Revert 'Revert "send invitations for shared calendars"'

This is basically the original commit, but with the addition that
CalDavBackend::getCalendarObjectByUID() also takes object in writable
shared calendars in to account and adjusts their uri s.t. the Sabre
library can find the returned object uri in the user's calendar
collection.

Author: rotdrop

apps/dav/lib/CalDAV/CalDavBackend.php

@@ -2146,18 +2146,44 @@ public function searchPrincipalUri(string $principalUri,
 	 * @return string|null
 	 */
 	public function getCalendarObjectByUID($principalUri, $uid) {
+		// query for shared writable calendars
+		$principals = $this->principalBackend->getGroupMembership($principalUri, true);
+		$principals = array_merge($principals, $this->principalBackend->getCircleMembership($principalUri));
+
 		$query = $this->db->getQueryBuilder();
-		$query->selectAlias('c.uri', 'calendaruri')->selectAlias('co.uri', 'objecturi')
+		$query
+			->selectAlias('c.id', 'calendarid')
+			->selectAlias('c.principaluri', 'principaluri')
+			->selectAlias('c.uri', 'calendaruri')
+			->selectAlias('co.uri', 'objecturi')
+			->selectAlias('ds.access', 'access')
 			->from('calendarobjects', 'co')
 			->leftJoin('co', 'calendars', 'c', $query->expr()->eq('co.calendarid', 'c.id'))
-			->where($query->expr()->eq('c.principaluri', $query->createNamedParameter($principalUri)))
-			->andWhere($query->expr()->eq('co.uid', $query->createNamedParameter($uid)))
-			->andWhere($query->expr()->isNull('co.deleted_at'));
+			->leftJoin('co', 'dav_shares', 'ds', $query->expr()->eq('co.calendarid', 'ds.resourceid'))
+			->where($query->expr()->eq('co.uid', $query->createNamedParameter($uid)))
+			->andWhere($query->expr()->isNull('co.deleted_at'))
+			->andWhere($query->expr()->orX(
+				$query->expr()->eq('c.principaluri', $query->createNamedParameter($principalUri)),
+				$query->expr()->andX(
+					$query->expr()->in('ds.principaluri', $query->createParameter('shareprincipal')),
+					$query->expr()->eq('ds.type', $query->createParameter('type')),
+					$query->expr()->eq('ds.access', $query->createParameter('access')),
+				)
+			))
+			->setParameter('access', Backend::ACCESS_READ_WRITE)
+			->setParameter('type', 'calendar')
+			->setParameter('shareprincipal', $principals, \Doctrine\DBAL\Connection::PARAM_STR_ARRAY);
 		$stmt = $query->executeQuery();
 		$row = $stmt->fetch();
 		$stmt->closeCursor();
 		if ($row) {
-			return $row['calendaruri'] . '/' . $row['objecturi'];
+			if ($row['principaluri'] != $principalUri) {
+				[, $name] = Uri\split($row['principaluri']);
+				$calendarUri = $row['calendaruri'] . '_shared_by_' . $name;
+			} else {
+				$calendarUri = $row['calendaruri'];
+			}
+			return $calendarUri . '/' . $row['objecturi'];
 		}
 
 		return null;

apps/dav/lib/CalDAV/Schedule/Plugin.php

@@ -162,7 +162,53 @@ public function calendarObjectChange(RequestInterface $request, ResponseInterfac
 			$this->pathOfCalendarObjectChange = $request->getPath();
 		}
 
-		parent::calendarObjectChange($request, $response, $vCal, $calendarPath, $modified, $isNew);
+		//parent::calendarObjectChange($request, $response, $vCal, $calendarPath, $modified, $isNew);
+
+		if (!$this->scheduleReply($this->server->httpRequest)) {
+			return;
+		}
+
+		$calendarNode = $this->server->tree->getNodeForPath($calendarPath);
+
+		// Original code in parent class:
+		//
+		// $addresses = $this->getAddressesForPrincipal(
+		//  	$calendarNode->getOwner()
+		// );
+
+		// Allow also writable shared calendars:
+		$addresses = $this->getAddressesForPrincipal(
+			$calendarNode->getPrincipalURI()
+		);
+
+		if (!$isNew) {
+			$node = $this->server->tree->getNodeForPath($request->getPath());
+			$oldObj = Reader::read($node->get());
+		} else {
+			$oldObj = null;
+		}
+
+		$this->processICalendarChange($oldObj, $vCal, $addresses, [], $modified);
+
+		if ($oldObj) {
+			// Destroy circular references so PHP will GC the object.
+			$oldObj->destroy();
+		}
+	}
+
+	/**
+	 * This method checks the 'Schedule-Reply' header
+	 * and returns false if it's 'F', otherwise true.
+	 *
+	 * Copied from Sabre/DAV's Schedule plugin, because it's
+	 * private for whatever reason
+	 *
+	 * @param RequestInterface $request
+	 * @return bool
+	 */
+	private function scheduleReply(RequestInterface $request) {
+		$scheduleReply = $request->getHeader('Schedule-Reply');
+		return $scheduleReply !== 'F';
 	}
 
 	/**