@RestControllerAdvice
public class GlobalExceptionHandler {

    private static final Logger log = LoggerFactory.getLogger(GlobalExceptionHandler.class);

    // 404 - Kaynak bulunamadı
    @ExceptionHandler(ResourceNotFoundException.class)
    public ProblemDetail handleNotFound(ResourceNotFoundException ex) {
        ProblemDetail problem = ProblemDetail.forStatusAndDetail(
            HttpStatus.NOT_FOUND, ex.getMessage()
        );
        problem.setTitle("Kaynak Bulunamadı");
        problem.setProperty("errorCode", "RESOURCE_NOT_FOUND");
        problem.setProperty("timestamp", Instant.now());
        return problem;
    }

    // 400 - Validation hatası
    @ExceptionHandler(MethodArgumentNotValidException.class)
    public ProblemDetail handleValidation(MethodArgumentNotValidException ex) {
        ProblemDetail problem = ProblemDetail.forStatusAndDetail(
            HttpStatus.BAD_REQUEST, "Validasyon hatası"
        );

        Map<String, String> errors = new HashMap<>();
        ex.getBindingResult().getFieldErrors()
            .forEach(e -> errors.put(e.getField(), e.getDefaultMessage()));
        problem.setProperty("fieldErrors", errors);

        return problem;
    }

    // 500 - Beklenmeyen hata
    @ExceptionHandler(Exception.class)
    public ProblemDetail handleGeneric(Exception ex) {
        String correlationId = UUID.randomUUID().toString();
        log.error("Unexpected error [{}]: {}", correlationId, ex.getMessage(), ex);

        ProblemDetail problem = ProblemDetail.forStatusAndDetail(
            HttpStatus.INTERNAL_SERVER_ERROR, "Beklenmeyen bir hata oluştu"
        );
        problem.setProperty("correlationId", correlationId);
        return problem;
    }
}