/*
 * #!
 * Ontopia Navigator
 * #-
 * Copyright (C) 2001 - 2013 The Ontopia Project
 * #-
 * 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 net.ontopia.topicmaps.nav2.taglibs.tolog;

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;

import net.ontopia.topicmaps.nav2.taglibs.logic.ContextTag;

/**
 * EXPERIMENTAL: This is a servlet filter that pushes a tolog context
 * onto the stack. The filter is to be used so that the nested filters
 * are to have access to the tolog context.
 * 
 * Example web.xml configuration:
 *  
 * <pre>
 * <filter> 
 *   <filter-name>TologContextFilter</filter-name>
 *   <filter-class>net.ontopia.topicmaps.nav2.taglibs.tolog.TologContextFilter</filter-class>
 *   <init-param>
 *     <param-name>topicmap</param-name>
 *     <param-value>opera.xtm</param-value>
 *   </init-param>
 *   <init-param>
 *     <param-name>reqParam</param-name>
 *     <param-value>topicmap</param-value>
 *   </init-param>
 * </filter>
 * <filter-mapping>
 *   <filter-name>TologContextFilter</filter-name> 
 *   <url-pattern>/opera/*</url-pattern>
 * </filter-mapping>
 * </pre>
 * 
 * @since 3.0
 * 
 */
public class TologContextFilter implements Filter {

  protected String topicmapid_attribute;
  protected String topicmapid_parameter;
  protected String topicmapid;

  public void init(FilterConfig fconfig) throws ServletException {
    // override topic map request attribute name
    String aname = fconfig.getInitParameter("attribute");
    this.topicmapid_attribute = (aname == null ? ContextTag.TOPICMAPID_REQUEST_ATTRIBUTE: aname);  

    // override topic map request parameter name
    this.topicmapid_parameter = fconfig.getInitParameter("reqParam");

    // hardwire default topic map id
    this.topicmapid = fconfig.getInitParameter("topicmap");
  }

  public void doFilter(ServletRequest request, ServletResponse response,
      FilterChain chain) throws IOException, ServletException {

    // get hold of existing request attribute
    Object ptmid = request.getAttribute(topicmapid_attribute);
    
    try {
      String tmid = null;
      if (topicmapid_parameter != null)
        tmid = request.getParameter(topicmapid_parameter);
      if (tmid == null)
        tmid = topicmapid;

      // set request attribute
      request.setAttribute(topicmapid_attribute, tmid);
      
      // delegate to nested filters
      chain.doFilter(request, response);
      
    } finally {
      // reinstate old request attribute value
      request.setAttribute(topicmapid_attribute, ptmid);
    }
  }

  public void destroy() {
  }

}