var alreadyTapped = false
override func viewDidAppear(_ animated: Bool) {
    alreadyTapped = false
}
override func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
    if alreadyTapped { return }
    alreadyTapped = true
    performSegue(withIdentifier: Constants.Segue.DETAIL_VC, sender: collectionView.cellForItem(at: indexPath))
}

override func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        DispatchQueue.main.async {
            performSegue(withIdentifier: Constants.Segue.DETAIL_VC, sender: collectionView.cellForItem(at: indexPath))
        }
    }

var didSelectTime = Date()

func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {

    //MARK:- Prevent multiple calls. If elapsed time is less than 1 sec, do nothing
    if Date().timeIntervalSince(self.didSelectTime) < 1.0 {
        return
    }
    self.didSelectTime = Date()
    .....
}