def applyNegativePeriodPreferences(shift: Seq[Seq[Schedule]], periodPreferences: Seq[NursePeriodPreference]) : Option[Seq[Seq[Schedule]]] = {
    val negative = periodPreferences.filter(p => p.factor < 0)

    val result = for(p <- negative) yield {
      val period = p.period

      if(period.equals("afternoon")) {
        val result = shift.last.exists(s => s.nurse.name.equals(p.nurse.name))
        //val result = shift.map(s => s.filter(n => n.nurse.name.equals(p.nurse.name)))

        result
      } else if(period.equals("morning")) {
        val result = shift.head.exists(s => s.nurse.name.equals(p.nurse.name))

        result
      } else None
    }

    if(result.contains(true)) None else Option(shift)
  }

  def applyPositivePeriodPreferences(shift: Seq[Seq[Schedule]], periodPreferences: Seq[NursePeriodPreference]) : Option[Seq[Seq[Schedule]]] = {
    val positive = periodPreferences.filter(p => p.factor > 0)

    val result = for(p <- positive) yield {
      val period = p.period

      if(period.equals("afternoon")) {
        // Check if nurse exists in afternoon
        val result = shift.last.exists(s => s.nurse.name.equals(p.nurse.name))

        //Check if nurse exists in morning
        val resMorning = shift.head.exists(s => s.nurse.name.equals(p.nurse.name))

        if(resMorning) false else true

      } else if(period.equals("morning")) {
        val result = shift.head.exists(s => s.nurse.name.equals(p.nurse.name))

        val resAfternoon = shift.last.exists(s => s.nurse.name.equals(p.nurse.name))

        if(resAfternoon) false else true

      } else None
    }

    if(result.contains(false)) None else Option(shift)
  }