/**
 *#########################################################################
 * QBRSOAPServer.java.in: a template for a SOAPServer providing
 * basic Query, Browse, Retrieve web services for Greenstone 3.
 * Part of the Greenstone digital library suite from the New Zealand 
 * Digital Library Project at the University of Waikato, New Zealand.
 * <BR><BR>
 * Copyright (C) 2008 New Zealand Digital Library Project
 * <BR><BR>
 * 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.
 * <BR><BR>
 * 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.
 * <BR><BR>
 * @author ak19
 * based on Katherine Don's SOAPServer@sitename@ template file. 
 *########################################################################
 */

package org.greenstone.gsdl3;

import java.io.File;
import java.io.InputStream;

import java.util.Properties;
import java.util.Enumeration;
import java.util.Map;
import java.util.Map.Entry;
import java.util.HashMap;
import java.util.Set;
import java.util.Iterator;

import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.NodeList;
import org.w3c.dom.Node;

import org.greenstone.util.GlobalProperties;
import org.greenstone.gsdl3.core.MessageRouter;
import org.greenstone.gsdl3.util.GSFile;
import org.greenstone.gsdl3.util.GSXML;
import org.greenstone.gsdl3.util.UserContext;
import org.greenstone.gsdl3.util.XMLConverter;

import org.apache.log4j.Logger; // Import log4j classes

/* 
 * Add to $GSDLHOME/web/WEB-INF/server-config.wsdd:
 * <service name="GS3WebServices" provider="java:RPC">
 * <parameter name="allowedMethods" value="*"/>
 * <parameter name="className" value="org.greenstone.gs3services.GS3WebServices"/>
 * </service>
*/

/** Class that provides the basic Query, Browse and Retrieve (QBR) web service
 * operations for Greenstone 3.
 * It contains a MessageRouter that carries out all the tasks by calling the 
 * appropriate Greenstone functionality for each request message passed to it, 
 * and returning a response message.
 *  
 * All response messages are returned from the MessageRouter to clients invoking   
 * the web services. All return values are strings that represent XML messages.
 * 
 * Method help() reads from the file QBRWebServicesHelp.properties to list the web 
 * service operations available. Method helpWithMethod(String methodName) 
 * reads from the same file to display a description of the requested operation.
 * (These method descriptions are mostly the same as those in the Javadoc
 * comments.)
 * 
 * NOTE: The folder containing this web service class' properties helpFile 
 * should be on the classpath. (QBRWebServicesHelp.properties)
 * @author ak19
*/
public class QBRSOAPServer@sitename@ {
	/** site_name the MessageRouter works with, here set to "localsite" */
	protected String site_name = "@sitename@";

	/** Message Router object to pass requests messages to and which 
	 * will process them.*/
	protected MessageRouter mr = null;
	
	/** Container Document to create XML Nodes */
	protected Document doc=null;
	/** A converter class to parse XML and create Docs */
	protected XMLConverter converter=null;

	/** The Logger for this class */
	private static Logger LOG = Logger.getLogger(QBRSOAPServer@sitename@.class);
	
	/** Error message loading helpFile. Remains at "" if everything is fine */
	protected static String helpErrormessage = "";
	/** Properties map with mappings from methodname to help 
	 * description string. */ 
	protected static Properties properties;
	/** The help properties file describing the web service operations */
	protected static String helpFile = "QBRWebServicesHelp.properties";
	
	// static code block to initialise the help Properties from the helpFile
	static {
		properties = new Properties();
		// load the properties file from a location with respect to the 
		// the Web Service .class file
		InputStream input = null;
		try {	
			// load the properties file from a location with respect to the 
			// the Web Service .class file
			input 
			= QBRSOAPServer@sitename@.class.getClassLoader().getResourceAsStream(
					helpFile);
			if(input == null) {
				helpErrormessage = "Cannot find file " + helpFile + " to load.";
				LOG.warn(helpErrormessage);
			} else {
				properties.load(input);
				input.close();
			}
		} catch(Exception e) {
			helpErrormessage = "Exception loading properties from help file " 
				+ helpFile + "\n" + e.getMessage();
			LOG.warn("Exception loading properties from help file " 
				+ helpFile + "\n" + e.getMessage());
		}
	}
	
	
	/* Describe subset options for the various Greenstone3 modules */
	protected static final String mrSubsetOptions = // messageRouter 
		"collectionList serviceClusterList serviceList siteList"; 
	protected static final String csSubsetOptions = // collections and serviceClusters 
		"metadataList serviceList displayItemList";
	protected static final String serviceSubsetOptions = // services
		"paramList displayItemList";
	protected static final String structureOptions =
		"entire ancestors parent siblings children descendants"; // note the spelling
	protected static final String structureInfoOptions =
		"numSiblings siblingPosition numChildren";
	
		
	/** Constructor that initializes the web services' MessageRouter object 
	 * Reads from GlobalProperties to get gsdl3_home and set the sitename. */
	public QBRSOAPServer@sitename@() {
	    String gsdl3_home = GlobalProperties.getGSDL3Home();
		if (gsdl3_home == null || gsdl3_home.equals("")) {
		    LOG.error(
		    	"Couldn't access GSDL3Home from GlobalProperties.getGSDL3HOME,"
		    	+ "can't initialize the SOAP Server.");
		    return;
		}
		
		String site_home = GSFile.siteHome(gsdl3_home, this.site_name);
		
		File site_file = new File(site_home);
		if (!site_file.isDirectory()) {
		    LOG.error("The site directory "+site_file.getPath()
		    	+" doesn't exist. Can't initialize the SOAP Server.");
		    return;
		} 
		this.converter = new XMLConverter();
		this.doc = this.converter.newDOM();
		
		mr = new MessageRouter();
		mr.setSiteName(this.site_name);
		mr.configure();
    }
	
	/* (1) DESCRIBE MESSAGES, manual pages 35-41 */
	/** Sends a describe message to the MessageRouter.
	 * @param lang is the language of the display content in the response.
	 * @param subsetOption are the requested list of items to return in the 
	 * response. For the Message Router this can be collectionList, 
	 * serviceClusterList, serviceList, siteList 
	 * @see <a href="http://wiki.greenstone.org/wiki/index.php/Greenstone3">The Greenstone 3 Developer's Manual - pages 35-41</a>
	*/
	public String describe(String lang, String subsetOption) 
	{
		return describe("", lang, subsetOption, mrSubsetOptions);
	}
	
	/** For sending Describe messages to ServiceClusters.
	 * @param serviceCluster is the name of the Service Cluster that this describe 
	 * request is sent to. 
	 * @param lang is the language of the display content in the response
	 * @param subsetOption is the requested list of items to return in the response
	 * For Service Clusters this can be metadataList, serviceList, displayItemList.
	 * @see <a href="http://wiki.greenstone.org/wiki/index.php/Greenstone3">The Greenstone 3 Developer's Manual - pages 35-41</a>
	 */
	public String describeServiceCluster(
			String serviceCluster, String lang, String subsetOption)
	{
		return describe(serviceCluster, lang, subsetOption, csSubsetOptions);
	}
	
	/** For sending Describe messages to Collections.
	 * @param collection is the name of the Collection that this describe request 
	 * is sent to. 
	 * @param lang is the language of the display content in the response
	 * @param subsetOption is the requested list of items to return in the response
	 * For Collections this can be metadataList, serviceList and displayItemList.
	 * @see <a href="http://wiki.greenstone.org/wiki/index.php/Greenstone3">The Greenstone 3 Developer's Manual - pages 35-41</a>
	 */
	public String describeCollection(
			String collection, String lang, String subsetOption)
	{
		return describe(collection, lang, subsetOption, csSubsetOptions);
	}
	
	/**
	 * For sending a describe message to a Collection's Service.
	 * @see <a href="http://wiki.greenstone.org/wiki/index.php/Greenstone3">The Greenstone 3 Developer's Manual - pages 35-41</a>
	 * @param collection is the name of the Collection whose service 
	 * this describe request is sent to.
	 * @param service is the name of the Service (of that collection) to
	 * which this describe request is sent.
	 * @param lang is the language of the display content in the response
	 * @param subsetOption is the requested list of items to return in the response
	 * For Services this can be paramList, displayItemList */
	public String describeCollectionService(String collection, String service, 
			String lang, String subsetOption) 
	{
		return describe(collection + "/" + service, 
				lang, subsetOption, serviceSubsetOptions);
	}
	
	/** 
	 * For sending a describe message to a Service hosted by the Message Router 
	 * (no collection).
	 * @see <a href="http://wiki.greenstone.org/wiki/index.php/Greenstone3">The Greenstone 3 Developer's Manual - pages 35-41</a>
	 * @param service is the name of the MessageRouter's Service to which this 
	 * describe request is sent.
	 * @param lang is the language of the display content in the response
	 * @param subsetOption is the requested list of items to return in the response
	 * For Services this can be paramList, displayItemList 
	*/
	public String describeService(
			String service, String lang, String subsetOption) 
	{
		return describe(service, lang, subsetOption, serviceSubsetOptions);
	}
	
	/** For sending a describe message.
	 * If public, this method would give full access: a describe message that 
	 * lets the user specify all the details of who the receiver is, and what 
	 * details are requested. 
	 * @param to - the Greenstone module (MessageRouter, Collection, 
	 * ServiceCluster or (Collection-)Service to send this describe message to.
	 * (The module asked to describe itself.) 
	 * @param lang - the language of the display content in the response.
	 * @param subsetOption - the set of elements of the describe response that
	 * are requested. These vary depending on the GS3 module asked to describe
	 * itself.
	 * @param validSubsetOptions - the list of subsetOptions that are allowed
	 * for the module this describe message is sent to. Parameter subsetOption
	 * has to be among the list of validSubsetOptions.
	 * @see <a href="http://wiki.greenstone.org/wiki/index.php/Greenstone3">The Greenstone 3 Developer's Manual - pages 35-41</a>
	*/ 
	protected String describe(String to, String lang, 
			String subsetOption, String validSubsetOptions)
	{
		// Create message element: <message></message>
		Element message = this.doc.createElement(GSXML.MESSAGE_ELEM);
		// <message><request lang="en" to="" type="describe" uid="" /></message>
		Element request = GSXML.createBasicRequest(
				this.doc, GSXML.REQUEST_TYPE_DESCRIBE, to, new UserContext(lang, ""));
		
		// Check if only a subset of this Module Interface's data is asked
		// to be described
		if(!subsetOption.equals("")) {
			// Now deal with the value for subset param:
			// only deal with valid params for subset of to-ModuleInterface
			if(validSubsetOptions.indexOf(subsetOption) == -1)
				return error("Invalid List to be described. Choose one of:\n"
					+ validSubsetOptions);
			
			// else, append <paramList>
			// <param name="subset" value="subsetOption" /></paramList>
			Element paramList = this.doc.createElement(
					GSXML.PARAM_ELEM+GSXML.LIST_MODIFIER);
			// append <param name="subset" value=paramValue />
			// createParam(Document, name, value); 
			// Name needs to be "subset", but this can be either GSXML.SUBSET_PARAM
			// or GSXML.SYSTEM_SUBSET_ATT. It's the first one probably.
			paramList.appendChild(GSXML.createParameter(
							this.doc, GSXML.SUBSET_PARAM, subsetOption));
			request.appendChild(paramList);
		}
		message.appendChild(request);
		
		// Send it off to the Message Router and return the response
		return this.processInternal(message);
	}

	/* (2) Process-type message, QUERY-TYPE SERVICES - p.45 */
	/** For executing a (process-type message) query-type service.
	 * @see <a href="http://wiki.greenstone.org/wiki/index.php/Greenstone3">The Greenstone 3 Developer's Manual - page 45</a>
	 * @param collection is the name of the Collection whose query service this  
	 * query-process request is sent to. If "", then the Message Router is assumed.
	 * @param service is the name of the Query Service (of that collection) to  
	 * which  this request is sent.
	 * @param lang is the language of the display content in the response
	 * @param nameToValsMap is a Map of the (fieldname, value) pairs for the 
	 * parameters of the query. The field names should be those recognised by 
	 * Greenstone 3. That is, the names must exist for the (Collection-)Service Query that this 
	 * message is sent To (as given in 'to' argument). 
	 * For names of Greenstone-accepted arguments,
	 * @see <a href="http://wiki.greenstone.org/wiki/index.php/Actions_and_Arguments">Greenstone wiki - Actions and Arguments</a>
	*/
	public String query(String collection, String service, 
			String lang, Map nameToValsMap) 
	{ 	
		// <paramList></paramList>
		Element paramList = this.doc.createElement(
				GSXML.PARAM_ELEM+GSXML.LIST_MODIFIER);
		// <param>s: creating parameters of (name, value) pairs
		Set entrySet = nameToValsMap.entrySet();
		Iterator i = entrySet.iterator();
		while(i.hasNext()) {
			Entry entry = (Entry)i.next();
			String name = (String)entry.getKey();
			String value = (String)entry.getValue();
			paramList.appendChild(GSXML.createParameter(
					this.doc, name, value));
		}

		Element message = this.doc.createElement(GSXML.MESSAGE_ELEM);
		Element request = GSXML.createBasicRequest(
				this.doc, GSXML.REQUEST_TYPE_PROCESS, 
				collection+"/"+service, new UserContext(lang, ""));
		
		request.appendChild(paramList);
		message.appendChild(request);
		
		// Send it off to the Message Router and return the response
		return this.processInternal(message);	
	}

        /** 
	 * This method is used to perform the most basic query:
	 * it assumes defaults for all other parameters and provides only
	 * the query string. It is built on top of a TextQuery.
	 * @param collection is the Greenstone collection to be searched
	 * @param lang is the preferred language of the display content in 
	 * the response to be returned.
	 * @param query is the string to be sought in the Greenstone collection
	 * @return a Greenstone 3 XML response message for the query specifying 
	 * the search results.
	 */
	public String basicQuery(String collection, String lang, String query) {
		// The basicQuery is built on top of the TextQuery service
		final String queryService = "TextQuery";
		
		// (1) describe request on the TextQuery
		String queryDescription = describeCollectionService(
				collection, queryService, "en", "paramList"); // just get paramList
		//System.out.println(queryDescription);
		
		Document doc = this.converter.getDOM(queryDescription);
		NodeList nl = doc.getElementsByTagName(
				GSXML.PARAM_ELEM+GSXML.LIST_MODIFIER);
		
		Element paramList = null;
		if(nl.getLength() <= 0) { // no paramList in textQuery description means
				// no query field either: that means we can't continue
			return this.error("BasicQuery is not available for this collection" 
				+ " as it provides no TextQuery service.");
		} //else
		
		paramList = (Element)nl.item(0);
		nl = paramList.getElementsByTagName(GSXML.PARAM_ELEM);
		if(nl.getLength() <= 0) { // no params, means no query field, so return
			return this.error("BasicQuery is not available for this collection.");
		}
		
		// (2) get the defaults for each parameter and use that to set
		// the defaults
		Map params = new HashMap(nl.getLength()); // field name to value map
		for(int i = 0; i < nl.getLength(); i++) {
			Element param = (Element)nl.item(i);
			String paramName = param.getAttribute(GSXML.NAME_ATT);
			String def = param.getAttribute(GSXML.DEFAULT_ATT);
			if(def.equals("")) { 
				// if there's no default, the field must want the query String
				params.put(paramName, query);
			} else { // there is a default, use the default for this param
				params.put(paramName, def);
			}
		}
		
		// (3) Perform the query using defaults and return the response
		return this.query(collection, queryService, lang, params);
	}

		
	/* (3) RETRIEVE PROCESS METHODS - Manual, pp.47-49 */
	/** DocumentContentRetrieve request sent to a collection's 
	 * DocumentContentRetrieve service (see manual, p.48)
	 * @see <a href="http://wiki.greenstone.org/wiki/index.php/Greenstone3">The Greenstone 3 Developer's Manual - page 48</a>
	 * @param collection is the name of the Collection whose 
	 * DocumentContentRetrieve is requested 
	 * @param lang is the language of the display content in the response 
	 * @param docNodeIDs is the list of documentNodeIDs for which the
	 * content ought to be retrieved. */
	public String retrieveDocumentContent(
			String collection, String lang, String[] docNodeIDs) 
	{
		// creating <documentNodeList></documentNodeList>
		Element docNodeList = this.doc.createElement(
				GSXML.DOC_NODE_ELEM+GSXML.LIST_MODIFIER);
		
		// creating subelements: <documentNode nodeID="..." />
		for(int i = 0; i < docNodeIDs.length; i++) {
			Element docNode = this.doc.createElement(GSXML.DOC_NODE_ELEM);
			docNode.setAttribute(GSXML.NODE_ID_ATT, docNodeIDs[i]);
			docNodeList.appendChild(docNode);
		}

		Element message = doc.createElement(GSXML.MESSAGE_ELEM);
		Element request = GSXML.createBasicRequest(
				doc, GSXML.REQUEST_TYPE_PROCESS, 
				collection+"/DocumentContentRetrieve", new UserContext(lang, ""));
		
		// create an empty <paramlist /> element (as example in manual)
		Element paramlist = doc.createElement(
				GSXML.PARAM_ELEM+GSXML.LIST_MODIFIER);
		
		request.appendChild(paramlist);
		request.appendChild(docNodeList);
		message.appendChild(request);

		// Send it off to the Message Router and return the response
		return this.processInternal(message);
	}
	
	/** DocumentStructureRetrieve request sent to a collection's 
	 * DocumentStructureRetrieve service (manual pp.48, 49) to retrieve
	 * the entire document structure.
	 * @see <a href="http://wiki.greenstone.org/wiki/index.php/Greenstone3">The Greenstone 3 Developer's Manual - pages 48, 49</a>
	 * @param collection is the name of the Collection whose 
	 * DocumentStructureRetrieve is requested 
	 * @param lang is the language of the display content in the response 
	 * @param docNodeIDs is the list of documentNodeIDs for which the
	 * entire structure ought to be retrieved. */
	public String retrieveEntireDocumentStructure(String collection, 
			String lang, String[] docNodeIDs) 
	{
		return retrieveDocumentStructure(collection, lang, docNodeIDs, 
				new String[] { "entire" }, null);
	}
	
	/** DocumentStructureRetrieve request sent to a collection's 
	 * DocumentStructureRetrieve service (manual pp.48, 49) to retrieve
	 * the specified part of the document's structure.
	 * @see <a href="http://wiki.greenstone.org/wiki/index.php/Greenstone3">The Greenstone 3 Developer's Manual - pages 48, 49</a>
	 * @param collection is the name of the Collection whose 
	 * DocumentStructureRetrieve is requested 
	 * @param lang is the language of the display content in the response 
	 * @param docNodeIDs is the list of documentNodeIDs for which the
	 * structure ought to be retrieved. 
	 * @param structure specifies what structure information needs to
	 * be retrieved. The values can be one or more of ancestors, parent, 
	 * siblings, children, descendants (<b>note spelling</b>), entire.
	 * @param info - for specifying extra information to be retrieved. 
	 * Possible values for info parameters are numSiblings, siblingPosition, 
	 * numChildren */
	public String retrieveDocumentStructure(String collection, String lang,
			String[] docNodeIDs, String[] structure, String[] info)
	{
		// creating subelements: <documentNode nodeID="..." />
		Element docNodeList = this.doc.createElement(
				GSXML.DOC_NODE_ELEM+GSXML.LIST_MODIFIER);
		for(int i = 0; i < docNodeIDs.length; i++) {
			Element docNode = this.doc.createElement(GSXML.DOC_NODE_ELEM);
			docNode.setAttribute(GSXML.NODE_ID_ATT, docNodeIDs[i]);
			docNodeList.appendChild(docNode);
		} 
		
		Element message = doc.createElement(GSXML.MESSAGE_ELEM);
		Element request = GSXML.createBasicRequest(
				doc, GSXML.REQUEST_TYPE_PROCESS, 
				collection+"/DocumentStructureRetrieve", new UserContext(lang, ""));
		
		// Create the <paramlist></paramlist> element of param elements,
		// if any; and only if values are legal (that is, if they occur in  
		// static Strings structureOptions and structureInfoOptions):
		// <param name="structure" value = "structure[i]">
		// <param name="info" value = "info[i]">
		Element paramList = doc.createElement(
				GSXML.PARAM_ELEM+GSXML.LIST_MODIFIER);
		
		if(structure != null) {
			for(int i = 0; i < structure.length; i++) {
				if(structureOptions.indexOf(structure[i]) != -1) {
					paramList.appendChild(GSXML.createParameter(
							this.doc, "structure", structure[i]));					
				}
			} 
		}
		if(info != null) {
			for(int i = 0; i < info.length; i++) {
				if(structureInfoOptions.indexOf(info[i]) != -1) {
					paramList.appendChild(GSXML.createParameter(
							this.doc, "info", info[i]));
				}
			}
		}
		
		// paramList is allowed to be empty and may indeed be empty:
		request.appendChild(paramList);
		request.appendChild(docNodeList);
		message.appendChild(request);
		
		// Send it off to the Message Router and return the response
		return this.processInternal(message);
	}
	
	/* Retrieve for Doc Metadata: explained in the manual on page 47 */
	/** DocumentMetadataRetrieve request sent to a collection's 
	 * DocumentMetadataRetrieve service to retrieve all of a document's metadata. 
	 * @see <a href="http://wiki.greenstone.org/wiki/index.php/Greenstone3">The Greenstone 3 Developer's Manual - page 47</a>
	 * @param collection is the name of the Collection whose 
	 * DocumentMetadataRetrieve is requested 
	 * @param lang is the language of the display content in the response 
	 * @param docNodeIDs is the list of documentNodeIDs for which the
	 * structure ought to be retrieved. 
	*/
	public String retrieveAllDocumentMetadata(String collection, String lang,
			String[] docNodeIDs) 
	{
		// See bottom of manual p.44 for the fact that "all" is used
		// as the metaName value when retrieving all metadata for a doc
		return retrieveDocumentMetadata(collection, lang, docNodeIDs, 
				new String[]{ "all" });
	}
	
	/** DocumentMetadataRetrieve service to retrieve some specific 
	 * metadata values of a document. (Manual on page 47.)
	 * @see <a href="http://wiki.greenstone.org/wiki/index.php/Greenstone3">The Greenstone 3 Developer's Manual - page 47</a>
	 * @param collection is the name of the Collection whose 
	 * DocumentContentRetrieve is requested 
	 * @param lang is the language of the display content in the response 
	 * @param docNodeIDs is the list of documentNodeIDs for which the
	 * structure ought to be retrieved.
	 * @param metaNames is a list of metadata names which are requested  
	 * to be fetched for the specified documents */
	public String retrieveDocumentMetadata(String collection, String lang,
			String[] docNodeIDs, String[] metaNames)
	{
		return metadataRetrieve(collection+"/DocumentMetadataRetrieve",
				lang, docNodeIDs, metaNames, GSXML.DOC_NODE_ELEM);
	}

	/** Retrieve all classification Metadata for browsing (sent to the 
	 * ClassifierBrowseMetadataRetrieve service).
	 * @see <a href="http://wiki.greenstone.org/wiki/index.php/Greenstone3">The Greenstone 3 Developer's Manual - pages 47, 48</a>
	 * @param collection is the name of the Collection whose 
	 * ClassifierBrowseMetadataRetrieve service is called 
	 * @param categoryName - name of the browsing category, usually
	 * ClassifierBrowse. (If left as "", then it defaults to ClassifierBrowse) 
	 * @param lang is the language of the display content in the response 
	 * @param nodeIDs is the list of document or classifier NodeIDs 
	 * for which the metadata ought to be retrieved.*/
	public String retrieveAllBrowseMetadata(String collection, 
			String categoryName, String lang, String[] nodeIDs) 
	{
		if(categoryName.equals(""))
			categoryName = "ClassifierBrowse";
		// See bottom of manual p.47 for the fact that "all" is used as 
		// the metaName value when retrieving all metadata for a classifier
		return metadataRetrieve(collection+"/"+categoryName+"MetadataRetrieve", 
				lang, nodeIDs, new String[]{ "all" }, GSXML.CLASS_NODE_ELEM);
	}
	
	/** ClassifierBrowseMetadataRetrieve service to retrieve some specific 
	 * metadata values of a document. 
	 * @see <a href="http://wiki.greenstone.org/wiki/index.php/Greenstone3">The Greenstone 3 Developer's Manual - pages 47, 48</a>
	 * @param collection is the name of the Collection whose 
	 * ClassifierBrowseMetadataRetrieve service is called
	 * @param categoryName - name of the browsing category, usually
	 * ClassifierBrowse. (If left as "", then it defaults to ClassifierBrowse) 
	 * @param lang is the language of the display content in the response 
	 * @param nodeIDs is the list of document or classifier NodeIDs 
	 * for which the metadata ought to be retrieved.
	 * @param metaNames is a list of metadata names which are requested  
	 * to be fetched for the specified documents or classifiers */
	public String retrieveBrowseMetadata(String collection, String categoryName,  
			String lang, String[] nodeIDs, String[] metaNames) 
	{
		if(categoryName.equals(""))
			categoryName = "ClassifierBrowse";
		return metadataRetrieve(collection+"/"+categoryName+"MetadataRetrieve", 
				lang, nodeIDs, metaNames, GSXML.CLASS_NODE_ELEM);
	}
	
	/** Performs a metadata retrieve for documents and (browse) classification 
	 * hierarchies. Sends a Document- or ClassifierBrowse- MetadataRetrieve message 
	 * to the Document- or ClassifierBrowse- MetadataRetrieve service.
	 * @param to - the Document- or ClassifierBrowse- MetadataRetrieve service to
	 * send this metadata retrieve message to.
	 * @param lang - the language of the display content in the response
	 * @param nodeIDs - the list of (document or classifier) nodeIDs for which
	 * to retrieve the metadata for
	 * @param metaNames - a list specifiying the names of the metadata items 
	 * to be retrieved for each nodeID. E.g. "Title", but a list is allowed.
	 * @param NODE_ELEM - either of GSXML's names for the &lt;documentNode&gt; or 
	 * &lt;classifierNode&gt; elements.
	*/
	protected String metadataRetrieve(String to, String lang, 
			String[] nodeIDs, String[] metaNames, final String NODE_ELEM)
	{
		// create the <paramlist></paramlist> element of param elements:  
		// <param name="metadata" value = "metaName[i]">
		Element metadataParamList = this.doc.createElement(
				GSXML.PARAM_ELEM+GSXML.LIST_MODIFIER);
		for(int i = 0; i < metaNames.length; i++) {
			metadataParamList.appendChild(GSXML.createParameter(
					this.doc, GSXML.METADATA_ELEM, metaNames[i]));
		}
		
		// creating subelements: <documentNode nodeID="..." />
		// or <classifierNode nodeID="..." />
		Element nodeList = this.doc.createElement(
				NODE_ELEM+GSXML.LIST_MODIFIER);
		for(int i = 0; i < nodeIDs.length; i++) {
			Element docNode = this.doc.createElement(NODE_ELEM);
			docNode.setAttribute(GSXML.NODE_ID_ATT, nodeIDs[i]);
			nodeList.appendChild(docNode);
		} 
		
		Element message = doc.createElement(GSXML.MESSAGE_ELEM);
		Element request = GSXML.createBasicRequest(doc, 
				GSXML.REQUEST_TYPE_PROCESS, to, new UserContext(lang, ""));
		
		request.appendChild(metadataParamList);
		request.appendChild(nodeList);
		message.appendChild(request);
		
		// Send it off to the Message Router and return the response
		return this.processInternal(message);
	}
	
	/* (4) Classifier BROWSE PROCESS METHODS - p.46 */
	/** To send a browse request for all the descendants of a classifier node.
	 * Useful for getting the entire structure of a top-level &lt;classificationNode&gt;
	 * @see <a href="http://wiki.greenstone.org/wiki/index.php/Greenstone3">The Greenstone 3 Developer's Manual - page 46</a>
	 * @param collection is the name of the Collection whose browse Classifier
	 * Browse Service is called
	 * @param browseService is the name of the (Classifier) Browse Service (of 
	 * the given collection) to which this request message is sent. 
	 * @param lang is the language of the display content in the response 
	 * @param classifierNodeIDs is an array of classifierNodeIDs for which the
	 * structures ought to be retrieved.
	*/
	public String browseDescendants(String collection, String browseService, 
			String lang, String[] classifierNodeIDs) 
	{
		// We are at the top level, we want all the descendants:
		// <param name="structure" value = "descendants">
		// <classifierNodeList><classifier nodeID="CLx" /></classifierNodeList>
		return browse(collection, browseService, lang,   
				classifierNodeIDs, 
				new String[] {"descendants"}, new String[] {""}); // note the spelling
	}
	
	/** To send a browse request for specific parts of a classifier node 
	 * (children, ancestors, descendants). Useful for getting specific parts
	 * of the structure of a top-level &lt;classificationNode&gt;.
	 * @see <a href="http://wiki.greenstone.org/wiki/index.php/Greenstone3">The Greenstone 3 Developer's Manual - page 46</a> 
	 * @param collection is the name of the Collection whose browse Classifier
	 * Browse Service is called
	 * @param browseService is the name of the (Classifier) Browse Service (of 
	 * the given collection) to which this request message is sent. 
	 * @param lang is the language of the display content in the response 
	 * @param classifierNodeIDs is the list of classifierNodeIDs for which the
	 * structure ought to be retrieved.
	 * @param structureParams the list of parameters indicating what structure 
	 * information is requested. Accepted values are ancestors, parent, siblings,
	 * children, descendants.
	 * @param infoParams - structural info is requested. Can be numSiblings, 
	 * siblingPosition, numChildren
	*/
	public String browse(String collection, String browseService, String lang, 
			String[] classifierNodeIDs, String[] structureParams, String[] infoParams) 
	{
		if(browseService.equals(""))
			browseService = "ClassifierBrowse";
		
		// Create message element: <message></message>
		Element message = this.doc.createElement(GSXML.MESSAGE_ELEM);
		// <message><request lang="en" to="" type="process" uid="" /></message>
		Element request = GSXML.createBasicRequest(this.doc,
			GSXML.REQUEST_TYPE_PROCESS, collection+"/"+browseService, new UserContext(lang, ""));
		
		// <param name="structure" value = "structureParams[i]">
		Element paramList = this.doc.createElement(
				GSXML.PARAM_ELEM+GSXML.LIST_MODIFIER);
		for(int i = 0; i < structureParams.length; i++) {
			// check it is a valid structure parameter
			if(structureOptions.indexOf(structureParams[i]) != -1) {
				paramList.appendChild(GSXML.createParameter(
						this.doc, "structure", structureParams[i]));
			}
		}

		if(infoParams != null && !infoParams[0].equals("")) {
		    for(int i = 0; i < infoParams.length; i++) {
			if(structureInfoOptions.indexOf(infoParams[i]) != -1) {
			    paramList.appendChild(GSXML.createParameter(
						this.doc, "info", infoParams[i]));
			}
		    }
		}
		
		// <classifierNodeList><classifier nodeID="CLx" />
		// 		<classifier nodeID="CLy" /></classifierNodeList> 
		// where CLx and CLy are given in the parameter classifierNodeIDs
		Element classifierNodeList = this.doc.createElement(
				GSXML.CLASS_NODE_ELEM+GSXML.LIST_MODIFIER);
		for(int i = 0; i < classifierNodeIDs.length; i++) {
			Element classifier = this.doc.createElement(GSXML.CLASS_NODE_ELEM);
			classifier.setAttribute(GSXML.NODE_ID_ATT, classifierNodeIDs[i]);
			classifierNodeList.appendChild(classifier);
		}
		
		// now finish constructing the request message:
		request.appendChild(paramList);
		request.appendChild(classifierNodeList);
		message.appendChild(request);
		
		// Send it off to the Message Router and return the response
		return this.processInternal(message);
	}
	
	/** Called by most other methods in order to send the constructed message
	 * to the Greenstone's MessageRouter, intercept the response and return it.
	 * @param message is the XML message Element to send to GS3's MessageRouter.
	 * @return the XML response in String format. */
	protected String processInternal(Element message) {
	        if(LOG.isDebugEnabled()) { // or LOG.isEnabledFor(Level.DEBUG). 
		                           // Testing for this improves efficiency
		    LOG.debug(this.converter.getPrettyString(message));
		}
		
		// Let the messagerouter process the request message and get the response
		Element response = XMLConverter.nodeToElement(mr.process(message)); 
		      // won't be null except when Node returned is not an element
		      // otherwise, MR always returns some response

		// Return it as a String formatted for display
		String responseMsg = this.converter.getPrettyString(response); 
		                  // this.converter.getString(response);

		// In order to avoid "Content is not allowed in prolog" exception on the 
		// web services' client end (problem encountered in GS mailing list), need 
		// to make sure no characters (incl spaces) preceed the  XML sent back 
		// from here. It may also require the <?xml?> tag at the very start.
		if(responseMsg.charAt(0) == ' ') {
		    responseMsg = responseMsg.trim();
		}
		
		return "<?xml version=\"1.0\" encoding=\"UTF-8\"?>"+responseMsg;
	}
	
	/** Creates a String response message to represent an XML error response  
	 * message using the error specified in the message parameter. A String is 
	 * created because this method ensures that a response message is reliably 
	 * constructed (no exceptions are thrown) that can be sent to clients.
	 * @param errorMessage - the errormessage to be conveyed
	 * @return an XML response message containing an GS3 error element. */
	protected String error(String errorMessage) {
		StringBuffer buf = new StringBuffer("<" + GSXML.MESSAGE_ELEM + ">");
		buf.append("<" + GSXML.RESPONSE_ELEM + " " 
				+ GSXML.FROM_ATT + "=\"" + "Greenstone 3 Web Services\"" + ">");
		buf.append("<" + GSXML.ERROR_ELEM + " " 
			+ GSXML.ERROR_TYPE_ATT + "=\""+ GSXML.ERROR_TYPE_OTHER + "\"" + ">");
		buf.append(errorMessage+"\n");
		buf.append("</" + GSXML.ERROR_ELEM + ">");
		buf.append("</" + GSXML.RESPONSE_ELEM + ">");
		buf.append("</" + GSXML.MESSAGE_ELEM + ">");
		return buf.toString();
	}

	/*
	Look in file QBRWebServicesHelp.properties
	- Have a properties file that maps methodname to help string specific
	to the method.
	- Read it all in statically at the start of the class, into a Properties Map.
	- When this method is called, display the usage: "help methodname"
	and list all the available methods by going over the keys in the Map.
	- When the helpWithMethod(String methodname) method is called, return the 
	value of the Map for the methodname key. This value would be the help
	description for that method.		
	*/
	/** @return a help string for listing all the web service methods. */
	public static String help() {
		if(!helpErrormessage.equals("")) {
			return helpErrormessage;
		}
		
		StringBuffer helpString = new StringBuffer(
				"USAGE: helpWithMethod(String <method name>)\n");
		helpString.append(
				"\nNearly all the web service operations return a String\n"); 
		helpString.append(
				"representing a Greenstone 3 XML response message.\n");
		helpString.append("\nA list of all the method names: \n");
		
		Enumeration props = properties.keys();
		while(props.hasMoreElements()){
			String methodName = (String)props.nextElement();
			helpString.append("\t");
			helpString.append(methodName);
			helpString.append("\n");
		}
		
		return helpString.toString();
	}
	
	/** @param methodname is the name of the method to be described.  
	 * @return a help string for the given method, explaining what the method
	 * does, what parameters it expects and their types and what it returns.
	*/
	public static String helpWithMethod(String methodname) {
		if(!helpErrormessage.equals("")) {
			return helpErrormessage;
		}
		// else we can get the method's description from the properties
		// map loaded from the QBRWebServicesHelp.properties file:
		String helpString = properties.getProperty(methodname,
			"No description for " + methodname); // if the method does not exist
		
		return helpString;
	}
} // end web service class