public async Task AddCourseMemberAsync(int courseId, string teacherEmail)
{
bool teacherIsAlreadyAdded = courseRepository
.GetCourseTeachers(courseId)
.Any(t => t.User.Email == teacherEmail);
if (teacherIsAlreadyAdded)
{
throw new BadRequestException("The teacher is already added!");
}
Teacher teacher = await teacherRepository.GetByEmailAsync(teacherEmail);
Course course = await courseRepository.GetByIdAsync(courseId);
if (teacher.UniversityId != course.UniversityId)
{
throw new BadRequestException("Teacher of another university can't be added to this course!");
}
await courseRepository.AddCourseMemberAsync(courseId, teacher.UserId);
await courseRepository.SaveChangesAsync();
}