Change handling of objects which refer to deleted shares (#2640)

* add fake share for delete users and hash user id
* fix #2636

17 files changed, 256 insertions, 209 deletions

diff --git a/lib/Db/Comment.php b/lib/Db/Comment.php
index 6e6e9ef7..07ee8a9c 100644
--- a/lib/Db/Comment.php
+++ b/lib/Db/Comment.php
@@ -27,12 +27,6 @@ namespace OCA\Polls\Db;
 
 use JsonSerializable;
 
-use OCA\Polls\Helper\Container;
-use OCP\IUser;
-use OCP\IUserManager;
-use OCP\AppFramework\Db\Entity;
-use OCP\AppFramework\Db\DoesNotExistException;
-
 /**
  * @method int getId()
  * @method void setId(integer $value)
@@ -45,7 +39,7 @@ use OCP\AppFramework\Db\DoesNotExistException;
  * @method int getTimestamp()
  * @method void setTimestamp(integer $value)
  */
-class Comment extends Entity implements JsonSerializable {
+class Comment extends EntityWithUser implements JsonSerializable {
 	public const TABLE = 'polls_comments';
 
 	/** @var array $subComments */
@@ -63,17 +57,9 @@ class Comment extends Entity implements JsonSerializable {
 	/** @var string $comment */
 	protected $comment = '';
 
-	/** @var IUserManager */
-	private $userManager;
-
-	/** @var ShareMapper */
-	private $shareMapper;
-
 	public function __construct() {
 		$this->addType('pollId', 'int');
 		$this->addType('timestamp', 'int');
-		$this->userManager = Container::queryClass(IUserManager::class);
-		$this->shareMapper = Container::queryClass(ShareMapper::class);
 	}
 
 	/**
@@ -101,32 +87,4 @@ class Comment extends Entity implements JsonSerializable {
 	public function getSubComments(): array {
 		return $this->subComments;
 	}
-
-	public function getDisplayName(): string {
-		if (!strncmp($this->userId, 'deleted_', 8)) {
-			return 'Deleted User';
-		}
-
-		if ($this->getIsNoUser()) {
-			// get displayName from share
-			try {
-				$share = $this->shareMapper->findByPollAndUser($this->getPollId(), $this->userId);
-				return $share->getDisplayName();
-			} catch (DoesNotExistException $e) {
-				return $this->userId;
-			}
-		}
-		return $this->userManager->get($this->userId)->getDisplayName();
-	}
-
-	public function getUser(): array {
-		return [
-			'userId' => $this->getUserId(),
-			'displayName' => $this->getDisplayName(),
-			'isNoUser' => $this->getIsNoUser(),
-		];
-	}
-	public function getIsNoUser(): bool {
-		return !($this->userManager->get($this->userId) instanceof IUser);
-	}
 }
diff --git a/lib/Db/EntityWithUser.php b/lib/Db/EntityWithUser.php
new file mode 100644
index 00000000..6168ae22
--- /dev/null
+++ b/lib/Db/EntityWithUser.php
@@ -0,0 +1,86 @@
+<?php
+/**
+ * @copyright Copyright (c) 2017 Kai Schröer <git@schroeer.co>
+ *
+ * @author Kai Schröer <git@schroeer.co>
+ *
+ * @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\Polls\Db;
+
+use OCA\Polls\Exceptions\ShareNotFoundException;
+use OCA\Polls\Helper\Container;
+use OCP\AppFramework\Db\Entity;
+use OCP\IUser;
+use OCP\IUserManager;
+
+/**
+ * @method string getUserId()
+ * @method int getPollId()
+ */
+
+abstract class EntityWithUser extends Entity {
+	/** @var string $publicUserId */
+	protected $publicUserId = '';
+
+	public function getIsNoUser(): bool {
+		return !(Container::queryClass(IUserManager::class)->get($this->getUserId()) instanceof IUser);
+	}
+
+	public function getDisplayName(): string {
+		if (!$this->getUserId()) {
+			return '';
+		}
+		if ($this->getIsNoUser()) {
+			// get displayName from share
+			try {
+				$share = Container::queryClass(ShareMapper::class)->findByPollAndUser($this->getPollId(), $this->getUserId());
+			} catch (ShareNotFoundException $e) {
+				// User seems to be probaly deleted, use fake share
+				$share = Container::queryClass(ShareMapper::class)->getReplacement($this->getPollId(), $this->getUserId());
+			}
+			return $share->getDisplayName();
+		}
+
+		return Container::queryClass(IUserManager::class)->get($this->getUserId())->getDisplayName();
+	}
+
+	private function getPublicUserId(): string {
+		if (!$this->getUserId()) {
+			return '';
+		}
+
+		if ($this->publicUserId) {
+			return $this->publicUserId;
+		}
+
+		return $this->getUserId();
+	}
+
+	public function generateHashedUserId(): void {
+		$this->publicUserId = hash('md5', $this->getUserId());
+	}
+
+	public function getUser(): array {
+		return [
+			'userId' => $this->getPublicUserId(),
+			'displayName' => $this->getDisplayName(),
+			'isNoUser' => $this->getIsNoUser(),
+		];
+	}
+}
diff --git a/lib/Db/IEntityWithUser.php b/lib/Db/IEntityWithUser.php
new file mode 100644
index 00000000..5a2a7bd3
--- /dev/null
+++ b/lib/Db/IEntityWithUser.php
@@ -0,0 +1,46 @@
+<?php
+/**
+ * @copyright Copyright (c) 2017 Kai Schröer <git@schroeer.co>
+ *
+ * @author Kai Schröer <git@schroeer.co>
+ *
+ * @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\Polls\Db;
+
+interface IEntityWithUser {
+	/**
+	 * Is this object'suser or owner an internal user or external
+	 */
+	public function getUserId(): string;
+
+	/**
+	 * Returns the displayname of this object's user or owner
+	 */
+	public function getDisplayName(): string;
+
+	/**
+	 * Creates a hashed version of the userId
+	 */
+	public function generateHashedUserId(): void;
+
+	/**
+	 * Returns an array with user attributes for jsonSerialize()
+	 */
+	public function getUser(): array;
+}
diff --git a/lib/Db/Option.php b/lib/Db/Option.php
index 965d5fc3..9aea04fd 100644
--- a/lib/Db/Option.php
+++ b/lib/Db/Option.php
@@ -30,12 +30,6 @@ use DateTime;
 use DateTimeImmutable;
 use DateTimeZone;
 use JsonSerializable;
-
-use OCA\Polls\Helper\Container;
-use OCP\AppFramework\Db\Entity;
-use OCP\IUser;
-use OCP\IUserManager;
-use OCP\AppFramework\Db\DoesNotExistException;
 use OCP\IL10N;
 
 /**
@@ -58,7 +52,7 @@ use OCP\IL10N;
  * @method int getTimestamp()
  * @method void setTimestamp(integer $value)
  */
-class Option extends Entity implements JsonSerializable {
+class Option extends EntityWithUser implements JsonSerializable {
 	public const TABLE = 'polls_options';
 
 	/** @var int $pollId */
@@ -107,12 +101,6 @@ class Option extends Entity implements JsonSerializable {
 	/** @var bool $isBookedUp */
 	public $isBookedUp = false;
 
-	/** @var IUserManager */
-	private $userManager;
-
-	/** @var ShareMapper */
-	private $shareMapper;
-
 	public function __construct() {
 		$this->addType('released', 'int');
 		$this->addType('pollId', 'int');
@@ -120,8 +108,6 @@ class Option extends Entity implements JsonSerializable {
 		$this->addType('order', 'int');
 		$this->addType('confirmed', 'int');
 		$this->addType('duration', 'int');
-		$this->userManager = Container::queryClass(IUserManager::class);
-		$this->shareMapper = Container::queryClass(ShareMapper::class);
 	}
 
 	/**
@@ -145,15 +131,10 @@ class Option extends Entity implements JsonSerializable {
 				'votes' => $this->votes,
 				'isBookedUp' => $this->isBookedUp,
 			],
-			'owner' => [
-				'userId' => $this->getOwner(),
-				'displayName' => $this->getDisplayName(),
-				'isNoUser' => $this->getOwnerIsNoUser(),
-			],
+			'owner' => $this->getUser(),
 		];
 	}
 
-
 	public function getPollOptionText(): string {
 		if ($this->getTimestamp() && $this->getDuration()) {
 			return date('c', $this->getTimestamp()) . ' - ' . date('c', $this->getTimestamp() + $this->getDuration());
@@ -194,30 +175,6 @@ class Option extends Entity implements JsonSerializable {
 		$this->setOwner($userId);
 	}
 
-	// used for 1.9.0-beta1 installations
-	public function getOwner() : string {
-		if ($this->owner === 'disallow' || $this->owner === null) {
-			return '';
-		}
-		return $this->owner;
-	}
-
-	public function getDisplayName(): ?string {
-		if (!strncmp($this->getOwner(), 'deleted_', 8)) {
-			return 'Deleted User';
-		}
-	
-		if ($this->getOwnerIsNoUser()) {
-			try {
-				$share = $this->shareMapper->findByPollAndUser($this->getPollId(), $this->getOwner());
-				return $share->getDisplayName();
-			} catch (DoesNotExistException $e) {
-				return $this->getOwner();
-			}
-		}
-		return $this->userManager->get($this->getOwner())->getDisplayName();
-	}
-
 	public function getDateStringLocalized(DateTimeZone $timeZone, IL10N $l10n) {
 		$mutableFrom = DateTime::createFromImmutable($this->getDateObjectFrom($timeZone));
 		$mutableTo = DateTime::createFromImmutable($this->getDateObjectTo($timeZone));
@@ -251,9 +208,9 @@ class Option extends Entity implements JsonSerializable {
 		return $dateTimeFrom . ' - ' . $dateTimeTo;
 	}
 
-	private function getOwnerIsNoUser(): bool {
-		return !$this->userManager->get($this->getOwner()) instanceof IUser;
-	}
+	// private function getOwnerIsNoUser(): bool {
+	// 	return !$this->userManager->get($this->getOwner()) instanceof IUser;
+	// }
 
 	/**
 	 * Check, if the date option spans one or more whole days (from 00:00 to 24:00)
diff --git a/lib/Db/Poll.php b/lib/Db/Poll.php
index b22c710a..2b60161c 100644
--- a/lib/Db/Poll.php
+++ b/lib/Db/Poll.php
@@ -28,9 +28,6 @@ namespace OCA\Polls\Db;
 use JsonSerializable;
 use OCA\Polls\Exceptions\NoDeadLineException;
 use OCA\Polls\Helper\Container;
-use OCP\AppFramework\Db\Entity;
-use OCP\IUser;
-use OCP\IUserManager;
 use OCP\IURLGenerator;
 
 /**
@@ -78,7 +75,7 @@ use OCP\IURLGenerator;
  * @method void setMiscSettings(string $value)
  */
 
-class Poll extends Entity implements JsonSerializable {
+class Poll extends EntityWithUser implements JsonSerializable {
 	public const TABLE = 'polls_polls';
 	public const TYPE_DATE = 'datePoll';
 	public const TYPE_TEXT = 'textPoll';
@@ -165,9 +162,6 @@ class Poll extends Entity implements JsonSerializable {
 	/** @var IURLGenerator */
 	private $urlGenerator;
 
-	/** @var IUserManager */
-	private $userManager;
-
 	/** @var OptionMapper */
 	private $optionMapper;
 
@@ -185,9 +179,8 @@ class Poll extends Entity implements JsonSerializable {
 		$this->addType('important', 'int');
 		$this->addType('hideBookedUp', 'int');
 		$this->addType('useNo', 'int');
-		$this->urlGenerator = Container::queryClass(IURLGenerator::class);
-		$this->userManager = Container::queryClass(IUserManager::class);
 		$this->optionMapper = Container::queryClass(OptionMapper::class);
+		$this->urlGenerator = Container::queryClass(IURLGenerator::class);
 	}
 
 	/**
@@ -217,10 +210,7 @@ class Poll extends Entity implements JsonSerializable {
 			'hideBookedUp' => $this->getHideBookedUp(),
 			'useNo' => $this->getUseNo(),
 			'autoReminder' => $this->getAutoReminder(),
-			'owner' => [
-				'userId' => $this->getOwner(),
-				'displayName' => $this->getDisplayName(),
-			],
+			'owner' => $this->getUser(),
 		];
 	}
 
@@ -322,18 +312,16 @@ class Poll extends Entity implements JsonSerializable {
 		return htmlspecialchars($this->description);
 	}
 
-	public function getDisplayName(): string {
-		return $this->userManager->get($this->owner) instanceof IUser
-			? $this->userManager->get($this->owner)->getDisplayName()
-			: $this->owner;
-	}
-
 	private function setMiscSettingsArray(array $value) : void {
 		$this->setMiscSettings(json_encode($value));
 	}
 
-	private function getMiscSettingsArray() : ?array {
-		return json_decode($this->getMiscSettings(), true);
+	private function getMiscSettingsArray() : array {
+		if ($this->getMiscSettings()) {
+			return json_decode($this->getMiscSettings(), true);
+		}
+		
+		return [];
 	}
 
 	public function getTimeToDeadline(int $time = 0): ?int {
@@ -372,7 +360,6 @@ class Poll extends Entity implements JsonSerializable {
 		throw new NoDeadLineException();
 	}
 
-
 	/**
 	 * @param bool|string|int|array $value
 	 */
diff --git a/lib/Db/Share.php b/lib/Db/Share.php
index 153857eb..864cafef 100644
--- a/lib/Db/Share.php
+++ b/lib/Db/Share.php
@@ -221,8 +221,12 @@ class Share extends Entity implements JsonSerializable {
 		$this->setMiscSettings(json_encode($value));
 	}
 
-	private function getMiscSettingsArray() : ?array {
-		return json_decode($this->getMiscSettings(), true);
+	private function getMiscSettingsArray() : array {
+		if ($this->getMiscSettings()) {
+			return json_decode($this->getMiscSettings(), true);
+		}
+		
+		return [];
 	}
 
 	/**
diff --git a/lib/Db/ShareMapper.php b/lib/Db/ShareMapper.php
index 49228c42..d2716921 100644
--- a/lib/Db/ShareMapper.php
+++ b/lib/Db/ShareMapper.php
@@ -24,6 +24,9 @@
 
 namespace OCA\Polls\Db;
 
+use OCA\Polls\Exceptions\ShareNotFoundException;
+use OCA\Polls\Model\UserBase;
+use OCP\AppFramework\Db\DoesNotExistException;
 use OCP\AppFramework\Db\QBMapper;
 use OCP\DB\Exception;
 use OCP\DB\QueryBuilder\IQueryBuilder;
@@ -102,22 +105,44 @@ class ShareMapper extends QBMapper {
 		   	$qb->expr()->eq('user_id', $qb->createNamedParameter($userId, IQueryBuilder::PARAM_STR))
 		   );
 
-		return $this->findEntity($qb);
+		try {
+			return $this->findEntity($qb);
+		} catch (DoesNotExistException $e) {
+			throw new ShareNotFoundException("Share not found by userId and pollId");
+		}
 	}
 
 	/**
-	 * @throws \OCP\AppFramework\Db\DoesNotExistException if not found
+	 * Returns a fake share in case of deleted shares
 	 */
+	public function getReplacement($pollId, $userId): ?Share {
+		if (!$userId) {
+			return null;
+		}
+
+		$share = new Share;
+		$share->setUserId($userId);
+		$share->setPollId($pollId);
+		$share->setType(UserBase::TYPE_EXTERNAL);
+		$share->setToken('deleted_share_' . $userId . '_' . $pollId);
+		$share->setDisplayName('Deleted User');
+		return $share;
+	}
+
 	public function findByToken(string $token): Share {
 		$qb = $this->db->getQueryBuilder();
 
 		$qb->select('*')
-		   ->from($this->getTableName())
-		   ->where(
-		   	$qb->expr()->eq('token', $qb->createNamedParameter($token, IQueryBuilder::PARAM_STR))
-		   );
-
-		return $this->findEntity($qb);
+		->from($this->getTableName())
+		->where(
+			$qb->expr()->eq('token', $qb->createNamedParameter($token, IQueryBuilder::PARAM_STR))
+		);
+		
+		try {
+			return $this->findEntity($qb);
+		} catch (DoesNotExistException $e) {
+			throw new ShareNotFoundException('Token ' . $token . ' does not exist');
+		}
 	}
 
 	public function deleteByPoll(int $pollId): void {
diff --git a/lib/Db/Vote.php b/lib/Db/Vote.php
index 1c00c21e..243d9e6b 100644
--- a/lib/Db/Vote.php
+++ b/lib/Db/Vote.php
@@ -26,11 +26,6 @@
 namespace OCA\Polls\Db;
 
 use JsonSerializable;
-use OCA\Polls\Helper\Container;
-use OCP\IUser;
-use OCP\IUserManager;
-use OCP\AppFramework\Db\Entity;
-use OCP\AppFramework\Db\DoesNotExistException;
 
 /**
  * @method int getPollId()
@@ -44,7 +39,7 @@ use OCP\AppFramework\Db\DoesNotExistException;
  * @method string getVoteAnswer()
  * @method void setVoteAnswer(string $value)
  */
-class Vote extends Entity implements JsonSerializable {
+class Vote extends EntityWithUser implements JsonSerializable {
 	public const TABLE = 'polls_votes';
 
 	/** @var int $pollId */
@@ -62,18 +57,10 @@ class Vote extends Entity implements JsonSerializable {
 	/** @var string $voteAnswer */
 	protected $voteAnswer;
 
-	/** @var IUserManager */
-	private $userManager;
-
-	/** @var ShareMapper */
-	private $shareMapper;
-
 	public function __construct() {
 		$this->addType('id', 'int');
 		$this->addType('pollId', 'int');
 		$this->addType('voteOptionId', 'int');
-		$this->userManager = Container::queryClass(IUserManager::class);
-		$this->shareMapper = Container::queryClass(ShareMapper::class);
 	}
 
 	/**
@@ -85,31 +72,7 @@ class Vote extends Entity implements JsonSerializable {
 			'pollId' => $this->getPollId(),
 			'optionText' => $this->getVoteOptionText(),
 			'answer' => $this->getVoteAnswer(),
-			'user' => [
-				'userId' => $this->getUserId(),
-				'displayName' => $this->getDisplayName(),
-				'isNoUser' => $this->getIsNoUser(),
-			],
+			'user' => $this->getUser(),
 		];
 	}
-
-	public function getDisplayName(): string {
-		if (!strncmp($this->userId, 'deleted_', 8)) {
-			return 'Deleted User';
-		}
-
-		if ($this->getIsNoUser()) {
-			try {
-				$share = $this->shareMapper->findByPollAndUser($this->getPollId(), $this->userId);
-				return $share->getDisplayName();
-			} catch (DoesNotExistException $e) {
-				return $this->userId;
-			}
-		}
-		return $this->userManager->get($this->userId)->getDisplayName();
-	}
-
-	public function getIsNoUser(): bool {
-		return !($this->userManager->get($this->userId) instanceof IUser);
-	}
 }
diff --git a/lib/Exceptions/NotFoundException.php b/lib/Exceptions/NotFoundException.php
index bb678965..dbd70466 100644
--- a/lib/Exceptions/NotFoundException.php
+++ b/lib/Exceptions/NotFoundException.php
@@ -27,9 +27,8 @@ use OCP\AppFramework\Http;
 
 class NotFoundException extends Exception {
 	public function __construct(
-		string $e = 'Not found',
-		int $status = Http::STATUS_NOT_FOUND
+		string $e = 'Not found'
 	) {
-		parent::__construct($e, $status);
+		parent::__construct($e, Http::STATUS_NOT_FOUND);
 	}
 }
diff --git a/lib/Exceptions/ShareNotFoundException.php b/lib/Exceptions/ShareNotFoundException.php
new file mode 100644
index 00000000..60d88d89
--- /dev/null
+++ b/lib/Exceptions/ShareNotFoundException.php
@@ -0,0 +1,32 @@
+<?php
+/**
+ * @copyright Copyright (c) 2020 René Gieling <github@dartcafe.de>
+ *
+ * @author René Gieling <github@dartcafe.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\Polls\Exceptions;
+
+class ShareNotFoundException extends NotFoundException {
+	public function __construct(
+		string $e = 'Share not found'
+	) {
+		parent::__construct($e);
+	}
+}
diff --git a/lib/Model/Acl.php b/lib/Model/Acl.php
index bf492402..8c47be4c 100644
--- a/lib/Model/Acl.php
+++ b/lib/Model/Acl.php
@@ -33,6 +33,7 @@ use OCA\Polls\Db\OptionMapper;
 use OCA\Polls\Db\PollMapper;
 use OCA\Polls\Db\VoteMapper;
 use OCA\Polls\Db\ShareMapper;
+use OCA\Polls\Exceptions\ShareNotFoundException;
 use OCP\IUserManager;
 use OCP\IUserSession;
 use OCP\IGroupManager;
@@ -130,7 +131,7 @@ class Acl implements JsonSerializable {
 			$this->poll = $this->pollMapper->find($this->share->getPollId());
 			$this->validateShareAccess();
 			$this->request($permission);
-		} catch (DoesNotExistException $e) {
+		} catch (ShareNotFoundException $e) {
 			throw new NotAuthorizedException('Error loading share ' . $token);
 		}
 
diff --git a/lib/Model/Mail/NotificationMail.php b/lib/Model/Mail/NotificationMail.php
index 6b0ff2e2..d3b6ced3 100644
--- a/lib/Model/Mail/NotificationMail.php
+++ b/lib/Model/Mail/NotificationMail.php
@@ -108,6 +108,6 @@ class NotificationMail extends MailBase {
 			VoteEvent::SET => $this->l10n->t('%s has voted.', [$displayName]),
 		];
 
-		return $logStrings[$logItem->getMessageId()] ?? $logItem->getMessageId() . " (" . $displayName . ")";
+		return $logStrings[$logItem->getMessageId()] ?? $logItem->getMessageId() . ' (' . $displayName . ')';
 	}
 }
diff --git a/lib/Provider/ActivityProvider.php b/lib/Provider/ActivityProvider.php
index 5992b909..7c2ba47d 100644
--- a/lib/Provider/ActivityProvider.php
+++ b/lib/Provider/ActivityProvider.php
@@ -34,6 +34,7 @@ use OCP\Activity\IEventMerger;
 use OCP\Activity\IEvent;
 use OCA\Polls\Service\ActivityService;
 use OCA\Polls\Db\ShareMapper;
+use OCA\Polls\Exceptions\ShareNotFoundException;
 
 class ActivityProvider implements IProvider {
 	/** @var IFactory */
@@ -110,7 +111,12 @@ class ActivityProvider implements IProvider {
 					'name' => $actor->getDisplayName(),
 				];
 			} else {
-				$share = $this->shareMapper->findByPollAndUser($event->getObjectId(), $event->getAuthor());
+				try {
+					$share = $this->shareMapper->findByPollAndUser($event->getObjectId(), $event->getAuthor());
+				} catch (ShareNotFoundException $e) {
+					// User seems to be probaly deleted, use fake share
+					$share = $this->shareMapper->getReplacement($event->getObjectId(), $event->getAuthor());
+				}
 				$parameters['actor'] = [
 					'type' => 'guest',
 					'id' => $share->getUserId(),
diff --git a/lib/Service/AnonymizeService.php b/lib/Service/AnonymizeService.php
index c8321e19..af9f685e 100644
--- a/lib/Service/AnonymizeService.php
+++ b/lib/Service/AnonymizeService.php
@@ -28,7 +28,6 @@ use OCA\Polls\Db\Vote;
 use OCA\Polls\Db\VoteMapper;
 use OCA\Polls\Db\Comment;
 use OCA\Polls\Db\CommentMapper;
-use OCA\Polls\Db\Option;
 use OCA\Polls\Db\OptionMapper;
 use OCA\Polls\Db\Poll;
 
@@ -112,21 +111,13 @@ class AnonymizeService {
 		return;
 	}
 
-	/**
-	 * Replaces userIds with displayName to avoid exposing usernames in public polls
-	 */
 	public static function replaceUserId(&$arrayOrObject, string $userId) : void {
 		if (is_array($arrayOrObject)) {
 			foreach ($arrayOrObject as $item) {
 				if ($item->getUserId() === $userId) {
 					continue;
 				}
-				if ($item instanceof Comment || $item instanceof Vote) {
-					$item->setUserId($item->getDisplayName());
-				}
-				if ($item instanceof Option || $item instanceof Poll) {
-					$item->setOwner($item->getDisplayName());
-				}
+				$item->generateHashedUserId();
 			}
 			return;
 		}
@@ -135,13 +126,7 @@ class AnonymizeService {
 			return;
 		}
 
-		if ($arrayOrObject instanceof Option || $arrayOrObject instanceof Poll) {
-			$arrayOrObject->setOwner($arrayOrObject->getDisplayName());
-		}
-
-		if ($arrayOrObject instanceof Comment || $arrayOrObject instanceof Vote) {
-			$arrayOrObject->setUserId($arrayOrObject->getDisplayName());
-		}
+		$arrayOrObject->generateHashedUserId();
 
 		return;
 	}
diff --git a/lib/Service/PollService.php b/lib/Service/PollService.php
index c5b8a636..f9df6dbe 100644
--- a/lib/Service/PollService.php
+++ b/lib/Service/PollService.php
@@ -208,8 +208,12 @@ class PollService {
 
 	/**
 	 * get poll configuration
+	 *
+	 * @return (\OCA\Polls\Db\Comment|\OCA\Polls\Db\Option|\OCA\Polls\Db\Vote)[]|Poll
+	 *
+	 * @psalm-return Poll|array<\OCA\Polls\Db\Comment|\OCA\Polls\Db\Option|\OCA\Polls\Db\Vote>
 	 */
-	public function get(int $pollId) : Poll {
+	public function get(int $pollId) {
 		$this->acl->setPollId($pollId);
 		$this->poll = $this->pollMapper->find($pollId);
 
diff --git a/lib/Service/ShareService.php b/lib/Service/ShareService.php
index 9b23def4..ad6c452f 100644
--- a/lib/Service/ShareService.php
+++ b/lib/Service/ShareService.php
@@ -37,6 +37,7 @@ use OCA\Polls\Exceptions\InvalidShareTypeException;
 use OCA\Polls\Exceptions\ShareAlreadyExistsException;
 use OCA\Polls\Exceptions\NotFoundException;
 use OCA\Polls\Exceptions\InvalidUsernameException;
+use OCA\Polls\Exceptions\ShareNotFoundException;
 use OCA\Polls\Model\Acl;
 use OCA\Polls\Model\UserBase;
 use OCP\AppFramework\Db\DoesNotExistException;
@@ -144,13 +145,9 @@ class ShareService {
 	 * Get share by token for accessing the poll
 	 */
 	public function get(string $token, bool $validateShareType = false): Share {
-		try {
-			$this->share = $this->shareMapper->findByToken($token);
-			if ($validateShareType) {
-				$this->validateShareType();
-			}
-		} catch (DoesNotExistException $e) {
-			throw new NotFoundException('Token ' . $token . ' does not exist');
+		$this->share = $this->shareMapper->findByToken($token);
+		if ($validateShareType) {
+			$this->validateShareType();
 		}
 
 		// Exception: logged in user accesses the poll via public share link
@@ -184,15 +181,10 @@ class ShareService {
 	 * Change share type
 	 */
 	public function setType(string $token, string $type): Share {
-		try {
-			$this->share = $this->shareMapper->findByToken($token);
-			$this->acl->setPollId($this->share->getPollId(), Acl::PERMISSION_POLL_EDIT);
-			$this->share->setType($type);
-			$this->share = $this->shareMapper->update($this->share);
-		} catch (DoesNotExistException $e) {
-			throw new NotFoundException('Token ' . $token . ' does not exist');
-		}
-
+		$this->share = $this->shareMapper->findByToken($token);
+		$this->acl->setPollId($this->share->getPollId(), Acl::PERMISSION_POLL_EDIT);
+		$this->share->setType($type);
+		$this->share = $this->shareMapper->update($this->share);
 		$this->eventDispatcher->dispatchTyped(new ShareTypeChangedEvent($this->share));
 
 		return $this->share;
@@ -207,7 +199,7 @@ class ShareService {
 			$this->acl->setPollId($this->share->getPollId(), Acl::PERMISSION_POLL_EDIT);
 			$this->share->setPublicPollEmail($value);
 			$this->share = $this->shareMapper->update($this->share);
-		} catch (DoesNotExistException $e) {
+		} catch (ShareNotFoundException $e) {
 			throw new NotFoundException('Token ' . $token . ' does not exist');
 		}
 		$this->eventDispatcher->dispatchTyped(new ShareChangedRegistrationConstraintEvent($this->share));
@@ -338,7 +330,7 @@ class ShareService {
 			$this->share = $this->shareMapper->findByToken($token);
 			$this->acl->setPollId($this->share->getPollId(), Acl::PERMISSION_POLL_EDIT);
 			$this->shareMapper->delete($this->share);
-		} catch (DoesNotExistException $e) {
+		} catch (ShareNotFoundException $e) {
 			// silently catch
 		}
 
@@ -431,7 +423,7 @@ class ShareService {
 				throw new ShareAlreadyExistsException;
 			} catch (MultipleObjectsReturnedException $e) {
 				throw new ShareAlreadyExistsException;
-			} catch (DoesNotExistException $e) {
+			} catch (ShareNotFoundException $e) {
 				// continue
 			}
 		}
diff --git a/lib/Service/UserService.php b/lib/Service/UserService.php
index 2d41ccf7..39c865fe 100644
--- a/lib/Service/UserService.php
+++ b/lib/Service/UserService.php
@@ -26,8 +26,8 @@ namespace OCA\Polls\Service;
 use OCA\Polls\Db\Share;
 use OCA\Polls\Db\ShareMapper;
 use OCA\Polls\Db\VoteMapper;
-use OCA\Polls\Exceptions\Exception;
 use OCA\Polls\Exceptions\InvalidShareTypeException;
+use OCA\Polls\Exceptions\ShareNotFoundException;
 use OCA\Polls\Model\User\Admin;
 use OCA\Polls\Model\Group\Circle;
 use OCA\Polls\Model\Group\ContactGroup;
@@ -127,10 +127,12 @@ class UserService {
 		// Otherwise get it from a share that belongs to the poll and return the share user
 		try {
 			$share = $this->shareMapper->findByPollAndUser($pollId, $userId);
-			return $this->getUserFromShare($share);
-		} catch (Exception $e) {
-			return null;
+		} catch (ShareNotFoundException $e) {
+			// User seems to be probaly deleted, use fake share
+			$share = $this->shareMapper->getReplacement($pollId, $userId);
 		}
+
+		return $this->getUserFromShare($share);
 	}
 
 	/**