// ? 錯(cuò)誤示范：校驗(yàn)了，但沒(méi)管結(jié)果
@PostMapping("/user")
public ResponseEntity<String> createUser(@Valid @RequestBody UserDto userDto) {
    // 校驗(yàn)失敗了？沒(méi)關(guān)系，繼續(xù)執(zhí)行！
    userService.save(userDto); // 即使 email 為空，也照存不誤！
    return ResponseEntity.ok("success");
}

@PostMapping("/user")
public ResponseEntity<?> createUser(@Valid @RequestBody UserDto userDto, BindingResult bindingResult) {
    if (bindingResult.hasErrors()) {
        List<String> errors = bindingResult.getFieldErrors().stream()
            .map(fe -> fe.getField() + ": " + fe.getDefaultMessage())
            .collect(Collectors.toList());
        return ResponseEntity.badRequest().body(errors);
    }
    userService.save(userDto);
    return ResponseEntity.ok("success");
}

// ? 錯(cuò)誤示范：校驗(yàn)失效的“經(jīng)典陷阱”
@Service
public class UserService {

    @Autowired
    private UserController userController; // 別學(xué)這個(gè)！這是反模式！

    public void registerUser(String email, String name) {
        UserDto userDto = new UserDto(); // 手動(dòng) new！
        userDto.setEmail(email);
        userDto.setName(name);

        // ? 這里調(diào)用 Controller 方法，但 Spring 代理失效！
        userController.createUser(userDto); // @Valid 完全沒(méi)生效！
    }
}

@Service
public class UserService {

    @Autowired
    private Validator validator; // 注入標(biāo)準(zhǔn) JSR-303 Validator

    public void registerUser(String email, String name) {
        UserDto userDto = new UserDto();
        userDto.setEmail(email);
        userDto.setName(name);

        Set<ConstraintViolation<UserDto>> violations = validator.validate(userDto);
        if (!violations.isEmpty()) {
            throw new ValidationException(violations.stream()
                .map(v -> v.getPropertyPath() + ": " + v.getMessage())
                .collect(Collectors.joining("; ")));
        }

        userRepository.save(userDto);
    }
}

// ? 錯(cuò)誤示范：對(duì) Map 使用 @Valid，以為能校驗(yàn)內(nèi)容
@PostMapping("/batch")
public ResponseEntity<?> batchCreate(@Valid @RequestBody Map<String, Object> params) {
    // ? 完全無(wú)效！@Valid 對(duì) Map 無(wú)感！
    String email = (String) params.get("email");
    String name = (String) params.get("name");
    // ... 你得自己寫(xiě) if(email == null) ...
    return ResponseEntity.ok("ok");
}

// ? 正確：定義一個(gè)校驗(yàn)友好的 DTO
public class BatchCreateRequest {
    @Valid
    @NotNull
    @Size(min = 1, max = 100)
    private List<UserDto> users;

    // getter / setter
}

@PostMapping("/batch")
public ResponseEntity<?> batchCreate(@Valid @RequestBody BatchCreateRequest request) {
    // ? 這里會(huì)遞歸校驗(yàn) List<UserDto> 中每個(gè)元素
    request.getUsers().forEach(user -> userService.save(user));
    return ResponseEntity.ok("ok");
}

public class UserMapWrapper {
    @Valid
    @NotNull
    private Map<String, UserDto> users;

    // getter/setter
}

@RestControllerAdvice
public class GlobalValidationHandler {

    @ExceptionHandler(MethodArgumentNotValidException.class)
    public ResponseEntity<ErrorResponse> handleValidationException(MethodArgumentNotValidException ex) {
        ErrorResponse error = ErrorResponse.builder()
            .code("VALIDATION_FAILED")
            .message("參數(shù)校驗(yàn)失敗")
            .details(ex.getBindingResult().getFieldErrors().stream()
                .collect(Collectors.toMap(
                    fe -> fe.getField(),
                    fe -> fe.getDefaultMessage()
                )))
            .build();
        return ResponseEntity.badRequest().body(error);
    }

    @ExceptionHandler(ConstraintViolationException.class)
    public ResponseEntity<ErrorResponse> handleConstraintViolation(ConstraintViolationException ex) {
        ErrorResponse error = ErrorResponse.builder()
            .code("VALIDATION_FAILED")
            .message("參數(shù)校驗(yàn)失敗")
            .details(ex.getConstraintViolations().stream()
                .collect(Collectors.toMap(
                    v -> v.getPropertyPath().toString(),
                    v -> v.getMessage()
                )))
            .build();
        return ResponseEntity.badRequest().body(error);
    }
}

@Target({ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
@Constraint(validatedBy = EmailFormatValidator.class)
public @interface ValidEmail {
    String message() default "郵箱格式不正確";
    Class<?>[] groups() default {};
    Class<? extends Payload>[] payload() default {};
}

public class EmailFormatValidator implements ConstraintValidator<ValidEmail, String> {
    private static final String EMAIL_PATTERN = "^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\\.[a-zA-Z]{2,}$";

    @Override
    public boolean isValid(String email, ConstraintValidatorContext context) {
        return email != null && email.matches(EMAIL_PATTERN);
    }
}

@ValidEmail
private String email;

public interface CreateGroup {}
public interface UpdateGroup {}

public class UserDto {
    @NotNull(groups = CreateGroup.class)
    private Long id;

    @NotBlank(groups = {CreateGroup.class, UpdateGroup.class})
    private String name;

    @Email(groups = CreateGroup.class)
    private String email;
}

// Controller 中指定分組
@PostMapping("/create")
public ResponseEntity<?> create(@Validated(CreateGroup.class) @RequestBody UserDto userDto) {
    // 只校驗(yàn) CreateGroup 的規(guī)則，id 必須非空，email 必須合法
}

@PostMapping("/update")
public ResponseEntity<?> update(@Validated(UpdateGroup.class) @RequestBody UserDto userDto) {
    // id 可以為 null，但 name 必須存在
}