/*

   Licensed to the Apache Software Foundation (ASF) under one or more
   contributor license agreements.  See the NOTICE file distributed with
   this work for additional information regarding copyright ownership.
   The ASF licenses this file to You 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.test.svg;

import java.io.BufferedInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.io.StringWriter;

import java.net.URL;
import java.net.MalformedURLException;

import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.Locale;
import java.util.ResourceBundle;

import java.awt.Color;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.awt.image.RenderedImage;
import java.awt.image.WritableRaster;
import java.awt.image.ColorModel;

import org.apache.batik.ext.awt.image.GraphicsUtil;

import org.apache.batik.ext.awt.image.spi.ImageTagRegistry;
import org.apache.batik.ext.awt.image.spi.ImageWriter;
import org.apache.batik.ext.awt.image.spi.ImageWriterRegistry;
import org.apache.batik.ext.awt.image.renderable.Filter;

import org.apache.batik.util.ParsedURL;

import org.apache.batik.test.AbstractTest;
import org.apache.batik.test.DefaultTestReport;
import org.apache.batik.test.TestReport;

/**
 * Checks for regressions in rendering a specific SVG document.
 * The <tt>Test</tt> will rasterize and SVG document and
 * compare it to a reference image. The test passes if the
 * rasterized SVG and the reference image match exactly (i.e.,
 * all pixel values are the same).
 *
 * @author <a href="mailto:vhardy@apache.lorg">Vincent Hardy</a>
 * @version $Id: AbstractRenderingAccuracyTest.java 581141 2007-10-02 05:36:50Z cam $
 */
public abstract class AbstractRenderingAccuracyTest extends AbstractTest {
    /**
     * Error when temp file cannot be created
     * {0} = IOException message
     */
    public static final String ERROR_CANNOT_CREATE_TEMP_FILE
        = "SVGRenderingAccuracyTest.error.cannot.create.temp.file";

    /**
     * Error when temp file stream cannot be created
     * {0} = temp file's cannonical path
     * {1} = IOException message
     */
    public static final String ERROR_CANNOT_CREATE_TEMP_FILE_STREAM
        = "SVGRenderingAccuracyTest.error.cannot.create.temp.file.stream";

    /**
     * Error when the reference image cannot be opened
     * {0} = URI of the reference image
     * {1} = IOException message
     */
    public static final String ERROR_CANNOT_OPEN_REFERENCE_IMAGE
        = "SVGRenderingAccuracyTest.error.cannot.open.reference.image";

    /**
     * Error when the generated image cannot be read
     * {0} = Cannonical path of the temp generated image
     * {1} = IOException message
     */
    public static final String ERROR_CANNOT_OPEN_GENERATED_IMAGE
        = "SVGRenderingAccuracyTest.error.cannot.open.genereted.image";

    /**
     * Error when there is an IOException while comparing the
     * two reference raster image with the new raster image built
     * from the SVG.
     * {0} = URI of the reference image
     * {1} = Connical path for the temp generated image
     * {2} = IOException message.
     */
    public static final String ERROR_ERROR_WHILE_COMPARING_FILES
        = "SVGRenderingAccuracyTest.error.while.comparing.files";

    /**
     * Error when the generated image from the SVG file differs from
     * the reference image.
     */
    public static final String ERROR_SVG_RENDERING_NOT_ACCURATE
        = "SVGRenderingAccuracyTest.error.svg.rendering.not.accurate";

    /**
     * Entry describing the error
     */
    public static final String ENTRY_KEY_ERROR_DESCRIPTION
        = "SVGRenderingAccuracyTest.entry.key.error.description";

    /**
     * Entry describing the reference/generated image file
     */
    public static final String ENTRY_KEY_REFERENCE_GENERATED_IMAGE_URI
        = "SVGRenderingAccuracyTest.entry.key.reference.generated.image.file";

    /**
     * Entry describing the generated difference image
     */
    public static final String ENTRY_KEY_DIFFERENCE_IMAGE
        = "SVGRenderingAccuracyTest.entry.key.difference.image";

    /**
     * Entry describing that an internal error occured while
     * generating the test failure description
     */
    public static final String ENTRY_KEY_INTERNAL_ERROR
        = "SVGRenderingAccuracyTest.entry.key.internal.error";

    /**
     * Messages expressing that comparison images could not be
     * created:
     * {0} : exception class
     * {1} : exception message
     * {2} : exception stack trace.
     */
    public static final String COULD_NOT_GENERATE_COMPARISON_IMAGES
        = "SVGRenderingAccuracyTest.message.error.could.not.generate.comparison.images";

    /**
     * Messages expressing that an image could not be loaded.
     * {0} : URL for the reference image.
     */
    public static final String COULD_NOT_LOAD_IMAGE
        = "SVGRenderingAccuracyTest.message.error.could.not.load.image";

    /**
     * Message expressing that the variation URL could not be open
     * {0} : URL
     */
    public static final String COULD_NOT_OPEN_VARIATION_URL
        = "SVGRenderingAccuracyTest.message.warning.could.not.open.variation.url";

    /**
     * The gui resources file name
     */
    public static final String CONFIGURATION_RESOURCES =
        "org.apache.batik.test.svg.resources.Configuration";

    /**
     * Suffix used for comparison images
     */
    public static final String IMAGE_TYPE_COMPARISON = "_cmp";

    /**
     * Suffix used for diff images
     */
    public static final String IMAGE_TYPE_DIFF = "_diff";

    /**
     * Suffix used for saved images (e.g., comparison and diff images)
     */
    public static final String IMAGE_FILE_EXTENSION = ".png";

    /**
     * The configuration resource bundle
     */
    protected static ResourceBundle configuration;
    static {
        configuration = ResourceBundle.getBundle(CONFIGURATION_RESOURCES,
                                                 Locale.getDefault());
    }

    /**
     * Prefix for the temporary files created by Tests
     * of this class
     */
    public static final String TEMP_FILE_PREFIX
        = configuration.getString("temp.file.prefix");

    /**
     * Suffix for the temporary files created by
     * Tests of this class
     */
    public static final String TEMP_FILE_SUFFIX
        = configuration.getString("temp.file.suffix");

    /**
     * The URL where the SVG can be found.
     */
    protected URL svgURL;

    /**
     * The URL for the reference image
     */
    protected URL refImgURL;

    /**
     * A list of {@link URL}s of files containing an 'accepted'
     * variation from the reference image.
     */
    protected List variationURLs;

    /**
     * The File where the newly computed variation
     * should be saved if different from the
     * variationURL
     */
    protected File saveVariation;

    /**
     * The File where the candidate reference
     * should be saved if there is not candidate reference
     * or if it cannot be opened.
     */
    protected File candidateReference;

    /**
     * Temporary directory
     */
    protected static File tempDirectory;

    /**
     * Returns the temporary directory
     */
    public static File getTempDirectory(){
        if(tempDirectory == null){
            String tmpDir = System.getProperty("java.io.tmpdir");
            if(tmpDir == null){
                throw new Error();
            }

            tempDirectory = new File(tmpDir);
            if(!tempDirectory.exists()){
                throw new Error();
            }
        }
        return tempDirectory;
    }

    /**
     * Constructor.
     * @param svgURL the URL String for the SVG document being tested.
     * @param refImgURL the URL for the reference image.
     */
    public AbstractRenderingAccuracyTest(String svgURL,
                                    String refImgURL){
        setConfig(svgURL, refImgURL);
    }

    /**
     * For subclasses
     */
    protected AbstractRenderingAccuracyTest(){
    }

    /**
     * Sets this test's config.
     */
    public void setConfig(String svgURL,
                          String refImgURL){
        if(svgURL == null){
            throw new IllegalArgumentException();
        }

        if(refImgURL == null){
            throw new IllegalArgumentException();
        }

        this.svgURL = resolveURL(svgURL);
        this.refImgURL = resolveURL(refImgURL);
    }

    /**
     * Resolves the input string as follows.
     * + First, the string is interpreted as a file description.
     *   If the file exists, then the file name is turned into
     *   a URL.
     * + Otherwise, the string is supposed to be a URL. If it
     *   is an invalid URL, an IllegalArgumentException is thrown.
     */
    protected URL resolveURL(String url){
        // Is url a file?
        File f = (new File(url)).getAbsoluteFile();
        if(f.getParentFile().exists()){
            try{
                return f.toURL();
            }catch(MalformedURLException e){
                throw new IllegalArgumentException();
            }
        }

        // url is not a file. It must be a regular URL...
        try{
            return new URL(url);
        }catch(MalformedURLException e){
            throw new IllegalArgumentException(url);
        }
    }

    /**
     * Sets the File where the variation from the reference image should be
     * stored
     */
    public void setSaveVariation(File saveVariation){
        this.saveVariation = saveVariation;
    }

    public File getSaveVariation(){
        return saveVariation;
    }

    public String[] getVariationURLs() {
        if (variationURLs != null) {
            return (String[]) variationURLs.toArray(new String[0]);
        }
        return null;
    }

    /**
     * Adds a URL for an acceptable variation from the reference image.
     */
    public void addVariationURL(String variationURL) {
        if (this.variationURLs == null) {
            this.variationURLs = new LinkedList();
        }
        this.variationURLs.add(resolveURL(variationURL));
    }

    /**
     * See {@link #candidateReference}
     */
    public void setCandidateReference(File candidateReference){
        this.candidateReference = candidateReference;
    }

    public File getCandidateReference(){
        return candidateReference;
    }

    /**
     * Returns this <tt>Test</tt>'s name. The name is the
     * URL of the SVG being rendered.
     */
    public String getName(){
        if(this.name == null){
            return svgURL.toString();
        }
        return name;
    }

    /**
     * Requests this <tt>Test</tt> to run and produce a
     * report.
     *
     */
    public TestReport run() {
        DefaultTestReport report = new DefaultTestReport(this);

        //
        // First, do clean-up
        //
        if (candidateReference != null){
            if (candidateReference.exists()){
                candidateReference.delete();
            }
        }


        //
        // Render the SVG image into a raster. We call an
        // abstract method to convert the src into a raster in
        // a temporary file.
        File tmpFile = null;

        try{
            if (candidateReference != null)
                tmpFile = candidateReference;
            else
                tmpFile = File.createTempFile(TEMP_FILE_PREFIX,
                                              TEMP_FILE_SUFFIX,
                                              null);
        }catch(IOException e){
            report.setErrorCode(ERROR_CANNOT_CREATE_TEMP_FILE);
            report.setDescription(new TestReport.Entry[] {
                new TestReport.Entry
                (Messages.formatMessage(ENTRY_KEY_ERROR_DESCRIPTION, null),
                 Messages.formatMessage(ERROR_CANNOT_CREATE_TEMP_FILE,
                                        new Object[]{e.getMessage()}))
            });
            report.setPassed(false);
            return report;
        }


        FileOutputStream tmpFileOS = null;

        try{
            tmpFileOS = new FileOutputStream(tmpFile);
        }catch(IOException e){
            report.setErrorCode(ERROR_CANNOT_CREATE_TEMP_FILE_STREAM);
            report.setDescription(new TestReport.Entry[] {
                new TestReport.Entry
                (Messages.formatMessage(ENTRY_KEY_ERROR_DESCRIPTION, null),
                 Messages.formatMessage(ERROR_CANNOT_CREATE_TEMP_FILE_STREAM,
                                        new String[]{tmpFile.getAbsolutePath(),
                                                     e.getMessage()})) });
            report.setPassed(false);
            tmpFile.deleteOnExit();
            return report;
        }

        // Call abstract method to encode svgURL to tmpFileOS as a
        // raster.  If this returns a non-null test report then the
        // encoding failed and we should return that report.
        {
            TestReport encodeTR = encode(svgURL, tmpFileOS);
            if ((encodeTR != null) && ! encodeTR.hasPassed() ) {
                tmpFile.deleteOnExit();
                return encodeTR;
            }
        }

        //
        // Do a binary comparison of the encoded images.
        //
        InputStream refStream = null;
        InputStream newStream = null;
        try {
            refStream = new BufferedInputStream(refImgURL.openStream());
        }catch(IOException e){
            report.setErrorCode(ERROR_CANNOT_OPEN_REFERENCE_IMAGE);
            report.setDescription(new TestReport.Entry[]{
                new TestReport.Entry
                (Messages.formatMessage(ENTRY_KEY_ERROR_DESCRIPTION, null),
                 Messages.formatMessage(ERROR_CANNOT_OPEN_REFERENCE_IMAGE,
                                        new Object[]{refImgURL.toString(),
                                                     e.getMessage()}))
                });
            report.setPassed(false);
            // Try and save tmp file as a candidate variation
            if (candidateReference == null){
                tmpFile.delete();
            }
            return report;
        }

        try{
            newStream = new BufferedInputStream(new FileInputStream(tmpFile));
        }catch(IOException e){
            report.setErrorCode(ERROR_CANNOT_OPEN_GENERATED_IMAGE);
            report.setDescription(new TestReport.Entry[]{
                new TestReport.Entry
                (Messages.formatMessage(ENTRY_KEY_ERROR_DESCRIPTION, null),
                 Messages.formatMessage(ERROR_CANNOT_OPEN_GENERATED_IMAGE,
                                        new Object[]{tmpFile.getAbsolutePath(),
                                                     e.getMessage()}))});
            report.setPassed(false);
            tmpFile.delete();
            return report;
        }

        boolean accurate = false;
        try{
            accurate = compare(refStream, newStream);
        } catch(IOException e) {
            report.setErrorCode(ERROR_ERROR_WHILE_COMPARING_FILES);
            report.setDescription(new TestReport.Entry[]{
                new TestReport.Entry
                (Messages.formatMessage(ENTRY_KEY_ERROR_DESCRIPTION, null),
                 Messages.formatMessage(ERROR_ERROR_WHILE_COMPARING_FILES,
                                        new Object[]{refImgURL.toString(),
                                                     tmpFile.getAbsolutePath(),
                                                     e.getMessage()}))});
            report.setPassed(false);
            if (candidateReference == null){
                tmpFile.delete();
            }
            return report;
        }


        if(accurate){
            //
            // Yahooooooo! everything worked out well.
            //
            report.setPassed(true);
            tmpFile.delete();
            return report;
        }

        //
        // If the files still differ here, it means that even the
        // variation does not account for the difference return an
        // error
        //
        try {
            BufferedImage ref = getImage(refImgURL);
            BufferedImage gen = getImage(tmpFile);
            BufferedImage diff = buildDiffImage(ref, gen);

            //
            // If there is an accepted variation, check if it equals the
            // computed difference.
            //
            if (variationURLs != null) {
                Iterator it = variationURLs.iterator();
                while (it.hasNext()) {
                    URL variationURL = (URL) it.next();
                    File tmpDiff = imageToFile(diff, IMAGE_TYPE_DIFF);

                    InputStream variationURLStream = null;
                    try {
                        variationURLStream = variationURL.openStream();
                    } catch (IOException e) {
                        // Could not open variationURL stream. Just trace that
                        System.err.println
                            (Messages.formatMessage
                                (COULD_NOT_OPEN_VARIATION_URL,
                                 new Object[] { variationURL.toString() }));
                    }

                    if (variationURLStream != null) {
                        InputStream refDiffStream =
                            new BufferedInputStream(variationURLStream);

                        InputStream tmpDiffStream =
                            new BufferedInputStream
                                (new FileInputStream(tmpDiff));

                        if (compare(refDiffStream, tmpDiffStream)) {
                            // We accept the generated result.
                            accurate = true;
                        }
                    }
                }
            }

            if (accurate) {
                //
                // Yahooooooo! everything worked out well, at least
                // with variation.
                report.setPassed(true);
                tmpFile.delete();
                return report;
            }

            System.err.println(">>>>>>>>>>>>>>>>>>>>>> "+
                               "Rendering is not accurate");
            if(saveVariation != null){
                // There is a computed variation different from the
                // referenced variation and there is a place where the new
                // variation should be saved.
                saveImage(diff, saveVariation);
            }

            // Build two images:
            // a. One with the reference image and the newly generated image
            // b. One with the difference between the two images and the set
            //    of different pixels.
            BufferedImage cmp = makeCompareImage(ref, gen);
            File cmpFile = imageToFile(cmp, IMAGE_TYPE_COMPARISON);
            File diffFile = imageToFile(diff, IMAGE_TYPE_DIFF);

            report.setErrorCode(ERROR_SVG_RENDERING_NOT_ACCURATE);
            report.setDescription(new TestReport.Entry[]{
                new TestReport.Entry
                (Messages.formatMessage(ENTRY_KEY_ERROR_DESCRIPTION, null),
                 Messages.formatMessage(ERROR_SVG_RENDERING_NOT_ACCURATE, null)),
                new TestReport.Entry
                (Messages.formatMessage(ENTRY_KEY_REFERENCE_GENERATED_IMAGE_URI,
                                        null), cmpFile),
                new TestReport.Entry
                (Messages.formatMessage(ENTRY_KEY_DIFFERENCE_IMAGE, null),
                 diffFile) });
        }catch(Exception e){
            report.setErrorCode(ERROR_SVG_RENDERING_NOT_ACCURATE);
            StringWriter trace = new StringWriter();
            e.printStackTrace(new PrintWriter(trace));

            report.setDescription(new TestReport.Entry[]{
                new TestReport.Entry
                (Messages.formatMessage(ENTRY_KEY_ERROR_DESCRIPTION, null),
                 Messages.formatMessage(ERROR_SVG_RENDERING_NOT_ACCURATE, null)),
                new TestReport.Entry
                (Messages.formatMessage(ENTRY_KEY_INTERNAL_ERROR, null),
                 Messages.formatMessage(COULD_NOT_GENERATE_COMPARISON_IMAGES,
                                        new Object[]{e.getClass().getName(),
                                                     e.getMessage(),
                                                     trace.toString()})) });
        }

        if (candidateReference == null){
            tmpFile.delete();
        }

        report.setPassed(false);
        return report;
    }

    public abstract TestReport encode(URL srcURL, FileOutputStream fos);

    /**
     * Compare the two input streams
     */
    protected boolean compare(InputStream refStream,
                              InputStream newStream)
        throws IOException{
        int b, nb;
        do {
            b = refStream.read();
            nb = newStream.read();
        } while (b != -1 && nb != -1 && b == nb);
        refStream.close();
        newStream.close();
        return (b == nb);
    }

    /**
     * Saves an image in a given File
     */
    protected void saveImage(BufferedImage img, File imgFile)
        throws IOException {
        if(!imgFile.exists()){
            imgFile.createNewFile();
        }
        OutputStream out = new FileOutputStream(imgFile);
        try {
            saveImage(img, out);
        } finally {
            out.close();
        }
    }

    /**
     * Saves an image in a given File
     */
    protected void saveImage(BufferedImage img, OutputStream os)
            throws IOException {
        ImageWriter writer = ImageWriterRegistry.getInstance()
            .getWriterFor("image/png");
        writer.writeImage(img, os);
    }

    /**
     * Builds a new BufferedImage that is the difference between the
     * two input images
     */
    public static BufferedImage buildDiffImage(BufferedImage ref,
                                               BufferedImage gen) {
        BufferedImage diff = new BufferedImage(ref.getWidth(),
                                               ref.getHeight(),
                                               BufferedImage.TYPE_INT_ARGB);
        WritableRaster refWR = ref.getRaster();
        WritableRaster genWR = gen.getRaster();
        WritableRaster dstWR = diff.getRaster();

        boolean refPre = ref.isAlphaPremultiplied();
        if (!refPre) {
            ColorModel     cm = ref.getColorModel();
            cm = GraphicsUtil.coerceData(refWR, cm, true);
            ref = new BufferedImage(cm, refWR, true, null);
        }
        boolean genPre = gen.isAlphaPremultiplied();
        if (!genPre) {
            ColorModel     cm = gen.getColorModel();
            cm = GraphicsUtil.coerceData(genWR, cm, true);
            gen = new BufferedImage(cm, genWR, true, null);
        }


        int w=ref.getWidth();
        int h=ref.getHeight();
        int y, i,val;
        int [] refPix = null;
        int [] genPix = null;
        for (y=0; y<h; y++) {
            refPix = refWR.getPixels  (0, y, w, 1, refPix);
            genPix = genWR.getPixels  (0, y, w, 1, genPix);
            for (i=0; i<refPix.length; i++) {
                val = ((genPix[i]-refPix[i])*10)+128;
                if ((val & 0xFFFFFF00) != 0)
                    if ((val & 0x80000000) != 0) val = 0;
                    else                         val = 255;
                genPix[i] = val;
            }
            dstWR.setPixels(0, y, w, 1, genPix);
        }

        if (!genPre) {
            ColorModel cm = gen.getColorModel();
            cm = GraphicsUtil.coerceData(genWR, cm, false);
        }

        if (!refPre) {
            ColorModel cm = ref.getColorModel();
            cm = GraphicsUtil.coerceData(refWR, cm, false);
        }

        return diff;
    }

    /**
     * Loads an image from a File
     */
    protected BufferedImage getImage(File file)
        throws Exception {
        return getImage(file.toURL());
    }

    /**
     * Loads an image from a URL
     */
    protected BufferedImage getImage(URL url)
        throws IOException {
        ImageTagRegistry reg = ImageTagRegistry.getRegistry();
        Filter filt = reg.readURL(new ParsedURL(url));
        if(filt == null)
            throw new IOException(Messages.formatMessage
                                  (COULD_NOT_LOAD_IMAGE,
                                   new Object[]{url.toString()}));

        RenderedImage red = filt.createDefaultRendering();
        if(red == null)
            throw new IOException(Messages.formatMessage
                                  (COULD_NOT_LOAD_IMAGE,
                                   new Object[]{url.toString()}));

        BufferedImage img = new BufferedImage(red.getWidth(),
                                              red.getHeight(),
                                              BufferedImage.TYPE_INT_ARGB);
        red.copyData(img.getRaster());

        return img;
    }

    /**
     *
     */
    protected BufferedImage makeCompareImage(BufferedImage ref,
                                             BufferedImage gen){
        BufferedImage cmp = new BufferedImage(ref.getWidth()*2,
                                              ref.getHeight(),
                                              BufferedImage.TYPE_INT_ARGB);

        Graphics2D g = cmp.createGraphics();
        g.setPaint(Color.white);
        g.fillRect(0, 0, cmp.getWidth(), cmp.getHeight());
        g.drawImage(ref, 0, 0, null);
        g.translate(ref.getWidth(), 0);
        g.drawImage(gen, 0, 0, null);
        g.dispose();

        return cmp;
    }

    /**
     * Creates a File into which the input image is
     * saved.
     * If there is a "file" component in the SVG url,
     * then a temporary file is created with that
     * name and the imageType suffix in the temp
     * directory of the test-reports directory.
     */
    protected File imageToFile(BufferedImage img,
                               String imageType)
        throws IOException {
        String file = getURLFile(svgURL);

        File imageFile = null;
        if( !"".equals(file) ){
            imageFile = makeTempFileName(file, imageType);
        }
        else{
            imageFile = makeRandomFileName(imageType);
        }

        imageFile.deleteOnExit();

        saveImage(img, imageFile);

        return imageFile;
    }

    /**
     * Extracts the file portion of the URL
     */
    protected String getURLFile(URL url){
        String path = url.getPath();
        int n = path.lastIndexOf('/');
        if(n == -1){
            return path;
        }
        else{
            if(n<path.length()){
                return path.substring(n+1, path.length());
            }
            else{
                return "";
            }
        }
    }

    protected File makeTempFileName(String svgFileName,
                                    String imageType){
        int dotIndex = svgFileName.lastIndexOf('.');
        if( dotIndex == -1){
            return getNextTempFileName(svgFileName + imageType);
        }
        else{
            return getNextTempFileName
                (svgFileName.substring(0, dotIndex) +
                 imageType + IMAGE_FILE_EXTENSION);
        }
    }

    protected File getNextTempFileName(String fileName){
        File f = new File(getTempDirectory(), fileName);
        if(!f.exists()){
            return f;
        }
        else{
            return getNextTempFileName(fileName,
                                       1);
        }
    }

    protected File getNextTempFileName(String fileName,
                                       int instance){
        // First, create a 'versioned' file name
        int n = fileName.lastIndexOf('.');
        String iFileName = fileName + instance;
        if(n != -1){
            iFileName = fileName.substring(0, n) + instance
                + fileName.substring(n, fileName.length());
        }

        File r = new File(getTempDirectory(), iFileName);
        if(!r.exists()){
            return r;
        }
        else{
            return getNextTempFileName(fileName,
                                       instance + 1);
        }
    }

    /**
     * Creates a temporary File into which the input image is
     * saved.
     */
    protected File makeRandomFileName(String imageType)
        throws IOException {

        return File.createTempFile(TEMP_FILE_PREFIX,
                                   TEMP_FILE_SUFFIX + imageType,
                                   null);
    }
}
