/*

   Copyright 2002-2003  The Apache Software Foundation 

   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 org.apache.batik.apps.svgbrowser;

import java.io.File;
import java.io.StringReader;
import java.io.StringWriter;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.transform.Source;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.URIResolver;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;
import javax.xml.transform.stream.StreamSource;

import org.apache.batik.dom.svg.SAXSVGDocumentFactory;
import org.apache.batik.dom.svg.SVGDOMImplementation;
import org.apache.batik.dom.util.DOMUtilities;
import org.apache.batik.dom.util.HashTable;
import org.apache.batik.util.ParsedURL;
import org.apache.batik.util.SVGConstants;
import org.apache.batik.util.XMLResourceDescriptor;
import org.w3c.dom.Attr;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.NamedNodeMap;
import org.w3c.dom.Node;
import org.w3c.dom.ProcessingInstruction;
import org.w3c.dom.svg.SVGDocument;

/**
 * A <tt>SquiggleInputHandler</tt> that handles XSLT transformable
 * XML documents.
 * This implementation of the <tt>SquiggleInputHandler</tt> class
 * handles XML files by looking for the first
 * &lt;?xml-stylesheet ... ?&gt; processing instruction referencing
 * an xsl document. In case there is one, the transform is applied to the 
 * input XML file and the handler checks that the result is an 
 * SVG document with an SVG root.
 *
 * @author <a mailto="vincent.hardy@sun.com">Vincent Hardy</a>
 * @version $Id$
 */
public class XMLInputHandler implements SquiggleInputHandler {
    public static final String[] XVG_MIME_TYPES = 
    { "image/xml+xsl+svg" };

    public static final String[] XVG_FILE_EXTENSIONS =
    { ".xml", ".xsl" };

    public static final String ERROR_NO_XML_STYLESHEET_PROCESSING_INSTRUCTION
        = "XMLInputHandler.error.no.xml.stylesheet.processing.instruction";

    public static final String ERROR_TRANSFORM_OUTPUT_NOT_SVG
        = "XMLInputHandler.error.transform.output.not.svg";

    public static final String ERROR_TRANSFORM_PRODUCED_NO_CONTENT
        = "XMLInputHandler.error.transform.produced.no.content";

    public static final String ERROR_TRANSFORM_OUTPUT_WRONG_NS
        = "XMLInputHandler.error.transform.output.wrong.ns";

    public static final String ERROR_RESULT_GENERATED_EXCEPTION 
        = "XMLInputHandler.error.result.generated.exception";

    public static final String XSL_PROCESSING_INSTRUCTION_TYPE
        = "text/xsl";

    public static final String PSEUDO_ATTRIBUTE_TYPE
        = "type";

    public static final String PSEUDO_ATTRIBUTE_HREF
        = "href";

    /**
     * Returns the list of mime types handled by this handler.
     */
    public String[] getHandledMimeTypes() {
        return XVG_MIME_TYPES;
    }
    
    /**
     * Returns the list of file extensions handled by this handler
     */
    public String[] getHandledExtensions() {
        return XVG_FILE_EXTENSIONS;
    }

    /**
     * Returns a description for this handler
     */
    public String getDescription() {
        return "";
    }

    /**
     * Returns true if the input file can be handled by the handler
     */
    public boolean accept(File f) {
        return f.isFile() && accept(f.getPath());
    }

    /**
     * Returns true if the input URI can be handled by the handler
     */
    public boolean accept(ParsedURL purl) {
        if (purl == null) {
            return false;
        }

        // <!> Note: this should be improved to rely on Mime Type 
        //     when the http protocol is used. This will use the 
        //     ParsedURL.getContentType method.

        String path = purl.getPath();        
        return accept(path);
    }

    /**
     * Return true if the resource with the given path can 
     * be handled.
     */
    public boolean accept(String path) {
        if (path == null) {
            return false;
        }

        for (int i=0; i<XVG_FILE_EXTENSIONS.length; i++) {
            if (path.endsWith(XVG_FILE_EXTENSIONS[i])) {
                return true;
            }
        }

        return false;
    }

    /**
     * Handles the given input for the given JSVGViewerFrame
     */
    public void handle(ParsedURL purl, JSVGViewerFrame svgViewerFrame) throws Exception {
        String uri = purl.toString();

        TransformerFactory tFactory 
            = TransformerFactory.newInstance();
        
        // First, load the input XML document into a generic DOM tree
        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
        dbf.setValidating(false);
        dbf.setNamespaceAware(true);

        DocumentBuilder db = dbf.newDocumentBuilder();

        Document inDoc = db.parse(uri);
       
        // Now, look for <?xml-stylesheet ...?> processing instructions
        String xslStyleSheetURI 
            = extractXSLProcessingInstruction(inDoc);
        
        if (xslStyleSheetURI == null) {
            // Assume that the input file is a literal result template
            xslStyleSheetURI = uri;
        }

        ParsedURL parsedXSLStyleSheetURI 
            = new ParsedURL(uri, xslStyleSheetURI);

        Transformer transformer
            = tFactory.newTransformer
            (new StreamSource(parsedXSLStyleSheetURI.toString()));

        // Set the URIResolver to properly handle document() and xsl:include
        transformer.setURIResolver
            (new DocumentURIResolver(parsedXSLStyleSheetURI.toString()));

        // Now, apply the transformation to the input document.
        //
        // <!> Due to issues with namespaces, the transform creates the 
        //     result in a stream which is parsed. This is sub-optimal
        //     but this was the only solution found to be able to 
        //     generate content in the proper namespaces.
        //
        // SVGOMDocument outDoc = 
        //   (SVGOMDocument)impl.createDocument(svgNS, "svg", null);
        // outDoc.setURLObject(new URL(uri));
        // transformer.transform
        //     (new DOMSource(inDoc),
        //     new DOMResult(outDoc.getDocumentElement()));
        //
        StringWriter sw = new StringWriter();
        StreamResult result = new StreamResult(sw);
        transformer.transform(new DOMSource(inDoc),
                              result);
        sw.flush();
        sw.close();

        String parser = XMLResourceDescriptor.getXMLParserClassName();
        SAXSVGDocumentFactory f = new SAXSVGDocumentFactory(parser);
        SVGDocument outDoc = null;

        try {
            outDoc = f.createSVGDocument
                (uri, new StringReader(sw.toString()));
        } catch (Exception e) {
            System.err.println("======================================");
            System.err.println(sw.toString());
            System.err.println("======================================");
            
            throw new IllegalArgumentException
                (Resources.getString(ERROR_RESULT_GENERATED_EXCEPTION));
        }

        // Patch the result tree to go under the root node
        // checkAndPatch(outDoc);
        
        svgViewerFrame.getJSVGCanvas().setSVGDocument(outDoc);
        svgViewerFrame.setSVGDocument(outDoc,
                                      uri,
                                      outDoc.getTitle());
    }

    /**
     * This method checks that the generated content is SVG.
     *
     * This method accounts for the fact that the root svg's first child
     * is the result of the transform. It moves all its children under the root
     * and sets the attributes
     */
    protected void checkAndPatch(Document doc) {
        Element root = doc.getDocumentElement();
        Node realRoot = root.getFirstChild();
        String svgNS = SVGDOMImplementation.SVG_NAMESPACE_URI;

        if (realRoot == null) {
            throw new IllegalArgumentException
                (Resources.getString(ERROR_TRANSFORM_PRODUCED_NO_CONTENT));
        }

        if (realRoot.getNodeType() != Node.ELEMENT_NODE
            || 
            !SVGConstants.SVG_SVG_TAG.equals(realRoot.getLocalName())) {
            throw new IllegalArgumentException
                (Resources.getString(ERROR_TRANSFORM_OUTPUT_NOT_SVG));
        }

        if (!svgNS.equals(realRoot.getNamespaceURI())) {
            throw new IllegalArgumentException
                (Resources.getString(ERROR_TRANSFORM_OUTPUT_WRONG_NS));
        }

        Node child = realRoot.getFirstChild();
        while ( child != null ) {
            root.appendChild(child);
            child = realRoot.getFirstChild();
        }

        NamedNodeMap attrs = realRoot.getAttributes();
        int n = attrs.getLength();
        for (int i=0; i<n; i++) {
            root.setAttributeNode((Attr)attrs.item(i));
        }

        root.removeChild(realRoot);
    }

    /**
     * Extracts the first XSL processing instruction from the input 
     * XML document. 
     */
    protected String extractXSLProcessingInstruction(Document doc) {
        Node child = doc.getFirstChild();
        while (child != null) {
            if (child.getNodeType() == Node.PROCESSING_INSTRUCTION_NODE) {
                ProcessingInstruction pi 
                    = (ProcessingInstruction)child;
                
                HashTable table = new HashTable();
                DOMUtilities.parseStyleSheetPIData(pi.getData(),
                                                   table);

                Object type = table.get(PSEUDO_ATTRIBUTE_TYPE);
                if (XSL_PROCESSING_INSTRUCTION_TYPE.equals(type)) {
                    Object href = table.get(PSEUDO_ATTRIBUTE_HREF);
                    if (href != null) {
                        return href.toString();
                    } else {
                        return null;
                    }
                }
            }
            child = child.getNextSibling();
        }

        return null;
    }

    /**
     * Implements the URIResolver interface so that relative urls used in 
     * transformations are resolved properly.
     */
    public class DocumentURIResolver implements URIResolver {
        String documentURI;

        public DocumentURIResolver(String documentURI) {
            this.documentURI = documentURI;
        }

        public Source resolve(String href, String base) {
            if (base == null || "".equals(base)) {
                base = documentURI;
            }

            ParsedURL purl = new ParsedURL(base, href);

            return new StreamSource(purl.toString());
        }
    }
}
