bring textfield above keyboard in a scrollview

scroll.swift

func textFieldShouldBeginEditing(_ textField: UITextField) -> Bool {
        let textfieldPos = scrollView.convert(textField.frame.origin, to: view).y
        let textFieldHght = textField.frame.size.height

        let scrollViewHght = scrollView.frame.size.height
        
        if (textfieldPos + textFieldHght) > (scrollViewHght - 250) {
        
            var duration : Double
            if isKeyBoardVisible {
                duration = 0.2
            }
            else {
                duration = 0.5
            }
            
            UIView.animate(withDuration: duration, animations: {
                self.scrollView.contentOffset = CGPoint(x: 0, y: (textfieldPos + textFieldHght) - (scrollViewHght - 250) + 40)
            })
        }
        
        return true
    }