/*
 *    XMLTransformer.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.util;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileWriter;
import java.io.InputStreamReader;
import java.io.StringReader;
import java.io.StringWriter;
import java.io.UnsupportedEncodingException;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;

import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.transform.ErrorListener;
import javax.xml.transform.Source;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerConfigurationException;
import javax.xml.transform.TransformerException;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMResult;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;
import javax.xml.transform.stream.StreamSource;

import org.apache.log4j.Logger;
import org.greenstone.util.GlobalProperties;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;

/**
 * XMLTransformer - utility class for greenstone
 * 
 * transforms xml using xslt
 * 
 * @author Katherine Don
 * @version $Revision: 26457 $
 */
public class XMLTransformer
{
	private static int debugFileCount = 0; // for unique filenames when debugging XML transformations with physical files

	static Logger logger = Logger.getLogger(org.greenstone.gsdl3.util.XMLTransformer.class.getName());

	/** The transformer factory we're using */
	TransformerFactory t_factory = null;

	/**
	 * The no-arguments constructor.
	 * 
	 * Any exceptions thrown are caught internally
	 * 
	 * @see javax.xml.transform.TransformerFactory
	 */
	public XMLTransformer()
	{
		// http://download.oracle.com/docs/cd/E17476_01/javase/1.5.0/docs/api/index.html?javax/xml/transform/TransformerFactory.html states that
		// TransformerFactory.newInstance() looks in jar files for a Factory specified in META-INF/services/javax.xml.transform.TransformerFactory, 
		// else it will use the "platform default"
		// In this case: xalan.jar's META-INF/services/javax.xml.transform.TransformerFactory contains org.apache.xalan.processor.TransformerFactoryImpl
		// as required.

		// This means we no longer have to do a System.setProperty("javax.xml.transform.TransformerFactory", "org.apache.xalan.processor.TransformerFactoryImpl");
		// followed by a this.t_factory = org.apache.xalan.processor.TransformerFactoryImpl.newInstance();
		// The System.setProperty step to force the TransformerFactory implementation that gets used, conflicts with
		// Fedora (visiting the Greenstone server pages breaks the Greenstone-tomcat hosted Fedora pages) as Fedora 
		// does not include the xalan.jar and therefore can't then find the xalan TransformerFactory explicitly set.

		// Gone back to forcing use of xalan transformer, since other jars like crimson.jar, which may be on some
		// classpaths, could be be chosen as the TransformerFactory implementation over xalan. This is what used to
		// give problems before. Instead, have placed copies of the jars that Fedora needs (xalan.jar and serializer.jar 
		// and the related xsltc.jar which it may need) into packages/tomcat/lib so that it's on the server's classpath
		// and will be found by Fedora.

		// make sure we are using the xalan transformer
		System.setProperty("javax.xml.transform.TransformerFactory", "org.apache.xalan.processor.TransformerFactoryImpl");
		try
		{
			this.t_factory = org.apache.xalan.processor.TransformerFactoryImpl.newInstance();
			//this.t_factory = TransformerFactory.newInstance();
			this.t_factory.setErrorListener(new TransformErrorListener()); // handle errors in the xml Source used to instantiate transformers
		}
		catch (Exception e)
		{
			logger.error("exception creating t_factory " + e.getMessage());
		}
	}

	/**
	 * Transform an XML document using a XSLT stylesheet
	 * 
	 * @param stylesheet
	 *            a filename for an XSLT stylesheet
	 * @param xml_in
	 *            the XML to be transformed
	 * @return the transformed XML
	 */
	public String transform(String stylesheet, String xml_in)
	{

		try
		{
			TransformErrorListener transformerErrorListener = (TransformErrorListener) this.t_factory.getErrorListener();
			transformerErrorListener.setStylesheet(stylesheet);
			// Use the TransformerFactory to process the stylesheet Source and generate a Transformer.
			Transformer transformer = this.t_factory.newTransformer(new StreamSource(stylesheet));

			// Use the Transformer to transform an XML Source and send the output to a Result object.
			StringWriter output = new StringWriter();
			StreamSource streamSource = new StreamSource(new StringReader(xml_in));
			transformer.setErrorListener(new TransformErrorListener(stylesheet, streamSource));
			transformer.transform(streamSource, new StreamResult(output));
			return output.toString();
		}
		catch (TransformerConfigurationException e)
		{
			logger.error("couldn't create transformer object: " + e.getMessageAndLocation());
			logger.error(e.getLocationAsString());
			return "";
		}
		catch (TransformerException e)
		{
			logger.error("couldn't transform the source: " + e.getMessageAndLocation());
			return "";
		}
	}

	public String transformToString(Document stylesheet, Document source)
	{
		return transformToString(stylesheet, source, null);
	}

	public String transformToString(Document stylesheet, Document source, HashMap parameters)
	{

		try
		{
			TransformErrorListener transformerErrorListener = (TransformErrorListener) this.t_factory.getErrorListener();
			transformerErrorListener.setStylesheet(stylesheet);
			// Use the TransformerFactory to process the stylesheet Source and generate a Transformer.
			Transformer transformer = this.t_factory.newTransformer(new DOMSource(stylesheet));
			if (parameters != null)
			{
				Set params = parameters.entrySet();
				Iterator i = params.iterator();
				while (i.hasNext())
				{
					Map.Entry m = (Map.Entry) i.next();
					transformer.setParameter((String) m.getKey(), m.getValue());
				}
			}
			//transformer.setParameter("page_lang", source.getDocumentElement().getAttribute(GSXML.LANG_ATT));

			// Use the Transformer to transform an XML Source and send the output to a Result object.
			StringWriter output = new StringWriter();
			DOMSource domSource = new DOMSource(source);

			transformer.setErrorListener(new TransformErrorListener(stylesheet, domSource));
			transformer.transform(domSource, new StreamResult(output));
			return output.toString();
		}
		catch (TransformerConfigurationException e)
		{
			logger.error("couldn't create transformer object: " + e.getMessageAndLocation());
			logger.error(e.getLocationAsString());
			return "";
		}
		catch (TransformerException e)
		{
			logger.error("couldn't transform the source: " + e.getMessageAndLocation());
			return "";
		}
	}

	/**
	 * Transform an XML document using a XSLT stylesheet, but using a DOMResult
	 * whose node should be set to the Document donated by resultNode
	 */
	public Node transform_withResultNode(Document stylesheet, Document source, Document resultNode)
	{
		return transform(stylesheet, source, null, null, resultNode);
	}

	public Node transform(Document stylesheet, Document source)
	{
		return transform(stylesheet, source, null, null, null);
	}

	public Node transform(Document stylesheet, Document source, HashMap<String, Comparable> parameters)
	{
		return transform(stylesheet, source, parameters, null, null);
	}

	public Node transform(Document stylesheet, Document source, HashMap<String, Comparable> parameters, Document docDocType)
	{
		return transform(stylesheet, source, parameters, docDocType, null);
	}

	protected Node transform(Document stylesheet, Document source, HashMap<String, Comparable> parameters, Document docDocType, Document resultNode)
	{
		try
		{
			// Use the TransformerFactory to process the stylesheet Source and generate a Transformer.
			TransformErrorListener transformerErrorListener = (TransformErrorListener) this.t_factory.getErrorListener();
			transformerErrorListener.setStylesheet(stylesheet);
			Transformer transformer = this.t_factory.newTransformer(new DOMSource(stylesheet));
			//logger.info("XMLTransformer transformer is " + transformer); //done in ErrorListener

			if (parameters != null)
			{
				Set params = parameters.entrySet();
				Iterator i = params.iterator();
				while (i.hasNext())
				{
					Map.Entry m = (Map.Entry) i.next();
					transformer.setParameter((String) m.getKey(), m.getValue());
				}
			}

			// When we transform the DOMResult, we need to make sure the result of
			// the transformation has a DocType. For that to happen, we need to create
			// the DOMResult using a Document with a predefined docType.
			// If we don't have a DocType then do the transformation with a DOMResult
			// that does not contain any doctype (like we use to do before).
			DOMResult result = docDocType == null ? new DOMResult() : new DOMResult(docDocType);
			if (resultNode != null)
			{
				result.setNode(resultNode);
			}
			DOMSource domSource = new DOMSource(source);
			transformer.setErrorListener(new TransformErrorListener(stylesheet, domSource));
			transformer.transform(domSource, result);
			return result.getNode(); // pass the entire document
		}
		catch (TransformerConfigurationException e)
		{
			return transformError("XMLTransformer.transform(Doc, Doc, HashMap, Doc)" + "\ncouldn't create transformer object", e);
		}
		catch (TransformerException e)
		{
			return transformError("XMLTransformer.transform(Doc, Doc, HashMap, Doc)" + "\ncouldn't transform the source", e);
		}
	}

	public Node transform(File stylesheet, File source)
	{
		return transform(stylesheet, source, null);
	}

	// debugAsFile is only to be set to true when either the stylesheet or source parameters 
	// are not objects of type File. The debugAsFile variable is passed into the 
	// TransformErrorListener. When set to true, the TransformErrorListener will itself create
	// two files containing the stylesheet and source XML, and try to transform the new source
	// file with the stylesheet file for debugging purposes.
	protected Node transform(File stylesheet, File source, Document docDocType)
	{
		try
		{
			TransformErrorListener transformerErrorListener = (TransformErrorListener) this.t_factory.getErrorListener();
			transformerErrorListener.setStylesheet(stylesheet);
			Transformer transformer = this.t_factory.newTransformer(new StreamSource(new InputStreamReader(new FileInputStream(stylesheet), "UTF-8")));
			DOMResult result = (docDocType == null) ? new DOMResult() : new DOMResult(docDocType);
			StreamSource streamSource = new StreamSource(new InputStreamReader(new FileInputStream(source), "UTF-8"));

			transformer.setErrorListener(new TransformErrorListener(stylesheet, streamSource));

			transformer.transform(streamSource, result);
			return result.getNode().getFirstChild();
		}
		catch (TransformerConfigurationException e)
		{
			return transformError("XMLTransformer.transform(File, File)" + "\ncouldn't create transformer object for files\n" + stylesheet + "\n" + source, e);
		}
		catch (TransformerException e)
		{
			return transformError("XMLTransformer.transform(File, File)" + "\ncouldn't transform the source for files\n" + stylesheet + "\n" + source, e);
		}
		catch (UnsupportedEncodingException e)
		{
			return transformError("XMLTransformer.transform(File, File)" + "\ncouldn't read file due to an unsupported encoding\n" + stylesheet + "\n" + source, e);
		}
		catch (FileNotFoundException e)
		{
			return transformError("XMLTransformer.transform(File, File)" + "\ncouldn't find the file specified\n" + stylesheet + "\n" + source, e);
		}
	}

	// Given a heading string on the sort of transformation error that occurred and the exception object itself, 
	// this method prints the exception to the tomcat window (system.err) and the greenstone log and then returns
	// an xhtml error page that is constructed from it.
	protected Node transformError(String heading, Exception e)
	{
		String message = heading + "\n" + e.getMessage();
		logger.error(heading + ": " + e.getMessage());

		if (e instanceof TransformerException)
		{
			String location = ((TransformerException) e).getLocationAsString();
			if (location != null)
			{
				logger.error(location);
				message = message + "\n" + location;
			}
		}
		System.err.println("****\n" + message + "\n****");
		return constructErrorXHTMLPage(message);
	}

	// Given an error message, splits it into separate lines based on any newlines present and generates an xhtml page
	// (xml Element)  with paragraphs for each line. This is then returned so that it can be displayed in the browser.
	public static Element constructErrorXHTMLPage(String message)
	{
		try
		{
			String[] lines = message.split("\n");

			Document xhtmlDoc = DocumentBuilderFactory.newInstance().newDocumentBuilder().newDocument();
			// <html></html>
			Node htmlNode = xhtmlDoc.createElement("html");
			xhtmlDoc.appendChild(htmlNode);
			// <head></head>
			Node headNode = xhtmlDoc.createElement("head");
			htmlNode.appendChild(headNode);
			// <title></title>
			Node titleNode = xhtmlDoc.createElement("title");
			headNode.appendChild(titleNode);
			Node titleString = xhtmlDoc.createTextNode("Error occurred");
			titleNode.appendChild(titleString);

			// <body></body>
			Node bodyNode = xhtmlDoc.createElement("body");
			htmlNode.appendChild(bodyNode);

			// finally put the message in the body
			Node h1Node = xhtmlDoc.createElement("h1");
			bodyNode.appendChild(h1Node);
			Node headingString = xhtmlDoc.createTextNode("The following error occurred:");
			h1Node.appendChild(headingString);

			//Node textNode = xhtmlDoc.createTextNode(message);
			//bodyNode.appendChild(textNode);

			for (int i = 0; i < lines.length; i++)
			{
				Node pNode = xhtmlDoc.createElement("p");
				Node textNode = xhtmlDoc.createTextNode(lines[i]);
				pNode.appendChild(textNode);
				bodyNode.appendChild(pNode);
			}

			return xhtmlDoc.getDocumentElement();

		}
		catch (Exception e)
		{
			String errmsg = "Exception trying to construct error xhtml page from message: " + message + "\n" + e.getMessage();
			System.err.println(errmsg);
			logger.error(errmsg);
			return null;
		}
	}

	// ErrorListener class for both Transformer objects and TransformerFactory objects.
	// This class can be used to register a handler for any fatal errors, errors and warnings that
	// may occur when either transforming an xml file with an xslt stylesheet using the XMLTransformer,
	// or when instantiating a Transformer object using the XMLTransformer's TransformerFactory member var.
	// The latter case occurs when the xml Source used to instantiate a Transformer from a TransformerFactory
	// is invalid in some manner, which results in a null Transformer object. However, as no 
	// TransformerConfigurationException or TransformerException are thrown in this case, the errors 
	// would have not been noticed until things go wrong later when trying to use the (null) Transformer.
	//
	// The errors caught by this ErrorListener class are printed both to the greenstone.log and to the 
	// tomcat console (System.err), and the error message is stored in the errorMessage variable so that 
	// it can be retrieved and be used to generate an xhtml error page.
	public class TransformErrorListener implements ErrorListener
	{
		protected String errorMessage = null;
		protected String stylesheet = null;
		protected Source source = null; // can be DOMSource or StreamSource
		protected boolean debugAsFile = true; // true if xslt or source are not real physical files

		// *********** METHODS TO BE CALLED WHEN SETTING AN ERROR LISTENER ON TRANSFORMERFACTORY OBJECTS
		// The default constructor is only for when setting an ErrorListener on TransformerFactory objects
		public TransformErrorListener()
		{
			this.stylesheet = null;
			this.source = null;
			XMLTransformer.debugFileCount++;
		}

		public void setStylesheet(Document xslt)
		{
			this.debugAsFile = true;
			this.stylesheet = GSXML.elementToString(xslt.getDocumentElement(), true);
			this.source = null;
		}

		public void setStylesheet(String xslt)
		{
			this.debugAsFile = true;
			this.stylesheet = xslt;
			this.source = null;
		}

		public void setStylesheet(File xslt)
		{
			this.debugAsFile = false; // if this constructor is called, we're dealing with physical files for both xslt and source			
			this.stylesheet = xslt.getAbsolutePath();
			this.source = null;
		}

		// *********** METHODS TO BE CALLED WHEN SETTING AN ERROR LISTENER ON TRANSFORMERFACTORY OBJECTS
		// When setting an ErrorListener on Transformer object, the ErrorListener takes a Stylesheet xslt and a Source		
		public TransformErrorListener(String xslt, Source source)
		{
			this.stylesheet = xslt;
			this.source = source;
			XMLTransformer.debugFileCount++;
		}

		public TransformErrorListener(Document xslt, Source source)
		{
			this.stylesheet = GSXML.elementToString(xslt.getDocumentElement(), true);
			this.source = source;
			XMLTransformer.debugFileCount++;
		}

		public TransformErrorListener(File xslt, Source source)
		{
			this.debugAsFile = false; // if this constructor is called, we're dealing with physical files for both xslt and source
			this.source = source;
			this.stylesheet = xslt.getAbsolutePath(); // not necessary to get the string from the file
			// all we were going to do with it *on error* was write it out to a file anyway		
		}

		// *********** METHODS CALLED AUTOMATICALLY ON ERROR

		//  Receive notification of a recoverable error.
		public void error(TransformerException exception)
		{
			handleError("Error:\n", exception);
		}

		// Receive notification of a non-recoverable error.
		public void fatalError(TransformerException exception)
		{
			handleError("Fatal Error:\n", exception);
		}

		// Receive notification of a warning.
		public void warning(TransformerException exception)
		{
			handleError("Warning:\n", exception);
		}

		public String toString(TransformerException e)
		{
			String msg = "Exception encountered was:\n\t";
			String location = e.getLocationAsString();
			if (location != null)
			{
				msg = msg + "Location: " + location + "\n\t";
			}

			return msg + "Message: " + e.getMessage();
		}

		// clears the errorPage variable after the first call to this method
		public String getErrorMessage()
		{
			String errMsg = this.errorMessage;
			if (this.errorMessage != null)
			{
				this.errorMessage = null;
			}
			return errMsg;
		}

		// sets the errorMessage member variable to the data stored in the exception
		// and writes the errorMessage to the logger and tomcat's System.err
		protected void handleError(String errorType, TransformerException exception)
		{

			this.errorMessage = errorType + toString(exception);

			// If either the stylesheet or the source to be transformed with it were not files,
			// so that the transformation was performed in-memory, then the "location" information
			// during the error handling (if any) wouldn't have been helpful.
			// To allow proper debugging, we write both stylesheet and source out as physical files
			// and perform the same transformation again, so that when a transformation error does 
			// occur, the files are not in-memory but can be viewed, and any location information
			// for the error given by the ErrorListener will be sensible (instead of the unhelpful
			// "line#0 column#0 in file://somewhere/dummy.xsl").
			// Note that if the stylesheet and the source it is to transform were both physical 
			// files to start off with, we will not need to perform the same transformation again
			// since the error reporting would have provided accurate locations for those.
			if (debugAsFile)
			{

				performTransformWithPhysicalFiles(); // will give accurate line numbers

				// No need to print out the current error message (seen in the Else statement below), 
				// as the recursive call to XMLTransformer.transform(File, File, false) in method
				// performTransformWithPhysicalFiles() will do this for us.
			}
			else
			{
				// printing out the error message
				// since !debugAsFile, we are dealing with physical files, 
				// variable stylesheet would have stored the filename instead of contents
				this.errorMessage = this.errorMessage + "\nstylesheet filename: " + stylesheet;

				this.errorMessage += "\nException CAUSE:\n" + exception.getCause();
				System.err.println("\n****Error transforming xml:\n" + this.errorMessage + "\n****\n");
				//System.err.println("Stylesheet was:\n + this.stylesheet + "************END STYLESHEET***********\n\n");		    

				logger.error(this.errorMessage);

				// now print out the source to a file, and run the stylesheet on it using a transform()
				// then any error will be referring to one of these two input files.
			}
		}

		// This method will redo the transformation that went wrong with *real* files: 
		// it writes out the stylesheet and source XML to files first, then performs the transformation
		// to get the actual line location of where things went wrong (instead of "line#0 column#0 in dummy.xsl")
		protected void performTransformWithPhysicalFiles()
		{
			File webLogsTmpFolder = new File(GlobalProperties.getGSDL3Home() + File.separator + "logs" + File.separator + "tmp");
			if (!webLogsTmpFolder.exists())
			{
				webLogsTmpFolder.mkdirs(); // create any necessary folders
			}
			File styleFile = new File(webLogsTmpFolder + File.separator + "stylesheet" + XMLTransformer.debugFileCount + ".xml");
			File sourceFile = new File(webLogsTmpFolder + File.separator + "source" + XMLTransformer.debugFileCount + ".xml");
			try
			{
				// write stylesheet to a file called stylesheet_systemID in tmp
				FileWriter styleSheetWriter = new FileWriter(styleFile);
				styleSheetWriter.write(stylesheet, 0, stylesheet.length());
				styleSheetWriter.flush();
				styleSheetWriter.close();
			}
			catch (Exception e)
			{
				System.err.println("*** Exception when trying to write out stylesheet to " + styleFile.getAbsolutePath());
			}

			if (this.source != null)
			{ // ErrorListener was set on a Transformer object
				try
				{
					FileWriter srcWriter = new FileWriter(sourceFile);
					String contents = "";
					if (source instanceof DOMSource)
					{
						DOMSource domSource = (DOMSource) source;
						Document doc = (Document) domSource.getNode();
						contents = GSXML.elementToString(doc.getDocumentElement(), true);
						//contents = GSXML.xmlNodeToXMLString(domSource.getNode());
					}
					else if (source instanceof StreamSource)
					{
						StreamSource streamSource = (StreamSource) source;
						BufferedReader reader = new BufferedReader(streamSource.getReader());
						String line = "";
						while ((line = reader.readLine()) != null)
						{
							contents = contents + line + "\n";
						}
					}
					srcWriter.write(contents, 0, contents.length());
					srcWriter.flush();
					srcWriter.close();
				}
				catch (Exception e)
				{
					System.err.println("*** Exception when trying to write out stylesheet to " + sourceFile.getAbsolutePath());
				}
			}

			System.err.println("*****************************************");
			System.err.println("Look for stylesheet in: " + styleFile.getAbsolutePath());
			if (this.source != null)
			{ // ErrorListener was set on a Transformer object
				System.err.println("Look for source XML in: " + sourceFile.getAbsolutePath());
			}

			// now perform the transform again, which will assign another TransformErrorListener
			// but since debuggingAsFile is turned off, we won't recurse into this section of
			// handling the error again
			if (this.source != null)
			{ // ErrorListener was set on a Transformer object
				XMLTransformer.this.transform(styleFile, sourceFile); // calls the File, File version, so debugAsFile will be false		
			}
			else
			{ // ErrorListener was set on a TransformerFactory object

				// The recursive step in this case is to perform the instantiation 
				// of the Transformer object again.
				// Only one TransformerFactory object per XMLTransformer, 
				// and only one TransformerHandler object set on any TransformerFactory
				// But the stylesheet used to create a Transformer from that TransformerFactory
				// object changes each time, by calls to setStylesheet(), 
				// Therefore, the debugAsFile state for the single TransformerFactory's 
				// TransformerHandler changes each time also.

				try
				{
					debugAsFile = false;
					this.stylesheet = styleFile.getAbsolutePath();
					//TransformErrorListener transformerErrorListener = (TransformErrorListener)XMLTransformer.this.t_factory.getErrorListener();
					//transformerErrorListener.setStylesheet(styleFile);
					Transformer transformer = XMLTransformer.this.t_factory.newTransformer(new StreamSource(styleFile));
					if (transformer == null)
					{
						String msg = "XMLTransformer transformer is " + transformer;
						logger.info(msg);
						System.out.println(msg + "\n****\n");
					}
				}
				catch (TransformerConfigurationException e)
				{
					String message = "Couldn't create transformer object: " + e.getMessageAndLocation();
					logger.error(message);
					logger.error(e.getLocationAsString());
					System.out.println(message);
				}
			}
		}
	}
}