Function to download audio file from url and save it in documents directory

DownloadAndSaveAudioFile.swift

func downloadAndSaveAudioFile(_ audioFile: String, completion: @escaping (String) -> Void) {
        
        //Create directory if not present
        let paths = NSSearchPathForDirectoriesInDomains(FileManager.SearchPathDirectory.libraryDirectory, FileManager.SearchPathDomainMask.userDomainMask, true)
        let documentDirectory = paths.first! as NSString
        let soundDirPathString = documentDirectory.appendingPathComponent("Sounds")
        
        do {
            try FileManager.default.createDirectory(atPath: soundDirPathString, withIntermediateDirectories: true, attributes:nil)
            print("directory created at \(soundDirPathString)")
        } catch let error as NSError {
            print("error while creating dir : \(error.localizedDescription)");
        }
        
        if let audioUrl = URL(string: audioFile) {     //http://freetone.org/ring/stan/iPhone_5-Alarm.mp3
            // create your document folder url
            let documentsUrl =  FileManager.default.urls(for: .libraryDirectory, in: .userDomainMask).first! as URL
            let documentsFolderUrl = documentsUrl.appendingPathComponent("Sounds")
            // your destination file url
            let destinationUrl = documentsFolderUrl.appendingPathComponent(audioUrl.lastPathComponent)
            
            print(destinationUrl)
            // check if it exists before downloading it
            if FileManager().fileExists(atPath: destinationUrl.path) {
                print("The file already exists at path")
            } else {
                //  if the file doesn't exist
                //  just download the data from your url
                DispatchQueue.global(qos: DispatchQoS.QoSClass.background).async(execute: {
                    if let myAudioDataFromUrl = try? Data(contentsOf: audioUrl){
                        // after downloading your data you need to save it to your destination url
                        if (try? myAudioDataFromUrl.write(to: destinationUrl, options: [.atomic])) != nil {
                            print("file saved")
                            completion(destinationUrl.absoluteString)
                        } else {
                            print("error saving file")
                            completion("")
                        }
                    }
                })
            }
        }
    }