BottomBarView.swift

//: A UIKit based Playground for presenting user interface
  
import UIKit
import PlaygroundSupport

let BALL: CGFloat = 100

class MyViewController : UIViewController {
    override func loadView() {
        let view = UIView()
        view.backgroundColor = UIColor.black

        let label = UILabel()
        label.frame = CGRect(x: 150, y: 200, width: 200, height: 20)
        label.text = "Hello World!"
        label.textColor = .black
        
        view.addSubview(label)

        let bottom = BottomBarView()
        bottom.translatesAutoresizingMaskIntoConstraints = false
//        bottom.radius = 30
        bottom.frame = CGRect.zero
        bottom.backgroundColor = UIColor.red

        view.addConstraint(NSLayoutConstraint(item: bottom, attribute: .trailing, relatedBy: .equal, toItem: view, attribute: .trailing, multiplier: 1, constant: 0))
        view.addConstraint(NSLayoutConstraint(item: bottom, attribute: .leading, relatedBy: .equal, toItem: view, attribute: .leading, multiplier: 1, constant: 0))
        view.addConstraint(NSLayoutConstraint(item: bottom, attribute: .bottom, relatedBy: .equal, toItem: view, attribute: .bottom, multiplier: 1, constant: 0))
        view.addConstraint(NSLayoutConstraint(item: bottom, attribute: .height, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute, multiplier: 1, constant: 131))

        view.addSubview(bottom)

        let button = UIView()
        button.translatesAutoresizingMaskIntoConstraints = false
        button.backgroundColor = UIColor.yellow
        button.layer.cornerRadius = 90/2.0

        view.addConstraint(NSLayoutConstraint(item: button, attribute: .width, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute, multiplier: 1, constant: 90))
        view.addConstraint(NSLayoutConstraint(item: button, attribute: .height, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute, multiplier: 1, constant: 90))
        view.addConstraint(NSLayoutConstraint(item: button, attribute: .top, relatedBy: .equal, toItem: bottom, attribute: .top, multiplier: 1, constant: 5.0))
        view.addConstraint(NSLayoutConstraint(item: button, attribute: .centerX, relatedBy: .equal, toItem: view, attribute: .centerX, multiplier: 1, constant: 0))

        view.addSubview(button)

        self.view = view

    }

}

final class BottomBarView: UIView {

  //private let MAGIC_NUMBER: CGFloat = 0.552284749831
  private let MAGIC_NUMBER: CGFloat = 0.5

  var radius: CGFloat = 30
  var ballRadius: CGFloat = BALL

  override func layoutSubviews() {
    super.layoutSubviews()
    roundCorners()
  }

  var controlPoints: [CGPoint] = []

  override func draw(_ rect: CGRect) {
    super.draw(rect)

//    guard let context = UIGraphicsGetCurrentContext() else {return}
//    context.addEllipse(in: CGRect(x: 10.0, y: 10.0, width: 10.0, height: 10.0))
//    context.setFillColor(UIColor.white.cgColor)
//    context.fillPath()
  }

  func roundCorners() {
    if layer.mask == nil && radius != 0 {

      let rect = self.bounds

      let path = UIBezierPath()
      path.move(to: CGPoint(x: 0.0, y: rect.height))

      path.addLine(to: CGPoint(x: 0.0, y: radius))
      path.addCurve(
        to: CGPoint(x: radius, y: 0.0),
        controlPoint1: CGPoint(x: 0.0, y: radius * MAGIC_NUMBER),
        controlPoint2: CGPoint(x: radius * MAGIC_NUMBER, y: 0.0))

      let firstPointStart = CGPoint(x: rect.width/2 - ballRadius/2 - radius, y: 0.0)
      path.addLine(to: firstPointStart)

      let firstPointEnd: CGPoint = CGPoint(x: firstPointStart.x + radius, y: firstPointStart.y + radius)
      path.addCurve(
        to: firstPointEnd,
        controlPoint1: CGPoint(x: firstPointStart.x + radius * MAGIC_NUMBER, y: firstPointStart.y),
        controlPoint2: CGPoint(x: firstPointEnd.x, y: firstPointEnd.y - radius * MAGIC_NUMBER))

      let middleLeft: CGPoint = CGPoint(x: firstPointEnd.x, y: ballRadius/2)
      path.addLine(to: middleLeft)

      let secondPointEnd: CGPoint = CGPoint(x: middleLeft.x + ballRadius/2, y: middleLeft.y + ballRadius/2)

      let offset = ballRadius * MAGIC_NUMBER
      print("offset \(offset)")

      path.addCurve(
        to: secondPointEnd,
        controlPoint1: CGPoint(x: firstPointEnd.x, y: secondPointEnd.y - offset),
        controlPoint2: CGPoint(x: firstPointEnd.x, y: secondPointEnd.y))

      let thirdPointStart: CGPoint = CGPoint(x: secondPointEnd.x + ballRadius/2, y: secondPointEnd.y - ballRadius/2)
      path.addCurve(
        to: thirdPointStart,
        controlPoint1: CGPoint(x: thirdPointStart.x, y: secondPointEnd.y),
        controlPoint2: CGPoint(x: thirdPointStart.x, y: secondPointEnd.y - (ballRadius * MAGIC_NUMBER)))

      let middleRight: CGPoint = CGPoint(x: thirdPointStart.x, y: firstPointEnd.y)
      path.addLine(to: middleRight)

      let fourthPoint: CGPoint = CGPoint(x: middleRight.x + radius, y: 0)
      path.addCurve(
        to: fourthPoint,
        controlPoint1: CGPoint(x: middleRight.x, y: radius * MAGIC_NUMBER),
        controlPoint2: CGPoint(x: middleRight.x + radius * MAGIC_NUMBER, y: 0))

      let endTop: CGPoint = CGPoint(x: rect.width - radius, y: 0)
      path.addLine(to: endTop)

      path.addCurve(
        to: CGPoint(x: rect.width, y: radius),
        controlPoint1: CGPoint(x: endTop.x + radius * MAGIC_NUMBER, y: 0),
        controlPoint2: CGPoint(x: rect.width, y: radius * MAGIC_NUMBER))

      path.addLine(to: CGPoint(x: rect.width, y: rect.height))

      path.close()

      let maskLayer = CAShapeLayer()
      maskLayer.path = path.cgPath
      layer.mask = maskLayer
    }
  }

}

// Present the view controller in the Live View window
let viewController = MyViewController()
viewController.preferredContentSize = CGSize(width: 300, height: 300)
PlaygroundPage.current.liveView = viewController