public function collections()
 {
     // Check for general library access
     if (!$this->permissions->canAccess($this->objectLibraryID)) {
         $this->e403();
     }
     if ($this->isWriteMethod()) {
         // Check for library write access
         if (!$this->permissions->canWrite($this->objectLibraryID)) {
             $this->e403("Write access denied");
         }
         // Make sure library hasn't been modified
         if (!$this->singleObject) {
             $libraryTimestampChecked = $this->checkLibraryIfUnmodifiedSinceVersion();
         }
         Zotero_Libraries::updateVersionAndTimestamp($this->objectLibraryID);
     }
     $collectionIDs = array();
     $collectionKeys = array();
     $results = array();
     // Single collection
     if ($this->singleObject) {
         $this->allowMethods(['HEAD', 'GET', 'PUT', 'PATCH', 'DELETE']);
         if (!Zotero_ID::isValidKey($this->objectKey)) {
             $this->e404();
         }
         $collection = Zotero_Collections::getByLibraryAndKey($this->objectLibraryID, $this->objectKey);
         if ($this->isWriteMethod()) {
             $collection = $this->handleObjectWrite('collection', $collection ? $collection : null);
             $this->queryParams['content'] = ['json'];
         }
         if (!$collection) {
             $this->e404("Collection not found");
         }
         $this->libraryVersion = $collection->version;
         if ($this->method == 'HEAD') {
             $this->end();
         }
         switch ($this->queryParams['format']) {
             case 'atom':
                 $this->responseXML = Zotero_Collections::convertCollectionToAtom($collection, $this->queryParams);
                 break;
             case 'json':
                 $json = $collection->toResponseJSON($this->queryParams, $this->permissions);
                 echo Zotero_Utilities::formatJSON($json);
                 break;
             default:
                 throw new Exception("Unexpected format '" . $this->queryParams['format'] . "'");
         }
     } else {
         $this->allowMethods(['HEAD', 'GET', 'POST', 'DELETE']);
         $this->libraryVersion = Zotero_Libraries::getUpdatedVersion($this->objectLibraryID);
         if ($this->scopeObject) {
             $this->allowMethods(array('GET'));
             switch ($this->scopeObject) {
                 case 'collections':
                     $collection = Zotero_Collections::getByLibraryAndKey($this->objectLibraryID, $this->scopeObjectKey);
                     if (!$collection) {
                         $this->e404("Collection not found");
                     }
                     $title = "Child Collections of ‘{$collection->name}'’";
                     $collectionIDs = $collection->getChildCollections();
                     break;
                 default:
                     throw new Exception("Invalid collections scope object '{$this->scopeObject}'");
             }
         } else {
             // Top-level items
             if ($this->subset == 'top') {
                 $this->allowMethods(array('GET'));
                 $title = "Top-Level Collections";
                 $results = Zotero_Collections::search($this->objectLibraryID, true, $this->queryParams);
             } else {
                 // Create a collection
                 if ($this->method == 'POST') {
                     $this->queryParams['format'] = 'writereport';
                     $obj = $this->jsonDecode($this->body);
                     $results = Zotero_Collections::updateMultipleFromJSON($obj, $this->queryParams, $this->objectLibraryID, $this->userID, $this->permissions, $libraryTimestampChecked ? 0 : 1, null);
                     if ($cacheKey = $this->getWriteTokenCacheKey()) {
                         Z_Core::$MC->set($cacheKey, true, $this->writeTokenCacheTime);
                     }
                     if ($this->apiVersion < 2) {
                         $uri = Zotero_API::getCollectionsURI($this->objectLibraryID);
                         $keys = array_merge(get_object_vars($results['success']), get_object_vars($results['unchanged']));
                         $queryString = "collectionKey=" . urlencode(implode(",", $keys)) . "&format=atom&content=json&order=collectionKeyList&sort=asc";
                         if ($this->apiKey) {
                             $queryString .= "&key=" . $this->apiKey;
                         }
                         $uri .= "?" . $queryString;
                         $this->queryParams = Zotero_API::parseQueryParams($queryString, $this->action, true, $this->apiVersion);
                         $title = "Collections";
                         $results = Zotero_Collections::search($this->objectLibraryID, false, $this->queryParams);
                     }
                 } else {
                     if ($this->method == 'DELETE') {
                         Zotero_DB::beginTransaction();
                         foreach ($this->queryParams['collectionKey'] as $collectionKey) {
                             Zotero_Collections::delete($this->objectLibraryID, $collectionKey);
                         }
                         Zotero_DB::commit();
                         $this->e204();
                     } else {
                         $title = "Collections";
                         $results = Zotero_Collections::search($this->objectLibraryID, false, $this->queryParams);
                     }
                 }
             }
         }
         if ($collectionIDs) {
             $this->queryParams['collectionIDs'] = $collectionIDs;
             $results = Zotero_Collections::search($this->objectLibraryID, false, $this->queryParams);
         }
         $options = ['action' => $this->action, 'uri' => $this->uri, 'results' => $results, 'requestParams' => $this->queryParams, 'permissions' => $this->permissions, 'head' => $this->method == 'HEAD'];
         switch ($this->queryParams['format']) {
             case 'atom':
                 $this->responseXML = Zotero_API::multiResponse(array_merge($options, ['title' => $this->getFeedNamePrefix($this->objectLibraryID) . $title]));
                 break;
             case 'json':
             case 'keys':
             case 'versions':
             case 'writereport':
                 Zotero_API::multiResponse($options);
                 break;
             default:
                 throw new Exception("Unexpected format '" . $this->queryParams['format'] . "'");
         }
     }
     $this->end();
 }