
+			$searchProperties,
+			$options,
+			$limit,
+			$offset,
+		);
+	}
+
+	public function getPermissions(): int {
+		// TODO: implement read-write sharing
+		return Constants::PERMISSION_READ;
+	}
+
+	public function isDeleted(): bool {
+		return false;
+	}
+
+	public function isShared(): bool {
+		return true;
+	}
+
+	public function isWritable(): bool {
+		return false;
+	}
+
+	public function isEnabled(): bool {
+		return $this->calendarInfo['{http://owncloud.org/ns}calendar-enabled'] ?? true;
+	}
+
+	public function delete(): void {
+		$this->federatedCalendar->delete();
+	}
+}
diff --git a/apps/dav/lib/CalDAV/Federation/FederatedCalendarMapper.php b/apps/dav/lib/CalDAV/Federation/FederatedCalendarMapper.php
index f2736ebddf3..26f71781c35 100644
--- a/apps/dav/lib/CalDAV/Federation/FederatedCalendarMapper.php
+++ b/apps/dav/lib/CalDAV/Federation/FederatedCalendarMapper.php
@@ -62,6 +62,9 @@ class FederatedCalendarMapper extends QBMapper {
 			return $this->findEntity($qb);
 		} catch (DoesNotExistException $e) {
 			return null;
+		} catch (MultipleObjectsReturnedException $e) {
+			// Should never happen
+			return null;
 		}
 	}
 
diff --git a/apps/dav/lib/CalDAV/Federation/FederatedCalendarProvider.php b/apps/dav/lib/CalDAV/Federation/FederatedCalendarProvider.php
index e6fa8f73edc..b7f13654287 100644
--- a/apps/dav/lib/CalDAV/Federation/FederatedCalendarProvider.php
+++ b/apps/dav/lib/CalDAV/Federation/FederatedCalendarProvider.php
@@ -23,7 +23,7 @@ class FederatedCalendarProvider implements ICalendarProvider {
 		if (!empty($calendarUris)) {
 			$calendars = array_filter(
 				$calendars,
-				static fn(FederatedCalendar $calendar) => in_array(
+				static fn(FederatedCalendarImpl $calendar) => in_array(
 					$calendar->getUri(),
 					$calendarUris,
 					true,
diff --git a/apps/dav/lib/CalDAV/Federation/FederatedCalendarService.php b/apps/dav/lib/CalDAV/Federation/FederatedCalendarService.php
index 9e76b1facb4..0173a986ba3 100644
--- a/apps/dav/lib/CalDAV/Federation/FederatedCalendarService.php
+++ b/apps/dav/lib/CalDAV/Federation/FederatedCalendarService.php
@@ -16,16 +16,16 @@ class FederatedCalendarService {
 	}
 
 	public function createFederatedCalendar(
-		FederatedCalendar $calendar,
-		string $principalUri,
+		FederatedCalendarImpl $calendar,
+		string                $principalUri,
 	): void {
 		$entity = $this->federatedCalendarToEntity($calendar, $principalUri);
 		$this->federatedCalendarsMapper->insert($entity);
 	}
 
 	private function federatedCalendarToEntity(
-		FederatedCalendar $calendar,
-		string $principalUri,
+		FederatedCalendarImpl $calendar,
+		string                $principalUri,
 	): FederatedCalendarEntity {
 		$entity = new FederatedCalendarEntity();
 		$entity->setPrincipalUri($principalUri);
diff --git a/apps/dav/lib/CalDAV/Federation/FederatedCalendar_actual.php b/apps/dav/lib/CalDAV/Federation/FederatedCalendar_actual.php
deleted file mode 100644
index deeb70b871e..00000000000
--- a/apps/dav/lib/CalDAV/Federation/FederatedCalendar_actual.php
+++ /dev/null
@@ -1,45 +0,0 @@
-<?php
-
-declare(strict_types=1);
-
-/**
- * SPDX-FileCopyrightText: 2025 Nextcloud GmbH and Nextcloud contributors
- * SPDX-License-Identifier: AGPL-3.0-or-later
- */
-
-namespace OCA\DAV\CalDAV\Federation;
-
-use OCA\DAV\CalDAV\CalDavBackend;
-use OCA\DAV\CalDAV\Calendar;
-use OCP\IConfig;
-use OCP\IL10N;
-use Psr\Log\LoggerInterface;
-use Sabre\CalDAV\Backend;
-
-class FederatedCalendar_actual extends Calendar {
-	public function __construct(
-		Backend\BackendInterface $caldavBackend,
-		$calendarInfo,
-		IL10N $l10n,
-		IConfig $config,
-		LoggerInterface $logger,
-		private FederatedCalendarMapper $federatedCalendarMapper,
-	) {
-		parent::__construct($caldavBackend, $calendarInfo, $l10n, $config, $logger);
-	}
-
-	public function delete() {
-		$this->federatedCalendarMapper->deleteById($this->getResourceId());
-	}
-
-	protected function getCalendarType(): int {
-		return CalDavBackend::CALENDAR_TYPE_FEDERATED;
-	}
-
-	/*
-	public function canWrite() {
-		// TODO: implement read-write sharing
-		return false;
-	}
-	*/
-}
diff --git a/apps/dav/lib/CalDAV/Federation/Protocol/CalendarFederationProtocolV1.php b/apps/dav/lib/CalDAV/Federation/Protocol/CalendarFederationProtocolV1.php
index 360d00c32ec..c21b3c5585c 100644
--- a/apps/dav/lib/CalDAV/Federation/Protocol/CalendarFederationProtocolV1.php
+++ b/apps/dav/lib/CalDAV/Federation/Protocol/CalendarFederationProtocolV1.php
@@ -16,11 +16,13 @@ class CalendarFederationProtocolV1 implements ICalendarFederationProtocol {
 	public const PROP_DISPLAY_NAME = 'displayName';
 	public const PROP_COLOR = 'color';
 	public const PROP_ACCESS = 'access';
+	public const PROP_COMPONENTS = 'components';
 
 	private string $url = '';
 	private string $displayName = '';
 	private ?string $color = null;
 	private int $access = 0;
+	private string $components = '';
 
 	/**
 	 * @throws CalendarProtocolParseException If parsing the raw protocol array fails.
@@ -45,16 +47,23 @@ class CalendarFederationProtocolV1 implements ICalendarFederationProtocol {
 			throw new CalendarProtocolParseException('Color is set but not a string');
 		}
 
+		// TODO: remove access until we have read-write support?
 		$access = $rawProtocol[self::PROP_ACCESS] ?? null;
 		if (!is_int($access)) {
 			throw new CalendarProtocolParseException('Access is missing or not an integer');
 		}
 
+		$components = $rawProtocol[self::PROP_COMPONENTS] ?? null;
+		if (!is_string($components)) {
+			throw new CalendarProtocolParseException('Supported calendar components are missing or not a string');
+		}
+
 		$protocol = new self();
 		$protocol->setUrl($url);
 		$protocol->setDisplayName($displayName);
 		$protocol->setColor($color);
 		$protocol->setAccess($access);
+		$protocol->setComponents($components);
 		return $protocol;
 	}
 
@@ -66,6 +75,7 @@ class CalendarFederationProtocolV1 implements ICalendarFederationProtocol {
 			self::PROP_DISPLAY_NAME => $this->getDisplayName(),
 			self::PROP_COLOR => $this->getColor(),
 			self::PROP_ACCESS => $this->getAccess(),
+			self::PROP_COMPONENTS => $this->getComponents(),
 		];
 	}
 
@@ -105,5 +115,13 @@ class CalendarFederationProtocolV1 implements ICalendarFederationProtocol {
 	public function setAccess(int $access): void {
 		$this->access = $access;
 	}
+
+	public function getComponents(): string {
+		return $this->components;
+	}
+
+	public function setComponents(string $components): void {
+		$this->components = $components;
+	}
 }
 
diff --git a/apps/dav/lib/CalDAV/Federation/RemoteUserCalendarHome.php b/apps/dav/lib/CalDAV/Federation/RemoteUserCalendarHome.php
index 32aee7f9771..af65142b3c9 100644
--- a/apps/dav/lib/CalDAV/Federation/RemoteUserCalendarHome.php
+++ b/apps/dav/lib/CalDAV/Federation/RemoteUserCalendarHome.php
@@ -24,21 +24,28 @@ use Sabre\DAV\Exception\NotFound;
 use Sabre\DAV\Node;
 
 class RemoteUserCalendarHome extends CalendarHome {
-	//private CalDavBackend $calDavBackend;
 	private readonly IL10N $l10n;
 	private readonly IConfig $config;
 	private readonly LoggerInterface $logger;
+	private readonly FederatedCalendarMapper $federatedCalendarMapper;
 
 	public function __construct(Backend\BackendInterface $caldavBackend, $principalInfo) {
 		parent::__construct($caldavBackend, $principalInfo);
 
-		//$this->calDavBackend = $caldavBackend;
+		// TODO: inject?
 		$this->l10n = Server::get(IL10NFactory::class)->get(Application::APP_ID);
 		$this->config = Server::get(IConfig::class);
 		$this->logger = Server::get(LoggerInterface::class);
+		$this->federatedCalendarMapper = Server::get(FederatedCalendarMapper::class);
 	}
 
 	public function getChild($name) {
+		// Usually, this should be optimized, but we can simply query all children here.
+		// Shares are selected by the sharee's principal, so there will be exactly one row for each
+		// calendar from this instance which has been shared with that particular remote user.
+		// Unless many calendars from this instance are shared with a single remote user, this
+		// should never be a performance concern.
+
 		/** @var Node[] $children */
 		$children = $this->getChildren();
 		foreach ($children as $child) {
@@ -47,6 +54,7 @@ class RemoteUserCalendarHome extends CalendarHome {
 			}
 		}
 
+
 		throw new NotFound("Node with name $name could not be found");
 	}
 
@@ -55,23 +63,27 @@ class RemoteUserCalendarHome extends CalendarHome {
 			return [];
 		}
 
-		$shares = $this->caldavBackend->getSharesByShareePrincipal($this->principalInfo['uri']);
-
 		$children = [];
+
+		$shares = $this->caldavBackend->getSharesByShareePrincipal($this->principalInfo['uri']);
 		foreach ($shares as $share) {
+			// Type Should always be "calendar" as the sharing service is scoped to calendars.
+			// Just to be sure ...
 			if ($share['type'] !== 'calendar') {
 				continue;
 			}
 
 			$calendar = $this->caldavBackend->getCalendarById($share['resourceid']);
-			$calendar['{' . \OCA\DAV\DAV\Sharing\Plugin::NS_OWNCLOUD . '}read-only'] = 1; // TODO: do not force read-only here
+			// TODO: implement read-write sharing
+			$calendar['{' . \OCA\DAV\DAV\Sharing\Plugin::NS_OWNCLOUD . '}read-only'] = 1;
 			$calendar['{' . \OCA\DAV\DAV\Sharing\Plugin::NS_OWNCLOUD . '}owner-principal'] = $this->principalInfo['uri'];
-			$children[] = new Calendar(
+			$children[] = new FederatedCalendar(
 				$this->caldavBackend,
 				$calendar,
 				$this->l10n,
 				$this->config,
 				$this->logger,
+				$this->federatedCalendarMapper,
 			);
 		}
 
diff --git a/apps/dav/lib/CalDAV/Federation/RemoteUserPrincipalParser.php b/apps/dav/lib/CalDAV/Federation/RemoteUserPrincipalParser.php
new file mode 100644
index 00000000000..f0a9f8e0c49
--- /dev/null
+++ b/apps/dav/lib/CalDAV/Federation/RemoteUserPrincipalParser.php
@@ -0,0 +1,18 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * SPDX-FileCopyrightText: 2025 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace OCA\DAV\CalDAV\Federation;
+
+class RemoteUserPrincipalParser {
+
+	public function parseEncodedPrincipal() {
+
+	}
+
+}
diff --git a/apps/dav/lib/CalDAV/Principal/RemoteUserCollection.php b/apps/dav/lib/CalDAV/Principal/RemoteUserCollection.php
index b8917262e3a..a6d1a3c294a 100644
--- a/apps/dav/lib/CalDAV/Principal/RemoteUserCollection.php
+++ b/apps/dav/lib/CalDAV/Principal/RemoteUserCollection.php
@@ -11,13 +11,10 @@ namespace OCA\DAV\CalDAV\Principal;
 
 use OCA\DAV\DAV\RemoteUserPrincipalBackend;
 use OCA\DAV\DAV\Sharing\SharingMapper;
-use OCP\Server;
 use Sabre\DAV\Exception\NotFound;
-//use Sabre\DAV\SimpleCollection;
 
 class RemoteUserCollection extends \Sabre\DAV\Collection {
-	private readonly SharingMapper $sharingMapper;
-	private bool $hasCachedAllChildren;
+	private bool $hasCachedAllChildren = false;
 
 	/** @var RemoteUser[] */
 	private array $children = [];
@@ -27,12 +24,8 @@ class RemoteUserCollection extends \Sabre\DAV\Collection {
 
 	public function __construct(
 		private readonly RemoteUserPrincipalBackend $principalBackend,
+		private readonly SharingMapper $sharingMapper,
 	) {
-		// TODO: inject
-		$this->sharingMapper = Server::get(SharingMapper::class);
-
-		//$children = $this->loadChildren();
-		//parent::__construct('remote-users', $children);
 	}
 
 	public function getName() {
@@ -58,9 +51,7 @@ class RemoteUserCollection extends \Sabre\DAV\Collection {
 	}
 
 	private function loadChildren(): array {
-		// TODO: do we need the resource type here as an argument?
 		$rows = $this->sharingMapper->getRemoteUserPrincipalUris('calendar');
-
 		return array_map(fn (array $row) => $this->rowToRemoteUser($row['principaluri']), $rows);
 	}
 
@@ -68,8 +59,7 @@ class RemoteUserCollection extends \Sabre\DAV\Collection {
 		if (isset($this->childrenByName[$name])) {
 			$child = $this->childrenByName[$name];
 			if ($child === null) {
-				// TODO: add message
-				throw new NotFound();
+				throw new NotFound("Principal not found: $name");
 			}
 
 			return $child;
@@ -82,14 +72,19 @@ class RemoteUserCollection extends \Sabre\DAV\Collection {
 			}
 		}
 
+		// TODO: check the following claim
+		// It makes sense to load and cache only a single principal here as there are two main usage
+		// patterns: Either all principals are loaded via getChildren() (when listing) or a single,
+		// specific one is requested by path.
 		$principalUri = "principals/remote-users/$name";
-		// TODO: do we need the resource type here as an argument?
 		if ($this->sharingMapper->hasRemoteUserPrincipalUri('calendar', $principalUri)) {
 			$remoteUser = $this->rowToRemoteUser($principalUri);
 			$this->childrenByName[$name] = $remoteUser;
 			return $remoteUser;
 		}
 
+		// Skip next search
+		$this->childrenByName[$name] = null;
 		throw new NotFound();
 	}
 
diff --git a/apps/dav/lib/CalDAV/Sharing/Backend.php b/apps/dav/lib/CalDAV/Sharing/Backend.php
index 2403cafa18b..71bbbf237f3 100644
--- a/apps/dav/lib/CalDAV/Sharing/Backend.php
+++ b/apps/dav/lib/CalDAV/Sharing/Backend.php
@@ -31,4 +31,8 @@ class Backend extends SharingBackend {
 	) {
 		parent::__construct($this->userManager, $this->groupManager, $this->principalBackend, $this->remoteUserPrincipalBackend, $this->cacheFactory, $this->service, $this->federationSharingService, $this->logger);
 	}
+
+	public function getShareByCalendarName(string $principal, string $calendarName): array {
+		return $this->service->getShareByCalendarName($principal, $calendarName);
+	}
 }
diff --git a/apps/dav/lib/CalDAV/Sharing/Service.php b/apps/dav/lib/CalDAV/Sharing/Service.php
index 4f0554f09bd..67315b1673f 100644
--- a/apps/dav/lib/CalDAV/Sharing/Service.php
+++ b/apps/dav/lib/CalDAV/Sharing/Service.php
@@ -18,4 +18,7 @@ class Service extends SharingService {
 	) {
 		parent::__construct($mapper);
 	}
+
+	public function getShareByCalendarName(string $principal, string $calendarName): array {
+	}
 }
diff --git a/apps/dav/lib/Command/CreateCalendar.php b/apps/dav/lib/Command/CreateCalendar.php
index 033b5f8d347..afcae136822 100644
--- a/apps/dav/lib/Command/CreateCalendar.php
+++ b/apps/dav/lib/Command/CreateCalendar.php
@@ -9,6 +9,7 @@ namespace OCA\DAV\Command;
 
 use OC\KnownUser\KnownUserService;
 use OCA\DAV\CalDAV\CalDavBackend;
+use OCA\DAV\CalDAV\Federation\FederatedCalendarMapper;
 use OCA\DAV\CalDAV\Proxy\ProxyMapper;
 use OCA\DAV\CalDAV\Sharing\Backend;
 use OCA\DAV\Connector\Sabre\Principal;
@@ -80,6 +81,7 @@ class CreateCalendar extends Command {
 			$dispatcher,
 			$config,
 			Server::get(Backend::class),
+			Server::get(FederatedCalendarMapper::class),
 		);
 		$caldav->createCalendar("principals/users/$user", $name, []);
 		return self::SUCCESS;
diff --git a/apps/dav/lib/DAV/RemoteUserPrincipalBackend.php b/apps/dav/lib/DAV/RemoteUserPrincipalBackend.php
index 16053062107..0be289d343e 100644
--- a/apps/dav/lib/DAV/RemoteUserPrincipalBackend.php
+++ b/apps/dav/lib/DAV/RemoteUserPrincipalBackend.php
@@ -9,44 +9,62 @@ declare(strict_types=1);
 
 namespace OCA\DAV\DAV;
 
+use OCA\DAV\DAV\Sharing\SharingMapper;
 use OCP\Federation\ICloudIdManager;
-use OCP\Server;
 use Sabre\DAVACL\PrincipalBackend\BackendInterface;
 
 class RemoteUserPrincipalBackend implements BackendInterface {
 	public const PRINCIPAL_PREFIX = 'principals/remote-users';
 
-	private readonly ICloudIdManager $cloudIdManager;
+	private bool $hasCachedAllChildren = false;
 
-	public function __construct() {
-		// TODO: inject
-		$this->cloudIdManager = Server::get(ICloudIdManager::class);
+	/** @var array<string, mixed>[] */
+	private array $principals = [];
+
+	/** @var array<string, array<string, mixed>|null> */
+	private array $principalsByPath = [];
+
+	public function __construct(
+		private readonly ICloudIdManager $cloudIdManager,
+		private readonly SharingMapper $sharingMapper,
+	) {
 	}
 
 	public function getPrincipalsByPrefix($prefixPath) {
-		// We don't know about all the remote principals on all remote instances
-		return [];
+		if ($prefixPath !== self::PRINCIPAL_PREFIX) {
+			return [];
+		}
+
+		if (!$this->hasCachedAllChildren) {
+			$this->loadChildren();
+			$this->hasCachedAllChildren = true;
+		}
+
+		return $this->principals;
 	}
 
 	public function getPrincipalByPath($path) {
-		if (!str_starts_with($path, self::PRINCIPAL_PREFIX . '/')) {
+		[$prefix] = \Sabre\Uri\split($path);
+		if ($prefix !== self::PRINCIPAL_PREFIX) {
 			return null;
 		}
 
-		[,, $encodedPrincipal] = explode('/', $path);
-		[$encodedCloudId, $scope] = explode('|', base64_decode($encodedPrincipal));
-		try {
-			$cloudId = $this->cloudIdManager->resolveCloudId($encodedCloudId);
-		} catch (\InvalidArgumentException $e) {
+		if (isset($this->principalsByPath[$path])) {
+			return $this->principalsByPath[$path];
+		}
+
+		// TODO: check the following claim
+		// It makes sense to load and cache only a single principal here as there are two main usage
+		// patterns: Either all principals are loaded via getChildren() (when listing) or a single,
+		// specific one is requested by path.
+		if (!$this->sharingMapper->hasShareWithPrincipalUri('calendar', $path)) {
+			$this->principalsByPath[$path] = null;
 			return null;
 		}
 
-		return [
-			'uri' => $path,
-			'{DAV:}displayname' => $cloudId->getDisplayId(),
-			'{http://nextcloud.com/ns}scope' => $scope,
-			//'{http://nextcloud.com/ns}federated-by' => $cloudId->getId(),
-		];
+		$principal = $this->principalUriToPrincipal($path);
+		$this->principalsByPath[$path] = $principal;
+		return $principal;
 	}
 
 	public function updatePrincipal($path, \Sabre\DAV\PropPatch $propPatch) {
@@ -84,6 +102,42 @@ class RemoteUserPrincipalBackend implements BackendInterface {
 	}
 
 	public function setGroupMemberSet($principal, array $members) {
-		throw new \Sabre\DAV\Exception('Setting members of the group is not supported yet');
+		throw new \Sabre\DAV\Exception('Adding members to remote user is not supported');
+	}
+
+	/**
+	 * @psalm-return list<string, string> [$cloudId, $scope]
+	 */
+	private function decodeRemoteUserPrincipalName(string $name): array {
+		[$cloudId, $scope] = explode('|', base64_decode($name));
+		return [$cloudId, $scope];
+	}
+
+	/**
+	 * @return array<string, array>
+	 */
+	private function principalUriToPrincipal(string $principalUri): array {
+		[, $name] = \Sabre\Uri\split($principalUri);
+		[$encodedCloudId, $scope] = $this->decodeRemoteUserPrincipalName($name);
+		$cloudId = $this->cloudIdManager->resolveCloudId($encodedCloudId);
+		return [
+			'uri' => $principalUri,
+			'{DAV:}displayname' => $cloudId->getDisplayId(),
+			'{http://nextcloud.com/ns}cloud-id' => $cloudId,
+			'{http://nextcloud.com/ns}federation-scope' => $scope,
+		];
+	}
+
+	private function loadChildren(): array {
+		$rows = $this->sharingMapper->getPrincipalUrisByPrefix('calendar', self::PRINCIPAL_PREFIX);
+		$this->principals = array_map(
+			fn (array $row) => $this->principalUriToPrincipal($row['principaluri']),
+			$rows,
+		);
+
+		$this->principalsByPath = [];
+		foreach ($this->principals as $child) {
+			$this->principalsByPath[$child['uri']] = $child;
+		}
 	}
 }
diff --git a/apps/dav/lib/DAV/Sharing/SharingMapper.php b/apps/dav/lib/DAV/Sharing/SharingMapper.php
index e3da42e0123..64767af5421 100644
--- a/apps/dav/lib/DAV/Sharing/SharingMapper.php
+++ b/apps/dav/lib/DAV/Sharing/SharingMapper.php
@@ -7,6 +7,7 @@ declare(strict_types=1);
  */
 namespace OCA\DAV\DAV\Sharing;
 
+use OCP\DB\Exception;
 use OCP\DB\QueryBuilder\IQueryBuilder;
 use OCP\IDBConnection;
 
@@ -148,12 +149,23 @@ class SharingMapper {
 			->executeStatement();
 	}
 
-	public function hasRemoteUserPrincipalUri(string $resourceType, string $principalUri): bool {
+	/**
+	 * @throws \OCP\DB\Exception
+	 */
+	public function hasShareWithPrincipalUri(string $resourceType, string $principalUri): bool {
 		$query = $this->db->getQueryBuilder();
 		$result = $query->selectDistinct($query->func()->count('*'))
 			->from('dav_shares')
-			->where($query->expr()->eq('principaluri', $query->createNamedParameter($principalUri, IQueryBuilder::PARAM_STR), IQueryBuilder::PARAM_STR))
-			->andWhere($query->expr()->eq('type', $query->createNamedParameter($resourceType, IQueryBuilder::PARAM_STR), IQueryBuilder::PARAM_STR))
+			->where($query->expr()->eq(
+				'principaluri',
+				$query->createNamedParameter($principalUri, IQueryBuilder::PARAM_STR),
+				IQueryBuilder::PARAM_STR,
+			))
+			->andWhere($query->expr()->eq(
+				'type',
+				$query->createNamedParameter($resourceType, IQueryBuilder::PARAM_STR),
+				IQueryBuilder::PARAM_STR,
+			))
 			->executeQuery();
 
 		$count = (int)$result->fetchOne();
@@ -162,12 +174,24 @@ class SharingMapper {
 		return $count > 0;
 	}
 
-	public function getRemoteUserPrincipalUris(string $resourceType): array {
+	/**
+	 * @return array{principaluri: string}[]
+	 * @throws \OCP\DB\Exception
+	 */
+	public function getPrincipalUrisByPrefix(string $resourceType, string $prefix): array {
 		$query = $this->db->getQueryBuilder();
 		$result = $query->selectDistinct('principaluri')
 			->from('dav_shares')
-			->where($query->expr()->like('principaluri', $query->createNamedParameter('principals/remote-users/%')))
-			->andWhere($query->expr()->eq('type', $query->createNamedParameter($resourceType)))
+			->where($query->expr()->like(
+				'principaluri',
+				$query->createNamedParameter("$prefix/%", IQueryBuilder::PARAM_STR),
+				IQueryBuilder::PARAM_STR,
+			))
+			->andWhere($query->expr()->eq(
+				'type',
+				$query->createNamedParameter($resourceType, IQueryBuilder::PARAM_STR)),
+				IQueryBuilder::PARAM_STR,
+			)
 			->executeQuery();
 
 		$rows = $result->fetchAll();
diff --git a/apps/dav/lib/Migration/Version1034Date20250605132605.php b/apps/dav/lib/Migration/Version1034Date20250605132605.php
index 3267ea80be0..57e478a6ac3 100644
--- a/apps/dav/lib/Migration/Version1034Date20250605132605.php
+++ b/apps/dav/lib/Migration/Version1034Date20250605132605.php
@@ -84,6 +84,10 @@ class Version1034Date20250605132605 extends SimpleMigrationStep {
 				'notnull' => true,
 				'length' => 255,
 			]);
+			$federatedCalendarsTable->addColumn('components', Types::STRING, [
+				'notnull' => true,
+				'length' => 255,
+			]);
 			$federatedCalendarsTable->setPrimaryKey(['id']);
 		}
 
diff --git a/apps/dav/lib/RootCollection.php b/apps/dav/lib/RootCollection.php
index 4fc682ceace..07d5649b015 100644
--- a/apps/dav/lib/RootCollection.php
+++ b/apps/dav/lib/RootCollection.php
@@ -11,8 +11,8 @@ use OC\KnownUser\KnownUserService;
 use OCA\DAV\AppInfo\PluginManager;
 use OCA\DAV\CalDAV\CalDavBackend;
 use OCA\DAV\CalDAV\CalendarRoot;
+use OCA\DAV\CalDAV\Federation\FederatedCalendarMapper;
 use OCA\DAV\CalDAV\Principal\Collection;
-use OCA\DAV\CalDAV\Principal\RemoteUserCollection;
 use OCA\DAV\CalDAV\Proxy\ProxyMapper;
 use OCA\DAV\CalDAV\PublicCalendarRoot;
 use OCA\DAV\CalDAV\ResourceBooking\ResourcePrincipalBackend;
@@ -78,7 +78,7 @@ class RootCollection extends SimpleCollection {
 		$groupPrincipalBackend = new GroupPrincipalBackend($groupManager, $userSession, $shareManager, $config);
 		$calendarResourcePrincipalBackend = new ResourcePrincipalBackend($db, $userSession, $groupManager, $logger, $proxyMapper);
 		$calendarRoomPrincipalBackend = new RoomPrincipalBackend($db, $userSession, $groupManager, $logger, $proxyMapper);
-		$remoteUserPrincipalBackend = new RemoteUserPrincipalBackend();
+		$remoteUserPrincipalBackend = Server::get(RemoteUserPrincipalBackend::class);
 		// as soon as debug mode is enabled we allow listing of principals
 		$disableListing = !$config->getSystemValue('debug', false);
 
@@ -105,6 +105,7 @@ class RootCollection extends SimpleCollection {
 			$dispatcher,
 			$config,
 			$calendarSharingBackend,
+			Server::get(FederatedCalendarMapper::class),
 			false,
 		);
 		$userCalendarRoot = new CalendarRoot($userPrincipalBackend, $caldavBackend, 'principals/users', $logger);
diff --git a/apps/dav/tests/unit/CalDAV/AbstractCalDavBackend.php b/apps/dav/tests/unit/CalDAV/AbstractCalDavBackend.php
index c1d8e8609b6..40b8b455dd4 100644
--- a/apps/dav/tests/unit/CalDAV/AbstractCalDavBackend.php
+++ b/apps/dav/tests/unit/CalDAV/AbstractCalDavBackend.php
@@ -9,10 +9,13 @@ namespace OCA\DAV\Tests\unit\CalDAV;
 
 use OC\KnownUser\KnownUserService;
 use OCA\DAV\CalDAV\CalDavBackend;
+use OCA\DAV\CalDAV\Federation\FederatedCalendarMapper;
+use OCA\DAV\CalDAV\Federation\FederationSharingService;
 use OCA\DAV\CalDAV\Proxy\ProxyMapper;
 use OCA\DAV\CalDAV\Sharing\Backend as SharingBackend;
 use OCA\DAV\CalDAV\Sharing\Service;
 use OCA\DAV\Connector\Sabre\Principal;
+use OCA\DAV\DAV\RemoteUserPrincipalBackend;
 use OCA\DAV\DAV\Sharing\SharingMapper;
 use OCP\Accounts\IAccountManager;
 use OCP\App\IAppManager;
@@ -53,6 +56,9 @@ abstract class AbstractCalDavBackend extends TestCase {
 	private ISecureRandom $random;
 	protected SharingBackend $sharingBackend;
 	protected IDBConnection $db;
+	protected RemoteUserPrincipalBackend&MockObject $remoteUserPrincipalBackend;
+	protected FederationSharingService&MockObject $federationSharingService;
+	protected FederatedCalendarMapper&MockObject $federatedCalendarMapper;
 	public const UNIT_TEST_USER = 'principals/users/caldav-unit-test';
 	public const UNIT_TEST_USER1 = 'principals/users/caldav-unit-test1';
 	public const UNIT_TEST_GROUP = 'principals/groups/caldav-unit-test-group';
@@ -92,12 +98,17 @@ abstract class AbstractCalDavBackend extends TestCase {
 		$this->random = Server::get(ISecureRandom::class);
 		$this->logger = $this->createMock(LoggerInterface::class);
 		$this->config = $this->createMock(IConfig::class);
+		$this->remoteUserPrincipalBackend = $this->createMock(RemoteUserPrincipalBackend::class);
+		$this->federationSharingService = $this->createMock(FederationSharingService::class);
+		$this->federatedCalendarMapper = $this->createMock(FederatedCalendarMapper::class);
 		$this->sharingBackend = new SharingBackend(
 			$this->userManager,
 			$this->groupManager,
 			$this->principal,
+			$this->remoteUserPrincipalBackend,
 			$this->createMock(ICacheFactory::class),
 			new Service(new SharingMapper($this->db)),
+			$this->federationSharingService,
 			$this->logger);
 		$this->backend = new CalDavBackend(
 			$this->db,
@@ -108,6 +119,7 @@ abstract class AbstractCalDavBackend extends TestCase {
 			$this->dispatcher,
 			$this->config,
 			$this->sharingBackend,
+			$this->federatedCalendarMapper,
 			false,
 		);
 
diff --git a/apps/dav/tests/unit/CalDAV/PublicCalendarRootTest.php b/apps/dav/tests/unit/CalDAV/PublicCalendarRootTest.php
index 075681eff7f..4a640208d4a 100644
--- a/apps/dav/tests/unit/CalDAV/PublicCalendarRootTest.php
+++ b/apps/dav/tests/unit/CalDAV/PublicCalendarRootTest.php
@@ -7,6 +7,7 @@ namespace OCA\DAV\Tests\unit\CalDAV;
 
 use OCA\DAV\CalDAV\CalDavBackend;
 use OCA\DAV\CalDAV\Calendar;
+use OCA\DAV\CalDAV\Federation\FederatedCalendarMapper;
 use OCA\DAV\CalDAV\PublicCalendar;
 use OCA\DAV\CalDAV\PublicCalendarRoot;
 use OCA\DAV\Connector\Sabre\Principal;
@@ -18,6 +19,7 @@ use OCP\IL10N;
 use OCP\IUserManager;
 use OCP\Security\ISecureRandom;
 use OCP\Server;
+use PHPUnit\Framework\MockObject\MockObject;
 use Psr\Log\LoggerInterface;
 use Test\TestCase;
 
@@ -50,6 +52,8 @@ class PublicCalendarRootTest extends TestCase {
 	/** @var LoggerInterface */
 	private $logger;
 
+	protected FederatedCalendarMapper&MockObject $federatedCalendarMapper;
+
 	protected function setUp(): void {
 		parent::setUp();
 
@@ -59,6 +63,7 @@ class PublicCalendarRootTest extends TestCase {
 		$this->groupManager = $this->createMock(IGroupManager::class);
 		$this->random = Server::get(ISecureRandom::class);
 		$this->logger = $this->createMock(LoggerInterface::class);
+		$this->federatedCalendarMapper = $this->createMock(FederatedCalendarMapper::class);
 		$dispatcher = $this->createMock(IEventDispatcher::class);
 		$config = $this->createMock(IConfig::class);
 		$sharingBackend = $this->createMock(\OCA\DAV\CalDAV\Sharing\Backend::class);
@@ -80,6 +85,7 @@ class PublicCalendarRootTest extends TestCase {
 			$dispatcher,
 			$config,
 			$sharingBackend,
+			$this->federatedCalendarMapper,
 			false,
 		);
 		$this->l10n = $this->getMockBuilder(IL10N::class)
diff --git a/apps/federation/lib/Command/SyncFederationCalendars.php b/apps/federation/lib/Command/SyncFederationCalendars.php
index bca430068a8..4dc2ea7ba58 100644
--- a/apps/federation/lib/Command/SyncFederationCalendars.php
+++ b/apps/federation/lib/Command/SyncFederationCalendars.php
@@ -30,6 +30,10 @@ class SyncFederationCalendars extends Command {
 
 	protected function execute(InputInterface $input, OutputInterface $output): int {
 		$calendarCount = $this->federatedCalendarMapper->countAll();
+		if ($calendarCount === 0) {
+			$output->writeln('There are no federated calendars');
+			return 0;
+		}
 
 		$progress = new ProgressBar($output, $calendarCount);
 		$progress->start();