Introduce new enabled option for CodeHarbor

* Fix tests to ensure they work independent of config option

app/controllers/codeharbor_links_controller.rb

@@ -2,10 +2,11 @@
 
 class CodeharborLinksController < ApplicationController
   include CommonBehavior
+  before_action :verify_codeharbor_activation
   before_action :set_codeharbor_link, only: %i[show edit update destroy]
 
   def new
-    base_url = CodeOcean::Config.new(:code_ocean).read[:codeharbor][:url]
+    base_url = CodeOcean::Config.new(:code_ocean).read[:codeharbor][:url] || ''
     @codeharbor_link = CodeharborLink.new(push_url: base_url + '/import_exercise', check_uuid_url: base_url + '/import_uuid_check')
     authorize!
   end
@@ -36,6 +37,10 @@ class CodeharborLinksController < ApplicationController
     authorize @codeharbor_link
   end
 
+  def verify_codeharbor_activation
+    raise Pundit::NotAuthorizedError unless policy(CodeharborLink).enabled?
+  end
+
   def set_codeharbor_link
     @codeharbor_link = CodeharborLink.find(params[:id])
     @codeharbor_link.user = current_user

app/policies/codeharbor_link_policy.rb

@@ -8,23 +8,27 @@ class CodeharborLinkPolicy < ApplicationPolicy
   end
 
   def new?
-    teacher? || admin?
+    enabled? && (teacher? || admin?)
   end
 
   def create?
-    teacher? || admin?
+    enabled? && (teacher? || admin?)
   end
 
   def edit?
-    owner?
+    enabled? && owner?
   end
 
   def update?
-    owner?
+    enabled? && owner?
   end
 
   def destroy?
-    owner?
+    enabled? && owner?
+  end
+
+  def enabled?
+    CodeOcean::Config.new(:code_ocean).read[:codeharbor][:enabled]
   end
 
   private