# ENTITIES


@Entity
@Table(name = "course")
@Getter
@NoArgsConstructor
public class Course {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(nullable = false, name = "course_name")
    private String courseName;

    @Column(nullable = false, name = "description")
    private String description;


    @OneToMany(mappedBy = "course", cascade = {CascadeType.DETACH, CascadeType.MERGE, CascadeType.PERSIST, CascadeType.REFRESH})
    @JsonBackReference
    private Set<Student> courseStudents;

    public void addStudent(Student student){
        if(courseStudents == null)
            courseStudents = new HashSet<>();

        courseStudents.add(student);
    }

    public Course(String courseName, String description) {
        this.courseName = courseName;
        this.description = description;
    }
}


@Entity
@Table(name = "student")
@NoArgsConstructor
@Getter
@AllArgsConstructor
@JsonIgnoreProperties({"hibernateLazyInitializer", "handler"})
public class Student {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(nullable = false)
    private String name;

    @Column(nullable = false)
    private String surname;

    @NaturalId
    private String identificationString;

    @ManyToOne(cascade = {CascadeType.DETACH, CascadeType.MERGE, CascadeType.PERSIST, CascadeType.REFRESH}, fetch = FetchType.LAZY)
    @JoinColumn(name = "course_id")
    @JsonManagedReference
    private Course course;

    public void setCourse(Course course) {
        this.course = course;
    }

    public Student(String name, String surname, String identificationString) {
        this.name = name;
        this.surname = surname;
        this.identificationString = identificationString;
    }

    public Student(String name, String surname, String identificationString, Course course) {
        this.name = name;
        this.surname = surname;
        this.identificationString = identificationString;
        this.course = course;
    }
}


#DTOs

@Data
@Getter
@AllArgsConstructor
public class GetStudentDTO {
    private Long id;
    private String name;
    private String surname;
    private String identificationString;
    private Course course;
}


@Getter
public class SaveStudentDTO {
    @JsonProperty
    private String name;

    @JsonProperty
    private String surname;

    @JsonProperty
    private String idString;

    @JsonProperty
    private Long idCourse;
}

#MAPPER FOR DTO
@Component
public class GetStudentMapper {

    public GetStudentDTO toDto(Student student) {
        Long id = student.getId();
        String name = student.getName();
        String surname = student.getSurname();
        String idString = student.getIdentificationString();
        Course course = student.getCourse();
        return new GetStudentDTO(id, name, surname, idString, course);
    }

    public Student toStudent(GetStudentDTO studentDTO) {
        return new Student(studentDTO.getId(), studentDTO.getName(), studentDTO.getSurname(), studentDTO.getIdentificationString(), studentDTO.getCourse());
    }
}

#STUDENT SERVICE
@Service
public class StudentService {
    StudentRepository studentRepository;
    CourseRepository courseRepository;

    @Autowired
    public StudentService(StudentRepository studentRepository, CourseRepository courseRepository) {
        this.studentRepository = studentRepository;
        this.courseRepository = courseRepository;
    }

    @Transactional
    public Student save(Student student){
        return studentRepository.save(student);
    }

    @Transactional
    public List<Student> findAll(){
        return studentRepository.findAll();

    }
}

#CONTROLLER

@RequestMapping(path = "/students")
@RestController
public class StudentController {

    private final StudentService studentService;
    private final CourseService courseService;
    private final GetStudentMapper studentMapper;

    @Autowired
    public StudentController(StudentService studentService, CourseService courseService, GetStudentMapper studentMapper) {
        this.studentService = studentService;
        this.courseService = courseService;
        this.studentMapper = studentMapper;
    }

    @PostMapping(path = "/")
    ResponseEntity<?> addStudent(@RequestBody SaveStudentDTO studentToAdd){

        Optional<Course> course = courseService.findById(studentToAdd.getIdCourse());
        //check if course exists
        if (course.isPresent()){
            Student student = studentService.save(
                new Student(
                    studentToAdd.getName(),
                    studentToAdd.getSurname(),
                    studentToAdd.getIdString(),
                    course.get()
                )
            );
            course.get().addStudent(student);
            return ResponseEntity.ofNullable(student);
        }

        return (ResponseEntity<?>) ResponseEntity.badRequest();
    }

    @GetMapping(path = "/")
    ResponseEntity<?> getStudents(){
        List<GetStudentDTO> students = studentService.findAll().stream().map(studentMapper::toDto).toList();
        return ResponseEntity.ok(students);
    }
}