FrameAnimator.swift

class AbsoluteFrameAnimator: NSObject {
    
    private var absoluteFrame: CGRect = CGRect.zero
    
    init(duration: CGFloat) {
        self.duration = duration
    }
    
    private let duration: CGFloat
    private var blurEffectStyle: UIBlurEffect.Style = .light
    
    enum DimTransitionMode: Int {
        case present, dismiss
    }
    
    private lazy var blurEffectView: UIVisualEffectView? = {
        let blurEffect = UIBlurEffect(style: blurEffectStyle)
        let blurEffectView = UIVisualEffectView(effect: blurEffect)
        return blurEffectView
    }()
    
    private var transitionMode: DimTransitionMode = .present
    
    func transitionMode(_ transMode: DimTransitionMode, blurStyle: UIBlurEffect.Style = .light, startingFrame: CGRect = CGRect.zero) {
        transitionMode = transMode
        blurEffectStyle = blurStyle
        absoluteFrame = startingFrame
    }
}

extension AbsoluteFrameAnimator: UIViewControllerAnimatedTransitioning {
    
    func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
        return TimeInterval(duration)
    }
    
    func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
        transitionMode == .present ? presentInTransitionContext(transitionContext) : dismissInTransitionContext(transitionContext)
    }
    
    fileprivate func presentInTransitionContext(_ transitionContext: UIViewControllerContextTransitioning) {
        
        guard let  presentedView = transitionContext.view(forKey: UITransitionContextViewKey.to) else  {
            return
        }
        let containerView = transitionContext.containerView
        
        blurEffectView?.effect = nil
        if let blurEffectView = blurEffectView {
            containerView.addSubview(blurEffectView)
            blurEffectView.fillSuperview()
        }
        
        containerView.addSubview(presentedView)
        
        presentedView.translatesAutoresizingMaskIntoConstraints = false
        let topConstraint = presentedView.topAnchor.constraint(equalTo: containerView.topAnchor, constant: absoluteFrame.origin.y)
        let leadingConstraint = presentedView.leadingAnchor.constraint(equalTo: containerView.leadingAnchor, constant: absoluteFrame.origin.x)
        let widthConstraint = presentedView.widthAnchor.constraint(equalToConstant: absoluteFrame.width)
        let heightConstraint = presentedView.heightAnchor.constraint(equalToConstant: absoluteFrame.height)
        let constraints = [topConstraint, leadingConstraint, widthConstraint, heightConstraint]
        constraints.forEach {$0.isActive = true }
        
        //        presentedView.frame = absoluteFrame // if we want to handle the frame isntead.
        containerView.layoutIfNeeded()
        UIView.animate(withDuration: 0.7, delay: 0, usingSpringWithDamping: 0.7, initialSpringVelocity: 0.7, options: .curveEaseOut, animations: {
            self.blurEffectView?.effect = UIBlurEffect(style: self.blurEffectStyle)
            constraints.forEach {$0.isActive = true }
            //            presentedView.frame = containerView.frame
            presentedView.fillSuperview()
            containerView.layoutIfNeeded()
        }, completion: { _ in
            let didComplete = !transitionContext.transitionWasCancelled
            transitionContext.completeTransition(didComplete)
        })
    }
    
    fileprivate func dismissInTransitionContext(_ transitionContext: UIViewControllerContextTransitioning) {
        
        guard let returningView = transitionContext.view(forKey: UITransitionContextViewKey.from) else {
            return
        }
        let containerView = transitionContext.containerView
        
        returningView.layer.cornerRadius = 16.0 // should have the same corner radius of the cell tapped.
        returningView.clipsToBounds = true
        containerView.layoutIfNeeded()
        
        if let collectionView = returningView.subviews.first as? CardDashBoardExpandedView {
            if collectionView.cardDashBoardCollectionView.contentOffset != CGPoint.zero {
                collectionView.cardDashBoardCollectionView.setContentOffset(CGPoint.zero, animated: true)
            }
            collectionView.cardDashBoardCollectionView.backgroundColor = returningView.backgroundColor
        }
        
        UIView.animate(withDuration: 0.7, delay: 0, usingSpringWithDamping: 0.7, initialSpringVelocity: 0.7, options: .curveEaseOut, animations: {
            self.blurEffectView?.effect = nil
            var frame = self.absoluteFrame
            frame.size.width = self.absoluteFrame.width
            returningView.frame = frame
            containerView.layoutIfNeeded()
        }, completion: { _ in
            let didComplete = !transitionContext.transitionWasCancelled
            transitionContext.completeTransition(didComplete)
        })
    }
}

// This also needs this to get the frame position

extension UICollectionViewCell {
    
    func absoluteCoordinateFrame() -> CGRect? {
        guard let superView = superview else { return nil }
        return superView.convert(frame, to: nil)
    }
}

// example of use...


    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        
        guard let cell = collectionView.cellForItem(at: indexPath) else { return }
        guard let absoluteFrame = cell.absoluteCoordinateFrame() else { return }
        
        // use absoluteFrame to pass it to the transition -> the absoluteFrame is the starting and ending frame, which is the tapped cell. 

    }