Make a stretchy & blurry collection header

StretchyHeader.swift

class Layout: UICollectionViewFlowLayout {
	// Recompute layout on scroll
	override func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) -> Bool {
		return true
	}
	
	// Update header size based on content offset (and keep it at the top)
	override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
		let layoutAttributes = super.layoutAttributes(in: rect)
		
		layoutAttributes?.forEach {
			if $0.representedElementKind == UICollectionView.elementKindSectionHeader && $0.indexPath.section == 0 {
				guard let collectionView = collectionView else { return }
				
				let contentOffsetY = collectionView.contentOffset.y
				
				// Update header only when scrolling from top to bottom
				guard contentOffset <= 0 else { return }
				
				let width = collectionView.frame.width
				let height = $0.frame.height - contentOffsetY
				$0.frame = CGRect(x: 0, y: contentOffsetY, width: width, height: height)
			}
		}
		
		return layoutAttributes
	}
}

class HeaderView: UICollectionReusableView {
	var animator: UIViewPropertyAnimator?
	
	func setupBlur() {
		animator = UIViewPropertyAnimator(duration: 3.0, curve: .linear) { [weak self] in
			let blurEffect = UIBlurEffect(style: .regular)
			let visualEffectView = UIVisualEffectView(effect: blurEffect)
			
			self?.addSubview(visualEffectView)
			// Don't forget the constraints
		}
	}
}

class CollectionViewController: UICollectionViewController {
	override func scrollViewDidScroll(_ scrollView: UIScrollView) {
		let contentOffsetY = scrollView.contentOffset.y
		
		// Remove blur when scrolling from bottom to top
		if contentOffsetY > 0 {
			headerView?.animator?.fractionComplete = 0
			return
		}
		
		// Displays the blur accordingly
		headerView?.animator?.fractionComplete = abs(contentOffsetY) / 100
	}
}