View with inside corners

CornerInsideView

final class CornerInsideView: UIView {
    
    var corner: UIRectCorner? {
        didSet {
            setup()
        }
    }
    var radius: CGFloat = 0
    
    private func setup() {
        var degrees: CGFloat = 0 //the value in degrees
        
        guard let corner = corner else { return }
    
        switch corner {
        case .topRight:
            degrees = 270
        case .bottomRight:
            degrees = 180
        case .bottomLeft:
            degrees = 0
        case .topLeft:
            degrees = 45
        default:
            break
        }
        
        transform = CGAffineTransform(rotationAngle: degrees * CGFloat.pi / 2)
    }
    
    override func layoutSubviews() {
        let mask = CAShapeLayer()
        mask.frame = layer.bounds
        
        let path = UIBezierPath()
        let radius: CGFloat = self.radius
        let rect = mask.bounds
        path.move(to: CGPoint(x: rect.maxX, y: rect.maxY))
        path.addLine(to: CGPoint(x: rect.minX, y: rect.maxY))
        
        path.addArc(withCenter: CGPoint(x: rect.minX + radius,
                                        y: rect.maxY - radius),
                    radius: radius,
                    startAngle: CGFloat.pi,
                    endAngle: CGFloat.pi/2,
                    clockwise: false)
        
        path.close()
        
        mask.path = path.cgPath
        layer.mask = mask
    }
}