Merge pull request #2335 from nextcloud/grouping-for-activities

Bring back grouping for activities

5 files changed, 412 insertions, 109 deletions

diff --git a/apps/files/lib/Activity/Provider.php b/apps/files/lib/Activity/Provider.php
index f1ffb851203..863e7644059 100644
--- a/apps/files/lib/Activity/Provider.php
+++ b/apps/files/lib/Activity/Provider.php
@@ -22,6 +22,7 @@
 namespace OCA\Files\Activity;
 
 use OCP\Activity\IEvent;
+use OCP\Activity\IEventMerger;
 use OCP\Activity\IManager;
 use OCP\Activity\IProvider;
 use OCP\IL10N;
@@ -43,6 +44,9 @@ class Provider implements IProvider {
 	/** @var IUserManager */
 	protected $userManager;
 
+	/** @var IEventMerger */
+	protected $eventMerger;
+
 	/** @var string[] cached displayNames - key is the UID and value the displayname */
 	protected $displayNames = [];
 
@@ -51,12 +55,14 @@ class Provider implements IProvider {
 	 * @param IURLGenerator $url
 	 * @param IManager $activityManager
 	 * @param IUserManager $userManager
+	 * @param IEventMerger $eventMerger
 	 */
-	public function __construct(IL10N $l, IURLGenerator $url, IManager $activityManager, IUserManager $userManager) {
+	public function __construct(IL10N $l, IURLGenerator $url, IManager $activityManager, IUserManager $userManager, IEventMerger $eventMerger) {
 		$this->l = $l;
 		$this->url = $url;
 		$this->activityManager = $activityManager;
 		$this->userManager = $userManager;
+		$this->eventMerger = $eventMerger;
 	}
 
 	/**
@@ -71,165 +77,134 @@ class Provider implements IProvider {
 			throw new \InvalidArgumentException();
 		}
 
-		if ($previousEvent instanceof IEvent && $event->getSubject() !== $previousEvent->getSubject()) {
-			// Different subject means not the same string, so no grouping
-			$previousEvent = null;
-		}
-
 		if ($this->activityManager->isFormattingFilteredObject()) {
 			try {
-				return $this->parseShortVersion($event);
+				return $this->parseShortVersion($event, $previousEvent);
 			} catch (\InvalidArgumentException $e) {
 				// Ignore and simply use the long version...
 			}
 		}
 
-		return $this->parseLongVersion($event);
+		return $this->parseLongVersion($event, $previousEvent);
 	}
 
 	/**
 	 * @param IEvent $event
+	 * @param IEvent|null $previousEvent
 	 * @return IEvent
 	 * @throws \InvalidArgumentException
 	 * @since 11.0.0
 	 */
-	public function parseShortVersion(IEvent $event) {
-		$parsedParameters = $this->getParsedParameters($event->getSubject(), $event->getSubjectParameters());
-		$richParameters = $this->getRichParameters($event->getSubject(), $event->getSubjectParameters());
+	public function parseShortVersion(IEvent $event, IEvent $previousEvent = null) {
+		$parsedParameters = $this->getParameters($event->getSubject(), $event->getSubjectParameters());
 
 		if ($event->getSubject() === 'created_by') {
-			$event->setParsedSubject($this->l->t('Created by %s', [$parsedParameters[1]]))
-				->setRichSubject($this->l->t('Created by {user1}'), ['user1' => $richParameters['user1']])
-				->setIcon($this->url->getAbsoluteURL($this->url->imagePath('files', 'add-color.svg')));
+			$subject = $this->l->t('Created by {user}');
+			$event->setIcon($this->url->getAbsoluteURL($this->url->imagePath('files', 'add-color.svg')));
 		} else if ($event->getSubject() === 'changed_by') {
-			$event->setParsedSubject($this->l->t('Changed by %2$s', [$parsedParameters[1]]))
-				->setRichSubject($this->l->t('Changed by {user1}'), ['user1' => $richParameters['user1']])
-				->setIcon($this->url->getAbsoluteURL($this->url->imagePath('files', 'change.svg')));
+			$subject = $this->l->t('Changed by {user}');
+			$event->setIcon($this->url->getAbsoluteURL($this->url->imagePath('files', 'change.svg')));
 		} else if ($event->getSubject() === 'deleted_by') {
-			$event->setParsedSubject($this->l->t('Deleted by %2$s', [$parsedParameters[1]]))
-				->setRichSubject($this->l->t('Deleted by {user1}'), ['user1' => $richParameters['user1']])
-				->setIcon($this->url->getAbsoluteURL($this->url->imagePath('files', 'delete-color.svg')));
+			$subject = $this->l->t('Deleted by {user}');
+			$event->setIcon($this->url->getAbsoluteURL($this->url->imagePath('files', 'delete-color.svg')));
 		} else if ($event->getSubject() === 'restored_by') {
-			$event->setParsedSubject($this->l->t('Restored by %2$s', [$parsedParameters[1]]))
-				->setRichSubject($this->l->t('Restored by {user1}'), ['user1' => $richParameters['user1']]);
+			$subject = $this->l->t('Restored by {user}');
 		} else if ($event->getSubject() === 'renamed_by') {
-			$event->setParsedSubject($this->l->t('Renamed by %2$s', [$parsedParameters[1]]))
-				->setRichSubject($this->l->t('Renamed by {user1}'), ['user1' => $richParameters['user1']])
-				->setIcon($this->url->getAbsoluteURL($this->url->imagePath('files', 'change.svg')));
+			$subject = $this->l->t('Renamed by {user}');
+			$event->setIcon($this->url->getAbsoluteURL($this->url->imagePath('files', 'change.svg')));
 		} else if ($event->getSubject() === 'moved_by') {
-			$event->setParsedSubject($this->l->t('Moved by %2$s', [$parsedParameters[1]]))
-				->setRichSubject($this->l->t('Moved by {user1}'), ['user1' => $richParameters['user1']])
-				->setIcon($this->url->getAbsoluteURL($this->url->imagePath('files', 'change.svg')));
+			$subject = $this->l->t('Moved by {user}');
+			$event->setIcon($this->url->getAbsoluteURL($this->url->imagePath('files', 'change.svg')));
 		} else {
 			throw new \InvalidArgumentException();
 		}
 
+		$this->setSubjects($event, $subject, $parsedParameters);
+
+		$event = $this->eventMerger->mergeEvents('user', $event, $previousEvent);
+
 		return $event;
 	}
 
 	/**
 	 * @param IEvent $event
+	 * @param IEvent|null $previousEvent
 	 * @return IEvent
 	 * @throws \InvalidArgumentException
 	 * @since 11.0.0
 	 */
-	public function parseLongVersion(IEvent $event) {
-		$parsedParameters = $this->getParsedParameters($event->getSubject(), $event->getSubjectParameters());
-		$richParameters = $this->getRichParameters($event->getSubject(), $event->getSubjectParameters());
+	public function parseLongVersion(IEvent $event, IEvent $previousEvent = null) {
+		$parsedParameters = $this->getParameters($event->getSubject(), $event->getSubjectParameters());
 
 		if ($event->getSubject() === 'created_self') {
-			$event->setParsedSubject($this->l->t('You created %1$s', $parsedParameters))
-				->setRichSubject($this->l->t('You created {file1}'), $richParameters)
-				->setIcon($this->url->getAbsoluteURL($this->url->imagePath('files', 'add-color.svg')));
+			$subject = $this->l->t('You created {file}');
+			$event->setIcon($this->url->getAbsoluteURL($this->url->imagePath('files', 'add-color.svg')));
 		} else if ($event->getSubject() === 'created_by') {
-			$event->setParsedSubject($this->l->t('%2$s created %1$s', $parsedParameters))
-				->setRichSubject($this->l->t('{user1} created {file1}'), $richParameters)
-				->setIcon($this->url->getAbsoluteURL($this->url->imagePath('files', 'add-color.svg')));
+			$subject = $this->l->t('{user} created {file}');
+			$event->setIcon($this->url->getAbsoluteURL($this->url->imagePath('files', 'add-color.svg')));
 		} else if ($event->getSubject() === 'created_public') {
-			$event->setParsedSubject($this->l->t('%1$s was created in a public folder', $parsedParameters))
-				->setRichSubject($this->l->t('{file1} was created in a public folder'), $richParameters)
-				->setIcon($this->url->getAbsoluteURL($this->url->imagePath('files', 'add-color.svg')));
+			$subject = $this->l->t('{file} was created in a public folder');
+			$event->setIcon($this->url->getAbsoluteURL($this->url->imagePath('files', 'add-color.svg')));
 		} else if ($event->getSubject() === 'changed_self') {
-			$event->setParsedSubject($this->l->t('You changed %1$s', $parsedParameters))
-				->setRichSubject($this->l->t('You changed {file1}'), $richParameters)
-				->setIcon($this->url->getAbsoluteURL($this->url->imagePath('files', 'change.svg')));
+			$subject = $this->l->t('You changed {file}');
+			$event->setIcon($this->url->getAbsoluteURL($this->url->imagePath('files', 'change.svg')));
 		} else if ($event->getSubject() === 'changed_by') {
-			$event->setParsedSubject($this->l->t('%2$s changed %1$s', $parsedParameters))
-				->setRichSubject($this->l->t('{user1} changed {file1}'), $richParameters)
-				->setIcon($this->url->getAbsoluteURL($this->url->imagePath('files', 'change.svg')));
+			$subject = $this->l->t('{user} changed {file}');
+			$event->setIcon($this->url->getAbsoluteURL($this->url->imagePath('files', 'change.svg')));
 		} else if ($event->getSubject() === 'deleted_self') {
-			$event->setParsedSubject($this->l->t('You deleted %1$s', $parsedParameters))
-				->setRichSubject($this->l->t('You deleted {file1}'), $richParameters)
-				->setIcon($this->url->getAbsoluteURL($this->url->imagePath('files', 'delete-color.svg')));
+			$subject = $this->l->t('You deleted {file}');
+			$event->setIcon($this->url->getAbsoluteURL($this->url->imagePath('files', 'delete-color.svg')));
 		} else if ($event->getSubject() === 'deleted_by') {
-			$event->setParsedSubject($this->l->t('%2$s deleted %1$s', $parsedParameters))
-				->setRichSubject($this->l->t('{user1} deleted {file1}'), $richParameters)
-				->setIcon($this->url->getAbsoluteURL($this->url->imagePath('files', 'delete-color.svg')));
+			$subject = $this->l->t('{user} deleted {file}');
+			$event->setIcon($this->url->getAbsoluteURL($this->url->imagePath('files', 'delete-color.svg')));
 		} else if ($event->getSubject() === 'restored_self') {
-			$event->setParsedSubject($this->l->t('You restored %1$s', $parsedParameters))
-				->setRichSubject($this->l->t('You restored {file1}'), $richParameters);
+			$subject = $this->l->t('You restored {file}');
 		} else if ($event->getSubject() === 'restored_by') {
-			$event->setParsedSubject($this->l->t('%2$s restored %1$s', $parsedParameters))
-				->setRichSubject($this->l->t('{user1} restored {file1}'), $richParameters);
+			$subject = $this->l->t('{user} restored {file}');
 		} else if ($event->getSubject() === 'renamed_self') {
-			$event->setParsedSubject($this->l->t('You renamed %2$s to %1$s', $parsedParameters))
-				->setRichSubject($this->l->t('You renamed {file2} to {file1}'), $richParameters)
-				->setIcon($this->url->getAbsoluteURL($this->url->imagePath('files', 'change.svg')));
+			$subject = $this->l->t('You renamed {oldfile} to {newfile}');
+			$event->setIcon($this->url->getAbsoluteURL($this->url->imagePath('files', 'change.svg')));
 		} else if ($event->getSubject() === 'renamed_by') {
-			$event->setParsedSubject($this->l->t('%2$s renamed %3$s to %1$s', $parsedParameters))
-				->setRichSubject($this->l->t('{user1} renamed {file2} to {file1}'), $richParameters)
-				->setIcon($this->url->getAbsoluteURL($this->url->imagePath('files', 'change.svg')));
+			$subject = $this->l->t('{user} renamed {oldfile} to {newfile}');
+			$event->setIcon($this->url->getAbsoluteURL($this->url->imagePath('files', 'change.svg')));
 		} else if ($event->getSubject() === 'moved_self') {
-			$event->setParsedSubject($this->l->t('You moved %2$s to %1$s', $parsedParameters))
-				->setRichSubject($this->l->t('You moved {file2} to {file1}'), $richParameters)
-				->setIcon($this->url->getAbsoluteURL($this->url->imagePath('files', 'change.svg')));
+			$subject = $this->l->t('You moved {oldfile} to {newfile}');
+			$event->setIcon($this->url->getAbsoluteURL($this->url->imagePath('files', 'change.svg')));
 		} else if ($event->getSubject() === 'moved_by') {
-			$event->setParsedSubject($this->l->t('%2$s moved %3$s to %1$s', $parsedParameters))
-				->setRichSubject($this->l->t('{user1} moved {file2} to {file1}'), $richParameters)
-				->setIcon($this->url->getAbsoluteURL($this->url->imagePath('files', 'change.svg')));
+			$subject = $this->l->t('{user} moved {oldfile} to {newfile}');
+			$event->setIcon($this->url->getAbsoluteURL($this->url->imagePath('files', 'change.svg')));
 		} else {
 			throw new \InvalidArgumentException();
 		}
 
+		$this->setSubjects($event, $subject, $parsedParameters);
+
+		$event = $this->eventMerger->mergeEvents('file', $event, $previousEvent);
+
+		if ($event->getChildEvent() === null) {
+			// Couldn't group by file, maybe we can group by user
+			$event = $this->eventMerger->mergeEvents('user', $event, $previousEvent);
+		}
+
 		return $event;
 	}
 
-	protected function getParsedParameters($subject, array $parameters) {
-		switch ($subject) {
-			case 'created_self':
-			case 'created_public':
-			case 'changed_self':
-			case 'deleted_self':
-			case 'restored_self':
-			return [
-				array_shift($parameters[0]),
-			];
-			case 'created_by':
-			case 'changed_by':
-			case 'deleted_by':
-			case 'restored_by':
-				return [
-					array_shift($parameters[0]),
-					$parameters[1],
-				];
-			case 'renamed_self':
-			case 'moved_self':
-				return [
-					array_shift($parameters[0]),
-					array_shift($parameters[1]),
-				];
-			case 'renamed_by':
-			case 'moved_by':
-				return [
-					array_shift($parameters[0]),
-					$parameters[1],
-					array_shift($parameters[2]),
-				];
+	protected function setSubjects(IEvent $event, $subject, array $parameters) {
+		$placeholders = $replacements = [];
+		foreach ($parameters as $placeholder => $parameter) {
+			$placeholders[] = '{' . $placeholder . '}';
+			if ($parameter['type'] === 'file') {
+				$replacements[] = trim($parameter['path'], '/');
+			} else {
+				$replacements[] = $parameter['name'];
+			}
 		}
-		return [];
+
+		$event->setParsedSubject(str_replace($placeholders, $replacements, $subject))
+			->setRichSubject($subject, $parameters);
 	}
 
-	protected function getRichParameters($subject, array $parameters) {
+	protected function getParameters($subject, array $parameters) {
 		switch ($subject) {
 			case 'created_self':
 			case 'created_public':
@@ -237,28 +212,28 @@ class Provider implements IProvider {
 			case 'deleted_self':
 			case 'restored_self':
 				return [
-					'file1' => $this->getRichFileParameter($parameters[0]),
+					'file' => $this->getRichFileParameter($parameters[0]),
 				];
 			case 'created_by':
 			case 'changed_by':
 			case 'deleted_by':
 			case 'restored_by':
 				return [
-					'file1' => $this->getRichFileParameter($parameters[0]),
-					'user1' => $this->getRichUserParameter($parameters[1]),
+					'file' => $this->getRichFileParameter($parameters[0]),
+					'user' => $this->getRichUserParameter($parameters[1]),
 				];
 			case 'renamed_self':
 			case 'moved_self':
 				return [
-					'file1' => $this->getRichFileParameter($parameters[0]),
-					'file2' => $this->getRichFileParameter($parameters[1]),
+					'newfile' => $this->getRichFileParameter($parameters[0]),
+					'oldfile' => $this->getRichFileParameter($parameters[1]),
 				];
 			case 'renamed_by':
 			case 'moved_by':
 				return [
-					'file1' => $this->getRichFileParameter($parameters[0]),
-					'user1' => $this->getRichUserParameter($parameters[1]),
-					'file2' => $this->getRichFileParameter($parameters[2]),
+					'newfile' => $this->getRichFileParameter($parameters[0]),
+					'user' => $this->getRichUserParameter($parameters[1]),
+					'oldfile' => $this->getRichFileParameter($parameters[2]),
 				];
 		}
 		return [];
diff --git a/lib/private/Activity/EventMerger.php b/lib/private/Activity/EventMerger.php
new file mode 100644
index 00000000000..91e79068665
--- /dev/null
+++ b/lib/private/Activity/EventMerger.php
@@ -0,0 +1,256 @@
+<?php
+/**
+ * @copyright Copyright (c) 2016 Joas Schilling <coding@schilljs.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 OC\Activity;
+
+use OCP\Activity\IEvent;
+use OCP\Activity\IEventMerger;
+use OCP\IL10N;
+
+class EventMerger implements IEventMerger {
+
+	/** @var IL10N */
+	protected $l10n;
+
+	/**
+	 * @param IL10N $l10n
+	 */
+	public function __construct(IL10N $l10n) {
+		$this->l10n = $l10n;
+	}
+
+	/**
+	 * Combines two events when possible to have grouping:
+	 *
+	 * Example1: Two events with subject '{user} created {file}' and
+	 * $mergeParameter file with different file and same user will be merged
+	 * to '{user} created {file1} and {file2}' and the childEvent on the return
+	 * will be set, if the events have been merged.
+	 *
+	 * Example2: Two events with subject '{user} created {file}' and
+	 * $mergeParameter file with same file and same user will be merged to
+	 * '{user} created {file1}' and the childEvent on the return will be set, if
+	 * the events have been merged.
+	 *
+	 * The following requirements have to be met, in order to be merged:
+	 * - Both events need to have the same `getApp()`
+	 * - Both events must not have a message `getMessage()`
+	 * - Both events need to have the same subject `getSubject()`
+	 * - Both events need to have the same object type `getObjectType()`
+	 * - The time difference between both events must not be bigger then 3 hours
+	 * - Only up to 5 events can be merged.
+	 * - All parameters apart from such starting with $mergeParameter must be
+	 *   the same for both events.
+	 *
+	 * @param string $mergeParameter
+	 * @param IEvent $event
+	 * @param IEvent|null $previousEvent
+	 * @return IEvent
+	 */
+	public function mergeEvents($mergeParameter, IEvent $event, IEvent $previousEvent = null) {
+		// No second event => can not combine
+		if (!$previousEvent instanceof IEvent) {
+			return $event;
+		}
+
+		// Different app => can not combine
+		if ($event->getApp() !== $previousEvent->getApp()) {
+			return $event;
+		}
+
+		// Message is set => can not combine
+		if ($event->getMessage() !== '' || $previousEvent->getMessage() !== '') {
+			return $event;
+		}
+
+		// Different subject => can not combine
+		if ($event->getSubject() !== $previousEvent->getSubject()) {
+			return $event;
+		}
+
+		// Different object type => can not combine
+		if ($event->getObjectType() !== $previousEvent->getObjectType()) {
+			return $event;
+		}
+
+		// More than 3 hours difference => can not combine
+		if (abs($event->getTimestamp() - $previousEvent->getTimestamp()) > 3 * 60 * 60) {
+			return $event;
+		}
+
+		// Other parameters are not the same => can not combine
+		try {
+			list($combined, $parameters) = $this->combineParameters($mergeParameter, $event, $previousEvent);
+		} catch (\UnexpectedValueException $e) {
+			return $event;
+		}
+
+		try {
+			$newSubject = $this->getExtendedSubject($event->getRichSubject(), $mergeParameter, $combined);
+			$parsedSubject = $this->generateParsedSubject($newSubject, $parameters);
+
+			$event->setRichSubject($newSubject, $parameters)
+				->setParsedSubject($parsedSubject)
+				->setChildEvent($previousEvent);
+		} catch (\UnexpectedValueException $e) {
+			return $event;
+		}
+
+		return $event;
+	}
+
+	/**
+	 * @param string $mergeParameter
+	 * @param IEvent $event
+	 * @param IEvent $previousEvent
+	 * @return array
+	 * @throws \UnexpectedValueException
+	 */
+	protected function combineParameters($mergeParameter, IEvent $event, IEvent $previousEvent) {
+		$params1 = $event->getRichSubjectParameters();
+		$params2 = $previousEvent->getRichSubjectParameters();
+		$params = [];
+
+		$combined = 0;
+
+		// Check that all parameters from $event exist in $previousEvent
+		foreach ($params1 as $key => $parameter) {
+			if (preg_match('/^' . $mergeParameter . '(\d+)?$/', $key)) {
+				if (!$this->checkParameterAlreadyExits($params, $mergeParameter, $parameter)) {
+					$combined++;
+					$params[$mergeParameter . $combined] = $parameter;
+				}
+				continue;
+			}
+
+			if (!isset($params2[$key]) || $params2[$key] !== $parameter) {
+				// Parameter missing on $previousEvent or different => can not combine
+				throw new \UnexpectedValueException();
+			}
+
+			$params[$key] = $parameter;
+		}
+
+		// Check that all parameters from $previousEvent exist in $event
+		foreach ($params2 as $key => $parameter) {
+			if (preg_match('/^' . $mergeParameter . '(\d+)?$/', $key)) {
+				if (!$this->checkParameterAlreadyExits($params, $mergeParameter, $parameter)) {
+					$combined++;
+					$params[$mergeParameter . $combined] = $parameter;
+				}
+				continue;
+			}
+
+			if (!isset($params1[$key]) || $params1[$key] !== $parameter) {
+				// Parameter missing on $event or different => can not combine
+				throw new \UnexpectedValueException();
+			}
+
+			$params[$key] = $parameter;
+		}
+
+		return [$combined, $params];
+	}
+
+	/**
+	 * @param array[] $parameters
+	 * @param string $mergeParameter
+	 * @param array $parameter
+	 * @return bool
+	 */
+	protected function checkParameterAlreadyExits($parameters, $mergeParameter, $parameter) {
+		foreach ($parameters as $key => $param) {
+			if (preg_match('/^' . $mergeParameter . '(\d+)?$/', $key)) {
+				if ($param === $parameter) {
+					return true;
+				}
+			}
+		}
+		return false;
+	}
+
+	/**
+	 * @param string $subject
+	 * @param string $parameter
+	 * @param int $counter
+	 * @return mixed
+	 */
+	protected function getExtendedSubject($subject, $parameter, $counter) {
+		switch ($counter) {
+			case 1:
+				$replacement = '{' . $parameter . '1}';
+				break;
+			case 2:
+				$replacement = $this->l10n->t(
+					'%1$s and %2$s',
+					['{' . $parameter . '1}', '{' . $parameter . '2}']
+				);
+				break;
+			case 3:
+				$replacement = $this->l10n->t(
+					'%1$s, %2$s and %3$s',
+					['{' . $parameter . '1}', '{' . $parameter . '2}', '{' . $parameter . '3}']
+				);
+				break;
+			case 4:
+				$replacement = $this->l10n->t(
+					'%1$s, %2$s, %3$s and %4$s',
+					['{' . $parameter . '1}', '{' . $parameter . '2}', '{' . $parameter . '3}', '{' . $parameter . '4}']
+				);
+				break;
+			case 5:
+				$replacement = $this->l10n->t(
+					'%1$s, %2$s, %3$s, %4$s and %5$s',
+					['{' . $parameter . '1}', '{' . $parameter . '2}', '{' . $parameter . '3}', '{' . $parameter . '4}', '{' . $parameter . '5}']
+				);
+				break;
+			default:
+				throw new \UnexpectedValueException();
+		}
+
+		return str_replace(
+			'{' . $parameter . '}',
+			$replacement,
+			$subject
+		);
+	}
+
+	/**
+	 * @param string $subject
+	 * @param array[] $parameters
+	 * @return string
+	 */
+	protected function generateParsedSubject($subject, $parameters) {
+		$placeholders = $replacements = [];
+		foreach ($parameters as $placeholder => $parameter) {
+			$placeholders[] = '{' . $placeholder . '}';
+			if ($parameter['type'] === 'file') {
+				$replacements[] = trim($parameter['path'], '/');
+			} else if (isset($parameter['name'])) {
+				$replacements[] = $parameter['name'];
+			} else {
+				$replacements[] = $parameter['id'];
+			}
+		}
+
+		return str_replace($placeholders, $replacements, $subject);
+	}
+}
diff --git a/lib/private/AppFramework/DependencyInjection/DIContainer.php b/lib/private/AppFramework/DependencyInjection/DIContainer.php
index 48c9b6f4589..148a15172ac 100644
--- a/lib/private/AppFramework/DependencyInjection/DIContainer.php
+++ b/lib/private/AppFramework/DependencyInjection/DIContainer.php
@@ -98,6 +98,9 @@ class DIContainer extends SimpleContainer implements IAppContainer {
 		$this->registerService('OCP\\Activity\\IManager', function($c) {
 			return $this->getServer()->getActivityManager();
 		});
+		$this->registerService(\OCP\Activity\IEventMerger::class, function($c) {
+			return $this->getServer()->query(\OCP\Activity\IEventMerger::class);
+		});
 
 		$this->registerService('OCP\\ICache', function($c) {
 			return $this->getServer()->getCache();
diff --git a/lib/private/Server.php b/lib/private/Server.php
index 1d3d588e9fc..797b7a4b823 100644
--- a/lib/private/Server.php
+++ b/lib/private/Server.php
@@ -401,6 +401,11 @@ class Server extends ServerContainer implements IServerContainer {
 				$c->query(IValidator::class)
 			);
 		});
+		$this->registerService(\OCP\Activity\IEventMerger::class, function (Server $c) {
+			return new \OC\Activity\EventMerger(
+				$c->getL10N('lib')
+			);
+		});
 		$this->registerAlias(IValidator::class, Validator::class);
 		$this->registerService('AvatarManager', function (Server $c) {
 			return new AvatarManager(
diff --git a/lib/public/Activity/IEventMerger.php b/lib/public/Activity/IEventMerger.php
new file mode 100644
index 00000000000..8bd8e540770
--- /dev/null
+++ b/lib/public/Activity/IEventMerger.php
@@ -0,0 +1,64 @@
+<?php
+/**
+ * @copyright Copyright (c) 2016 Joas Schilling <coding@schilljs.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 OCP\Activity;
+
+
+/**
+ * Interface EventMerger
+ *
+ * @package OCP\Activity
+ * @since 11.0
+ */
+interface IEventMerger {
+
+	/**
+	 * Combines two events when possible to have grouping:
+	 *
+	 * Example1: Two events with subject '{user} created {file}' and
+	 * $mergeParameter file with different file and same user will be merged
+	 * to '{user} created {file1} and {file2}' and the childEvent on the return
+	 * will be set, if the events have been merged.
+	 *
+	 * Example2: Two events with subject '{user} created {file}' and
+	 * $mergeParameter file with same file and same user will be merged to
+	 * '{user} created {file1}' and the childEvent on the return will be set, if
+	 * the events have been merged.
+	 *
+	 * The following requirements have to be met, in order to be merged:
+	 * - Both events need to have the same `getApp()`
+	 * - Both events must not have a message `getMessage()`
+	 * - Both events need to have the same subject `getSubject()`
+	 * - Both events need to have the same object type `getObjectType()`
+	 * - The time difference between both events must not be bigger then 3 hours
+	 * - Only up to 5 events can be merged.
+	 * - All parameters apart from such starting with $mergeParameter must be
+	 *   the same for both events.
+	 *
+	 * @param string $mergeParameter
+	 * @param IEvent $event
+	 * @param IEvent|null $previousEvent
+	 * @return IEvent
+	 * @since 11.0
+	 */
+	public function mergeEvents($mergeParameter, IEvent $event, IEvent $previousEvent = null);
+
+}