Allow apps to provide Calendars in user's calendarHome

Signed-off-by: Georg Ehrke <developer@georgehrke.com>

9 files changed, 590 insertions, 3 deletions

diff --git a/apps/dav/composer/composer/autoload_classmap.php b/apps/dav/composer/composer/autoload_classmap.php
index e6948d1151e..35fd9b76ac9 100644
--- a/apps/dav/composer/composer/autoload_classmap.php
+++ b/apps/dav/composer/composer/autoload_classmap.php
@@ -42,6 +42,8 @@ return array(
     'OCA\\DAV\\CalDAV\\CalendarObject' => $baseDir . '/../lib/CalDAV/CalendarObject.php',
     'OCA\\DAV\\CalDAV\\CalendarRoot' => $baseDir . '/../lib/CalDAV/CalendarRoot.php',
     'OCA\\DAV\\CalDAV\\ICSExportPlugin\\ICSExportPlugin' => $baseDir . '/../lib/CalDAV/ICSExportPlugin/ICSExportPlugin.php',
+    'OCA\\DAV\\CalDAV\\Integration\\ExternalCalendar' => $baseDir . '/../lib/CalDAV/Integration/ExternalCalendar.php',
+    'OCA\\DAV\\CalDAV\\Integration\\ICalendarProvider' => $baseDir . '/../lib/CalDAV/Integration/ICalendarProvider.php',
     'OCA\\DAV\\CalDAV\\InvitationResponse\\InvitationResponseServer' => $baseDir . '/../lib/CalDAV/InvitationResponse/InvitationResponseServer.php',
     'OCA\\DAV\\CalDAV\\Outbox' => $baseDir . '/../lib/CalDAV/Outbox.php',
     'OCA\\DAV\\CalDAV\\Plugin' => $baseDir . '/../lib/CalDAV/Plugin.php',
diff --git a/apps/dav/composer/composer/autoload_static.php b/apps/dav/composer/composer/autoload_static.php
index 4a26ceb040f..f23b425cd8f 100644
--- a/apps/dav/composer/composer/autoload_static.php
+++ b/apps/dav/composer/composer/autoload_static.php
@@ -57,6 +57,8 @@ class ComposerStaticInitDAV
         'OCA\\DAV\\CalDAV\\CalendarObject' => __DIR__ . '/..' . '/../lib/CalDAV/CalendarObject.php',
         'OCA\\DAV\\CalDAV\\CalendarRoot' => __DIR__ . '/..' . '/../lib/CalDAV/CalendarRoot.php',
         'OCA\\DAV\\CalDAV\\ICSExportPlugin\\ICSExportPlugin' => __DIR__ . '/..' . '/../lib/CalDAV/ICSExportPlugin/ICSExportPlugin.php',
+        'OCA\\DAV\\CalDAV\\Integration\\ExternalCalendar' => __DIR__ . '/..' . '/../lib/CalDAV/Integration/ExternalCalendar.php',
+        'OCA\\DAV\\CalDAV\\Integration\\ICalendarProvider' => __DIR__ . '/..' . '/../lib/CalDAV/Integration/ICalendarProvider.php',
         'OCA\\DAV\\CalDAV\\InvitationResponse\\InvitationResponseServer' => __DIR__ . '/..' . '/../lib/CalDAV/InvitationResponse/InvitationResponseServer.php',
         'OCA\\DAV\\CalDAV\\Outbox' => __DIR__ . '/..' . '/../lib/CalDAV/Outbox.php',
         'OCA\\DAV\\CalDAV\\Plugin' => __DIR__ . '/..' . '/../lib/CalDAV/Plugin.php',
diff --git a/apps/dav/lib/AppInfo/PluginManager.php b/apps/dav/lib/AppInfo/PluginManager.php
index 7063a150b4d..6a44332ddb2 100644
--- a/apps/dav/lib/AppInfo/PluginManager.php
+++ b/apps/dav/lib/AppInfo/PluginManager.php
@@ -25,6 +25,7 @@
 namespace OCA\DAV\AppInfo;
 
 use OC\ServerContainer;
+use OCA\DAV\CalDAV\Integration\ICalendarProvider;
 use OCP\App\IAppManager;
 use OCP\AppFramework\QueryException;
 
@@ -59,6 +60,13 @@ class PluginManager {
 	private $collections = null;
 
 	/**
+	 * Calendar plugins
+	 *
+	 * @var array
+	 */
+	private $calendarPlugins = null;
+
+	/**
 	 * Contstruct a PluginManager
 	 *
 	 * @param ServerContainer $container server container for resolving plugin classes
@@ -94,10 +102,23 @@ class PluginManager {
 	}
 
 	/**
+	 * Returns an array of app-registered calendar plugins
+	 *
+	 * @return array
+	 */
+	public function getCalendarPlugins():array {
+		if (null === $this->calendarPlugins) {
+			$this->populate();
+		}
+		return $this->calendarPlugins;
+	}
+
+	/**
 	 * Retrieve plugin and collection list and populate attributes
 	 */
 	private function populate() {
 		$this->plugins = [];
+		$this->calendarPlugins = [];
 		$this->collections = [];
 		foreach ($this->appManager->getInstalledApps() as $app) {
 			// load plugins and collections from info.xml
@@ -107,6 +128,7 @@ class PluginManager {
 			}
 			$this->loadSabrePluginsFromInfoXml($this->extractPluginList($info));
 			$this->loadSabreCollectionsFromInfoXml($this->extractCollectionList($info));
+			$this->loadSabreCalendarPluginsFromInfoXml($this->extractCalendarPluginList($info));
 		}
 	}
 
@@ -140,6 +162,21 @@ class PluginManager {
 		return [];
 	}
 
+	private function extractCalendarPluginList(array $array):array {
+		if (isset($array['sabre']) && is_array($array['sabre'])) {
+			if (isset($array['sabre']['calendar-plugins']) && is_array($array['sabre']['calendar-plugins'])) {
+				if (isset($array['sabre']['calendar-plugins']['plugin'])) {
+					$items = $array['sabre']['calendar-plugins']['plugin'];
+					if (!is_array($items)) {
+						$items = [$items];
+					}
+					return $items;
+				}
+			}
+		}
+		return [];
+	}
+
 	private function loadSabrePluginsFromInfoXml(array $plugins) {
 		foreach ($plugins as $plugin) {
 			try {
@@ -168,4 +205,24 @@ class PluginManager {
 		}
 	}
 
+	private function loadSabreCalendarPluginsFromInfoXml(array $calendarPlugins):void {
+		foreach ($calendarPlugins as $calendarPlugin) {
+			try {
+				$instantiatedCalendarPlugin = $this->container->query($calendarPlugin);
+			} catch (QueryException $e) {
+				if (class_exists($calendarPlugin)) {
+					$instantiatedCalendarPlugin = new $calendarPlugin();
+				} else {
+					throw new \Exception("Sabre calendar-plugin class '$calendarPlugin' is unknown and could not be loaded");
+				}
+			}
+
+			if (!($instantiatedCalendarPlugin instanceof ICalendarProvider)) {
+				throw new \Exception("Sabre calendar-plugin class '$calendarPlugin' does not implement ICalendarProvider interface");
+			}
+
+			$this->calendarPlugins[] = $instantiatedCalendarPlugin;
+		}
+	}
+
 }
diff --git a/apps/dav/lib/CalDAV/CalendarHome.php b/apps/dav/lib/CalDAV/CalendarHome.php
index b491c2304d2..ce29ed12db6 100644
--- a/apps/dav/lib/CalDAV/CalendarHome.php
+++ b/apps/dav/lib/CalDAV/CalendarHome.php
@@ -26,6 +26,9 @@
 
 namespace OCA\DAV\CalDAV;
 
+use OCA\DAV\AppInfo\PluginManager;
+use OCA\DAV\CalDAV\Integration\ExternalCalendar;
+use OCA\DAV\CalDAV\Integration\ICalendarProvider;
 use Sabre\CalDAV\Backend\BackendInterface;
 use Sabre\CalDAV\Backend\NotificationSupport;
 use Sabre\CalDAV\Backend\SchedulingSupport;
@@ -44,6 +47,9 @@ class CalendarHome extends \Sabre\CalDAV\CalendarHome {
 	/** @var \OCP\IConfig */
 	private $config;
 
+	/** @var PluginManager */
+	private $pluginManager;
+
 	/** @var bool */
 	private $returnCachedSubscriptions=false;
 
@@ -51,6 +57,10 @@ class CalendarHome extends \Sabre\CalDAV\CalendarHome {
 		parent::__construct($caldavBackend, $principalInfo);
 		$this->l10n = \OC::$server->getL10N('dav');
 		$this->config = \OC::$server->getConfig();
+		$this->pluginManager = new PluginManager(
+			\OC::$server,
+			\OC::$server->getAppManager()
+		);
 	}
 
 	/**
@@ -66,7 +76,7 @@ class CalendarHome extends \Sabre\CalDAV\CalendarHome {
 	function createExtendedCollection($name, MkCol $mkCol) {
 		$reservedNames = [BirthdayService::BIRTHDAY_CALENDAR_URI];
 
-		if (in_array($name, $reservedNames)) {
+		if (\in_array($name, $reservedNames, true) || ExternalCalendar::doesViolateReservedName($name)) {
 			throw new MethodNotAllowed('The resource you tried to create has a reserved name');
 		}
 
@@ -104,6 +114,14 @@ class CalendarHome extends \Sabre\CalDAV\CalendarHome {
 			}
 		}
 
+		foreach ($this->pluginManager->getCalendarPlugins() as $calendarPlugin) {
+			/** @var ICalendarProvider $calendarPlugin */
+			$calendars = $calendarPlugin->fetchAllForCalendarHome($this->principalInfo['uri']);
+			foreach ($calendars as $calendar) {
+				$objects[] = $calendar;
+			}
+		}
+
 		return $objects;
 	}
 
@@ -139,7 +157,21 @@ class CalendarHome extends \Sabre\CalDAV\CalendarHome {
 					return new Subscription($this->caldavBackend, $subscription);
 				}
 			}
+		}
+
+		if (ExternalCalendar::isAppGeneratedCalendar($name)) {
+			[$appId, $calendarUri] = ExternalCalendar::splitAppGeneratedCalendarUri($name);
 
+			foreach ($this->pluginManager->getCalendarPlugins() as $calendarPlugin) {
+				/** @var ICalendarProvider $calendarPlugin */
+				if ($calendarPlugin->getAppId() !== $appId) {
+					continue;
+				}
+
+				if ($calendarPlugin->hasCalendarInCalendarHome($this->principalInfo['uri'], $calendarUri)) {
+					return $calendarPlugin->getCalendarInCalendarHome($this->principalInfo['uri'], $calendarUri);
+				}
+			}
 		}
 
 		throw new NotFound('Node with name \'' . $name . '\' could not be found');
@@ -155,7 +187,7 @@ class CalendarHome extends \Sabre\CalDAV\CalendarHome {
 		return $this->caldavBackend->calendarSearch($principalUri, $filters, $limit, $offset);
 	}
 
-	
+
 	public function enableCachedSubscriptionsForThisRequest() {
 		$this->returnCachedSubscriptions = true;
 	}
diff --git a/apps/dav/lib/CalDAV/Integration/ExternalCalendar.php b/apps/dav/lib/CalDAV/Integration/ExternalCalendar.php
new file mode 100644
index 00000000000..88d43f0bb55
--- /dev/null
+++ b/apps/dav/lib/CalDAV/Integration/ExternalCalendar.php
@@ -0,0 +1,132 @@
+<?php
+/**
+ * @copyright 2020, Georg Ehrke <oc.list@georgehrke.com>
+ *
+ * @author Georg Ehrke <oc.list@georgehrke.com>
+ *
+ * @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\Integration;
+
+use Sabre\CalDAV;
+use Sabre\DAV;
+
+/**
+ * Class ExternalCalendar
+ *
+ * @package OCA\DAV\CalDAV\Integration
+ * @since 19.0.0
+ */
+abstract class ExternalCalendar implements CalDAV\ICalendar, DAV\IProperties {
+
+	/** @var string */
+	private const PREFIX = 'app-generated';
+
+	/**
+	 * @var string
+	 *
+	 * Double dash is a valid delimiter,
+	 * because it will always split the calendarURIs correctly:
+	 * - our prefix contains only one dash and won't be split
+	 * - appIds are not allowed to contain dashes as per spec:
+	 * > must contain only lowercase ASCII characters and underscore
+	 * - explode has a limit of three, so even if the app-generated
+	 *   calendar uri has double dashes, it won't be split
+	 */
+	private const DELIMITER = '--';
+
+	/** @var string */
+	private $appId;
+
+	/** @var string */
+	private $calendarUri;
+
+	/**
+	 * ExternalCalendar constructor.
+	 *
+	 * @param string $appId
+	 * @param string $calendarUri
+	 */
+	public function __construct(string $appId, string $calendarUri) {
+		$this->appId = $appId;
+		$this->calendarUri = $calendarUri;
+	}
+
+	/**
+	 * @inheritDoc
+	 */
+	final public function getName() {
+		return implode(self::DELIMITER, [
+			self::PREFIX,
+			$this->appId,
+			$this->calendarUri,
+		]);
+	}
+
+	/**
+	 * @inheritDoc
+	 */
+	final public function setName($name) {
+		throw new DAV\Exception\MethodNotAllowed('Renaming calendars is not yet supported');
+	}
+
+	/**
+	 * @inheritDoc
+	 */
+	final public function createDirectory($name) {
+		throw new DAV\Exception\MethodNotAllowed('Creating collections in calendar objects is not allowed');
+
+	}
+
+	/**
+	 * Checks whether the calendar uri is app-generated
+	 *
+	 * @param string $calendarUri
+	 * @return bool
+	 */
+	public static function isAppGeneratedCalendar(string $calendarUri):bool {
+		return strpos($calendarUri, self::PREFIX) === 0 && substr_count($calendarUri, self::DELIMITER) >= 2;
+	}
+
+	/**
+	 * Splits an app-generated calendar-uri into appId and calendarUri
+	 *
+	 * @param string $calendarUri
+	 * @return array
+	 */
+	public static function splitAppGeneratedCalendarUri(string $calendarUri):array {
+		$array = array_slice(explode(self::DELIMITER, $calendarUri, 3), 1);
+		// Check the array has expected amount of elements
+		// and none of them is an empty string
+		if (\count($array) !== 2 || \in_array('', $array, true)) {
+			throw new \InvalidArgumentException('Provided calendar uri was not app-generated');
+		}
+
+		return $array;
+	}
+
+	/**
+	 * Checks whether a calendar-name, the user wants to create, violates
+	 * the reserved name for calendar uris
+	 *
+	 * @param string $calendarUri
+	 * @return bool
+	 */
+	public static function doesViolateReservedName(string $calendarUri):bool {
+		return strpos($calendarUri, self::PREFIX) === 0;
+	}
+}
diff --git a/apps/dav/lib/CalDAV/Integration/ICalendarProvider.php b/apps/dav/lib/CalDAV/Integration/ICalendarProvider.php
new file mode 100644
index 00000000000..29f5f113ef5
--- /dev/null
+++ b/apps/dav/lib/CalDAV/Integration/ICalendarProvider.php
@@ -0,0 +1,73 @@
+<?php
+/**
+ * @copyright 2020, Georg Ehrke <oc.list@georgehrke.com>
+ *
+ * @author Georg Ehrke <oc.list@georgehrke.com>
+ *
+ * @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\Integration;
+
+use Sabre\CalDAV\ICalendar;
+
+/**
+ * Interface ICalendarProvider
+ *
+ * @package OCA\DAV\CalDAV\Integration
+ * @since 19.0.0
+ */
+interface ICalendarProvider {
+
+	/**
+	 * Provides the appId of the plugin
+	 *
+	 * @since 19.0.0
+	 * @return string AppId
+	 */
+	public function getAppId(): string;
+
+	/**
+	 * Fetches all calendars for a given principal uri
+	 *
+	 * @since 19.0.0
+	 * @param string $principalUri E.g. principals/users/user1
+	 * @return ExternalCalendar[] Array of all calendars
+	 */
+	public function fetchAllForCalendarHome(string $principalUri): array;
+
+	/**
+	 * Checks whether plugin has a calendar for a given principalUri and calendarUri
+	 *
+	 * @since 19.0.0
+	 * @param string $principalUri E.g. principals/users/user1
+	 * @param string $calendarUri E.g. personal
+	 * @return bool True if calendar for principalUri and calendarUri exists, false otherwise
+	 */
+	public function hasCalendarInCalendarHome(string $principalUri, string $calendarUri): bool;
+
+	/**
+	 * Fetches a calendar for a given principalUri and calendarUri
+	 * Returns null if calendar does not exist
+	 *
+	 * @since 19.0.0
+	 * @param string $principalUri E.g. principals/users/user1
+	 * @param string $calendarUri E.g. personal
+	 * @return ExternalCalendar|null Calendar if it exists, null otherwise
+	 */
+	public function getCalendarInCalendarHome(string $principalUri, string $calendarUri): ?ExternalCalendar;
+
+}
diff --git a/apps/dav/tests/unit/AppInfo/PluginManagerTest.php b/apps/dav/tests/unit/AppInfo/PluginManagerTest.php
index e1b852b6a80..0d181f914a1 100644
--- a/apps/dav/tests/unit/AppInfo/PluginManagerTest.php
+++ b/apps/dav/tests/unit/AppInfo/PluginManagerTest.php
@@ -28,6 +28,7 @@ namespace OCA\DAV\Tests\unit\AppInfo;
 use OC\App\AppManager;
 use OC\ServerContainer;
 use OCA\DAV\AppInfo\PluginManager;
+use OCA\DAV\CalDAV\Integration\ICalendarProvider;
 use Test\TestCase;
 
 /**
@@ -53,6 +54,12 @@ class PluginManagerTest extends TestCase {
 						'\OCA\DAV\ADavApp\PluginTwo',
 					],
 				],
+				'calendar-plugins' => [
+					'plugin' => [
+						'\OCA\DAV\ADavApp\CalendarPluginOne',
+						'\OCA\DAV\ADavApp\CalendarPluginTwo',
+					],
+				],
 				'collections' => [
 					'collection' => [
 						'\OCA\DAV\ADavApp\CollectionOne',
@@ -67,6 +74,9 @@ class PluginManagerTest extends TestCase {
 				'plugins' => [
 					'plugin' => '\OCA\DAV\ADavApp2\PluginOne',
 				],
+				'calendar-plugins' => [
+					'plugin' => '\OCA\DAV\ADavApp2\CalendarPluginOne',
+				],
 				'collections' => [
 					'collection' => '\OCA\DAV\ADavApp2\CollectionOne',
 				],
@@ -81,13 +91,20 @@ class PluginManagerTest extends TestCase {
 
 		$pluginManager = new PluginManager($server, $appManager);
 
+		$calendarPlugin1 = $this->createMock(ICalendarProvider::class);
+		$calendarPlugin2 = $this->createMock(ICalendarProvider::class);
+		$calendarPlugin3 = $this->createMock(ICalendarProvider::class);
+
 		$server->method('query')
 			->will($this->returnValueMap([
 				['\OCA\DAV\ADavApp\PluginOne', true, 'dummyplugin1'],
 				['\OCA\DAV\ADavApp\PluginTwo', true, 'dummyplugin2'],
+				['\OCA\DAV\ADavApp\CalendarPluginOne', true, $calendarPlugin1],
+				['\OCA\DAV\ADavApp\CalendarPluginTwo', true, $calendarPlugin2],
 				['\OCA\DAV\ADavApp\CollectionOne', true, 'dummycollection1'],
 				['\OCA\DAV\ADavApp\CollectionTwo', true, 'dummycollection2'],
 				['\OCA\DAV\ADavApp2\PluginOne', true, 'dummy2plugin1'],
+				['\OCA\DAV\ADavApp2\CalendarPluginOne', true, $calendarPlugin3],
 				['\OCA\DAV\ADavApp2\CollectionOne', true, 'dummy2collection1'],
 			]));
 
@@ -96,6 +113,11 @@ class PluginManagerTest extends TestCase {
 			'dummyplugin2',
 			'dummy2plugin1',
 		];
+		$expectedCalendarPlugins = [
+			$calendarPlugin1,
+			$calendarPlugin2,
+			$calendarPlugin3,
+		];
 		$expectedCollections = [
 			'dummycollection1',
 			'dummycollection2',
@@ -103,6 +125,7 @@ class PluginManagerTest extends TestCase {
 		];
 
 		$this->assertEquals($expectedPlugins, $pluginManager->getAppPlugins());
+		$this->assertEquals($expectedCalendarPlugins, $pluginManager->getCalendarPlugins());
 		$this->assertEquals($expectedCollections, $pluginManager->getAppCollections());
 	}
 }
diff --git a/apps/dav/tests/unit/CalDAV/CalendarHomeTest.php b/apps/dav/tests/unit/CalDAV/CalendarHomeTest.php
index c811cb8b5a1..364286edd4b 100644
--- a/apps/dav/tests/unit/CalDAV/CalendarHomeTest.php
+++ b/apps/dav/tests/unit/CalDAV/CalendarHomeTest.php
@@ -24,8 +24,14 @@
 
 namespace OCA\DAV\Tests\unit\CalDAV;
 
+use OCA\DAV\AppInfo\PluginManager;
 use OCA\DAV\CalDAV\CalDavBackend;
 use OCA\DAV\CalDAV\CalendarHome;
+use OCA\DAV\CalDAV\Integration\ExternalCalendar;
+use OCA\DAV\CalDAV\Integration\ICalendarProvider;
+use OCA\DAV\CalDAV\Outbox;
+use Sabre\CalDAV\Schedule\Inbox;
+use Sabre\DAV\Exception\NotFound;
 use Sabre\DAV\MkCol;
 use Test\TestCase;
 
@@ -37,6 +43,9 @@ class CalendarHomeTest extends TestCase {
 	/** @var array */
 	private $principalInfo = [];
 
+	/** @var PluginManager */
+	private $pluginManager;
+
 	/** @var CalendarHome */
 	private $calendarHome;
 
@@ -47,9 +56,16 @@ class CalendarHomeTest extends TestCase {
 		$this->principalInfo = [
 			'uri' => 'user-principal-123',
 		];
+		$this->pluginManager = $this->createMock(PluginManager::class);
 
 		$this->calendarHome = new CalendarHome($this->backend,
 			$this->principalInfo);
+
+		// Replace PluginManager with our mock
+		$reflection = new \ReflectionClass($this->calendarHome);
+		$reflectionProperty = $reflection->getProperty('pluginManager');
+		$reflectionProperty->setAccessible(true);
+		$reflectionProperty->setValue($this->calendarHome, $this->pluginManager);
 	}
 
 	public function testCreateCalendarValidName() {
@@ -69,7 +85,6 @@ class CalendarHomeTest extends TestCase {
 		$this->calendarHome->createExtendedCollection('name123', $mkCol);
 	}
 
-	
 	public function testCreateCalendarReservedName() {
 		$this->expectException(\Sabre\DAV\Exception\MethodNotAllowed::class);
 		$this->expectExceptionMessage('The resource you tried to create has a reserved name');
@@ -79,4 +94,136 @@ class CalendarHomeTest extends TestCase {
 
 		$this->calendarHome->createExtendedCollection('contact_birthdays', $mkCol);
 	}
+
+	public function testCreateCalendarReservedNameAppGenerated() {
+		$this->expectException(\Sabre\DAV\Exception\MethodNotAllowed::class);
+		$this->expectExceptionMessage('The resource you tried to create has a reserved name');
+
+		/** @var MkCol | \PHPUnit_Framework_MockObject_MockObject $mkCol */
+		$mkCol = $this->createMock(MkCol::class);
+
+		$this->calendarHome->createExtendedCollection('app-generated--example--foo-1', $mkCol);
+	}
+
+	public function testGetChildren():void {
+		$this->backend
+			->expects($this->at(0))
+			->method('getCalendarsForUser')
+			->with('user-principal-123')
+			->willReturn([]);
+
+		$this->backend
+			->expects($this->at(1))
+			->method('getSubscriptionsForUser')
+			->with('user-principal-123')
+			->willReturn([]);
+
+		$calendarPlugin1 = $this->createMock(ICalendarProvider::class);
+		$calendarPlugin1
+			->expects($this->once())
+			->method('fetchAllForCalendarHome')
+			->with('user-principal-123')
+			->willReturn(['plugin1calendar1', 'plugin1calendar2']);
+
+		$calendarPlugin2 = $this->createMock(ICalendarProvider::class);
+		$calendarPlugin2
+			->expects($this->once())
+			->method('fetchAllForCalendarHome')
+			->with('user-principal-123')
+			->willReturn(['plugin2calendar1', 'plugin2calendar2']);
+
+		$this->pluginManager
+			->expects($this->once())
+			->method('getCalendarPlugins')
+			->with()
+			->willReturn([$calendarPlugin1, $calendarPlugin2]);
+
+		$actual = $this->calendarHome->getChildren();
+
+		$this->assertCount(6, $actual);
+		$this->assertInstanceOf(Inbox::class, $actual[0]);
+		$this->assertInstanceOf(Outbox::class, $actual[1]);
+		$this->assertEquals('plugin1calendar1', $actual[2]);
+		$this->assertEquals('plugin1calendar2', $actual[3]);
+		$this->assertEquals('plugin2calendar1', $actual[4]);
+		$this->assertEquals('plugin2calendar2', $actual[5]);
+	}
+
+	public function testGetChildNonAppGenerated():void {
+		$this->backend
+			->expects($this->at(0))
+			->method('getCalendarsForUser')
+			->with('user-principal-123')
+			->willReturn([]);
+
+		$this->backend
+			->expects($this->at(1))
+			->method('getSubscriptionsForUser')
+			->with('user-principal-123')
+			->willReturn([]);
+
+		$this->pluginManager
+			->expects($this->never())
+			->method('getCalendarPlugins');
+
+		$this->expectException(\Sabre\DAV\Exception\NotFound::class);
+		$this->expectExceptionMessage('Node with name \'personal\' could not be found');
+
+		$this->calendarHome->getChild('personal');
+	}
+
+	public function testGetChildAppGenerated():void {
+		$this->backend
+			->expects($this->at(0))
+			->method('getCalendarsForUser')
+			->with('user-principal-123')
+			->willReturn([]);
+
+		$this->backend
+			->expects($this->at(1))
+			->method('getSubscriptionsForUser')
+			->with('user-principal-123')
+			->willReturn([]);
+
+		$calendarPlugin1 = $this->createMock(ICalendarProvider::class);
+		$calendarPlugin1
+			->expects($this->once())
+			->method('getAppId')
+			->with()
+			->willReturn('calendar_plugin_1');
+		$calendarPlugin1
+			->expects($this->never())
+			->method('hasCalendarInCalendarHome');
+		$calendarPlugin1
+			->expects($this->never())
+			->method('getCalendarInCalendarHome');
+
+		$externalCalendarMock = $this->createMock(ExternalCalendar::class);
+
+		$calendarPlugin2 = $this->createMock(ICalendarProvider::class);
+		$calendarPlugin2
+			->expects($this->once())
+			->method('getAppId')
+			->with()
+			->willReturn('calendar_plugin_2');
+		$calendarPlugin2
+			->expects($this->once())
+			->method('hasCalendarInCalendarHome')
+			->with('user-principal-123', 'calendar-uri-from-backend')
+			->willReturn(true);
+		$calendarPlugin2
+			->expects($this->once())
+			->method('getCalendarInCalendarHome')
+			->with('user-principal-123', 'calendar-uri-from-backend')
+			->willReturn($externalCalendarMock);
+
+		$this->pluginManager
+			->expects($this->once())
+			->method('getCalendarPlugins')
+			->with()
+			->willReturn([$calendarPlugin1, $calendarPlugin2]);
+
+		$actual = $this->calendarHome->getChild('app-generated--calendar_plugin_2--calendar-uri-from-backend');
+		$this->assertEquals($externalCalendarMock, $actual);
+	}
 }
diff --git a/apps/dav/tests/unit/CalDAV/Integration/ExternalCalendarTest.php b/apps/dav/tests/unit/CalDAV/Integration/ExternalCalendarTest.php
new file mode 100644
index 00000000000..a6698087155
--- /dev/null
+++ b/apps/dav/tests/unit/CalDAV/Integration/ExternalCalendarTest.php
@@ -0,0 +1,119 @@
+<?php
+/**
+ * @copyright 2020, Georg Ehrke <oc.list@georgehrke.com>
+ *
+ * @author Georg Ehrke <oc.list@georgehrke.com>
+ *
+ * @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\Tests\unit\CalDAV\Integration;
+
+use OCA\DAV\CalDAV\Integration\ExternalCalendar;
+use Test\TestCase;
+
+class ExternalCalendarTest extends TestCase {
+
+	private $abstractExternalCalendar;
+
+	protected function setUp(): void {
+		parent::setUp();
+
+		$this->abstractExternalCalendar =
+			$this->getMockForAbstractClass(ExternalCalendar::class, ['example-app-id', 'calendar-uri-in-backend']);
+	}
+
+	public function testGetName():void {
+		// Check that the correct name is returned
+		$this->assertEquals('app-generated--example-app-id--calendar-uri-in-backend',
+			$this->abstractExternalCalendar->getName());
+
+		// Check that the method is final and can't be overriden by other classes
+		$reflectionMethod = new \ReflectionMethod(ExternalCalendar::class, 'getName');
+		$this->assertTrue($reflectionMethod->isFinal());
+	}
+
+	public function testSetName():void {
+		// Check that the method is final and can't be overriden by other classes
+		$reflectionMethod = new \ReflectionMethod(ExternalCalendar::class, 'setName');
+		$this->assertTrue($reflectionMethod->isFinal());
+
+		$this->expectException(\Sabre\DAV\Exception\MethodNotAllowed::class);
+		$this->expectExceptionMessage('Renaming calendars is not yet supported');
+
+		$this->abstractExternalCalendar->setName('other-name');
+	}
+
+	public function createDirectory():void {
+		// Check that the method is final and can't be overriden by other classes
+		$reflectionMethod = new \ReflectionMethod(ExternalCalendar::class, 'createDirectory');
+		$this->assertTrue($reflectionMethod->isFinal());
+
+		$this->expectException(\Sabre\DAV\Exception\MethodNotAllowed::class);
+		$this->expectExceptionMessage('Creating collections in calendar objects is not allowed');
+
+		$this->abstractExternalCalendar->createDirectory('other-name');
+	}
+
+	public function testIsAppGeneratedCalendar():void {
+		$this->assertFalse(ExternalCalendar::isAppGeneratedCalendar('personal'));
+		$this->assertFalse(ExternalCalendar::isAppGeneratedCalendar('work'));
+		$this->assertFalse(ExternalCalendar::isAppGeneratedCalendar('contact_birthdays'));
+		$this->assertFalse(ExternalCalendar::isAppGeneratedCalendar('company'));
+		$this->assertFalse(ExternalCalendar::isAppGeneratedCalendar('app-generated'));
+		$this->assertFalse(ExternalCalendar::isAppGeneratedCalendar('app-generated--example'));
+
+		$this->assertTrue(ExternalCalendar::isAppGeneratedCalendar('app-generated--deck--board-1'));
+		$this->assertTrue(ExternalCalendar::isAppGeneratedCalendar('app-generated--example--foo-2'));
+		$this->assertTrue(ExternalCalendar::isAppGeneratedCalendar('app-generated--example--foo--2'));
+	}
+
+	/**
+	 * @dataProvider splitAppGeneratedCalendarUriDataProvider
+	 */
+	public function testSplitAppGeneratedCalendarUriInvalid(string $name):void {
+		$this->expectException(\InvalidArgumentException::class);
+		$this->expectExceptionMessage('Provided calendar uri was not app-generated');
+
+		ExternalCalendar::splitAppGeneratedCalendarUri($name);
+	}
+
+	public function splitAppGeneratedCalendarUriDataProvider():array {
+		return [
+			['personal'],
+			['foo_shared_by_admin'],
+			['contact_birthdays'],
+		];
+	}
+
+	public function testSplitAppGeneratedCalendarUri():void {
+		$this->assertEquals(['deck', 'board-1'], ExternalCalendar::splitAppGeneratedCalendarUri('app-generated--deck--board-1'));
+		$this->assertEquals(['example', 'foo-2'], ExternalCalendar::splitAppGeneratedCalendarUri('app-generated--example--foo-2'));
+		$this->assertEquals(['example', 'foo--2'], ExternalCalendar::splitAppGeneratedCalendarUri('app-generated--example--foo--2'));
+	}
+
+	public function testDoesViolateReservedName():void {
+		$this->assertFalse(ExternalCalendar::doesViolateReservedName('personal'));
+		$this->assertFalse(ExternalCalendar::doesViolateReservedName('work'));
+		$this->assertFalse(ExternalCalendar::doesViolateReservedName('contact_birthdays'));
+		$this->assertFalse(ExternalCalendar::doesViolateReservedName('company'));
+
+		$this->assertTrue(ExternalCalendar::doesViolateReservedName('app-generated'));
+		$this->assertTrue(ExternalCalendar::doesViolateReservedName('app-generated-calendar'));
+		$this->assertTrue(ExternalCalendar::doesViolateReservedName('app-generated--deck-123'));
+	}
+}