extended-button.swift

class Button: UIButton, ExtendedTouchable {
    var touchableSurface: UIView?
    
    override func layoutSubviews() {
        super.layoutSubviews()
        setupTouchableArea()
    }
    
    override func hitTest(_ point: CGPoint, with event: UIEvent?) -> UIView? {
        guard isEnabled, !isHidden, alpha != 0.0 else {
            return nil
        }
        
        guard let touchableSurface = touchableSurface, touchableSurface.frame.contains(point) else {
            return super.hitTest(point, with: event)
        }
        
        return self
    }
}

/// Touchable functionality, extended to cover a potentially larger surface area on screen
protocol ExtendedTouchable: class {
    /// Subview that is the outline for the extended touchable area
    var touchableSurface: UIView? { get set }

    /// Create the extended touchable area
    func setupTouchableArea()
}

// MARK: - UIControl
extension ExtendedTouchable where Self: UIControl {
    func setupTouchableArea() {
        if bounds.size.width > .minimumButtonDimension, bounds.size.height > .minimumButtonDimension {
            touchableSurface?.removeFromSuperview()
            touchableSurface = nil
            return
        }
        
        if touchableSurface == nil {
            touchableSurface = {
                let view = UIView()
                view.backgroundColor = .clear

                // For debug
//                backgroundColor = #colorLiteral(red: 0.06274509804, green: 0.1254901961, blue: 0.4117647059, alpha: 0.2008240582)
//                view.backgroundColor = #colorLiteral(red: 0.06274509804, green: 0.1254901961, blue: 0.4117647059, alpha: 0.2008240582)
                
                addSubview(view)
                sendSubview(toBack: view)
                
                view.translatesAutoresizingMaskIntoConstraints = false
                view.centerXAnchor.constraint(equalTo: centerXAnchor).isActive = true
                view.centerYAnchor.constraint(equalTo: centerYAnchor).isActive = true
                view.widthAnchor.constraint  (equalToConstant: max(bounds.size.width,  .minimumButtonDimension)).isActive = true
                view.heightAnchor.constraint (equalToConstant: max(bounds.size.height, .minimumButtonDimension)).isActive = true
                
                return view
            }()
        }
    }
}

// MARK: - CGFloat constants
private extension CGFloat {
    static let minimumButtonDimension: CGFloat = 44.0
}