Flip an NSScrollView Properly

FlippingClipView.swift

/// Pins the document to the top-left of the clip view
final class FlippingClipView: NSClipView {
	
	override func constrainBoundsRect(_ proposedBounds: NSRect) -> NSRect {
		var constrained = super.constrainBoundsRect(proposedBounds)
		
		guard let documentHeight = documentView?.frame.height else {
			return constrained
		}
		
		if documentHeight < proposedBounds.height {
			constrained.origin.y -= constrained.height - documentHeight
			constrained.size.height = documentHeight
		}
		
		return constrained
	}
	
}