/*
 *    OAIServer.java
 *    Copyright (C) 2002 New Zealand Digital Library, http://www.nzdl.org
 *
 *    This program 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 2 of the License, or
 *    (at your option) any later version.
 *
 *    This program 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 this program; if not, write to the Free Software
 *    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */
package org.greenstone.gsdl3;

import org.greenstone.gsdl3.comms.*;
import org.greenstone.gsdl3.core.*;
import org.greenstone.gsdl3.util.*;
import org.greenstone.gsdl3.action.PageAction; // used to get the default action
import org.w3c.dom.*;
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.util.Enumeration;
import java.util.HashSet;
import java.io.File;

import org.apache.log4j.*;

/** a servlet to serve the OAI metadata harvesting - we are using servlets instead
 * of cgi
 * the init method is called only once - the first time the servlet classes
 * are loaded. Each time a request comes in to the servlet, the session()
 * method is called in a new thread (calls doGet/doPut etc)
 * takes the verb= type args and builds a simple request to send to
 * the oai receptionist, which returns a result in xml, conforming to the OAI-PMH
 * protocol.
 * @see Receptionist
 */
/**
 * OAI server configuration instructions *
 *
 */
public class OAIServer extends HttpServlet {
  
  /** the receptionist to send messages to */
  protected OAIReceptionist recept=null;
  /** the default language - is specified by setting a servlet param,
   * otherwise DEFAULT_LANG is used*/
  protected String default_lang= null;
  /** The default default - used if a default lang is not specified
   * in the servlet params */
  protected final String DEFAULT_LANG = "en";

  /** a converter class to parse XML and create Docs
   * This is only used for generating internal requests passed to MessageRouter.
   * The response message is generated by parsing an existing xml skeleton file (web/WEB-INF/oaixml/oaiversion2.xml, for example).
   */
  protected XMLConverter converter=null;
  /** container Document to create XML Nodes (but only request to the oai receptionist,
   *  not response (which is created in OAIXML.java) created by converter class */
  protected Document doc=null;
  
  /** A HashSet which contains all the legal verbs. */
  protected HashSet verb_set = null;
  /** A HashSet which contains all the legal oai keys in the key/value argument pair. */
  protected HashSet param_set = null;
  /** The name of the site with which we will finally be dealing, whether it is a local site or a remote site through a communicator.*/
  protected String site = "";
  
  static Logger logger = Logger.getLogger(org.greenstone.gsdl3.OAIServer.class.getName());
  
  /** initialise the servlet
   */
  public void init(ServletConfig config) throws ServletException {
    // always call super.init, i.e., HttpServlet.;
    super.init(config);
    this.default_lang = config.getInitParameter(GSConstants.DEFAULT_LANG);
    
    initVerbs();
    initParams();
    
    String site_name = config.getInitParameter(GSConstants.SITE_NAME);
    String remote_site_name = null;
    String remote_site_type = null;
    String remote_site_address = null;
    
    if (site_name == null) {
      // no local site, try for communicator (remote site)
      remote_site_name = config.getInitParameter("remote_site_name");
      remote_site_type = config.getInitParameter("remote_site_type");
      remote_site_address = config.getInitParameter("remote_site_address");
      if (remote_site_name == null || remote_site_type == null || remote_site_address == null) {
        System.err.println("initialisation paramters not all set!");
        System.err.println("if site_name is not set, then you must have remote_site_name, remote_site_type and remote_site_address set");
        System.exit(1);
      }
    }
    
    if (this.default_lang == null) {
      // choose english
      this.default_lang = DEFAULT_LANG;
    }
    
    // the receptionist -the servlet will talk to this
    this.recept = new OAIReceptionist();
    
    // the receptionist uses a MessageRouter or Communicator to send its requests to. We either create a MessageRouter here for the designated site (if site_name set), or we create a Communicator for a remote site. The is given to teh Receptionist, and the servlet never talks to it again.directly.
    if (site_name != null) {
      //this site_name could consist of comma separated more than one site name.
      String mr_name = (String)config.getInitParameter("messagerouter_class");
      MessageRouter message_router = null;
      if (mr_name == null) { // just use the normal MR *********
        message_router = new MessageRouter();
      } else { // try the specified one
        try {
          message_router = (MessageRouter)Class.forName("org.greenstone.gsdl3.core."+mr_name).newInstance();
        } catch (Exception e) { // cant use this new one, so use normal one
          System.err.println("OAIServlet configure exception when trying to use a new MessageRouter "+mr_name+": "+e.getMessage());
          e.printStackTrace();
          message_router = new MessageRouter();
        }
      }
      
      message_router.setSiteName(site_name);
      // lots of work is done in this step; see MessageRouter.java
      message_router.configure();
      this.recept.setSiteName(site_name);
      this.recept.setMessageRouter(message_router);
      
    } else {      
      // talking to a remote site, create a communicator
      Communicator communicator = null;
      // we need to create the XML to configure the communicator
      Element site_elem = this.doc.createElement(GSXML.SITE_ELEM);
      site_elem.setAttribute(GSXML.TYPE_ATT, remote_site_type);
      site_elem.setAttribute(GSXML.NAME_ATT, remote_site_name);
      site_elem.setAttribute(GSXML.ADDRESS_ATT, remote_site_address);
      
      if (remote_site_type.equals(GSXML.COMM_TYPE_SOAP_JAVA)) {
        communicator = new SOAPCommunicator();
      } else {
        System.err.println("OAIServlet.init Error: invalid Communicator type: "+remote_site_type);
        System.exit(1);
      }
      
      if (!communicator.configure(site_elem)) {
        System.err.println("OAIServlet.init Error: Couldn't configure communicator");
        System.exit(1);
      }
      this.recept.setSiteName(remote_site_name);
      this.recept.setMessageRouter(communicator);
    }
    // used for composing internal xml requests, but not xml responses.
    // the converter may be used to get pretty xml, though.    
    this.converter = new XMLConverter();
    this.doc = this.converter.newDOM();

    // Read in OAIConfig.xml (residing web/WEB-INF/classes/) and 
    //use it to configure the receptionist. The init() is also called in which
    //the resumption token file is read in and all expired tokens cleared.
    Element oai_config = OAIXML.getOAIConfigXML();
      if (oai_config == null) {
        logger.error("Fail to parse oai config file OAIConfig.xml.");
        return;
      }   
    // pass it to the receptionist
    this.recept.configure(oai_config);
    
  }//end of init()
  
  private void initVerbs() {
    verb_set = new HashSet();
    verb_set.add(OAIXML.GET_RECORD);
    verb_set.add(OAIXML.LIST_RECORDS);
    verb_set.add(OAIXML.LIST_IDENTIFIERS);
    verb_set.add(OAIXML.LIST_SETS);
    verb_set.add(OAIXML.LIST_METADATA_FORMATS);
    verb_set.add(OAIXML.IDENTIFY);
  }
  
  private void initParams() {
    param_set = new HashSet();
    param_set.add(OAIXML.METADATA_PREFIX);
    param_set.add(OAIXML.FROM);
    param_set.add(OAIXML.UNTIL);
    param_set.add(OAIXML.SET);
    param_set.add(OAIXML.RESUMPTION_TOKEN);
    param_set.add(OAIXML.IDENTIFIER);
  }
  private void logUsageInfo(HttpServletRequest request){
    String usageInfo = "";
    
    //logged info = general-info + session-info
    usageInfo =
      request.getContextPath()+" "+ //session id
      request.getServletPath()+" "+ //serlvet
      "["+request.getQueryString()+"]" +" "+ //the query string
      "["+usageInfo.trim()+"]" +" "+ // params stored in a session
      request.getRemoteAddr()+" "+   //remote address
      request.getHeader("user-agent")+" "; //the remote brower info
    
    logger.info(usageInfo);   
  }
  /** return true if the url is in the form of baseURL?verb=..., 
   */
  private boolean validate(String query, String verb) {
    //Here in OAIServer, only the verbs are validated. All the validation for individual verb
    // is taken in their doXXX() methods.
    if(query == null || !query.startsWith(OAIXML.VERB+"=")) {
      return false;
    }
    if (!verb_set.contains(verb)) {
      return false;
    }
    return true;
  }
  private String getVerb(String query) {
    if (query == null) return "";
    int verb_start_index = query.indexOf("=") + 1;// first occurence of '='
    int verb_end_index = query.indexOf("&");
    if(verb_end_index == -1) {
      return query.substring(verb_start_index);
    }
    return query.substring(verb_start_index, verb_end_index);
  }
  public void doGet(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {
    PrintWriter out = response.getWriter();
    logUsageInfo(request);
    //out.println("url="+request.getRequestURL());// /oaiserver    
    //out.println("query="+request.getQueryString());// is /greenstone3

    // oai always requires the content type be text/xml
    request.setCharacterEncoding("UTF-8");
    response.setContentType("text/xml;charset=UTF-8");
    
    //
    String lang = request.getParameter(GSParams.LANGUAGE);
    if (lang==null || lang.equals("")) {
      // use the default
      lang = this.default_lang;
    }
    //we don't get the baseURL from the http request because what we get might be different from the one known publicly due to local network redirection.
    //For example, puka.cs.waikato.ac.nz vs www.greenstone.org
    //String base_url = request.getRequestURL().toString();
    String query = request.getQueryString();
    String[] pairs = (query==null)? null : query.split("&");//split into key/value pairs
    String verb = getVerb(query);
    Element xml_response = OAIXML.createBasicResponse(verb, pairs);
    Element verb_elem = null;
    
    if (validate(query, verb) == false) {
      if (verb_set.contains(verb) == false) {
        logger.error(OAIXML.BAD_VERB + ": " + query);
        verb_elem = OAIXML.createErrorElement(OAIXML.BAD_VERB, OAIXML.ILLEGAL_OAI_VERB);
      } else {
        //must be something else other than bad verbs caused an error, so bad argument
        logger.error(OAIXML.BAD_ARGUMENT + ": " + query);
        verb_elem = OAIXML.createErrorElement(OAIXML.BAD_ARGUMENT, "");
      } 
      xml_response.appendChild(verb_elem);
      //this line never got displayed
      //out.println("<?xml version='1.0' encoding='UTF-8' ?>");
      out.println(this.converter.getPrettyString(xml_response));
      return;
    }//end of if(validate
    
    // The query is valid, we can now
    // compose the request message to the receptionist
    Element xml_message = this.doc.createElement(GSXML.MESSAGE_ELEM);
    Element xml_request = this.doc.createElement(GSXML.REQUEST_ELEM);
    // The type attribute is set to be 'oaiService' from OAIServer to OAIReceptionist.
    //xml_request.setAttribute(GSXML.TYPE_ATT, OAIXML.OAI_SERVICE);
    xml_request.setAttribute(GSXML.LANG_ATT, lang);
    xml_request.setAttribute(GSXML.TO_ATT, verb);
    addParams(xml_request, pairs);
    
    //xml_request.setAttribute(GSXML.OUTPUT_ATT, output);????
    xml_message.appendChild(xml_request);
         
    Node xml_result = this.recept.process (xml_message);
    if (xml_result == null) {
      logger.info("xml_result is null");
      verb_elem = OAIXML.createErrorElement("Internal error", "");
      xml_response.appendChild(verb_elem);
    } else {
    
      /** All response elements are in the form (with a corresponding verb name):
       *                                        <message>
                                                  <response>
                                                    <verb>
                                                    ...
       *                                              <resumptionToken>
       *                                              .. this is optional!
       *                                              </resumptionToken>
       *                                            </verb>
       *                                          </response>       
       *                                        </message>
       */
      Node res = GSXML.getChildByTagName(xml_result, OAIXML.RESPONSE);
      if(res == null) {
        logger.info("response element in xml_result is null");
        verb_elem = OAIXML.createErrorElement("Internal error", "");
      } else {
        verb_elem = GSXML.getFirstElementChild(res);
      }
      
      if(OAIXML.oai_version.equals(OAIXML.OAI_VERSION2) ||
         verb_elem.getTagName().equals(OAIXML.ERROR)) {
        xml_response.appendChild(xml_response.getOwnerDocument().importNode(verb_elem, true));
      } else {
        GSXML.copyAllChildren(xml_response, verb_elem);
      }
    }
    out.println (this.converter.getPrettyString (xml_response));
    return; 
  }
  /** append parameter elements to the request sent to the receptionist*/
  public void addParams(Element request, String[] pairs) {
    // no params apart from the verb
    if (pairs == null || pairs.length < 2) return ;
    
      /**the request xml is composed in the form: <request>
       *                                            <param name=.../>
       *                                            <param name=.../>
       *                                          </request>
       *(No paramList element in between).
       */    
    for (int i=1; i<pairs.length; i++) {
      //the first pair in pairs is the verb=xxx
      int index = pairs[i].indexOf("=");
      if(index != -1){ //just a double check
        Element param = this.doc.createElement(OAIXML.PARAM);
        param.setAttribute(OAIXML.NAME, pairs[i].substring(0, index));
        param.setAttribute(OAIXML.VALUE, OAIXML.oaiDecode(pairs[i].substring(index + 1)));
        request.appendChild(param);
      }
    } 
  }
  public void doPost(HttpServletRequest request,
    HttpServletResponse response)
    throws ServletException, IOException {
    doGet(request,response);    
  }
}