object signals {
  println("Welcome to the Scala worksheet")       //> Welcome to the Scala worksheet

  // this is how one declares a class with three fields in Scala:
case class Note(val amplitude: Double, val frequency: Double, val duration: Double = 1.0)

// a sample score for testing purposes:
val symphony1 =
   List(Note(3, 30), Note(3.1, 40, .25), Note(3.2, 10, .5),
         Note(2.1, 5, -.75), Note(15.9, 2))       //> symphony1  : List[signals.Note] = List(Note(3.0,30.0,1.0), Note(3.1,40.0,0.2
                                                  //| 5), Note(3.2,10.0,0.5), Note(2.1,5.0,-0.75), Note(15.9,2.0,1.0))

   //iterative for
  def maxAmp1(score: List[Note]) = {
     var result = 0.0
     for(note <- score if 0 < note.amplitude){
         result = note.amplitude
         }
     result
  }                                               //> maxAmp1: (score: List[signals.Note])Double
  println("Max amp = " + maxAmp1(symphony1))      //> Max amp = 15.9

 /*
  def maxAmp2(score: List[Note]):Double = {
      if (score == Nil) 0.0
      else if (0 < score.head.amplitude) score.head.amplitude + amplitude(score.tail)
      else amplitude(score.tail)
      }

  }*/

  def maxAmp3(score: List[Note]) = {
     def helper(result: Double, unseen: List[Note]): Double =
        if (unseen == Nil) result
        else if  (0 < unseen.head.duration)
             helper(result + unseen.head.duration, unseen.tail)
             else helper(result, unseen.tail)
     helper(0.0, score)
  }                                               //> maxAmp3: (score: List[signals.Note])Double

 def noise(note: Note) = note.duration < 0        //> noise: (note: signals.Note)Boolean

    def filterNoise(score: List[Note]): List[Note] = {
     var result: List[Note] = Nil
     for(note <- score) if (!noise(note)) result = result :+ note
     result
  }                                               //> filterNoise: (score: List[signals.Note])List[signals.Note]

  def filterNoise2(score: List[Note]): List[Note] = {
  if (score == Nil) Nil
  else if (noise(score.head)) filterNoise(score.tail)
  else score.head :: filterNoise(score.tail)
  }                                               //> filterNoise2: (score: List[signals.Note])List[signals.Note]
    filterNoise(symphony1)                    //> res0: List[signals.Note] = List(Note(3.0,30.0,1.0), Note(3.1,40.0,0.25), No
                                                  //| te(3.2,10.0,0.5), Note(15.9,2.0,1.0))


  def filterNoise3(score: List[Note]): List[Note] = {
  score.filter((n:Note) => !noise(n))

  }                                               //> filterNoise3: (score: List[signals.Note])List[signals.Note]
    filterNoise2(symphony1)                       //> res1: List[signals.Note] = List(Note(3.0,30.0,1.0), Note(3.1,40.0,0.25), No
                                                  //| te(3.2,10.0,0.5), Note(15.9,2.0,1.0))

  filterNoise3(symphony1)                         //> res2: List[signals.Note] = List(Note(3.0,30.0,1.0), Note(3.1,40.0,0.25), No
                                                  //| te(3.2,10.0,0.5), Note(15.9,2.0,1.0))
}