[Kotlin] Move files to specified folders

/* This short code was used to move downloaded images from folders marked by (1), (2), (3) or " " to project folders */

public class FileManager(var source : String, var dest : String) {

    val destDirs : ArrayList<String>

    {
        destDirs = arrayListOf("drawable-xxxhdpi", "drawable-xxhdpi", "drawable-xhdpi", "drawable-hdpi")
        makeValid()
    }

    public fun doWork() {
        readDirectory(File(source))
    }

    private fun readDirectory(dir : File) {
        for (file in dir.listFiles()) {
            if (file.isDirectory()) readDirectory(file)
            else if (file.getName().endsWith(".png")) moveFile(file)
        }
    }

    private fun moveFile(file : File) {
        val istream = FileInputStream(file)
        val ostream = FileOutputStream(getDestPath(file))
        val buffer = ByteArray(1024)
        var read : Int
        while (true) {
            read = istream.read(buffer)
            if (read == -1) break;
            else ostream.write(buffer, 0, read)
        }
        ostream.flush()
        ostream.close()
        istream.close()
    }

    private fun getDestPath(file : File) : String {
        val fileDir = file.getParent()
        var result = dest
        for (name in destDirs) {
            if (fileDir.contains("(${destDirs.indexOf(name)})")) {
                return result + File.separator + name + File.separator + file.getName()
            }
        }
        return result + File.separator + destDirs[0] + File.separator + file.getName()
    }

    private fun makeValid() {
        if (dest[dest.length()-1].equals(File.separator))
            dest = dest.substring(0, dest.lastIndexOf(File.separator)-1)
        for (name in destDirs) {
            val folder = File(dest + File.separator + name)
            if (!folder.exists()) {
                folder.mkdir()
            }
        }
    }
}