<?php

declare(strict_types=1);

/**
 * @copyright 2020 Christoph Wurst <christoph@winzerhof-wurst.at>
 *
 * @author 2020 Christoph Wurst <christoph@winzerhof-wurst.at>
 *
 * @license GNU AGPL version 3 or any later version
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as
 * published by the Free Software Foundation, either version 3 of the
 * License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

namespace OCA\Mail\Service\Sync;

use Horde_Imap_Client;
use Horde_Imap_Client_Exception;
use OCA\Mail\Account;
use OCA\Mail\Contracts\IMailManager;
use OCA\Mail\Db\Mailbox;
use OCA\Mail\Db\MailboxMapper;
use OCA\Mail\Db\MessageMapper as DatabaseMessageMapper;
use OCA\Mail\Events\SynchronizationEvent;
use OCA\Mail\Events\NewMessagesSynchronized;
use OCA\Mail\Exception\ClientException;
use OCA\Mail\Exception\IncompleteSyncException;
use OCA\Mail\Exception\MailboxLockedException;
use OCA\Mail\Exception\MailboxNotCachedException;
use OCA\Mail\Exception\ServiceException;
use OCA\Mail\Exception\UidValidityChangedException;
use OCA\Mail\Exception\MailboxDoesNotSupportModSequencesException;
use OCA\Mail\IMAP\IMAPClientFactory;
use OCA\Mail\IMAP\MessageMapper as ImapMessageMapper;
use OCA\Mail\IMAP\Sync\Request;
use OCA\Mail\IMAP\Sync\Synchronizer;
use OCA\Mail\Model\IMAPMessage;
use OCA\Mail\Support\PerformanceLogger;
use OCP\EventDispatcher\IEventDispatcher;
use Psr\Log\LoggerInterface;
use Throwable;
use function array_chunk;
use function array_filter;
use function array_map;
use function sprintf;

class ImapToDbSynchronizer {

	/** @var int */
	public const MAX_NEW_MESSAGES = 5000;

	/** @var DatabaseMessageMapper */
	private $dbMapper;

	/** @var IMAPClientFactory */
	private $clientFactory;

	/** @var ImapMessageMapper */
	private $imapMapper;

	/** @var MailboxMapper */
	private $mailboxMapper;

	/** @var DatabaseMessageMapper */
	private $messageMapper;

	/** @var Synchronizer */
	private $synchronizer;

	/** @var IEventDispatcher */
	private $dispatcher;

	/** @var PerformanceLogger */
	private $performanceLogger;

	/** @var LoggerInterface */
	private $logger;

	/** @var IMailManager */
	private $mailManager;

	public function __construct(DatabaseMessageMapper $dbMapper,
								IMAPClientFactory $clientFactory,
								ImapMessageMapper $imapMapper,
								MailboxMapper $mailboxMapper,
								DatabaseMessageMapper $messageMapper,
								Synchronizer $synchronizer,
								IEventDispatcher $dispatcher,
								PerformanceLogger $performanceLogger,
								LoggerInterface $logger,
								IMailManager $mailManager) {
		$this->dbMapper = $dbMapper;
		$this->clientFactory = $clientFactory;
		$this->imapMapper = $imapMapper;
		$this->mailboxMapper = $mailboxMapper;
		$this->messageMapper = $messageMapper;
		$this->synchronizer = $synchronizer;
		$this->dispatcher = $dispatcher;
		$this->performanceLogger = $performanceLogger;
		$this->logger = $logger;
		$this->mailManager = $mailManager;
	}

	/**
	 * @throws ClientException
	 * @throws ServiceException
	 */
	public function syncAccount(Account $account,
								LoggerInterface $logger,
								bool $force = false,
								int $criteria = Horde_Imap_Client::SYNC_NEWMSGSUIDS | Horde_Imap_Client::SYNC_FLAGSUIDS | Horde_Imap_Client::SYNC_VANISHEDUIDS): void {
		$rebuildThreads = false;
		foreach ($this->mailboxMapper->findAll($account) as $mailbox) {
			if (!$mailbox->isInbox() && !$mailbox->getSyncInBackground()) {
				$logger->debug("Skipping mailbox sync for " . $mailbox->getId());
				continue;
			}
			$logger->debug("Syncing " . $mailbox->getId());
			$rebuildThreads = $rebuildThreads || $this->sync(
				$account,
				$mailbox,
				$logger,
				$criteria,
				null,
				$force,
				true
			);
		}
		$this->dispatcher->dispatchTyped(
			new SynchronizationEvent(
				$account,
				$logger,
				$rebuildThreads,
			)
		);
	}

	/**
	 * Clear all cached data of a mailbox
	 *
	 * @param Account $account
	 * @param Mailbox $mailbox
	 *
	 * @throws MailboxLockedException
	 * @throws ServiceException
	 */
	public function clearCache(Account $account,
							   Mailbox $mailbox): void {
		$id = $account->getId() . ":" . $mailbox->getName();
		try {
			$this->mailboxMapper->lockForNewSync($mailbox);
			$this->mailboxMapper->lockForChangeSync($mailbox);
			$this->mailboxMapper->lockForVanishedSync($mailbox);

			$this->resetCache($account, $mailbox);
		} catch (Throwable $e) {
			throw new ServiceException("Could not clear mailbox cache for $id: " . $e->getMessage(), 0, $e);
		} finally {
			$this->mailboxMapper->unlockFromNewSync($mailbox);
			$this->mailboxMapper->unlockFromChangedSync($mailbox);
			$this->mailboxMapper->unlockFromVanishedSync($mailbox);
		}
	}

	/**
	 * Wipe all cached messages of a mailbox from the database
	 *
	 * Warning: the caller has to ensure the mailbox is locked
	 *
	 * @param Account $account
	 * @param Mailbox $mailbox
	 */
	private function resetCache(Account $account, Mailbox $mailbox): void {
		$id = $account->getId() . ":" . $mailbox->getName();
		$this->messageMapper->deleteAll($mailbox);
		$this->logger->debug("All messages of $id cleared");
		$mailbox->setSyncNewToken(null);
		$mailbox->setSyncChangedToken(null);
		$mailbox->setSyncVanishedToken(null);
		$this->mailboxMapper->update($mailbox);
	}

	/**
	 * @throws ClientException
	 * @throws MailboxNotCachedException
	 * @throws ServiceException
	 * @return bool whether to rebuild threads or not
	 */
	public function sync(Account $account,
						 Mailbox $mailbox,
						 LoggerInterface $logger,
						 int $criteria = Horde_Imap_Client::SYNC_NEWMSGSUIDS | Horde_Imap_Client::SYNC_FLAGSUIDS | Horde_Imap_Client::SYNC_VANISHEDUIDS,
						 array $knownUids = null,
						 bool $force = false,
						 bool $batchSync = false): bool {
		$rebuildThreads = true;
		if ($mailbox->getSelectable() === false) {
			return $rebuildThreads;
		}

		if ($force || ($criteria & Horde_Imap_Client::SYNC_NEWMSGSUIDS)) {
			$logger->debug("Locking mailbox " . $mailbox->getId() . " for new messages sync");
			$this->mailboxMapper->lockForNewSync($mailbox);
		}
		if ($force || ($criteria & Horde_Imap_Client::SYNC_FLAGSUIDS)) {
			$logger->debug("Locking mailbox " . $mailbox->getId() . " for changed messages sync");
			$this->mailboxMapper->lockForChangeSync($mailbox);
		}
		if ($force || ($criteria & Horde_Imap_Client::SYNC_VANISHEDUIDS)) {
			$logger->debug("Locking mailbox " . $mailbox->getId() . " for vanished messages sync");
			$this->mailboxMapper->lockForVanishedSync($mailbox);
		}

		try {
			if ($force
				|| $mailbox->getSyncNewToken() === null
				|| $mailbox->getSyncChangedToken() === null
				|| $mailbox->getSyncVanishedToken() === null) {
				$logger->debug("Running initial sync for " . $mailbox->getId());
				$this->runInitialSync($account, $mailbox, $logger);
			} else {
				try {
					$logger->debug("Running partial sync for " . $mailbox->getId());
					// Only rebuild threads if there were new or vanished messages
					$rebuildThreads = $this->runPartialSync($account, $mailbox, $logger, $criteria, $knownUids);
				} catch (UidValidityChangedException $e) {
					$logger->warning('Mailbox UID validity changed. Wiping cache and performing full sync for ' . $mailbox->getId());
					$this->resetCache($account, $mailbox);
					$logger->debug("Running initial sync for " . $mailbox->getId() . " after cache reset");
					$this->runInitialSync($account, $mailbox, $logger);
				} catch (MailboxDoesNotSupportModSequencesException $e) {
					$logger->warning('Mailbox does not support mod-sequences error occured. Wiping cache and performing full sync for ' . $mailbox->getId(), [
						'exception' => $e,
					]);
					$this->resetCache($account, $mailbox);
					$logger->debug("Running initial sync for " . $mailbox->getId() . " after cache reset - no mod-sequences error");
					$this->runInitialSync($account, $mailbox, $logger);
				}
			}
		} catch (ServiceException $e) {
			// Just rethrow, don't wrap into another exception
			throw $e;
		} catch (Throwable $e) {
			throw new ServiceException('Sync failed for ' . $account->getId() . ':' . $mailbox->getName() . ': ' . $e->getMessage(), 0, $e);
		} finally {
			if ($force || ($criteria & Horde_Imap_Client::SYNC_VANISHEDUIDS)) {
				$logger->debug("Unlocking mailbox " . $mailbox->getId() . " from vanished messages sync");
				$this->mailboxMapper->unlockFromVanishedSync($mailbox);
			}
			if ($force || ($criteria & Horde_Imap_Client::SYNC_FLAGSUIDS)) {
				$logger->debug("Unlocking mailbox " . $mailbox->getId() . " from changed messages sync");
				$this->mailboxMapper->unlockFromChangedSync($mailbox);
			}
			if ($force || ($criteria & Horde_Imap_Client::SYNC_NEWMSGSUIDS)) {
				$logger->debug("Unlocking mailbox " . $mailbox->getId() . " from new messages sync");
				$this->mailboxMapper->unlockFromNewSync($mailbox);
			}
		}

		if (!$batchSync) {
			$this->dispatcher->dispatchTyped(
				new SynchronizationEvent(
					$account,
					$this->logger,
					$rebuildThreads,
				)
			);
		}

		return $rebuildThreads;
	}

	/**
	 * @throws ServiceException
	 * @throws IncompleteSyncException
	 */
	private function runInitialSync(Account $account,
									Mailbox $mailbox,
									LoggerInterface  $logger): void {
		$perf = $this->performanceLogger->startWithLogger(
			'Initial sync ' . $account->getId() . ':' . $mailbox->getName(),
			$logger
		);

		$highestKnownUid = $this->dbMapper->findHighestUid($mailbox);
		$client = $this->clientFactory->getClient($account, false);
		try {
			try {
				$imapMessages = $this->imapMapper->findAll(
					$client,
					$mailbox->getName(),
					self::MAX_NEW_MESSAGES,
					$highestKnownUid ?? 0,
					$logger,
					$perf
				);
				$perf->step(sprintf('fetch %d messages from IMAP', count($imapMessages)));
			} catch (Horde_Imap_Client_Exception $e) {
				throw new ServiceException('Can not get messages from mailbox ' . $mailbox->getName() . ': ' . $e->getMessage(), 0, $e);
			}

			foreach (array_chunk($imapMessages['messages'], 500) as $chunk) {
				$messages = array_map(function (IMAPMessage $imapMessage) use ($mailbox, $account) {
					return $imapMessage->toDbMessage($mailbox->getId(), $account->getMailAccount());
				}, $chunk);
				$this->dbMapper->insertBulk($account, ...$messages);
				$perf->step(sprintf('persist %d messages in database', count($chunk)));
				// Free the memory
				unset($messages);
			}

			if (!$imapMessages['all']) {
				// We might need more attempts to fill the cache
				$loggingMailboxId = $account->getId() . ':' . $mailbox->getName();
				$total = $imapMessages['total'];
				$cached = count($this->messageMapper->findAllUids($mailbox));
				$perf->step('find number of cached UIDs');

				$perf->end();
				throw new IncompleteSyncException("Initial sync is not complete for $loggingMailboxId ($cached of $total messages cached).");
			}

			$mailbox->setSyncNewToken($client->getSyncToken($mailbox->getName()));
			$mailbox->setSyncChangedToken($client->getSyncToken($mailbox->getName()));
			$mailbox->setSyncVanishedToken($client->getSyncToken($mailbox->getName()));
		} finally {
			$client->logout();
		}
		$this->mailboxMapper->update($mailbox);

		$perf->end();
	}

	/**
	 * @param int[] $knownUids
	 *
	 * @throws ServiceException
	 * @throws UidValidityChangedException
	 * @return bool whether there are new or vanished messages
	 */
	private function runPartialSync(Account $account,
									Mailbox $mailbox,
									LoggerInterface $logger,
									int $criteria,
									array $knownUids = null): bool {
		$newOrVanished = false;
		$perf = $this->performanceLogger->startWithLogger(
			'partial sync ' . $account->getId() . ':' . $mailbox->getName(),
			$logger
		);

		$client = $this->clientFactory->getClient($account);
		try {
			$uids = $knownUids ?? $this->dbMapper->findAllUids($mailbox);
			$perf->step('get all known UIDs');

			if ($criteria & Horde_Imap_Client::SYNC_NEWMSGSUIDS) {
				$response = $this->synchronizer->sync(
					$client,
					new Request(
						$mailbox->getName(),
						$mailbox->getSyncNewToken(),
						$uids
					),
					Horde_Imap_Client::SYNC_NEWMSGSUIDS
				);
				$perf->step('get new messages via Horde');

				$highestKnownUid = $this->dbMapper->findHighestUid($mailbox);
				if ($highestKnownUid === null) {
					// Everything is relevant
					$newMessages = $response->getNewMessages();
				} else {
					// Filter out anything that is already in the DB. Ideally this never happens, but if there is an error
					// during a consecutive chunk INSERT, the sync token won't be updated. In that case the same message(s)
					// will be seen as *new* and therefore cause conflicts.
					$newMessages = array_filter($response->getNewMessages(), function (IMAPMessage $imapMessage) use ($highestKnownUid) {
						return $imapMessage->getUid() > $highestKnownUid;
					});
				}

				foreach (array_chunk($newMessages, 500) as $chunk) {
					$dbMessages = array_map(function (IMAPMessage $imapMessage) use ($mailbox, $account) {
						return $imapMessage->toDbMessage($mailbox->getId(), $account->getMailAccount());
					}, $chunk);

					$this->dbMapper->insertBulk($account, ...$dbMessages);

					$this->dispatcher->dispatch(
						NewMessagesSynchronized::class,
						new NewMessagesSynchronized($account, $mailbox, $dbMessages)
					);
					$perf->step('classified a chunk of new messages');
				}
				$perf->step('persist new messages');

				$mailbox->setSyncNewToken($client->getSyncToken($mailbox->getName()));
				$newOrVanished = !empty($newMessages);
			}
			if ($criteria & Horde_Imap_Client::SYNC_FLAGSUIDS) {
				$response = $this->synchronizer->sync(
					$client,
					new Request(
						$mailbox->getName(),
						$mailbox->getSyncChangedToken(),
						$uids
					),
					Horde_Imap_Client::SYNC_FLAGSUIDS
				);
				$perf->step('get changed messages via Horde');

				$permflagsEnabled = $this->mailManager->isPermflagsEnabled($client, $account, $mailbox->getName());

				foreach (array_chunk($response->getChangedMessages(), 500) as $chunk) {
					$this->dbMapper->updateBulk($account, $permflagsEnabled, ...array_map(static function (IMAPMessage $imapMessage) use ($mailbox, $account) {
						return $imapMessage->toDbMessage($mailbox->getId(), $account->getMailAccount());
					}, $chunk));
				}
				$perf->step('persist changed messages');

				// If a list of UIDs was *provided* (as opposed to loaded from the DB,
				// we can not assume that all changes were detected, hence this is kinda
				// a silent sync and we don't update the change token until the next full
				// mailbox sync
				if ($knownUids === null) {
					$mailbox->setSyncChangedToken($client->getSyncToken($mailbox->getName()));
				}
			}
			if ($criteria & Horde_Imap_Client::SYNC_VANISHEDUIDS) {
				$response = $this->synchronizer->sync(
					$client,
					new Request(
						$mailbox->getName(),
						$mailbox->getSyncVanishedToken(),
						$uids
					),
					Horde_Imap_Client::SYNC_VANISHEDUIDS
				);
				$perf->step('get vanished messages via Horde');

				foreach (array_chunk($response->getVanishedMessageUids(), 500) as $chunk) {
					$this->dbMapper->deleteByUid($mailbox, ...$chunk);
				}
				$perf->step('delete vanished messages');

				// If a list of UIDs was *provided* (as opposed to loaded from the DB,
				// we can not assume that all changes were detected, hence this is kinda
				// a silent sync and we don't update the vanish token until the next full
				// mailbox sync
				if ($knownUids === null) {
					$mailbox->setSyncVanishedToken($client->getSyncToken($mailbox->getName()));
				}
				$newOrVanished = $newOrVanished || !empty($response->getVanishedMessageUids());
			}
		} finally {
			$client->logout();
		}
		$this->mailboxMapper->update($mailbox);
		$perf->end();

		return $newOrVanished;
	}
}
