SelfSizingButton.swift

class Button: UIButton {
  
  var outset: CGSize = CGSize.zero
  
  var shouldFitContentVertically: Bool = false {
    didSet {
      if shouldFitContentVertically {
        titleLabel?.lineBreakMode = .byWordWrapping
        titleLabel?.numberOfLines = 0
      }
    }
  }
  
  private var cachedFrame: CGRect = .zero
  private let buttonEdgeOffset: CGFloat = 6 // Magic UIKit offset for buttons.
  
  override func didMoveToSuperview() {
    super.didMoveToSuperview()
    cachedFrame = frame
  }
  
  override func layoutSubviews() {
    super.layoutSubviews()
    if frame.width != cachedFrame.width {
      invalidateIntrinsicContentSize()
    }
    cachedFrame = frame
  }
  
  override var intrinsicContentSize: CGSize {
    var size = super.intrinsicContentSize
    guard shouldFitContentVertically, let titleLabel = titleLabel else { return size }
    
    let fittingSize = titleLabel.systemLayoutSizeFitting(CGSize(width: bounds.width, height: .greatestFiniteMagnitude))
    let fitHeight = fittingSize.height
      + (contentEdgeInsets.top + contentEdgeInsets.bottom)
      + (titleEdgeInsets.top + titleEdgeInsets.bottom)
      + (buttonEdgeOffset * 2)
    size.height = max(size.height, fitHeight)
    return size
  }
  
  override func hitTest(_ point: CGPoint, with event: UIEvent?) -> UIView? {
    guard !isHidden else { return nil }
    let touchableRect = self.bounds.insetBy(dx: -outset.width, dy: -outset.height)
    return touchableRect.contains(point) ? self: nil
  }
}