/**
 * This code sample was written by Bruno Lowagie in answer to this question:
 * http://stackoverflow.com/questions/26580912/pdf-convert-to-black-and-white-pngs
 */
package sandbox.images;

import com.itextpdf.text.DocumentException;
import com.itextpdf.text.Image;
import com.itextpdf.text.pdf.PRStream;
import com.itextpdf.text.pdf.PdfDictionary;
import com.itextpdf.text.pdf.PdfImage;
import com.itextpdf.text.pdf.PdfName;
import com.itextpdf.text.pdf.PdfReader;
import com.itextpdf.text.pdf.PdfStamper;
import com.itextpdf.text.pdf.PdfStream;
import com.itextpdf.text.pdf.parser.PdfImageObject;

import java.awt.image.BufferedImage;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;

import javax.imageio.ImageIO;
import sandbox.WrapToTest;

@WrapToTest
public class ReplaceImage {
    
    public static final String SRC = "resources/pdfs/image.pdf";
    public static final String DEST = "results/images/image_replaced.pdf";

    public static void main(String[] args) throws DocumentException, IOException {
        File file = new File(DEST);
        file.getParentFile().mkdirs();
        new ReplaceImage().manipulatePdf(SRC, DEST);
    }

    public void manipulatePdf(String src, String dest) throws DocumentException, IOException {
        PdfReader reader = new PdfReader(src);
        PdfDictionary page = reader.getPageN(1);
        PdfDictionary resources = page.getAsDict(PdfName.RESOURCES);
        PdfDictionary xobjects = resources.getAsDict(PdfName.XOBJECT);
        PdfName imgRef = xobjects.getKeys().iterator().next();
        PRStream stream = (PRStream) xobjects.getAsStream(imgRef);
        Image img = makeBlackAndWhitePng(new PdfImageObject(stream));
        PdfImage image = new PdfImage(makeBlackAndWhitePng(new PdfImageObject(stream)), "", null);
        replaceStream(stream, image);
        PdfStamper stamper = new PdfStamper(reader, new FileOutputStream(dest));
        stamper.close();
        reader.close();
    }
    
    public static Image makeBlackAndWhitePng(PdfImageObject image) throws IOException, DocumentException {
        BufferedImage bi = image.getBufferedImage();
        BufferedImage newBi = new BufferedImage(bi.getWidth(), bi.getHeight(), BufferedImage.TYPE_USHORT_GRAY);
        newBi.getGraphics().drawImage(bi, 0, 0, null);
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        ImageIO.write(newBi, "png", baos);
        return Image.getInstance(baos.toByteArray());
    }
    
    public static void replaceStream(PRStream orig, PdfStream stream) throws IOException {
        orig.clear();
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        stream.writeContent(baos);
        orig.setData(baos.toByteArray(), false);
        for (PdfName name : stream.getKeys()) {
            orig.put(name, stream.get(name));
        }
    }
}