예외 처리 핸들러

// 표준 에러 응답
@Getter
@AllArgsConstructor
public class ErrorResponse {
    private final int status;
    private final String code;
    private final String message;
    private final LocalDateTime timestamp = LocalDateTime.now();
}

// 커스텀 예외 계층
public class BusinessException extends RuntimeException {
    private final ErrorCode errorCode;
    public BusinessException(ErrorCode code) {
        super(code.getMessage());
        this.errorCode = code;
    }
}

@Getter
@RequiredArgsConstructor
public enum ErrorCode {
    USER_NOT_FOUND(404, "USER_001", "사용자를 찾을 수 없습니다"),
    DUPLICATE_EMAIL(409, "USER_002", "이미 사용 중인 이메일입니다"),
    INVALID_TOKEN(401, "AUTH_001", "유효하지 않은 토큰입니다");

    private final int status;
    private final String code;
    private final String message;
}

// GlobalExceptionHandler.java
@RestControllerAdvice
public class GlobalExceptionHandler {
    @ExceptionHandler(BusinessException.class)
    public ResponseEntity<ErrorResponse> handle(BusinessException e) {
        ErrorCode code = e.getErrorCode();
        return ResponseEntity.status(code.getStatus())
            .body(new ErrorResponse(code.getStatus(), code.getCode(), code.getMessage()));
    }

    @ExceptionHandler(MethodArgumentNotValidException.class)
    public ResponseEntity<ErrorResponse> handle(MethodArgumentNotValidException e) {
        String message = e.getBindingResult().getFieldErrors().stream()
            .map(fe -> fe.getField() + ": " + fe.getDefaultMessage())
            .collect(Collectors.joining(", "));
        return ResponseEntity.badRequest()
            .body(new ErrorResponse(400, "VALID_001", message));
    }
}