package com.fx.monitor.examples;

import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import java.io.IOException;
import org.slf4j.MDC;

/**
 * 简单的 Servlet Filter 示例：提取/生成 traceId、记录 uri 与 duration 到 MDC。
 * 业务需将 MDC 中的字段通过 logback encoder 输出为 JSON 字段。
 */
public class LoggingFilter implements Filter {

    @Override
    public void init(FilterConfig filterConfig) throws ServletException { }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        HttpServletRequest req = (HttpServletRequest) request;
        String traceId = extractOrGenerate(req);
        try {
            MDC.put("traceId", traceId);
            MDC.put("uri", req.getRequestURI());
            long start = System.currentTimeMillis();
            chain.doFilter(request, response);
            long duration = System.currentTimeMillis() - start;
            MDC.put("duration", String.valueOf(duration));
        } finally {
            MDC.remove("traceId");
            MDC.remove("uri");
            MDC.remove("duration");
        }
    }

    @Override
    public void destroy() { }

    private String extractOrGenerate(HttpServletRequest req) {
        String incoming = req.getHeader("X-Trace-Id");
        if (incoming != null && !incoming.isEmpty()) return incoming;
        return java.util.UUID.randomUUID().toString();
    }
}