import java.io.*;
import java.util.Iterator;
import javax.imageio.*;
import javax.imageio.stream.*;
import java.awt.image.*;

public class ImageFileSizeReducer {

    public static void reduceImageQuality(int sizeThreshold, String srcImg, String destImg) throws Exception {
        float quality = 1.0f;

        File file = new File(srcImg);

        long fileSize = file.length();

        if (fileSize <= sizeThreshold) {
            System.out.println("Image file size is under threshold");
            return;
        }

        Iterator iter = ImageIO.getImageWritersByFormatName("jpeg");

        ImageWriter writer = (ImageWriter)iter.next();

        ImageWriteParam iwp = writer.getDefaultWriteParam();

        iwp.setCompressionMode(ImageWriteParam.MODE_EXPLICIT);

        FileInputStream inputStream = new FileInputStream(file);

        BufferedImage originalImage = ImageIO.read(inputStream);
        IIOImage image = new IIOImage(originalImage, null, null);

        float percent = 0.1f;   // 10% of 1

        while (fileSize > sizeThreshold) {
            if (percent >= quality) {
                percent = percent * 0.1f;
            }

            quality -= percent;

            File fileOut = new File(destImg);
            if (fileOut.exists()) {
                fileOut.delete();
            }
            FileImageOutputStream output = new FileImageOutputStream(fileOut);

            writer.setOutput(output);

            iwp.setCompressionQuality(quality);

            writer.write(null, image, iwp);

            File fileOut2 = new File(destImg);
            long newFileSize = fileOut2.length();
            if (newFileSize == fileSize) {
                // cannot reduce more, return
                break;
            } else {
                fileSize = newFileSize;
            }
            System.out.println("quality = " + quality + ", new file size = " + fileSize);
            output.close();
        }

        writer.dispose();
    }

    public static void main(String[] args) throws Exception {
        String srcPath = args[0];
        String destPath = args[1];
        int maxSize = Integer.parseInt(args[2]);

        reduceImageQuality(maxSize, srcPath, destPath);

        System.out.println("DONE");
    }
}