post method to update a tag's name

Takes 2 query parameters:
tag (old name) and tagName (which becomes the new name.)
Fixes: zotero#108

controllers/TagsController.php

@@ -28,7 +28,7 @@
 
 class TagsController extends ApiController {
 	public function tags() {
-		$this->allowMethods(['HEAD', 'GET', 'DELETE']);
+		$this->allowMethods(['HEAD', 'GET', 'DELETE', 'POST']);
 
 		if (!$this->permissions->canAccess($this->objectLibraryID)) {
 			$this->e403();
@@ -66,7 +66,7 @@ public function tags() {
 		}
 		// All tags
 		else {
-			$this->allowMethods(array('GET', 'DELETE'));
+			$this->allowMethods(array('GET', 'DELETE', 'POST'));
 
 			if ($this->scopeObject) {
 				$this->allowMethods(array('GET'));
@@ -197,6 +197,28 @@ public function tags() {
 				Zotero_DB::commit();
 				$this->e204();
 			}
+			else if ($this->method == 'POST') {
+				if (empty($this->queryParams['tag']) || empty($this->queryParams['tagName']) ) {
+					$this->e400("tag and tagName are required query parameters.");
+				}
+
+				$oldTagName = $this->queryParams['tag'];
+				$newTagName =  $this->queryParams['tagName'];					
+
+				$tagID = Zotero_Tags::getIDs($this->objectLibraryID, $oldTagName);
+				$tagCount = count($tagID);
+
+				// Make sure only one tag has been fetched
+				if ($tagCount != 1) {
+					$this->e400("Only one tag should be found to be renamed. Found: $tagCount");
+				}
+
+				$tag = Zotero_Tags::get($this->objectLibraryID, $tagID[0], true);
+				$tag->name = $newTagName;
+				$tag -> save();
+
+				$this->e204();
+			}
 			else {
 				$title = "Tags";
 				$results = Zotero_Tags::search($this->objectLibraryID, $this->queryParams);

model/API.inc.php

@@ -88,6 +88,7 @@ class Zotero_API {
 		'collectionKey' => [],
 		'searchKey' => [],
 		'tag' => '',
+		'tagName' => '',
 		'tagType' => '',
 		'since' => false,
 		'sincetime' => false,