var speechPlayer = AVAudioPlayer ()
var currentPlayingItems: [String] = []

fileprivate func prepareAudioItemsToPlay () {
var result: [String] = []

    if (introSwitch.isOn) {
    result.append ( "Intro")
    }

result += audioFileNamesForCurrentLessonType

currentPlayingItems = result.flatMap ({Bundle.main.path (forResource: $ 0, ofType: "m4a")})
currentPlayingItemNumber = 0

fileprivate var audioFileNamesForCurrentLessonType: [String] {
    guard let type = selectedLessonType else {return []}
    switch type {

    case .lesson1:
    if (statusSelection.selectedSegmentIndex == 0) {
    return ["A1", "A2", "A3", "A4", "A5"]
    }
    else if (statusSelection.selectedSegmentIndex == 1) {
    return ["A1", "A6", "A3, "A7", "A8", "A9","A10"]
    }
...
}

let durations:[String:Int] = ["A1": 1, "A2": 2, "A3": 3, "Intro": 120]
let fileNames:[String] = ["A1", "A3"]
let totalDuration = durations.filter{ fileNames.contains($0.key) }.values.reduce(0, +)