package com.example.logging;

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

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());
            // 如果能从认证/上下文拿到 userId，填入 MDC
            String userId = req.getHeader("X-User-Id");
            if (userId != null) MDC.put("userId", userId);

            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("userId");
            MDC.remove("duration");
        }
    }

    @Override
    public void destroy() {}

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