Calendar export and import

Signed-off-by: Christopher Ng <chrng8@gmail.com>

9 files changed, 717 insertions, 0 deletions

diff --git a/apps/dav/appinfo/info.xml b/apps/dav/appinfo/info.xml
index 8462ed1816d..88c4ee03ac3 100644
--- a/apps/dav/appinfo/info.xml
+++ b/apps/dav/appinfo/info.xml
@@ -56,6 +56,8 @@
 		<command>OCA\DAV\Command\SyncBirthdayCalendar</command>
 		<command>OCA\DAV\Command\SyncSystemAddressBook</command>
 		<command>OCA\DAV\Command\RemoveInvalidShares</command>
+		<command>OCA\DAV\Command\ExportCalendars</command>
+		<command>OCA\DAV\Command\ImportCalendar</command>
 	</commands>
 
 	<settings>
diff --git a/apps/dav/composer/composer/autoload_classmap.php b/apps/dav/composer/composer/autoload_classmap.php
index 9cfefaed1c8..bf0fe9cbf75 100644
--- a/apps/dav/composer/composer/autoload_classmap.php
+++ b/apps/dav/composer/composer/autoload_classmap.php
@@ -124,6 +124,8 @@ return array(
     'OCA\\DAV\\Command\\CreateAddressBook' => $baseDir . '/../lib/Command/CreateAddressBook.php',
     'OCA\\DAV\\Command\\CreateCalendar' => $baseDir . '/../lib/Command/CreateCalendar.php',
     'OCA\\DAV\\Command\\DeleteCalendar' => $baseDir . '/../lib/Command/DeleteCalendar.php',
+    'OCA\\DAV\\Command\\ExportCalendars' => $baseDir . '/../lib/Command/ExportCalendars.php',
+    'OCA\\DAV\\Command\\ImportCalendar' => $baseDir . '/../lib/Command/ImportCalendar.php',
     'OCA\\DAV\\Command\\ListCalendars' => $baseDir . '/../lib/Command/ListCalendars.php',
     'OCA\\DAV\\Command\\MoveCalendar' => $baseDir . '/../lib/Command/MoveCalendar.php',
     'OCA\\DAV\\Command\\RemoveInvalidShares' => $baseDir . '/../lib/Command/RemoveInvalidShares.php',
@@ -299,4 +301,7 @@ return array(
     'OCA\\DAV\\Upload\\UploadFile' => $baseDir . '/../lib/Upload/UploadFile.php',
     'OCA\\DAV\\Upload\\UploadFolder' => $baseDir . '/../lib/Upload/UploadFolder.php',
     'OCA\\DAV\\Upload\\UploadHome' => $baseDir . '/../lib/Upload/UploadHome.php',
+    'OCA\\DAV\\UserMigration\\CalendarMigrator' => $baseDir . '/../lib/UserMigration/CalendarMigrator.php',
+    'OCA\\DAV\\UserMigration\\CalendarMigratorException' => $baseDir . '/../lib/UserMigration/CalendarMigratorException.php',
+    'OCA\\DAV\\UserMigration\\InvalidCalendarException' => $baseDir . '/../lib/UserMigration/InvalidCalendarException.php',
 );
diff --git a/apps/dav/composer/composer/autoload_static.php b/apps/dav/composer/composer/autoload_static.php
index 01c24fe38c8..18bfd642960 100644
--- a/apps/dav/composer/composer/autoload_static.php
+++ b/apps/dav/composer/composer/autoload_static.php
@@ -139,6 +139,8 @@ class ComposerStaticInitDAV
         'OCA\\DAV\\Command\\CreateAddressBook' => __DIR__ . '/..' . '/../lib/Command/CreateAddressBook.php',
         'OCA\\DAV\\Command\\CreateCalendar' => __DIR__ . '/..' . '/../lib/Command/CreateCalendar.php',
         'OCA\\DAV\\Command\\DeleteCalendar' => __DIR__ . '/..' . '/../lib/Command/DeleteCalendar.php',
+        'OCA\\DAV\\Command\\ExportCalendars' => __DIR__ . '/..' . '/../lib/Command/ExportCalendars.php',
+        'OCA\\DAV\\Command\\ImportCalendar' => __DIR__ . '/..' . '/../lib/Command/ImportCalendar.php',
         'OCA\\DAV\\Command\\ListCalendars' => __DIR__ . '/..' . '/../lib/Command/ListCalendars.php',
         'OCA\\DAV\\Command\\MoveCalendar' => __DIR__ . '/..' . '/../lib/Command/MoveCalendar.php',
         'OCA\\DAV\\Command\\RemoveInvalidShares' => __DIR__ . '/..' . '/../lib/Command/RemoveInvalidShares.php',
@@ -314,6 +316,9 @@ class ComposerStaticInitDAV
         'OCA\\DAV\\Upload\\UploadFile' => __DIR__ . '/..' . '/../lib/Upload/UploadFile.php',
         'OCA\\DAV\\Upload\\UploadFolder' => __DIR__ . '/..' . '/../lib/Upload/UploadFolder.php',
         'OCA\\DAV\\Upload\\UploadHome' => __DIR__ . '/..' . '/../lib/Upload/UploadHome.php',
+        'OCA\\DAV\\UserMigration\\CalendarMigrator' => __DIR__ . '/..' . '/../lib/UserMigration/CalendarMigrator.php',
+        'OCA\\DAV\\UserMigration\\CalendarMigratorException' => __DIR__ . '/..' . '/../lib/UserMigration/CalendarMigratorException.php',
+        'OCA\\DAV\\UserMigration\\InvalidCalendarException' => __DIR__ . '/..' . '/../lib/UserMigration/InvalidCalendarException.php',
     );
 
     public static function getInitializer(ClassLoader $loader)
diff --git a/apps/dav/lib/CalDAV/CalendarImpl.php b/apps/dav/lib/CalDAV/CalendarImpl.php
index 1c36db68cca..87bed32428f 100644
--- a/apps/dav/lib/CalDAV/CalendarImpl.php
+++ b/apps/dav/lib/CalDAV/CalendarImpl.php
@@ -70,6 +70,13 @@ class CalendarImpl implements ICreateFromString {
 	}
 
 	/**
+	 * {@inheritDoc}
+	 */
+	public function getUri() {
+		return $this->calendarInfo['uri'];
+	}
+
+	/**
 	 * In comparison to getKey() this function returns a human readable (maybe translated) name
 	 * @return null|string
 	 * @since 13.0.0
diff --git a/apps/dav/lib/Command/ExportCalendars.php b/apps/dav/lib/Command/ExportCalendars.php
new file mode 100644
index 00000000000..770d6edc425
--- /dev/null
+++ b/apps/dav/lib/Command/ExportCalendars.php
@@ -0,0 +1,83 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * @copyright 2022 Christopher Ng <chrng8@gmail.com>
+ *
+ * @author Christopher Ng <chrng8@gmail.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\Command;
+
+use OC\Core\Command\Base;
+use OCA\DAV\UserMigration\CalendarMigrator;
+use OCA\DAV\UserMigration\CalendarMigratorException;
+use OCP\IUser;
+use OCP\IUserManager;
+use Symfony\Component\Console\Input\InputArgument;
+use Symfony\Component\Console\Input\InputInterface;
+use Symfony\Component\Console\Output\OutputInterface;
+
+class ExportCalendars extends Base {
+
+	/** @var IUserManager */
+	private $userManager;
+
+	/** @var CalendarMigrator */
+	private $calendarMigrator;
+
+	public function __construct(
+		IUserManager $userManager,
+		CalendarMigrator $calendarMigrator
+	) {
+		parent::__construct();
+		$this->userManager = $userManager;
+		$this->calendarMigrator = $calendarMigrator;
+	}
+
+	protected function configure() {
+		$this
+			->setName('dav:export-calendars')
+			->setDescription('Export the calendars of a user')
+			->addArgument(
+				'user',
+				InputArgument::REQUIRED,
+				'User to export',
+			);
+	}
+
+	protected function execute(InputInterface $input, OutputInterface $output): int {
+		$user = $this->userManager->get($input->getArgument('user'));
+
+		if (!$user instanceof IUser) {
+			$output->writeln('<error>User ' . $input->getArgument('user') . ' does not exist</error>');
+			return 1;
+		}
+
+		try {
+			$this->calendarMigrator->export($user, $output);
+		} catch (CalendarMigratorException $e) {
+			$output->writeln('<error>' . $e->getMessage() . '</error>');
+			return $e->getCode() !== 0 ? (int)$e->getCode() : 1;
+		}
+
+		return 0;
+	}
+}
diff --git a/apps/dav/lib/Command/ImportCalendar.php b/apps/dav/lib/Command/ImportCalendar.php
new file mode 100644
index 00000000000..193ecc3b29b
--- /dev/null
+++ b/apps/dav/lib/Command/ImportCalendar.php
@@ -0,0 +1,94 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * @copyright 2022 Christopher Ng <chrng8@gmail.com>
+ *
+ * @author Christopher Ng <chrng8@gmail.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\Command;
+
+use OC\Core\Command\Base;
+use OCA\DAV\UserMigration\CalendarMigrator;
+use OCA\DAV\UserMigration\CalendarMigratorException;
+use OCP\IUser;
+use OCP\IUserManager;
+use Symfony\Component\Console\Input\InputArgument;
+use Symfony\Component\Console\Input\InputInterface;
+use Symfony\Component\Console\Output\OutputInterface;
+
+class ImportCalendar extends Base {
+
+	/** @var IUserManager */
+	private $userManager;
+
+	/** @var CalendarMigrator */
+	private $calendarMigrator;
+
+	public function __construct(
+		IUserManager $userManager,
+		CalendarMigrator $calendarMigrator
+	) {
+		parent::__construct();
+		$this->userManager = $userManager;
+		$this->calendarMigrator = $calendarMigrator;
+	}
+
+	protected function configure() {
+		$this
+			->setName('dav:import-calendar')
+			->setDescription('Import a calendar to a user\'s account')
+			->addArgument(
+				'user',
+				InputArgument::REQUIRED,
+				'User to import the calendar for',
+			)
+			->addArgument(
+				'path',
+				InputArgument::REQUIRED,
+				'Path to the *.ics file',
+			);
+	}
+
+	protected function execute(InputInterface $input, OutputInterface $output): int {
+		$user = $this->userManager->get($input->getArgument('user'));
+
+		[
+			'basename' => $filename,
+			'dirname' => $srcDir,
+		] = pathinfo($input->getArgument('path'));
+
+
+		if (!$user instanceof IUser) {
+			$output->writeln('<error>User ' . $input->getArgument('user') . ' does not exist</error>');
+			return 1;
+		}
+
+		try {
+			$this->calendarMigrator->import($user, $srcDir, $filename, $output);
+		} catch (CalendarMigratorException $e) {
+			$output->writeln('<error>' . $e->getMessage() . '</error>');
+			return $e->getCode() !== 0 ? (int)$e->getCode() : 1;
+		}
+
+		return 0;
+	}
+}
diff --git a/apps/dav/lib/UserMigration/CalendarMigrator.php b/apps/dav/lib/UserMigration/CalendarMigrator.php
new file mode 100644
index 00000000000..c1252d7517a
--- /dev/null
+++ b/apps/dav/lib/UserMigration/CalendarMigrator.php
@@ -0,0 +1,457 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * @copyright 2022 Christopher Ng <chrng8@gmail.com>
+ *
+ * @author Christopher Ng <chrng8@gmail.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\UserMigration;
+
+use function Safe\fopen;
+use function Safe\substr;
+use OC\Files\Filesystem;
+use OC\Files\View;
+use OCA\DAV\CalDAV\CalDavBackend;
+use OCA\DAV\CalDAV\ICSExportPlugin\ICSExportPlugin;
+use OCA\DAV\CalDAV\Plugin as CalDAVPlugin;
+use OCA\DAV\Connector\Sabre\CachingTree;
+use OCA\DAV\Connector\Sabre\Server as SabreDavServer;
+use OCA\DAV\RootCollection;
+use OCP\Calendar\ICalendar;
+use OCP\Calendar\IManager as ICalendarManager;
+use OCP\Defaults;
+use OCP\IL10N;
+use OCP\IUser;
+use Sabre\DAV\Exception\BadRequest;
+use Sabre\DAV\Version as SabreDavVersion;
+use Sabre\VObject\Component as VObjectComponent;
+use Sabre\VObject\Component\VCalendar;
+use Sabre\VObject\Component\VTimeZone;
+use Sabre\VObject\Property\ICalendar\DateTime;
+use Sabre\VObject\Reader as VObjectReader;
+use Sabre\VObject\UUIDUtil;
+use Safe\Exceptions\FilesystemException;
+use Symfony\Component\Console\Output\OutputInterface;
+
+class CalendarMigrator {
+
+	private CalDavBackend $calDavBackend;
+
+	private ICalendarManager $calendarManager;
+
+	// ICSExportPlugin is injected as the mergeObjects() method is required and is not to be used as a SabreDAV server plugin
+	private ICSExportPlugin $icsExportPlugin;
+
+	private Defaults $defaults;
+
+	private IL10N $l10n;
+
+	private SabreDavServer $sabreDavServer;
+
+	public const USERS_URI_ROOT = 'principals/users/';
+
+	public const FILENAME_EXT = '.ics';
+
+	public const MIGRATED_URI_PREFIX = 'migrated-';
+
+	public function __construct(
+		CalDavBackend $calDavBackend,
+		ICalendarManager $calendarManager,
+		ICSExportPlugin $icsExportPlugin,
+		Defaults $defaults,
+		IL10N $l10n
+	) {
+		$this->calDavBackend = $calDavBackend;
+		$this->calendarManager = $calendarManager;
+		$this->icsExportPlugin = $icsExportPlugin;
+		$this->defaults = $defaults;
+		$this->l10n = $l10n;
+
+		$root = new RootCollection();
+		$this->sabreDavServer = new SabreDavServer(new CachingTree($root));
+		$this->sabreDavServer->addPlugin(new CalDAVPlugin());
+	}
+
+	public function getPrincipalUri(IUser $user): string {
+		return CalendarMigrator::USERS_URI_ROOT . $user->getUID();
+	}
+
+	/**
+	 * @return array{name: string, vCalendar: VCalendar}
+	 *
+	 * @throws CalendarMigratorException
+	 * @throws InvalidCalendarException
+	 */
+	public function getCalendarExportData(IUser $user, ICalendar $calendar): array {
+		$userId = $user->getUID();
+		$calendarId = $calendar->getKey();
+		$calendarInfo = $this->calDavBackend->getCalendarById($calendarId);
+
+		if (!empty($calendarInfo)) {
+			$uri = $calendarInfo['uri'];
+			$path = CalDAVPlugin::CALENDAR_ROOT . "/$userId/$uri";
+
+			// NOTE implementation below based on \Sabre\CalDAV\ICSExportPlugin::httpGet()
+
+			$properties = $this->sabreDavServer->getProperties($path, [
+				'{DAV:}resourcetype',
+				'{DAV:}displayname',
+				'{http://sabredav.org/ns}sync-token',
+				'{DAV:}sync-token',
+				'{http://apple.com/ns/ical/}calendar-color',
+			]);
+
+			// Filter out invalid (e.g. deleted) calendars
+			if (!isset($properties['{DAV:}resourcetype']) || !$properties['{DAV:}resourcetype']->is('{' . CalDAVPlugin::NS_CALDAV . '}calendar')) {
+				throw new InvalidCalendarException();
+			}
+
+			// NOTE implementation below based on \Sabre\CalDAV\ICSExportPlugin::generateResponse()
+
+			$calDataProp = '{' . CalDAVPlugin::NS_CALDAV . '}calendar-data';
+			$calendarNode = $this->sabreDavServer->tree->getNodeForPath($path);
+			$nodes = $this->sabreDavServer->getPropertiesIteratorForPath($path, [$calDataProp], 1);
+
+			$blobs = [];
+			foreach ($nodes as $node) {
+				if (isset($node[200][$calDataProp])) {
+					$blobs[$node['href']] = $node[200][$calDataProp];
+				}
+			}
+
+			$mergedCalendar = $this->icsExportPlugin->mergeObjects(
+				$properties,
+				$blobs,
+			);
+
+			return [
+				'name' => $calendarNode->getName(),
+				'vCalendar' => $mergedCalendar,
+			];
+		}
+
+		throw new CalendarMigratorException();
+	}
+
+	/**
+	 * @return array<int, array{name: string, vCalendar: VCalendar}>
+	 *
+	 * @throws CalendarMigratorException
+	 */
+	public function getCalendarExports(IUser $user): array {
+		$principalUri = $this->getPrincipalUri($user);
+
+		return array_values(array_filter(array_map(
+			function (ICalendar $calendar) use ($user) {
+				try {
+					return $this->getCalendarExportData($user, $calendar);
+				} catch (CalendarMigratorException $e) {
+					throw new CalendarMigratorException();
+				} catch (InvalidCalendarException $e) {
+					// Allow this exception as invalid (e.g. deleted) calendars are not to be exported
+				}
+			},
+			$this->calendarManager->getCalendarsForPrincipal($principalUri),
+		)));
+	}
+
+	public function getUniqueCalendarUri(IUser $user, string $initialCalendarUri): string {
+		$principalUri = $this->getPrincipalUri($user);
+		$initialCalendarUri = substr($initialCalendarUri, 0, strlen(CalendarMigrator::MIGRATED_URI_PREFIX)) === CalendarMigrator::MIGRATED_URI_PREFIX
+			? $initialCalendarUri
+			: CalendarMigrator::MIGRATED_URI_PREFIX . $initialCalendarUri;
+
+		$existingCalendarUris = array_map(
+			fn (ICalendar $calendar) => $calendar->getUri(),
+			$this->calendarManager->getCalendarsForPrincipal($principalUri),
+		);
+
+		$calendarUri = $initialCalendarUri;
+		$acc = 1;
+		while (in_array($calendarUri, $existingCalendarUris, true)) {
+			$calendarUri = $initialCalendarUri . "-$acc";
+			++$acc;
+		}
+
+		return $calendarUri;
+	}
+
+	/**
+	 * @throws CalendarMigratorException
+	 */
+	protected function writeExport(IUser $user, string $data, string $destDir, string $filename, OutputInterface $output): void {
+		$userId = $user->getUID();
+
+		\OC::$server->getUserFolder($userId);
+		Filesystem::initMountPoints($userId);
+
+		$view = new View();
+
+		if ($view->file_put_contents("$destDir/$filename", $data) === false) {
+			throw new CalendarMigratorException('Could not export calendar');
+		}
+
+		$output->writeln("<info>✅ Exported calendar of <$userId> into $destDir/$filename</info>");
+	}
+
+	public function export(IUser $user, OutputInterface $output): void {
+		$userId = $user->getUID();
+
+		try {
+			$calendarExports = $this->getCalendarExports($user);
+		} catch (CalendarMigratorException $e) {
+			$output->writeln("<error>Error exporting <$userId> calendars</error>");
+		}
+
+		if (empty($calendarExports)) {
+			$output->writeln("<info>User <$userId> has no calendars to export</info>");
+		}
+
+		/**
+		 * @var string $name
+		 * @var VCalendar $vCalendar
+		 */
+		foreach ($calendarExports as ['name' => $name, 'vCalendar' => $vCalendar]) {
+			// Set filename to sanitized calendar name appended with the date
+			$filename = preg_replace('/[^a-zA-Z0-9-_ ]/um', '', $name) . '_' . date('Y-m-d') . CalendarMigrator::FILENAME_EXT;
+
+			$this->writeExport(
+				$user,
+				$vCalendar->serialize(),
+				// TESTING directory does not automatically get created so just write to user directory, this will be put in a zip with all other user_migration data
+				// "/$userId/export/$appId",
+				"/$userId",
+				$filename,
+				$output,
+			);
+		}
+	}
+
+	/**
+	 * Return an associative array mapping Time Zone ID to VTimeZone component
+	 *
+	 * @return array<string, VTimeZone>
+	 */
+	public function getCalendarTimezones(VCalendar $vCalendar): array {
+		/** @var VTimeZone[] $calendarTimezones */
+		$calendarTimezones = array_values(array_filter(
+			$vCalendar->getComponents(),
+			fn ($component) => $component->name === 'VTIMEZONE',
+		));
+
+		/** @var array<string, VTimeZone> $calendarTimezoneMap */
+		$calendarTimezoneMap = [];
+		foreach ($calendarTimezones as $vTimeZone) {
+			$calendarTimezoneMap[$vTimeZone->getTimeZone()->getName()] = $vTimeZone;
+		}
+
+		return $calendarTimezoneMap;
+	}
+
+	/**
+	 * @return VTimeZone[]
+	 */
+	public function getTimezonesForComponent(VCalendar $vCalendar, VObjectComponent $component): array {
+		$componentTimezoneIds = [];
+
+		foreach ($component->children() as $child) {
+			if ($child instanceof DateTime && isset($child->parameters['TZID'])) {
+				$timezoneId = $child->parameters['TZID']->getValue();
+				if (!in_array($timezoneId, $componentTimezoneIds, true)) {
+					$componentTimezoneIds[] = $timezoneId;
+				}
+			}
+		}
+
+		$calendarTimezoneMap = $this->getCalendarTimezones($vCalendar);
+
+		return array_values(array_filter(array_map(
+			fn (string $timezoneId) => $calendarTimezoneMap[$timezoneId],
+			$componentTimezoneIds,
+		)));
+	}
+
+	public function sanitizeComponent(VObjectComponent $component): VObjectComponent {
+		// Operate on the component clone to prevent mutation of the original
+		$componentClone = clone $component;
+
+		// Remove RSVP parameters to prevent automatically sending invitation emails to attendees on import
+		foreach ($componentClone->children() as $child) {
+			if (
+				$child->name === 'ATTENDEE'
+				&& isset($child->parameters['RSVP'])
+			) {
+				unset($child->parameters['RSVP']);
+			}
+		}
+
+		return $componentClone;
+	}
+
+	/**
+	 * @return VObjectComponent[]
+	 */
+	public function getRequiredImportComponents(VCalendar $vCalendar, VObjectComponent $component): array {
+		$component = $this->sanitizeComponent($component);
+		/** @var array<int, VTimeZone> $timezoneComponents */
+		$timezoneComponents = $this->getTimezonesForComponent($vCalendar, $component);
+		return [
+			...$timezoneComponents,
+			$component,
+		];
+	}
+
+	public function initCalendarObject(): VCalendar {
+		$vCalendarObject = new VCalendar();
+		$vCalendarObject->PRODID = $this->sabreDavServer::$exposeVersion
+			? '-//SabreDAV//SabreDAV ' . SabreDavVersion::VERSION . '//EN'
+			: '-//SabreDAV//SabreDAV//EN';
+		return $vCalendarObject;
+	}
+
+	public function importCalendarObject(int $calendarId, VCalendar $vCalendarObject): void {
+		try {
+			$this->calDavBackend->createCalendarObject(
+				$calendarId,
+				UUIDUtil::getUUID() . CalendarMigrator::FILENAME_EXT,
+				$vCalendarObject->serialize(),
+				CalDavBackend::CALENDAR_TYPE_CALENDAR,
+			);
+		} catch (BadRequest $e) {
+			// Rollback creation of calendar on error
+			$this->calDavBackend->deleteCalendar($calendarId, true);
+		}
+	}
+
+	/**
+	 * @throws CalendarMigratorException
+	 */
+	public function importCalendar(IUser $user, string $filename, string $initialCalendarUri, VCalendar $vCalendar): void {
+		$principalUri = $this->getPrincipalUri($user);
+		$calendarUri = $this->getUniqueCalendarUri($user, $initialCalendarUri);
+
+		$calendarId = $this->calDavBackend->createCalendar($principalUri, $calendarUri, [
+			'{DAV:}displayname' => isset($vCalendar->{'X-WR-CALNAME'}) ? $vCalendar->{'X-WR-CALNAME'}->getValue() : $this->l10n->t('Migrated calendar (%1$s)', [$filename]),
+			'{http://apple.com/ns/ical/}calendar-color' => isset($vCalendar->{'X-APPLE-CALENDAR-COLOR'}) ? $vCalendar->{'X-APPLE-CALENDAR-COLOR'}->getValue() : $this->defaults->getColorPrimary(),
+			'components' => implode(
+				',',
+				array_reduce(
+					$vCalendar->getComponents(),
+					function (array $componentNames, VObjectComponent $component) {
+						/** @var array<int, string> $componentNames */
+						return !in_array($component->name, $componentNames, true)
+							? [...$componentNames, $component->name]
+							: $componentNames;
+					},
+					[],
+				)
+			),
+		]);
+
+		/** @var VObjectComponent[] $calendarComponents */
+		$calendarComponents = array_values(array_filter(
+			$vCalendar->getComponents(),
+			// VTIMEZONE components are handled separately and added to the calendar object only if depended on by the component
+			fn (VObjectComponent $component) => $component->name !== 'VTIMEZONE',
+		));
+
+		/** @var array<string, VObjectComponent[]> $groupedCalendarComponents */
+		$groupedCalendarComponents = [];
+		/** @var VObjectComponent[] $ungroupedCalendarComponents */
+		$ungroupedCalendarComponents = [];
+
+		foreach ($calendarComponents as $component) {
+			if (isset($component->UID)) {
+				$uid = $component->UID->getValue();
+				// Components with the same UID (e.g. recurring events) are grouped together into a single calendar object
+				if (isset($groupedCalendarComponents[$uid])) {
+					$groupedCalendarComponents[$uid][] = $component;
+				} else {
+					$groupedCalendarComponents[$uid] = [$component];
+				}
+			} else {
+				$ungroupedCalendarComponents[] = $component;
+			}
+		}
+
+		foreach ($groupedCalendarComponents as $uid => $components) {
+			// Construct and import a calendar object containing all components of a group
+			$vCalendarObject = $this->initCalendarObject();
+			foreach ($components as $component) {
+				foreach ($this->getRequiredImportComponents($vCalendar, $component) as $component) {
+					$vCalendarObject->add($component);
+				}
+			}
+			$this->importCalendarObject($calendarId, $vCalendarObject);
+		}
+
+		foreach ($ungroupedCalendarComponents as $component) {
+			// Construct and import a calendar object for a single component
+			$vCalendarObject = $this->initCalendarObject();
+			foreach ($this->getRequiredImportComponents($vCalendar, $component) as $component) {
+				$vCalendarObject->add($component);
+			}
+			$this->importCalendarObject($calendarId, $vCalendarObject);
+		}
+	}
+
+	/**
+	 * @throws FilesystemException
+	 * @throws CalendarMigratorException
+	 */
+	public function import(IUser $user, string $srcDir, string $filename, OutputInterface $output): void {
+		$userId = $user->getUID();
+
+		try {
+			/** @var VCalendar $vCalendar */
+			$vCalendar = VObjectReader::read(
+				fopen("$srcDir/$filename", 'r'),
+				VObjectReader::OPTION_FORGIVING,
+			);
+		} catch (FilesystemException $e) {
+			throw new FilesystemException("Failed to read file: \"$srcDir/$filename\"");
+		}
+
+		$problems = $vCalendar->validate();
+		if (empty($problems)) {
+			$splitFilename = explode('_', $filename, 2);
+			if (count($splitFilename) !== 2) {
+				$output->writeln("<error>Invalid filename, filename must be of the format: \"<calendar_name>_YYYY-MM-DD" . CalendarMigrator::FILENAME_EXT . "\"</error>");
+				throw new CalendarMigratorException();
+			}
+			[$initialCalendarUri, $suffix] = $splitFilename;
+
+			$this->importCalendar(
+				$user,
+				$filename,
+				$initialCalendarUri,
+				$vCalendar,
+			);
+
+			$vCalendar->destroy();
+
+			$output->writeln("<info>✅ Imported calendar \"$filename\" into account of <$userId></info>");
+		} else {
+			throw new CalendarMigratorException("Invalid data contained in \"$srcDir/$filename\"");
+		}
+	}
+}
diff --git a/apps/dav/lib/UserMigration/CalendarMigratorException.php b/apps/dav/lib/UserMigration/CalendarMigratorException.php
new file mode 100644
index 00000000000..91bac58ffac
--- /dev/null
+++ b/apps/dav/lib/UserMigration/CalendarMigratorException.php
@@ -0,0 +1,32 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * @copyright 2022 Christopher Ng <chrng8@gmail.com>
+ *
+ * @author Christopher Ng <chrng8@gmail.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\UserMigration;
+
+use Exception;
+
+class CalendarMigratorException extends Exception {
+}
diff --git a/apps/dav/lib/UserMigration/InvalidCalendarException.php b/apps/dav/lib/UserMigration/InvalidCalendarException.php
new file mode 100644
index 00000000000..0e42ef1bc20
--- /dev/null
+++ b/apps/dav/lib/UserMigration/InvalidCalendarException.php
@@ -0,0 +1,32 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * @copyright 2022 Christopher Ng <chrng8@gmail.com>
+ *
+ * @author Christopher Ng <chrng8@gmail.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\UserMigration;
+
+use Exception;
+
+class InvalidCalendarException extends Exception {
+}