How to save pictures in a photo library swift?

I am Swift beginner and just completed my Photo camera function in my app. The problem which I have now is that when I take a photo from the camera, it is not saved into the photo library on my iPhone. Everything works perfectly I am able to take pictures, but when I check in Photos, it seems that they are not saved. I had checked for similar questions, but I haven't found a proper answer, I see that they are people who add buttons to access the photo library directly but I do not need such a button. The only function, I require is taking a picture and when the user clicks select photo to save it in the Photos.

So far I have used this:

class ViewController: UIViewController, UIImagePickerControllerDelegate,UINavigationControllerDelegate{
 let imagePicker: UIImagePickerController! = UIImagePickerController()
   override func viewDidLoad() {
    super.viewDidLoad()
    imagePicker.delegate = self
    let upSwipe = UISwipeGestureRecognizer(target: self, action: #selector(handleSwipes))
    upSwipe.direction = .up
    view.addGestureRecognizer(upSwipe)
}

and the function:

func handleSwipes(sender:UISwipeGestureRecognizer) {
        if (sender.direction == .up){
            if ( UIImagePickerController.isSourceTypeAvailable(.camera)){
                if UIImagePickerController.availableCaptureModes(for: .rear) != nil {
                    imagePicker.allowsEditing = false
                    imagePicker.sourceType = .camera
                    imagePicker.cameraCaptureMode = .photo
                    present(imagePicker,animated: true, completion: {})
       }
            }

Here is what I get on my iPhone: I only want when the user chooses to use the photo, the photo itself to be saved in the gallery, as simple as that.

Before anything you need to have the "Privacy - Photo Library Additions Usage Description" to your info.plist otherwise your app will crash

Use this:

func imagePickerController(_ picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [String : Any]) {
        if let pickedImage = info[UIImagePickerControllerOriginalImage] as? UIImage{
            UIImageWriteToSavedPhotosAlbum(pickedImage, self, #selector(image(_:didFinishSavingWithError:contextInfo:)), nil)
            dismiss(animated: true, completion: nil)
        }
    }

And then, add the following function (The same function that saltTigerK wrote)

func image(_ image: UIImage, didFinishSavingWithError error: Error?, contextInfo: UnsafeRawPointer) {
    if let error = error {
        // we got back an error!
        let ac = UIAlertController(title: "Save error", message: error.localizedDescription, preferredStyle: .alert)
        ac.addAction(UIAlertAction(title: "OK", style: .default))
        present(ac, animated: true)
    } else {
        let ac = UIAlertController(title: "Saved!", message: "Your altered image has been saved to your photos.", preferredStyle: .alert)
        ac.addAction(UIAlertAction(title: "OK", style: .default))
        present(ac, animated: true)
    }
}

Source: https://www.hackingwithswift.com/read/13/5/saving-to-the-ios-photo-library