import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.concurrent.ConcurrentHashMap;

@WebFilter(urlPatterns = "/*")
public class RateLimitFilter implements Filter {

    private static class IpStats {
        int requestCount = 0;
        int error404Count = 0;
        long lastResetTime = System.currentTimeMillis();
    }

    // 存储IP的请求统计信息
    private final ConcurrentHashMap<String, IpStats> ipStatsMap = new ConcurrentHashMap<>();
    // 存储被封禁的IP及其解封时间
    private final ConcurrentHashMap<String, Long> blackListMap = new ConcurrentHashMap<>();

    // 配置参数
    private static final int MAX_REQUESTS_PER_MINUTE = 300;
    private static final int MAX_404_COUNT = 300;
    private static final long BLOCK_TIME_MILLIS = 30 * 60 * 1000; // 30分钟

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        String ip = request.getRemoteAddr();
        long currentTime = System.currentTimeMillis();

        // 检查是否被封禁
        Long blockUntil = blackListMap.get(ip);
        if (blockUntil != null && blockUntil > currentTime) {
            ((HttpServletResponse) response).setStatus(429); // 太多请求
            response.getWriter().write("访问受限，请稍后重试。");
            return;
        } else if (blockUntil != null && blockUntil <= currentTime) {
            // 解封
            blackListMap.remove(ip);
        }

        // 统计请求信息
        IpStats stats = ipStatsMap.computeIfAbsent(ip, k -> new IpStats());

        // 存在跨分钟的情况，重置统计
        if (currentTime - stats.lastResetTime > 60 * 1000) {
            stats.requestCount = 0;
            stats.error404Count = 0;
            stats.lastResetTime = currentTime;
        }

        // 请求计数
        stats.requestCount++;
        ipStatsMap.put(ip, stats);

        // 处理请求
        // 使用自定义Response包装器捕获状态码
        StatusCaptureResponseWrapper wrappedResponse = new StatusCaptureResponseWrapper((HttpServletResponse) response);
        chain.doFilter(request, wrappedResponse);

        // 判断响应状态码
        if (wrappedResponse.getStatus() == 404) {
            stats.error404Count++;
        }

        // 超过404阈值，加入黑名单
        if (stats.error404Count >= MAX_404_COUNT) {
            blackListMap.put(ip, currentTime + BLOCK_TIME_MILLIS);
            // 可选: 清理统计数据
            ipStatsMap.remove(ip);
        }
    }

    /**
     * 自定义ResponseWrapper，用于捕获状态码
     */
    private static class StatusCaptureResponseWrapper extends HttpServletResponseWrapper {
        private int httpStatus = 200;

        public StatusCaptureResponseWrapper(HttpServletResponse response) {
            super(response);
        }

        @Override
        public void setStatus(int sc) {
            super.setStatus(sc);
            this.httpStatus = sc;
        }

        @Override
        public void sendError(int sc) throws IOException {
            super.sendError(sc);
            this.httpStatus = sc;
        }

        @Override
        public void sendError(int sc, String msg) throws IOException {
            super.sendError(sc, msg);
            this.httpStatus = sc;
        }public int getStatus() {
            return this.httpStatus;
        }
    }
}