<?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 OCA\DAV\AppInfo\Application;
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 OCP\UserMigration\IExportDestination;
use OCP\UserMigration\IImportSource;
use OCP\UserMigration\IMigrator;
use OCP\UserMigration\ISizeEstimationMigrator;
use OCP\UserMigration\TMigratorBasicVersionHandling;
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 Symfony\Component\Console\Output\NullOutput;
use Symfony\Component\Console\Output\OutputInterface;
use Throwable;
use function substr;

class CalendarMigrator implements IMigrator, ISizeEstimationMigrator {

	use TMigratorBasicVersionHandling;

	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;

	private const USERS_URI_ROOT = 'principals/users/';

	private const FILENAME_EXT = '.ics';

	private const MIGRATED_URI_PREFIX = 'migrated-';

	private const EXPORT_ROOT = Application::APP_ID . '/calendars/';

	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());
	}

	private function getPrincipalUri(IUser $user): string {
		return CalendarMigrator::USERS_URI_ROOT . $user->getUID();
	}

	/**
	 * @return array{name: string, vCalendar: VCalendar}
	 *
	 * @throws CalendarMigratorException
	 * @throws InvalidCalendarException
	 */
	private function getCalendarExportData(IUser $user, ICalendar $calendar, OutputInterface $output): array {
		$userId = $user->getUID();
		$uri = $calendar->getUri();
		$path = CalDAVPlugin::CALENDAR_ROOT . "/$userId/$uri";

		/**
		 * @see \Sabre\CalDAV\ICSExportPlugin::httpGet() implementation reference
		 */

		$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();
		}

		/**
		 * @see \Sabre\CalDAV\ICSExportPlugin::generateResponse() implementation reference
		 */

		$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,
		);

		$problems = $mergedCalendar->validate();
		if (!empty($problems)) {
			$output->writeln('Skipping calendar "' . $properties['{DAV:}displayname'] . '" containing invalid calendar data');
			throw new InvalidCalendarException();
		}

		return [
			'name' => $calendarNode->getName(),
			'vCalendar' => $mergedCalendar,
		];
	}

	/**
	 * @return array<int, array{name: string, vCalendar: VCalendar}>
	 *
	 * @throws CalendarMigratorException
	 */
	private function getCalendarExports(IUser $user, OutputInterface $output): array {
		$principalUri = $this->getPrincipalUri($user);

		return array_values(array_filter(array_map(
			function (ICalendar $calendar) use ($user, $output) {
				try {
					return $this->getCalendarExportData($user, $calendar, $output);
				} catch (InvalidCalendarException $e) {
					// Allow this exception as invalid (e.g. deleted) calendars are not to be exported
					return null;
				}
			},
			$this->calendarManager->getCalendarsForPrincipal($principalUri),
		)));
	}

	/**
	 * @throws InvalidCalendarException
	 */
	private 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;

		if ($initialCalendarUri === '') {
			throw new InvalidCalendarException();
		}

		$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;
	}

	/**
	 * {@inheritDoc}
	 */
	public function getEstimatedExportSize(IUser $user): int|float {
		$calendarExports = $this->getCalendarExports($user, new NullOutput());
		$calendarCount = count($calendarExports);

		// 150B for top-level properties
		$size = ($calendarCount * 150) / 1024;

		$componentCount = array_sum(array_map(
			function (array $data): int {
				/** @var VCalendar $vCalendar */
				$vCalendar = $data['vCalendar'];
				return count($vCalendar->getComponents());
			},
			$calendarExports,
		));

		// 450B for each component (events, todos, alarms, etc.)
		$size += ($componentCount * 450) / 1024;

		return ceil($size);
	}

	/**
	 * {@inheritDoc}
	 */
	public function export(IUser $user, IExportDestination $exportDestination, OutputInterface $output): void {
		$output->writeln('Exporting calendars into ' . CalendarMigrator::EXPORT_ROOT . '…');

		$calendarExports = $this->getCalendarExports($user, $output);

		if (empty($calendarExports)) {
			$output->writeln('No calendars to export…');
		}

		try {
			/**
			 * @var string $name
			 * @var VCalendar $vCalendar
			 */
			foreach ($calendarExports as ['name' => $name, 'vCalendar' => $vCalendar]) {
				// Set filename to sanitized calendar name
				$filename = preg_replace('/[^a-z0-9-_]/iu', '', $name) . CalendarMigrator::FILENAME_EXT;
				$exportPath = CalendarMigrator::EXPORT_ROOT . $filename;

				$exportDestination->addFileContents($exportPath, $vCalendar->serialize());
			}
		} catch (Throwable $e) {
			throw new CalendarMigratorException('Could not export calendars', 0, $e);
		}
	}

	/**
	 * @return array<string, VTimeZone>
	 */
	private function getCalendarTimezones(VCalendar $vCalendar): array {
		/** @var VTimeZone[] $calendarTimezones */
		$calendarTimezones = 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[]
	 */
	private 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,
		)));
	}

	private function sanitizeComponent(VObjectComponent $component): VObjectComponent {
		// Operate on the component clone to prevent mutation of the original
		$component = clone $component;

		// Remove RSVP parameters to prevent automatically sending invitation emails to attendees on import
		foreach ($component->children() as $child) {
			if (
				$child->name === 'ATTENDEE'
				&& isset($child->parameters['RSVP'])
			) {
				unset($child->parameters['RSVP']);
			}
		}

		return $component;
	}

	/**
	 * @return VObjectComponent[]
	 */
	private function getRequiredImportComponents(VCalendar $vCalendar, VObjectComponent $component): array {
		$component = $this->sanitizeComponent($component);
		/** @var array<int, VTimeZone> $timezoneComponents */
		$timezoneComponents = $this->getTimezonesForComponent($vCalendar, $component);
		return [
			...$timezoneComponents,
			$component,
		];
	}

	private function initCalendarObject(): VCalendar {
		$vCalendarObject = new VCalendar();
		$vCalendarObject->PRODID = '-//IDN nextcloud.com//Migrated calendar//EN';
		return $vCalendarObject;
	}

	/**
	 * @throws InvalidCalendarException
	 */
	private function importCalendarObject(int $calendarId, VCalendar $vCalendarObject, string $filename, OutputInterface $output): void {
		try {
			$this->calDavBackend->createCalendarObject(
				$calendarId,
				UUIDUtil::getUUID() . CalendarMigrator::FILENAME_EXT,
				$vCalendarObject->serialize(),
				CalDavBackend::CALENDAR_TYPE_CALENDAR,
			);
		} catch (Throwable $e) {
			$output->writeln("Error creating calendar object, rolling back creation of \"$filename\" calendar…");
			$this->calDavBackend->deleteCalendar($calendarId, true);
			throw new InvalidCalendarException();
		}
	}

	/**
	 * @throws InvalidCalendarException
	 */
	private function importCalendar(IUser $user, string $filename, string $initialCalendarUri, VCalendar $vCalendar, OutputInterface $output): 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, $filename, $output);
		}

		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, $filename, $output);
		}
	}

	/**
	 * {@inheritDoc}
	 *
	 * @throws CalendarMigratorException
	 */
	public function import(IUser $user, IImportSource $importSource, OutputInterface $output): void {
		if ($importSource->getMigratorVersion($this->getId()) === null) {
			$output->writeln('No version for ' . static::class . ', skipping import…');
			return;
		}

		$output->writeln('Importing calendars from ' . CalendarMigrator::EXPORT_ROOT . '…');

		$calendarImports = $importSource->getFolderListing(CalendarMigrator::EXPORT_ROOT);
		if (empty($calendarImports)) {
			$output->writeln('No calendars to import…');
		}

		foreach ($calendarImports as $filename) {
			$importPath = CalendarMigrator::EXPORT_ROOT . $filename;
			try {
				/** @var VCalendar $vCalendar */
				$vCalendar = VObjectReader::read(
					$importSource->getFileAsStream($importPath),
					VObjectReader::OPTION_FORGIVING,
				);
			} catch (Throwable $e) {
				$output->writeln("Failed to read file \"$importPath\", skipping…");
				continue;
			}

			$problems = $vCalendar->validate();
			if (!empty($problems)) {
				$output->writeln("Invalid calendar data contained in \"$importPath\", skipping…");
				continue;
			}

			$splitFilename = explode('.', $filename, 2);
			if (count($splitFilename) !== 2) {
				$output->writeln("Invalid filename \"$filename\", expected filename of the format \"<calendar_name>" . CalendarMigrator::FILENAME_EXT . '", skipping…');
				continue;
			}
			[$initialCalendarUri, $ext] = $splitFilename;

			try {
				$this->importCalendar(
					$user,
					$filename,
					$initialCalendarUri,
					$vCalendar,
					$output,
				);
			} catch (InvalidCalendarException $e) {
				// Allow this exception to skip a failed import
			} finally {
				$vCalendar->destroy();
			}
		}
	}

	/**
	 * {@inheritDoc}
	 */
	public function getId(): string {
		return 'calendar';
	}

	/**
	 * {@inheritDoc}
	 */
	public function getDisplayName(): string {
		return $this->l10n->t('Calendar');
	}

	/**
	 * {@inheritDoc}
	 */
	public function getDescription(): string {
		return $this->l10n->t('Calendars including events, details and attendees');
	}
}
