Watching a directory with Scala Futures via Java nio

DirectoryFileCreationWatcher

class DirectoryFileCreationWatcher(directoryToWatch:Path) {
  import java.nio.file._
  import java.nio.file.StandardWatchEventKinds._
  import scala.concurrent.ExecutionContext.Implicits.global
  import scala.collection.JavaConversions._

  val watcher = FileSystems.getDefault.newWatchService

  // Work properly on Mac:
  //http://stackoverflow.com/questions/9588737/is-java-7-watchservice-slow-for-anyone-else
  val kinds:Array[Kind[_]] = Seq(StandardWatchEventKinds.ENTRY_CREATE).toArray
  directoryToWatch.register(watcher, kinds, SensitivityWatchEventModifier.HIGH.asInstanceOf[WatchEvent.Modifier])

  /**
   *
   * @param pathMatcher a function that returns true if this is the file we're looking for
   * @return a Future holding a Path that represents the directory in its "new" state
   */
  def awaitFile( pathMatcher: Path => Boolean):Future[Path] = Future[Path] {
    var foundMatch = false
    while (!foundMatch) {
      val watchKey = watcher.take // Blocks
      val events = watchKey.pollEvents
      foundMatch = events.exists { event =>
        val wep = event.asInstanceOf[WatchEvent[Path]]
        pathMatcher(wep.context)
      }
      watchKey.reset
    }
    directoryToWatch
  }
}

class DirectoryFileCreationWatcherSpec extends Specification {
  import java.nio.file._
  import scala.concurrent.ExecutionContext.Implicits.global
  import scala.collection.JavaConversions._

  isolated
  "DirectoryFileCreationWatcher" should {
    val watchedDir = Files.createTempDirectory("watchedDir")
    val testFileName = "testFile.txt"
    val secondTestFileName = "testFile2.txt"
    val waitToNoticeChange = 2000
    val noticeDelay = scala.concurrent.duration.FiniteDuration(waitToNoticeChange, "millis")
    val halfSecond = scala.concurrent.duration.FiniteDuration(500, "millis")

    def addFileToWatchedDir(fileName:String):java.io.File = {
      val f = new java.io.File(watchedDir.toFile, fileName)
      f.createNewFile
      println(s"added file ${f.getAbsolutePath}")
      f
    }

    "not notify the caller until the dir contains a matching file - any file" in {
      val future = new DirectoryFileCreationWatcher(watchedDir).awaitFile{ path =>
        true
      }

      future.isCompleted must beFalse

      addFileToWatchedDir(testFileName)

      Thread.sleep(waitToNoticeChange)
      future.isCompleted must beTrue
    }

    "notify the caller with the new contents of the dir - for any file" in {
      val future = new DirectoryFileCreationWatcher(watchedDir).awaitFile{ path =>
        true
      }

      watchedDir.toFile.list.contains(testFileName) must beFalse

      addFileToWatchedDir(testFileName)

      future.map { dirPath =>
        println(s"dirPath: ${dirPath.toFile.list.mkString}" )
        dirPath.toFile.list.contains(testFileName)
      } must beTrue.await(timeout = halfSecond, retries=4)
    }


    "not notify the caller until the dir contains a matching file - exact match on file" in {
      val future = new DirectoryFileCreationWatcher(watchedDir).awaitFile{ path =>
        path.endsWith(testFileName)
      }

      future.isCompleted must beFalse

      addFileToWatchedDir(secondTestFileName)

      Thread.sleep(waitToNoticeChange)
      future.isCompleted must beFalse


      addFileToWatchedDir(testFileName)
      Thread.sleep(waitToNoticeChange)

      future.isCompleted must beTrue

    }
  }