/*
    * This file is part of ***  M y C o R e  ***
    * See http://www.mycore.de/ for details.
    *
    * MyCoRe is free software: you can redistribute it and/or modify
    * it under the terms of the GNU General Public License as published by
    * the Free Software Foundation, either version 3 of the License, or
    * (at your option) any later version.
    *
   * MyCoRe is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU General Public License for more details.
   *
   * You should have received a copy of the GNU General Public License
   * along with MyCoRe.  If not, see <http://www.gnu.org/licenses/>.
   */
  
  package org.mycore.frontend.filter;
  
  import java.io.IOException;
  import java.util.regex.Pattern;
  
  import org.apache.logging.log4j.LogManager;
  import org.apache.logging.log4j.Logger;
  import org.mycore.common.config.MCRConfiguration2;
  
  import jakarta.servlet.Filter;
  import jakarta.servlet.FilterChain;
  import jakarta.servlet.FilterConfig;
  import jakarta.servlet.ServletException;
  import jakarta.servlet.ServletRequest;
  import jakarta.servlet.ServletResponse;
  import jakarta.servlet.http.HttpServletRequest;
  import jakarta.servlet.http.HttpSession;
  
  /**
   * Automatically closes HttpSession of certain user agents.
   * 
   * If the <code>User-Agent</code> header matches a regular expression
   * defined by the property <code>MCR.Filter.UserAgent</code>
   * (default: "<code>(bot|spider|crawler|mercator|slurp|seek|nagios)</code>") the
   * HTTP session is closed after the request.
   * @author Thomas Scheffler (yagee)
   */
  public class MCRUserAgentFilter implements Filter {
      private static Pattern agentPattern;
  
      private static final Logger LOGGER = LogManager.getLogger(MCRUserAgentFilter.class);
  
      @Override
      public void init(final FilterConfig arg0) throws ServletException {
          final String agentRegEx = MCRConfiguration2.getString("MCR.Filter.UserAgent")
              .orElse("(bot|spider|crawler|mercator|slurp|seek|nagios|Java)");
          agentPattern = Pattern.compile(agentRegEx);
      }
  
      @Override
      public void destroy() {
      }
  
      @Override
      public void doFilter(final ServletRequest sreq, final ServletResponse sres, final FilterChain chain)
          throws IOException, ServletException {
          final HttpServletRequest request = (HttpServletRequest) sreq;
          final boolean newSession = request.getSession(false) == null;
          chain.doFilter(sreq, sres);
          final HttpSession session = request.getSession(false);
          if (session != null && newSession) {
              final String userAgent = request.getHeader("User-Agent");
              if (userAgent != null) {
                  if (agentPattern.matcher(userAgent).find()) {
                      try {
                          LOGGER.info("Closing session: {} matches {}", userAgent, agentPattern);
                          session.invalidate();
                      } catch (IllegalStateException e) {
                          LOGGER.warn("Session was allready closed");
                      }
                  } else {
                      LOGGER.debug("{} does not match {}", userAgent, agentPattern);
                  }
              } else {
                  LOGGER.warn("No User-Agent was send.");
              }
          }
      }
  
  }