Play Next Song in AVAudioPlayer

I have a tableviewcontroller that has a list of songs, and whenever a user clicks on a song, it opens another view controller and plays it. I need help whith whenever the user presses the next button or previous so that it will play the previous or next song. Here's my tableviewcontroller:


import UIKit 

    class LibraryTableViewController: UITableViewController { 

        var titleText = ["Heroes", "Skyline", "In The Woods"] 
        var authorText = ["Kedam", "Kovan & Electro Light", "Max Pros"] 

        @IBOutlet var songList: UITableView! 

        override func viewDidLoad() { 
            super.viewDidLoad() 
        } 

        // MARK: - Table view data source 

        override func numberOfSections(in tableView: UITableView) -> Int { 
            // #warning Incomplete implementation, return the number of sections 
            return 1 
        } 

        override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int { 
            // #warning Incomplete implementation, return the number of rows 
            return titleText.count 
        } 

        //tableview delegate 

        override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell { 
            var cell : LibrarySongTableViewCell! = tableView.dequeueReusableCell(withIdentifier: "Library Cell") as! LibrarySongTableViewCell 
            if(cell == nil) 
            { 
                cell = Bundle.main.loadNibNamed("Library Cell", owner: self, options: nil)?[0] as! LibrarySongTableViewCell; 
            } 
            let titleTitle = titleText[indexPath.row] as String //NOT NSString 
            let authorTitle = authorText[indexPath.row] as String 
            cell.titleLabel.text=titleTitle 
            cell.authorLabel.text=authorTitle 
            cell.imageView?.image = UIImage(named: titleTitle) 
            cell.imageView?.layer.cornerRadius = 5 
            return cell as LibrarySongTableViewCell 

        } 

        override func prepare(for segue: UIStoryboardSegue, sender: Any?) 
        { 
            if segue.identifier == "toLibraryDetail" 
            { 
                let detailViewController = ((segue.destination) as! LibraryDetailViewController) 
                let indexPath = self.songList!.indexPathForSelectedRow! 
                let topicLabelText = titleText[indexPath.row] 
                let detailLabelText = authorText[indexPath.row] 
                detailViewController.titleLabelText = topicLabelText 
                detailViewController.authorLabelText = detailLabelText    
            }     

        }     

    }

Here is the view controller that the cell goes to to play the song:


import UIKit 
        import AVFoundation 
        import MediaPlayer 

        // audioPlayer Outlet 
        var libraryPlayer = AVAudioPlayer() 

        class LibraryDetailViewController: UITableViewController, AVAudioPlayerDelegate { 

            // Title and Author 
            var titleLabelText: String! 
            var authorLabelText: String! 
            @IBOutlet weak var albumArt: UIImageView! 
            @IBOutlet weak var titleText: UILabel! 
            // Image Outlets 
            @IBOutlet weak var authorText: UILabel! 
            @IBOutlet weak var blurredAlbumArt: UIImageView! 
            // Toolbar Outlets 
            @IBOutlet weak var toolbar: UIToolbar! 
            var playButton: UIBarButtonItem! 
            var pauseButton: UIBarButtonItem! 
            var flexibleSpace: UIBarButtonItem! 
            var nextButton: UIBarButtonItem! 
            var previousButton: UIBarButtonItem! 

            override func viewDidLoad() { 
                super.viewDidLoad() 
                // Customize Album Art 
                albumArt.image = UIImage(named: titleLabelText) 
                blurredAlbumArt.image = UIImage(named: titleLabelText) 
                albumArt.layer.cornerRadius = 10 
                // Set label text 
                titleText.text = titleLabelText 
                authorText.text = authorLabelText 

                // Create the audioPlayer 
                do { 

                    libraryPlayer = try AVAudioPlayer(contentsOf: URL.init(fileURLWithPath: Bundle.main.path(forResource: titleLabelText, ofType: "mp3")!)) 
                    libraryPlayer.delegate = self 


                    libraryPlayer.prepareToPlay() 

                    var audioSession = AVAudioSession.sharedInstance() 



                    do { 

                        try audioSession.setCategory(AVAudioSessionCategoryPlayback) 

                    } 

                } 

                catch { 

                    print(error)                
                } 
                //  Create ToolBar Buttons 
                playButton = UIBarButtonItem(barButtonSystemItem: UIBarButtonSystemItem.play, target: self, action: "playButtonTapped") 
                pauseButton = UIBarButtonItem(barButtonSystemItem: UIBarButtonSystemItem.pause, target: self, action: "pauseButtonTapped") 
                flexibleSpace = UIBarButtonItem(barButtonSystemItem: UIBarButtonSystemItem.flexibleSpace, target: self, action: nil) 
                previousButton = UIBarButtonItem(barButtonSystemItem: UIBarButtonSystemItem.rewind, target: self, action: "previousButtonTapped") 
                nextButton = UIBarButtonItem(barButtonSystemItem: UIBarButtonSystemItem.fastForward, target: self, action: "nextButtonTapped") 

                //  Customize ToolBar Buttons 
                previousButton.tintColor = UIColor.lightGray 
                nextButton.tintColor = UIColor.lightGray 

                toolbar.items = [flexibleSpace, previousButton, flexibleSpace, pauseButton, flexibleSpace, nextButton, flexibleSpace] 


                // Set the delegate 

                // Play 
                libraryPlayer.play() 



                // Do any additional setup after loading the view. 
            } 

            //  Play 
            func playButtonTapped() { 
                toolbar.items = [flexibleSpace, previousButton, flexibleSpace, pauseButton, flexibleSpace, nextButton, flexibleSpace]; 
                libraryPlayer.play() 
            } 

            //  Pause 
            func pauseButtonTapped() { 
                toolbar.items = [flexibleSpace, previousButton, flexibleSpace, playButton, flexibleSpace, nextButton, flexibleSpace]; 
                libraryPlayer.pause() 
            } 

            //  Previous 
            func previousButtonTapped() { 
    // NEED HELP HERE 
            } 

            //  Next 
            func nextButtonTapped() { 
    // NEED HELP HERE 
            } 

            override func viewDidDisappear(_ animated: Bool) { 
                libraryPlayer.pause() 
            } 

            override func viewDidAppear(_ animated: Bool) { 
                libraryPlayer.play() 
            } 

            override func didReceiveMemoryWarning() { 
                super.didReceiveMemoryWarning() 
                // Dispose of any resources that can be recreated. 
            } 


            @IBAction func dismiss(_ sender: Any) { 
                dismiss(animated: true, completion: nil) 
            } 
        }


Thanks so much for the help! I'm using Swift 3 and Xcode 8