Twitter Like Pull effect iOS

ViewController.swift

//Source: https://github.com/ariok/TB_TwitterUI

@IBOutlet weak var headerView: UIView!
@IBOutlet weak var scrollView: UIScrollView!

override viewDidLoad(){
  scrollView.delegate =  self
  /*
    Add below code for testing purposes. 
    scrollView.contentSize = CGSize(width: self.view.frame.size.width, height: 1024)
  */
}

 func scrollViewDidScroll(_ scrollView: UIScrollView) {
        let offset = scrollView.contentOffset.y
        var headerTransform = CATransform3DIdentity
        if offset < 0 {
            let headerScaleFactor:CGFloat = -(offset) / headerView.bounds.height
            let headerSizevariation = ((headerView.bounds.height * (1.0 + headerScaleFactor)) - headerView.bounds.height)/2.0
            headerTransform = CATransform3DTranslate(headerTransform, 0, headerSizevariation, 0)
            headerTransform = CATransform3DScale(headerTransform, 1.0 + headerScaleFactor, 1.0 + headerScaleFactor, 0)
            headerView.layer.transform = headerTransform
            
        }else{
            headerView.layer.transform = CATransform3DTranslate(headerTransform, 0, max(-40, -offset), 0)
        }
    }