Show each thread once per message list

Signed-off-by: Daniel Kesselberg <mail@danielkesselberg.de>
Signed-off-by: Christoph Wurst <christoph@winzerhof-wurst.at>

6 files changed, 417 insertions, 107 deletions

diff --git a/lib/Contracts/IMailManager.php b/lib/Contracts/IMailManager.php
index 76eb2f1d5..1eafd7b32 100644
--- a/lib/Contracts/IMailManager.php
+++ b/lib/Contracts/IMailManager.php
@@ -110,11 +110,11 @@ interface IMailManager {
 
 	/**
 	 * @param Account $account
-	 * @param int $messageId database message ID
+	 * @param string $threadRootId thread root id
 	 *
 	 * @return Message[]
 	 */
-	public function getThread(Account $account, int $messageId): array;
+	public function getThread(Account $account, string $threadRootId): array;
 
 	/**
 	 * @param Account $sourceAccount
@@ -263,4 +263,25 @@ interface IMailManager {
 	 * @throws ClientException if the given tag does not exist
 	 */
 	public function updateTag(int $id, string $displayName, string $color, string $userId): Tag;
+
+	/**
+	 * @param Account $srcAccount
+	 * @param Mailbox $srcMailbox
+	 * @param Account $dstAccount
+	 * @param Mailbox $dstMailbox
+	 * @param string $threadRootId
+	 * @return void
+	 * @throws ServiceException
+	 */
+	public function moveThread(Account $srcAccount, Mailbox $srcMailbox, Account $dstAccount, Mailbox $dstMailbox, string $threadRootId): void;
+
+	/**
+	 * @param Account $account
+	 * @param Mailbox $mailbox
+	 * @param string $threadRootId
+	 * @return void
+	 * @throws ClientException
+	 * @throws ServiceException
+	 */
+	public function deleteThread(Account $account, Mailbox $mailbox, string $threadRootId): void;
 }
diff --git a/lib/Controller/MessagesController.php b/lib/Controller/MessagesController.php
index a39de7001..e3cc7a3e7 100755
--- a/lib/Controller/MessagesController.php
+++ b/lib/Controller/MessagesController.php
@@ -307,7 +307,7 @@ class MessagesController extends Controller {
 			return new JSONResponse([], Http::STATUS_FORBIDDEN);
 		}
 
-		return new JSONResponse($this->mailManager->getThread($account, $id));
+		return new JSONResponse($this->mailManager->getThread($account, $message->getThreadRootId()));
 	}
 
 	/**
diff --git a/lib/Controller/ThreadController.php b/lib/Controller/ThreadController.php
new file mode 100755
index 000000000..eecc245a0
--- /dev/null
+++ b/lib/Controller/ThreadController.php
@@ -0,0 +1,123 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * @author Daniel Kesselberg <mail@danielkesselberg.de>
+ *
+ * Mail
+ *
+ * This code is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License, version 3,
+ * as published by the Free Software Foundation.
+ *
+ * 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, version 3,
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>
+ *
+ */
+
+namespace OCA\Mail\Controller;
+
+use OCA\Mail\Contracts\IMailManager;
+use OCA\Mail\Exception\ClientException;
+use OCA\Mail\Exception\ServiceException;
+use OCA\Mail\Service\AccountService;
+use OCP\AppFramework\Controller;
+use OCP\AppFramework\Db\DoesNotExistException;
+use OCP\AppFramework\Http;
+use OCP\AppFramework\Http\JSONResponse;
+use OCP\IRequest;
+use Psr\Log\LoggerInterface;
+
+class ThreadController extends Controller {
+
+	/** @var string */
+	private $currentUserId;
+
+	/** @var LoggerInterface */
+	private $logger;
+
+	/** @var AccountService */
+	private $accountService;
+
+	/** @var IMailManager */
+	private $mailManager;
+
+	public function __construct(string $appName,
+								IRequest $request,
+								string $UserId,
+								AccountService $accountService,
+								IMailManager $mailManager) {
+		parent::__construct($appName, $request);
+
+		$this->currentUserId = $UserId;
+		$this->accountService = $accountService;
+		$this->mailManager = $mailManager;
+	}
+
+	/**
+	 * @NoAdminRequired
+	 * @TrapError
+	 *
+	 * @param int $id
+	 * @param int $destMailboxId
+	 *
+	 * @return JSONResponse
+	 * @throws ClientException
+	 * @throws ServiceException
+	 */
+	public function move(int $id, int $destMailboxId): JSONResponse {
+		try {
+			$message = $this->mailManager->getMessage($this->currentUserId, $id);
+			$srcMailbox = $this->mailManager->getMailbox($this->currentUserId, $message->getMailboxId());
+			$srcAccount = $this->accountService->find($this->currentUserId, $srcMailbox->getAccountId());
+			$dstMailbox = $this->mailManager->getMailbox($this->currentUserId, $destMailboxId);
+			$dstAccount = $this->accountService->find($this->currentUserId, $dstMailbox->getAccountId());
+		} catch (DoesNotExistException $e) {
+			return new JSONResponse([], Http::STATUS_FORBIDDEN);
+		}
+
+		$this->mailManager->moveThread(
+			$srcAccount,
+			$srcMailbox,
+			$dstAccount,
+			$dstMailbox,
+			$message->getThreadRootId()
+		);
+
+		return new JSONResponse();
+	}
+
+	/**
+	 * @NoAdminRequired
+	 * @TrapError
+	 *
+	 * @param int $id
+	 *
+	 * @return JSONResponse
+	 * @throws ClientException
+	 * @throws ServiceException
+	 */
+	public function delete(int $id): JSONResponse {
+		try {
+			$message = $this->mailManager->getMessage($this->currentUserId, $id);
+			$mailbox = $this->mailManager->getMailbox($this->currentUserId, $message->getMailboxId());
+			$account = $this->accountService->find($this->currentUserId, $mailbox->getAccountId());
+		} catch (DoesNotExistException $e) {
+			return new JSONResponse([], Http::STATUS_FORBIDDEN);
+		}
+
+		$this->mailManager->deleteThread(
+			$account,
+			$mailbox,
+			$message->getThreadRootId()
+		);
+
+		return new JSONResponse();
+	}
+}
diff --git a/lib/Db/MessageMapper.php b/lib/Db/MessageMapper.php
index 6b79fb38a..203c877e6 100644
--- a/lib/Db/MessageMapper.php
+++ b/lib/Db/MessageMapper.php
@@ -25,29 +25,29 @@ declare(strict_types=1);
 
 namespace OCA\Mail\Db;
 
-use OCP\IUser;
-use function ltrim;
 use OCA\Mail\Account;
 use OCA\Mail\Address;
-use RuntimeException;
-use OCP\IDBConnection;
-use function array_map;
-use function get_class;
-use function mb_strcut;
-use function array_keys;
-use function array_combine;
-use function array_udiff;
 use OCA\Mail\AddressList;
+use OCA\Mail\IMAP\Threading\DatabaseMessage;
 use OCA\Mail\Service\Search\Flag;
-use OCP\AppFramework\Db\QBMapper;
-use OCP\DB\QueryBuilder\IQueryBuilder;
-use OCA\Mail\Service\Search\SearchQuery;
-use OCP\AppFramework\Utility\ITimeFactory;
 use OCA\Mail\Service\Search\FlagExpression;
-use OCA\Mail\IMAP\Threading\DatabaseMessage;
+use OCA\Mail\Service\Search\SearchQuery;
 use OCA\Mail\Support\PerformanceLogger;
 use OCP\AppFramework\Db\DoesNotExistException;
-use function \OCA\Mail\array_flat_map;
+use OCP\AppFramework\Db\QBMapper;
+use OCP\AppFramework\Utility\ITimeFactory;
+use OCP\DB\QueryBuilder\IQueryBuilder;
+use OCP\IDBConnection;
+use OCP\IUser;
+use RuntimeException;
+use function array_combine;
+use function array_keys;
+use function array_map;
+use function array_udiff;
+use function get_class;
+use function ltrim;
+use function mb_strcut;
+use function OCA\Mail\array_flat_map;
 
 /**
  * @template-extends QBMapper<Message>
@@ -442,6 +442,7 @@ class MessageMapper extends QBMapper {
 
 		return $ids;
 	}
+
 	/**
 	 * @param Message ...$messages
 	 *
@@ -552,34 +553,22 @@ class MessageMapper extends QBMapper {
 
 	/**
 	 * @param Account $account
-	 * @param int $messageId
+	 * @param string $threadRootId
 	 *
 	 * @return Message[]
 	 */
-	public function findThread(Account $account, int $messageId): array {
+	public function findThread(Account $account, string $threadRootId): array {
 		$qb = $this->db->getQueryBuilder();
-		$subQb1 = $this->db->getQueryBuilder();
-
-		$mailboxIdsQuery = $subQb1
-			->select('id')
-			->from('mail_mailboxes')
-			->where($qb->expr()->eq('account_id', $qb->createNamedParameter($account->getId(), IQueryBuilder::PARAM_INT)));
-
-		/**
-		 * Select the message with the given ID or any that has the same thread ID
-		 */
-		$selectMessages = $qb
-			->select('m2.*')
-			->from($this->getTableName(), 'm1')
-			->leftJoin('m1', $this->getTableName(), 'm2',  $qb->expr()->eq('m1.thread_root_id', 'm2.thread_root_id'))
+		$qb->select('messages.*')
+			->from($this->getTableName(), 'messages')
+			->join('messages', 'mail_mailboxes', 'mailboxes', $qb->expr()->eq('messages.mailbox_id', 'mailboxes.id', IQueryBuilder::PARAM_INT))
 			->where(
-				$qb->expr()->in('m1.mailbox_id', $qb->createFunction($mailboxIdsQuery->getSQL()), IQueryBuilder::PARAM_INT_ARRAY),
-				$qb->expr()->in('m2.mailbox_id', $qb->createFunction($mailboxIdsQuery->getSQL()), IQueryBuilder::PARAM_INT_ARRAY),
-				$qb->expr()->eq('m1.id', $qb->createNamedParameter($messageId, IQueryBuilder::PARAM_INT), IQueryBuilder::PARAM_INT),
-				$qb->expr()->isNotNull('m1.thread_root_id')
+				$qb->expr()->eq('mailboxes.account_id', $qb->createNamedParameter($account->getId(), IQueryBuilder::PARAM_INT)),
+				$qb->expr()->eq('messages.thread_root_id', $qb->createNamedParameter($threadRootId, IQueryBuilder::PARAM_STR), IQueryBuilder::PARAM_STR)
 			)
-			->orderBy('sent_at', 'desc');
-		return $this->findRelatedData($this->findEntities($selectMessages), $account->getUserId());
+			->orderBy('messages.sent_at', 'desc');
+
+		return $this->findRelatedData($this->findEntities($qb), $account->getUserId());
 	}
 
 	/**
@@ -593,10 +582,14 @@ class MessageMapper extends QBMapper {
 	public function findIdsByQuery(Mailbox $mailbox, SearchQuery $query, ?int $limit, array $uids = null): array {
 		$qb = $this->db->getQueryBuilder();
 
-		$select = $qb
-			->selectDistinct('m.id')
-			->addSelect('m.sent_at')
-			->from($this->getTableName(), 'm');
+		if ($this->needDistinct($query)) {
+			$select = $qb->selectDistinct(['m.id', 'm.sent_at']);
+		} else {
+			$select = $qb->select(['m.id', 'm.sent_at']);
+		}
+
+		$select->from($this->getTableName(), 'm')
+			->leftJoin('m', $this->getTableName(), 'm2', 'm.mailbox_id = m2.mailbox_id and m.thread_root_id = m2.thread_root_id and m.sent_at < m2.sent_at');
 
 		if (!empty($query->getFrom())) {
 			$select->innerJoin('m', 'mail_recipients', 'r0', 'm.id = r0.message_id');
@@ -612,7 +605,7 @@ class MessageMapper extends QBMapper {
 		}
 
 		$select->where(
-			$qb->expr()->eq('mailbox_id', $qb->createNamedParameter($mailbox->getId()), IQueryBuilder::PARAM_INT)
+			$qb->expr()->eq('m.mailbox_id', $qb->createNamedParameter($mailbox->getId()), IQueryBuilder::PARAM_INT)
 		);
 
 		if (!empty($query->getFrom())) {
@@ -641,7 +634,7 @@ class MessageMapper extends QBMapper {
 				$qb->expr()->orX(
 					...array_map(function (string $subject) use ($qb) {
 						return $qb->expr()->iLike(
-							'subject',
+							'm.subject',
 							$qb->createNamedParameter('%' . $this->db->escapeLikeParameter($subject) . '%', IQueryBuilder::PARAM_STR),
 							IQueryBuilder::PARAM_STR
 						);
@@ -652,31 +645,32 @@ class MessageMapper extends QBMapper {
 
 		if ($query->getCursor() !== null) {
 			$select->andWhere(
-				$qb->expr()->lt('sent_at', $qb->createNamedParameter($query->getCursor(), IQueryBuilder::PARAM_INT))
+				$qb->expr()->lt('m.sent_at', $qb->createNamedParameter($query->getCursor(), IQueryBuilder::PARAM_INT))
 			);
 		}
 		// createParameter
 		if ($uids !== null) {
 			$select->andWhere(
-				$qb->expr()->in('uid', $qb->createParameter('uids'))
+				$qb->expr()->in('m.uid', $qb->createParameter('uids'))
 			);
 		}
 		foreach ($query->getFlags() as $flag) {
-			$select->andWhere($qb->expr()->eq($this->flagToColumnName($flag), $qb->createNamedParameter($flag->isSet(), IQueryBuilder::PARAM_BOOL)));
+			$select->andWhere($qb->expr()->eq('m.' . $this->flagToColumnName($flag), $qb->createNamedParameter($flag->isSet(), IQueryBuilder::PARAM_BOOL)));
 		}
 		if (!empty($query->getFlagExpressions())) {
 			$select->andWhere(
 				...array_map(function (FlagExpression $expr) use ($select) {
-					return $this->flagExpressionToQuery($expr, $select);
+					return $this->flagExpressionToQuery($expr, $select, 'm');
 				}, $query->getFlagExpressions())
 			);
 		}
 
-		$select = $select
-			->orderBy('sent_at', 'desc');
+		$select->andWhere($qb->expr()->isNull('m2.id'));
+
+		$select->orderBy('m.sent_at', 'desc');
 
 		if ($limit !== null) {
-			$select = $select->setMaxResults($limit);
+			$select->setMaxResults($limit);
 		}
 
 		if ($uids !== null) {
@@ -697,10 +691,14 @@ class MessageMapper extends QBMapper {
 		$qb = $this->db->getQueryBuilder();
 		$qbMailboxes = $this->db->getQueryBuilder();
 
-		$select = $qb
-			->selectDistinct('m.id')
-			->addSelect('m.sent_at')
-			->from($this->getTableName(), 'm');
+		if ($this->needDistinct($query)) {
+			$select = $qb->selectDistinct(['m.id', 'm.sent_at']);
+		} else {
+			$select = $qb->select(['m.id', 'm.sent_at']);
+		}
+
+		$select->from($this->getTableName(), 'm')
+			->leftJoin('m', $this->getTableName(), 'm2', 'm.mailbox_id = m2.mailbox_id and m.thread_root_id = m2.thread_root_id and m.sent_at < m2.sent_at');
 
 		if (!empty($query->getFrom())) {
 			$select->innerJoin('m', 'mail_recipients', 'r0', 'm.id = r0.message_id');
@@ -720,7 +718,7 @@ class MessageMapper extends QBMapper {
 			->join('mb', 'mail_accounts', 'a', $qb->expr()->eq('a.id', 'mb.account_id', IQueryBuilder::PARAM_INT))
 			->where($qb->expr()->eq('a.user_id', $qb->createNamedParameter($user->getUID())));
 		$select->where(
-			$qb->expr()->in('mailbox_id', $qb->createFunction($selectMailboxIds->getSQL()), IQueryBuilder::PARAM_INT_ARRAY)
+			$qb->expr()->in('m.mailbox_id', $qb->createFunction($selectMailboxIds->getSQL()), IQueryBuilder::PARAM_INT_ARRAY)
 		);
 
 		if (!empty($query->getFrom())) {
@@ -749,7 +747,7 @@ class MessageMapper extends QBMapper {
 				$qb->expr()->orX(
 					...array_map(function (string $subject) use ($qb) {
 						return $qb->expr()->iLike(
-							'subject',
+							'm.subject',
 							$qb->createNamedParameter('%' . $this->db->escapeLikeParameter($subject) . '%', IQueryBuilder::PARAM_STR),
 							IQueryBuilder::PARAM_STR
 						);
@@ -760,30 +758,31 @@ class MessageMapper extends QBMapper {
 
 		if ($query->getCursor() !== null) {
 			$select->andWhere(
-				$qb->expr()->lt('sent_at', $qb->createNamedParameter($query->getCursor(), IQueryBuilder::PARAM_INT))
+				$qb->expr()->lt('m.sent_at', $qb->createNamedParameter($query->getCursor(), IQueryBuilder::PARAM_INT))
 			);
 		}
 		if ($uids !== null) {
 			$select->andWhere(
-				$qb->expr()->in('uid', $qb->createParameter('uids'))
+				$qb->expr()->in('m.uid', $qb->createParameter('uids'))
 			);
 		}
 		foreach ($query->getFlags() as $flag) {
-			$select->andWhere($qb->expr()->eq($this->flagToColumnName($flag), $qb->createNamedParameter($flag->isSet(), IQueryBuilder::PARAM_BOOL)));
+			$select->andWhere($qb->expr()->eq('m.' . $this->flagToColumnName($flag), $qb->createNamedParameter($flag->isSet(), IQueryBuilder::PARAM_BOOL)));
 		}
 		if (!empty($query->getFlagExpressions())) {
 			$select->andWhere(
 				...array_map(function (FlagExpression $expr) use ($select) {
-					return $this->flagExpressionToQuery($expr, $select);
+					return $this->flagExpressionToQuery($expr, $select, 'm');
 				}, $query->getFlagExpressions())
 			);
 		}
 
-		$select = $select
-			->orderBy('sent_at', 'desc');
+		$select->andWhere($qb->expr()->isNull('m2.id'));
+
+		$select->orderBy('m.sent_at', 'desc');
 
 		if ($limit !== null) {
-			$select = $select->setMaxResults($limit);
+			$select->setMaxResults($limit);
 		}
 
 		if ($uids !== null) {
@@ -800,17 +799,44 @@ class MessageMapper extends QBMapper {
 		}, $this->findEntities($select));
 	}
 
-	private function flagExpressionToQuery(FlagExpression $expr, IQueryBuilder $qb): string {
-		$operands = array_map(function (object $operand) use ($qb) {
+	/**
+	 * Return true when a distinct query is required.
+	 *
+	 * For the threaded message list it's necessary to self-join
+	 * the mail_messages table to figure out if we are the latest message
+	 * of a thread.
+	 *
+	 * Unfortunately a self-join on a larger table has a significant
+	 * performance impact. An database index (e.g. on thread_root_id)
+	 * could improve the query performance but adding an index is blocked by
+	 * - https://github.com/nextcloud/server/pull/25471
+	 * - https://github.com/nextcloud/mail/issues/4735
+	 *
+	 * We noticed a better query performance without distinct. As distinct is
+	 * only necessary when a search query is present (e.g. search for mail with
+	 * two recipients) it's reasonable to use distinct only for those requests.
+	 *
+	 * @param SearchQuery $query
+	 * @return bool
+	 */
+	private function needDistinct(SearchQuery $query): bool {
+		return !empty($query->getFrom())
+			|| !empty($query->getTo())
+			|| !empty($query->getCc())
+			|| !empty($query->getBcc());
+	}
+
+	private function flagExpressionToQuery(FlagExpression $expr, IQueryBuilder $qb, string $tableAlias): string {
+		$operands = array_map(function (object $operand) use ($qb, $tableAlias) {
 			if ($operand instanceof Flag) {
 				return $qb->expr()->eq(
-					$this->flagToColumnName($operand),
+					$tableAlias . '.' . $this->flagToColumnName($operand),
 					$qb->createNamedParameter($operand->isSet(), IQueryBuilder::PARAM_BOOL),
 					IQueryBuilder::PARAM_BOOL
 				);
 			}
 			if ($operand instanceof FlagExpression) {
-				return $this->flagExpressionToQuery($operand, $qb);
+				return $this->flagExpressionToQuery($operand, $qb, $tableAlias);
 			}
 
 			throw new RuntimeException('Invalid operand type ' . get_class($operand));
@@ -954,30 +980,38 @@ class MessageMapper extends QBMapper {
 	 * @return int[]
 	 */
 	public function findNewIds(Mailbox $mailbox, array $ids): array {
-		$sub = $this->db->getQueryBuilder();
-		$qb = $this->db->getQueryBuilder();
+		$select = $this->db->getQueryBuilder();
+		$subSelect = $this->db->getQueryBuilder();
+
+		$inExpression = [];
+		$notInExpression = [];
+
+		foreach (array_chunk($ids, 1000) as $chunk) {
+			$inExpression[] = $subSelect->expr()->in('id', $select->createNamedParameter($chunk, IQueryBuilder::PARAM_INT_ARRAY));
+			$notInExpression[] = $subSelect->expr()->notIn('m.id', $select->createNamedParameter($chunk, IQueryBuilder::PARAM_INT_ARRAY));
+		}
 
-		$subSelect = $sub
-			->select($sub->func()->max('uid'))
+		$subSelect
+			->select($subSelect->func()->min('sent_at'))
 			->from($this->getTableName())
 			->where(
-				$sub->expr()->eq('mailbox_id', $qb->createNamedParameter($mailbox->getId(), IQueryBuilder::PARAM_INT)),
-				$sub->expr()->in('id', $qb->createParameter('ids'))
+				$subSelect->expr()->eq('mailbox_id', $select->createNamedParameter($mailbox->getId(), IQueryBuilder::PARAM_INT)),
+				$subSelect->expr()->orX(...$inExpression)
 			);
 
-		$qb->select('id')
-			->from($this->getTableName())
+		$select
+			->select('m.id')
+			->from($this->getTableName(), 'm')
+			->leftJoin('m', $this->getTableName(), 'm2', 'm.mailbox_id = m2.mailbox_id and m.thread_root_id = m2.thread_root_id and m.sent_at < m2.sent_at')
 			->where(
-				$qb->expr()->eq('mailbox_id', $qb->createNamedParameter($mailbox->getId(), IQueryBuilder::PARAM_INT))
-			);
+				$select->expr()->eq('m.mailbox_id', $select->createNamedParameter($mailbox->getId(), IQueryBuilder::PARAM_INT)),
+				$select->expr()->andX(...$notInExpression),
+				$select->expr()->gt('m.sent_at', $select->createFunction('(' . $subSelect->getSQL() . ')'), IQueryBuilder::PARAM_INT),
+				$select->expr()->isNull('m2.id')
+			)
+			->orderBy('m.sent_at', 'desc');
 
-		return array_flat_map(function (array $chunk) use ($qb, $subSelect) {
-			$qb->setParameter('ids', $chunk, IQueryBuilder::PARAM_INT_ARRAY);
-			$select = $qb->andWhere(
-				$qb->expr()->gt('uid', $qb->createFunction('(' . $subSelect->getSQL() . ')'), IQueryBuilder::PARAM_INT)
-			);
-			return $this->findIds($select);
-		}, array_chunk($ids, 1000));
+		return $this->findIds($select);
 	}
 
 	/**
@@ -1073,7 +1107,7 @@ class MessageMapper extends QBMapper {
 		if (empty($rows)) {
 			return null;
 		}
-		return (int) $rows[0]['id'];
+		return (int)$rows[0]['id'];
 	}
 
 	/**
diff --git a/lib/Db/ThreadMapper.php b/lib/Db/ThreadMapper.php
new file mode 100644
index 000000000..991f46573
--- /dev/null
+++ b/lib/Db/ThreadMapper.php
@@ -0,0 +1,73 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * @copyright 2021 Daniel Kesselberg <mail@danielkesselberg.de>
+ *
+ * @author 2021 Daniel Kesselberg <mail@danielkesselberg.de>
+ *
+ * @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\Db;
+
+use OCP\AppFramework\Db\QBMapper;
+use OCP\DB\QueryBuilder\IQueryBuilder;
+use OCP\IDBConnection;
+
+/**
+ * @template-extends QBMapper<Message>
+ */
+class ThreadMapper extends QBMapper {
+	public function __construct(IDBConnection $db) {
+		parent::__construct($db, 'mail_messages');
+	}
+
+	/**
+	 * @return array<array-key, array{mailboxName: string, messageUid: int}>
+	 */
+	public function findMessageUidsAndMailboxNamesByAccountAndThreadRoot(MailAccount $mailAccount, string $threadRootId, bool $trash): array {
+		$qb = $this->db->getQueryBuilder();
+		$qb->select('messages.uid', 'mailboxes.name')
+			->from($this->tableName, 'messages')
+			->join('messages', 'mail_mailboxes', 'mailboxes', 'messages.mailbox_id = mailboxes.id')
+			->where(
+				$qb->expr()->eq('messages.thread_root_id', $qb->createNamedParameter($threadRootId, IQueryBuilder::PARAM_STR)),
+				$qb->expr()->eq('mailboxes.account_id', $qb->createNamedParameter($mailAccount->getId(), IQueryBuilder::PARAM_INT))
+			);
+
+		$trashMailboxId = $mailAccount->getTrashMailboxId();
+		if ($trashMailboxId !== null) {
+			if ($trash) {
+				$qb->andWhere($qb->expr()->eq('mailboxes.id', $qb->createNamedParameter($trashMailboxId, IQueryBuilder::PARAM_INT)));
+			} else {
+				$qb->andWhere($qb->expr()->neq('mailboxes.id', $qb->createNamedParameter($trashMailboxId, IQueryBuilder::PARAM_INT)));
+			}
+		}
+
+		$result = $qb->execute();
+		$rows = array_map(static function (array $row) {
+			return [
+				'messageUid' => (int)$row[0],
+				'mailboxName' => (string)$row[1]
+			];
+		}, $result->fetchAll(\PDO::FETCH_NUM));
+		$result->closeCursor();
+
+		return $rows;
+	}
+}
diff --git a/lib/Service/MailManager.php b/lib/Service/MailManager.php
index dd283f9f1..238b87900 100644
--- a/lib/Service/MailManager.php
+++ b/lib/Service/MailManager.php
@@ -35,6 +35,7 @@ use OCA\Mail\Db\Message;
 use OCA\Mail\Db\MessageMapper as DbMessageMapper;
 use OCA\Mail\Db\Tag;
 use OCA\Mail\Db\TagMapper;
+use OCA\Mail\Db\ThreadMapper;
 use OCA\Mail\Events\BeforeMessageDeletedEvent;
 use OCA\Mail\Events\MessageDeletedEvent;
 use OCA\Mail\Events\MessageFlaggedEvent;
@@ -87,17 +88,18 @@ class MailManager implements IMailManager {
 	/** @var DbMessageMapper */
 	private $dbMessageMapper;
 
-	/** @var TagMapper */
-	private $tagMapper;
-
 	/** @var IEventDispatcher */
 	private $eventDispatcher;
 
-	/**
-	 * @var LoggerInterface
-	 */
+	/** @var LoggerInterface */
 	private $logger;
 
+	/** @var TagMapper */
+	private $tagMapper;
+
+	/** @var ThreadMapper */
+	private $threadMapper;
+
 	public function __construct(IMAPClientFactory $imapClientFactory,
 								MailboxMapper $mailboxMapper,
 								MailboxSync $mailboxSync,
@@ -106,7 +108,8 @@ class MailManager implements IMailManager {
 								DbMessageMapper $dbMessageMapper,
 								IEventDispatcher $eventDispatcher,
 								LoggerInterface $logger,
-								TagMapper $tagMapper) {
+								TagMapper $tagMapper,
+								ThreadMapper $threadMapper) {
 		$this->imapClientFactory = $imapClientFactory;
 		$this->mailboxMapper = $mailboxMapper;
 		$this->mailboxSync = $mailboxSync;
@@ -116,6 +119,7 @@ class MailManager implements IMailManager {
 		$this->eventDispatcher = $eventDispatcher;
 		$this->logger = $logger;
 		$this->tagMapper = $tagMapper;
+		$this->threadMapper = $threadMapper;
 	}
 
 	public function getMailbox(string $uid, int $id): Mailbox {
@@ -155,13 +159,13 @@ class MailManager implements IMailManager {
 			throw new ServiceException(
 				"Could not get mailbox status: " .
 				$e->getMessage(),
-				(int) $e->getCode(),
+				(int)$e->getCode(),
 				$e
 			);
 		}
 		$this->folderMapper->detectFolderSpecialUse([$folder]);
 
-		$this->mailboxSync->sync($account, $this->logger,true);
+		$this->mailboxSync->sync($account, $this->logger, true);
 
 		return $this->mailboxMapper->find($account, $name);
 	}
@@ -182,14 +186,14 @@ class MailManager implements IMailManager {
 		} catch (Horde_Imap_Client_Exception | DoesNotExistException $e) {
 			throw new ServiceException(
 				"Could not load message",
-				(int) $e->getCode(),
+				(int)$e->getCode(),
 				$e
 			);
 		}
 	}
 
-	public function getThread(Account $account, int $messageId): array {
-		return $this->dbMessageMapper->findThread($account, $messageId);
+	public function getThread(Account $account, string $threadRootId): array {
+		return $this->dbMessageMapper->findThread($account, $threadRootId);
 	}
 
 	public function getMessageIdForUid(Mailbox $mailbox, $uid): ?int {
@@ -349,7 +353,7 @@ class MailManager implements IMailManager {
 		} catch (Horde_Imap_Client_Exception $e) {
 			throw new ServiceException(
 				"Could not set subscription status for mailbox " . $mailbox->getId() . " on IMAP: " . $e->getMessage(),
-				(int) $e->getCode(),
+				(int)$e->getCode(),
 				$e
 			);
 		}
@@ -357,7 +361,7 @@ class MailManager implements IMailManager {
 		/**
 		 * 2. Pull changes into the mailbox database cache
 		 */
-		$this->mailboxSync->sync($account, $this->logger,true);
+		$this->mailboxSync->sync($account, $this->logger, true);
 
 		/**
 		 * 3. Return the updated object
@@ -396,7 +400,7 @@ class MailManager implements IMailManager {
 		} catch (Horde_Imap_Client_Exception $e) {
 			throw new ServiceException(
 				"Could not set message flag on IMAP: " . $e->getMessage(),
-				(int) $e->getCode(),
+				(int)$e->getCode(),
 				$e
 			);
 		}
@@ -445,7 +449,7 @@ class MailManager implements IMailManager {
 			} catch (Horde_Imap_Client_Exception $e) {
 				throw new ServiceException(
 					"Could not set message keyword on IMAP: " . $e->getMessage(),
-					(int) $e->getCode(),
+					(int)$e->getCode(),
 					$e
 				);
 			}
@@ -520,7 +524,7 @@ class MailManager implements IMailManager {
 		/**
 		 * 2. Get the IMAP changes into our database cache
 		 */
-		$this->mailboxSync->sync($account, $this->logger,true);
+		$this->mailboxSync->sync($account, $this->logger, true);
 
 		/**
 		 * 3. Return the cached object with the new ID
@@ -605,7 +609,7 @@ class MailManager implements IMailManager {
 		} catch (Horde_Imap_Client_Exception $e) {
 			throw new ServiceException(
 				"Could not get message flag options from IMAP: " . $e->getMessage(),
-				(int) $e->getCode(),
+				(int)$e->getCode(),
 				$e
 			);
 		}
@@ -649,4 +653,59 @@ class MailManager implements IMailManager {
 
 		return $this->tagMapper->update($tag);
 	}
+
+	public function moveThread(Account $srcAccount, Mailbox $srcMailbox, Account $dstAccount, Mailbox $dstMailbox, string $threadRootId): void {
+		$mailAccount = $srcAccount->getMailAccount();
+		$messageInTrash = $srcMailbox->getId() === $mailAccount->getTrashMailboxId();
+
+		$messages = $this->threadMapper->findMessageUidsAndMailboxNamesByAccountAndThreadRoot(
+			$mailAccount,
+			$threadRootId,
+			$messageInTrash
+		);
+
+		foreach ($messages as $message) {
+			$this->logger->debug('move message', [
+				'messageId' => $message['messageUid'],
+				'srcMailboxId' => $srcMailbox->getId(),
+				'dstMailboxId' => $dstMailbox->getId()
+			]);
+
+			$this->moveMessage(
+				$srcAccount,
+				$message['mailboxName'],
+				$message['messageUid'],
+				$dstAccount,
+				$dstMailbox->getName()
+			);
+		}
+	}
+
+	/**
+	 * @throws ClientException
+	 * @throws ServiceException
+	 */
+	public function deleteThread(Account $account, Mailbox $mailbox, string $threadRootId): void {
+		$mailAccount = $account->getMailAccount();
+		$messageInTrash = $mailbox->getId() === $mailAccount->getTrashMailboxId();
+
+		$messages = $this->threadMapper->findMessageUidsAndMailboxNamesByAccountAndThreadRoot(
+			$mailAccount,
+			$threadRootId,
+			$messageInTrash
+		);
+
+		foreach ($messages as $message) {
+			$this->logger->debug('deleting message', [
+				'messageId' => $message['messageUid'],
+				'mailboxId' => $mailbox->getId(),
+			]);
+
+			$this->deleteMessage(
+				$account,
+				$message['mailboxName'],
+				$message['messageUid']
+			);
+		}
+	}
 }