override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {

    if indexPath.row > 0 {

        let path = NSSearchPathForDirectoriesInDomains(FileManager.SearchPathDirectory.documentDirectory, FileManager.SearchPathDomainMask.userDomainMask, true)
        print(path)
        let documentDirectoryPath:String = path[0]
        let fileManager = FileManager()
        let destinationURLForFile = URL(fileURLWithPath: documentDirectoryPath.appendingFormat("/file(indexPath.row).mp3"))


        if fileManager.fileExists(atPath: destinationURLForFile.path){

            self.performSegue(withIdentifier: "segue", sender: self)

        }else{

            index = indexPath.row

            let url = URL(string: "http:link(indexPath.row).mp3")!
            let downloadTaskLocal = backgroundSession.downloadTask(with: url)
            downloadTaskLocal.resume()
        }
    }
}

func urlSession(_ session: URLSession,
                downloadTask: URLSessionDownloadTask,
                didFinishDownloadingTo location: URL){

    let path = NSSearchPathForDirectoriesInDomains(FileManager.SearchPathDirectory.documentDirectory, FileManager.SearchPathDomainMask.userDomainMask, true)
    let documentDirectoryPath:String = path[0]
    let fileManager = FileManager()
    let destinationURLForFile = URL(fileURLWithPath: documentDirectoryPath.appendingFormat("/file(index).mp3"))

    do {
        try fileManager.moveItem(at: location, to: destinationURLForFile)
        }catch{
            print("error")
        }
}

fileManager.moveItem(at: location, to: destinationURLForFile)

let fileName = location.lastPathComponent

let destinationURLForFile = URL(fileURLWithPath: documentDirectoryPath.appendingFormat("/(fileName)"))