public function show(Course $course)
 {
     if (Enroll::where(['course_id' => $course->id, 'user_id' => Auth::user()->id])->ongoing()->exists() and $course->published()) {
         $lecture = $course->lectures()->first();
         $comments = $lecture->comments()->latest('created_at')->get();
         return view('courses.course', compact('course', 'lecture', 'comments'));
     }
     return view('courses.show', compact('course'));
 }