/*
    * 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 java.util.Arrays;
  import java.util.Set;
  import java.util.stream.Collectors;
  
  import org.apache.logging.log4j.LogManager;
  import org.apache.logging.log4j.Logger;
  import org.codelibs.fess.mylasta.direction.FessConfig;
  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 CPU load-based request control.
   * Returns HTTP 429 (Too Many Requests) when CPU usage exceeds configurable thresholds.
   * Web and API requests have independent threshold settings.
   */
  public class LoadControlFilter implements Filter {
  
      private static final Logger logger = LogManager.getLogger(LoadControlFilter.class);
  
      private static final int RETRY_AFTER_SECONDS = 60;
  
      private static final Set<String> STATIC_EXTENSIONS =
              Arrays.stream(new String[] { ".css", ".js", ".png", ".jpg", ".gif", ".ico", ".svg", ".woff", ".woff2", ".ttf", ".eot" })
                      .collect(Collectors.toSet());
  
      /**
       * Creates a new instance of LoadControlFilter.
       */
      public LoadControlFilter() {
          // 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 HttpServletRequest httpRequest = (HttpServletRequest) request;
          final HttpServletResponse httpResponse = (HttpServletResponse) response;
          final String path = httpRequest.getRequestURI().substring(httpRequest.getContextPath().length());
  
          if (isExcludedPath(path)) {
              chain.doFilter(request, response);
              return;
          }
  
          final boolean isApiPath = path.startsWith("/api/");
          final FessConfig fessConfig = ComponentUtil.getFessConfig();
          final int threshold = isApiPath ? fessConfig.getApiLoadControlAsInteger() : fessConfig.getWebLoadControlAsInteger();
  
          if (threshold >= 100) {
              chain.doFilter(request, response);
              return;
          }
  
          final short cpuPercent = ComponentUtil.getSystemHelper().getSearchEngineCpuPercent();
  
          if (cpuPercent < threshold) {
              chain.doFilter(request, response);
              return;
          }
  
          if (logger.isInfoEnabled()) {
              logger.info("Rejecting request due to high CPU load: path={}, cpu={}%, threshold={}%", path, cpuPercent, threshold);
          }
  
          if (isApiPath) {
              sendApiResponse(httpResponse);
          } else {
              httpResponse.sendError(429);
          }
     }
 
     /**
      * Checks if the given path should be excluded from load control.
      * @param path the request path
      * @return true if the path should be excluded
      */
     protected boolean isExcludedPath(final String path) {
         if (path.startsWith("/admin") || path.startsWith("/error") || path.startsWith("/login")) {
             return true;
         }
         final int dotIndex = path.lastIndexOf('.');
         if (dotIndex >= 0) {
             final String extension = path.substring(dotIndex);
             return STATIC_EXTENSIONS.contains(extension);
         }
         return false;
     }
 
     /**
      * Sends a 429 JSON response for API requests.
      * @param response the HTTP response
      * @throws IOException if an I/O error occurs
      */
     protected void sendApiResponse(final HttpServletResponse response) throws IOException {
         response.setStatus(429);
         response.setContentType("application/json;charset=UTF-8");
         response.setHeader("Retry-After", String.valueOf(RETRY_AFTER_SECONDS));
         response.getWriter()
                 .write("{\"response\":{\"status\":9,\"message\":\"Server is busy. Please retry after " + RETRY_AFTER_SECONDS
                         + " seconds.\",\"retry_after\":" + RETRY_AFTER_SECONDS + "}}");
     }
 }