if ( !function_exists( 'learn_press_course_content_summary' ) ) {
    /**
     * Display the content of a lesson in a course content
     * @return int
     */
    function learn_press_course_content_summary() {
        $lesson_id = isset( $_GET['lesson'] ) ? $_GET['lesson'] : '';
        echo $lesson_id;


        // this doesn't work
        // $book_id = isset( $_GET['book'] ) ? $_GET['book'] : '';
        // echo $book_id;

        global $post;
        // ensure that we are passing the lesson correctly
        if ( $lesson_id && ( 'lpr_lesson' == get_post_type( $lesson_id ) ) && ( $lesson = get_post( $lesson_id ) ) ) {
            //check if user enrolled this course or not
            $course_id    = get_the_ID();
            $user_id      = get_current_user_id();
            $user_courses = learn_press_get_user_courses( $user_id );
            $enrolled     = false;
            if ( isset( $user_courses ) && is_array( $user_courses ) ) {
                $enrolled = in_array( $course_id, $user_courses );
            }
            //if( !$enrolled && ! learn_press_is_lesson_preview( $lesson_id ) ) {
            if ( !learn_press_user_can_view_lesson( $lesson_id ) ) {
                echo "You have to enrolled to see lesson content";
                do_action( 'learn_press_course_content_course' );
                return 0;
            }

            // setup lesson as global post so we can uses the template function as in the loop
            $post = $lesson;
            setup_postdata( $post );
            do_action( 'learn_press_course_content_lesson', $post );

            // now reset the post to the course
            wp_reset_postdata();
        } else {
            do_action( 'learn_press_course_content_course' );
        }
    }
}