/*
    * Copyright 2012-2025 CodeLibs Project and the Others.
    *
    * Licensed under the Apache License, Version 2.0 (the "License");
    * you may not use this file except in compliance with the License.
    * You may obtain a copy of the License at
    *
    *     http://www.apache.org/licenses/LICENSE-2.0
    *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
   * either express or implied. See the License for the specific language
   * governing permissions and limitations under the License.
   */
  package org.codelibs.fess.filter;
  
  import java.io.IOException;
  
  import org.apache.logging.log4j.LogManager;
  import org.apache.logging.log4j.Logger;
  import org.codelibs.fess.helper.RateLimitHelper;
  import org.codelibs.fess.util.ComponentUtil;
  
  import jakarta.servlet.Filter;
  import jakarta.servlet.FilterChain;
  import jakarta.servlet.ServletException;
  import jakarta.servlet.ServletRequest;
  import jakarta.servlet.ServletResponse;
  import jakarta.servlet.http.HttpServletRequest;
  import jakarta.servlet.http.HttpServletResponse;
  
  /**
   * Filter for rate limiting to protect against bot attacks and excessive requests.
   * Tracks request counts per IP address and blocks excessive requests based on configurable thresholds.
   */
  public class RateLimitFilter implements Filter {
  
      private static final Logger logger = LogManager.getLogger(RateLimitFilter.class);
  
      /**
       * Creates a new instance of RateLimitFilter.
       */
      public RateLimitFilter() {
          // Default constructor
      }
  
      @Override
      public void doFilter(final ServletRequest request, final ServletResponse response, final FilterChain chain)
              throws IOException, ServletException {
          if (!ComponentUtil.available()) {
              chain.doFilter(request, response);
              return;
          }
  
          final RateLimitHelper rateLimitHelper = ComponentUtil.getRateLimitHelper();
  
          if (!rateLimitHelper.isEnabled()) {
              chain.doFilter(request, response);
              return;
          }
  
          final HttpServletRequest httpRequest = (HttpServletRequest) request;
          final HttpServletResponse httpResponse = (HttpServletResponse) response;
          final String clientIp = rateLimitHelper.getClientIp(httpRequest);
  
          if (logger.isDebugEnabled()) {
              logger.debug("Rate limit check: clientIp={}, path={}", clientIp, httpRequest.getRequestURI());
          }
  
          // Check if IP is blocked
          if (rateLimitHelper.isBlocked(clientIp)) {
              if (logger.isDebugEnabled()) {
                  logger.debug("Request blocked: clientIp={}", clientIp);
              }
              sendBlockedResponse(httpResponse);
              return;
          }
  
          // Check rate limit
          if (!rateLimitHelper.allowRequest(clientIp)) {
              if (logger.isDebugEnabled()) {
                  logger.debug("Rate limit exceeded: clientIp={}", clientIp);
              }
              sendRateLimitResponse(httpResponse, rateLimitHelper.getRetryAfterSeconds());
              return;
          }
  
          chain.doFilter(request, response);
      }
  
      /**
       * Send a 403 Forbidden response for blocked IPs.
       * @param response the HTTP response
       * @throws IOException if an I/O error occurs
       */
      protected void sendBlockedResponse(final HttpServletResponse response) throws IOException {
          response.setStatus(HttpServletResponse.SC_FORBIDDEN);
          response.setContentType("application/json;charset=UTF-8");
         response.getWriter().write("{\"error\":\"ip_blocked\",\"message\":\"Access denied.\"}");
     }
 
     /**
      * Send a 429 Too Many Requests response.
      * @param response the HTTP response
      * @param retryAfterSeconds the Retry-After header value
      * @throws IOException if an I/O error occurs
      */
     protected void sendRateLimitResponse(final HttpServletResponse response, final int retryAfterSeconds) throws IOException {
         response.setStatus(429); // Too Many Requests
         response.setContentType("application/json;charset=UTF-8");
         response.setHeader("Retry-After", String.valueOf(retryAfterSeconds));
         response.getWriter()
                 .write("{\"error\":\"rate_limit_exceeded\",\"message\":\"Too many requests. Please retry after " + retryAfterSeconds
                         + " seconds.\",\"retry_after\":" + retryAfterSeconds + "}");
     }
 }