Scala code to find (and move or remove) duplicate files

import java.nio.file.{Files, Paths, StandardCopyOption}
import java.security.DigestInputStream
import java.security.MessageDigest
import scala.collection.parallel.immutable.ParVector
import scala.io.Source
/**
 * WARNING: Moving files is a dangerous operation, and this code does not
 * rigorously check for errors. Use this code at your own risk.
 *
 * Notes
 * -----
 * - SHA-1 is what Git uses
 * - this code assumes you have a list of files generated by `find . -type f` inside
 * your pictures folder on a Mac computer
 */
object FindDuplicateFiles extends App {
 println("Getting all filenames ...")
 // (1) get a list of all picture files
 val basePictureDir = "/Users/al/Pictures"
 val inputFile = "/Users/al/Pictures/all_picture_files.txt" //mine has 28k lines
 val rawListOfPictureFiles = Source.fromFile(inputFile).getLines.toVector
 // filenames begin with "./", so drop those first two characters
 val canonListOfPhotos = rawListOfPictureFiles.map(fname => basePictureDir + "/" + fname.drop(2))
 println(s"Done reading ${canonListOfPhotos.size} filenames ...")
 // (2) get checksum for each file
 // early tests showed that a parallel vector was much faster than a regular vector
 // (though that was when the SHA-1 algorithm was very slow)
 val (checksumFilenameTuples: ParVector[(String, String)], time) = timer {
 println("Getting checksums ...")
 val parallelListOfPhotos = canonListOfPhotos.par
 val listOfChecksumsAndFilenames: ParVector[(String, String)] = for {
 f <- parallelListOfPhotos
 checksum = fileChecksum(f, MessageDigest.getInstance("SHA-1"))
 } yield (checksum, f)
 listOfChecksumsAndFilenames
 }
 println(s"Checksum run time: $time seconds")
 // (3) now have a Seq[checksum, filename], where checksum is probably duplicated.
 // want to convert this to a Map(checksum, Seq[Filename])
 println("creating the map ...")
 var checksumFilenamesMap = scala.collection.mutable.Map[String, Seq[String]]()
 for ((cksum, fname) <- checksumFilenameTuples.toVector) {
 if (checksumFilenamesMap.contains(cksum)) {
 println("FOUND A DUPLICATE")
 val oldSeq = checksumFilenamesMap(cksum) // get the old seq
 val newSeq = oldSeq :+ fname // add the new fname to that seq
 checksumFilenamesMap(cksum) = newSeq // update that element in the map
 } else {
 // the map doesn't contain the checksum, so just add a new entry
 checksumFilenamesMap(cksum) = Seq(fname)
 }
 }
 // (4) (optional) write all the `Map(checksum, Seq[Filename])` to a file
 println("writing to the file ...")
 import java.io._
 val pw = new PrintWriter(new File("/Users/al/Projects/Scala/DuplicateFiles/dups.dat"))
 for ((cksum,fnames) <- checksumFilenamesMap) {
 pw.write(s"cksum: $cksum, files: $fnames\n")
 }
 pw.close
 // (5) keep one copy of the file, and move the duplicates to my "dups" folder
 val dupsFolder = "/Users/al/Desktop/DuplicateImages"
 for ((cksum,fnames) <- checksumFilenamesMap) {
 if (fnames.size > 1) {
 // there are duplicate files
 val filenamesToMove = fnames.drop(1) //keep the first file, mv the rest
 for (originalCanonFilename <- filenamesToMove) {
 val baseFilename = (new File(originalCanonFilename)).getName //foo.jpg
 val nanoTime = System.nanoTime
 val newFilename = nanoTime + "-" + baseFilename //123-foo.jpg
 val newCanonFilename = dupsFolder + "/" + newFilename
 val path = Files.move(
 Paths.get(originalCanonFilename),
 Paths.get(newCanonFilename),
 StandardCopyOption.REPLACE_EXISTING
 )
 if (path != null) {
 //println(s"moved the file $baseFilename successfully")
 } else {
 println(s"could NOT move the file $baseFilename")
 }
 println("")
 }
 }
 }
 private def timer[A](blockOfCode: => A) = {
 val startTime = System.nanoTime
 val result = blockOfCode
 val stopTime = System.nanoTime
 val delta = stopTime - startTime
 (result, delta/1000000000d)
 }
 //TODO convert to use Option
 private def fileChecksum(filepath: String, mdIn: MessageDigest) = {
 var mdOut: MessageDigest = null
 var dis: DigestInputStream = null
 // file hashing with DigestInputStream
 try {
 // code is 132x slower w/o BufferedInputStream
 dis = new DigestInputStream(new BufferedInputStream(new FileInputStream(filepath)), mdIn)
 while (dis.read != -1) {
 //TODO this seems to be necessary; see dis.read() javadoc
 }
 mdOut = dis.getMessageDigest
 }
 catch {
 case ioe: IOException => {
 //TODO handle this
 System.err.println(ioe.getMessage)
 }
 }
 finally {
 if (dis != null) dis.close()
 }
 // return value
 convertBytesToHex(mdOut.digest)
 }
 def convertBytesToHex(bytes: Seq[Byte]): String = {
 val sb = new StringBuilder
 for (b <- bytes) {
 sb.append(String.format("%02x", Byte.box(b)))
 }
 sb.toString
 }
}