@Component
@Order(-100) // 最先执行
public class TraceHandler implements PipelineHandler {

    private static final String TRACE_ID = "X-Trace-Id";

    @Override
    public void before(SqlApiConfig config, Map<String, Object> params,
                        PipelineContext context) {
        // 优先用调用方传来的 TraceId（链路透传）
        String traceId = RequestContext.getHeader(TRACE_ID);
        if (traceId == null) {
            traceId = generateTraceId();
        }
        context.setTraceId(traceId);

        // 记录请求开始时间
        context.setStartTime(System.currentTimeMillis());

        // TraceId 放入 MDC，后续日志自动带上
        MDC.put("traceId", traceId);
        MDC.put("apiId", config.getApiId());
        MDC.put("apiPath", config.getApiPath());
    }

    @Override
    public void after(SqlApiConfig config, Object result,
                       PipelineContext context) {
        long elapsed = System.currentTimeMillis() - context.getStartTime();
        log.info("API 调用完成 traceId={} api={} elapsed={}ms rows={}",
            context.getTraceId(), config.getApiPath(), elapsed,
            result instanceof Collection ? ((Collection<?>) result).size() : 1);
        MDC.clear();
    }

    private String generateTraceId() {
        return UUID.randomUUID().toString().replace("-", "").substring(0, 16);
    }
}