add button action for https://www.raywenderlich.com/160653/design-patterns-ios-using-swift-part-22

button_action.swift

 
  func addAlbumAtIndex(album: Album, index: Int) {
    LibraryAPI.shared.addAlbum(album, at: index)
    currentAlbumIndex = index
    
    // everytime we change the albums, we need to reload the data and table.
    allAlbums = LibraryAPI.shared.getAlbums()
    horizontalScrollerView.reload()
    showDataForAlbum(at: currentAlbumIndex)
  }
  
  
  
  @IBAction func deleteAlbum(_ sender: UIBarButtonItem) {
    let deletedAlbum = allAlbums[currentAlbumIndex]
    let undoAction = (deletedAlbum, currentAlbumIndex)
    undoStack.insert(undoAction, at: 0)
    
    LibraryAPI.shared.deleteAlbum(at: currentAlbumIndex)
    allAlbums = LibraryAPI.shared.getAlbums()
    horizontalScrollerView.reload()
    showDataForAlbum(at: currentAlbumIndex)

    
    
    undoBarButtonItem.isEnabled = true
    if allAlbums.isEmpty {
      trashBarButtonItem.isEnabled = false
    }
  }
  
  @IBAction func undoAction(_ sender: UIBarButtonItem) {
    if undoStack.count > 0 {
      let (deletedAlbum, index) = undoStack.remove(at: 0)
      addAlbumAtIndex(album: deletedAlbum, index: index)
    }
    
    if undoStack.count == 0 {
      undoBarButtonItem.isEnabled = false
    }
    
    trashBarButtonItem.isEnabled = true
  }