$gradebook = new Gradebook();
$skill_gradebook = new SkillRelGradebook();
switch ($action) {
    case 'add':
        if (api_is_platform_admin() || api_is_drh()) {
            if (isset($_REQUEST['id']) && !empty($_REQUEST['id'])) {
                $skill_id = $skill->edit($_REQUEST);
            } else {
                $skill_id = $skill->add($_REQUEST);
            }
        }
        echo $skill_id;
        break;
    case 'delete_skill':
        if (api_is_platform_admin() || api_is_drh()) {
            echo $skill->delete($_REQUEST['skill_id']);
        }
        break;
    case 'find_skills':
        $skills = $skill->find('all', array('where' => array('name LIKE %?% ' => $_REQUEST['tag'])));
        $return_skills = array();
        foreach ($skills as $skill) {
            $skill['caption'] = $skill['name'];
            $skill['value'] = $skill['id'];
            $return_skills[] = $skill;
        }
        echo json_encode($return_skills);
        break;
    case 'get_gradebooks':
        $gradebooks = $gradebook_list = $gradebook->get_all();
        $gradebook_list = array();