/*
    * Licensed to the Apache Software Foundation (ASF) under one or more
    * contributor license agreements. See the NOTICE file distributed with
    * this work for additional information regarding copyright ownership.
    * The ASF licenses this file to You 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.apache.logging.log4j.web;
  
  import java.io.IOException;
  import javax.servlet.Filter;
  import javax.servlet.FilterChain;
  import javax.servlet.FilterConfig;
  import javax.servlet.ServletContext;
  import javax.servlet.ServletException;
  import javax.servlet.ServletRequest;
  import javax.servlet.ServletResponse;
  
  import org.apache.logging.log4j.Logger;
  import org.apache.logging.log4j.status.StatusLogger;
  
  /**
   * This is responsible for the following:
   * <ul>
   *     <li>Clearing the logger context when the application has finished starting up.</li>
   *     <li>Setting the logger context before processing a request and clearing it after processing a request.</li>
   *     <li>Setting the logger context when the application is starting to shut down.</li>
   * </ul>
   * This filter is a once-per-request filter. It is capable of filtering all the different types of requests
   * (standard, asynchronous, error, etc.) but will not apply processing if the filter matches multiple times on the same
   * logical request.
   */
  public class Log4jServletFilter implements Filter {
  
      private static final Logger LOGGER = StatusLogger.getLogger();
  
      static final String ALREADY_FILTERED_ATTRIBUTE = Log4jServletFilter.class.getName() + ".FILTERED";
  
      private ServletContext servletContext;
      private Log4jWebLifeCycle initializer;
  
      @Override
      public void init(final FilterConfig filterConfig) throws ServletException {
          this.servletContext = filterConfig.getServletContext();
          LOGGER.debug("Log4jServletFilter initialized.");
  
          this.initializer = WebLoggerContextUtils.getWebLifeCycle(this.servletContext);
          this.initializer.clearLoggerContext(); // the application is mostly finished starting up now
      }
  
      @Override
      public void doFilter(final ServletRequest request, final ServletResponse response, final FilterChain chain)
              throws IOException, ServletException {
          if (request.getAttribute(ALREADY_FILTERED_ATTRIBUTE) != null) {
              chain.doFilter(request, response);
          } else {
              request.setAttribute(ALREADY_FILTERED_ATTRIBUTE, Boolean.TRUE);
  
              try {
                  this.initializer.setLoggerContext();
  
                  chain.doFilter(request, response);
              } finally {
                  this.initializer.clearLoggerContext();
              }
          }
      }
  
      @Override
      public void destroy() {
          if (this.servletContext == null || this.initializer == null) {
              throw new IllegalStateException("Filter destroyed before it was initialized.");
          }
          LOGGER.debug("Log4jServletFilter destroyed.");
  
          this.initializer.setLoggerContext(); // the application is just now starting to shut down
      }
  }