improve logic for mod category management

lib/guardian/category_guardian.rb

@@ -1,17 +1,27 @@
 #mixin for all guardian methods dealing with category permisions
 module CategoryGuardian
+
   # Creating Method
-  def can_create_category?(parent)
-    is_admin? || (SiteSetting.allow_moderators_to_create_categories && is_moderator?)
+  def can_create_category?(parent=nil)
+    is_admin? ||
+    (
+      SiteSetting.allow_moderators_to_create_categories &&
+      is_moderator?
+    )
   end
 
   # Editing Method
   def can_edit_category?(category)
-    is_admin?
+    is_admin? ||
+    (
+      SiteSetting.allow_moderators_to_create_categories &&
+      is_moderator? &&
+      can_see_category?(category)
+    )
   end
 
   def can_delete_category?(category)
-    is_admin? &&
+    can_edit_category?(category) &&
     category.topic_count == 0 &&
     !category.uncategorized? &&
     !category.has_children?