open class VKPopupView: NSObject
{
    // MARK: Public properties

    /// Title of the `VKPopupView`. Appears above the contentView
    open var title: String?

    /// Content you want to display inside popup
    /// - Important: Max size of the contentView is `300x300`.
    /// - requires: `VKPopupView` will reset backgroundColor to `UIColor.clear`. It is done in order to match Apple's style
    open var contentView: UIView?
        {
        didSet
        {
            if let oldContent = oldValue
            {
                oldContent.removeFromSuperview()
            }

            if contentView != nil
            {
                self.adoptContentView()
            }
        }
    }

    /// Set background blur style
    /// - Note: Default is `UIBlurEffectStyle.light`
    open var backgroundBlurStyle: UIBlurEffectStyle  = .light
        {
        didSet
        {
            self.viewOverlay.effect = UIBlurEffect(style: backgroundBlurStyle)
        }
    }

    /// Set popup blur style
    /// - Note: Default is `UIBlurEffectStyle.extraLight`
    open var contentViewBlurStyle: UIBlurEffectStyle = .extraLight
        {
        didSet
        {
            self.containerView.effect = UIBlurEffect(style: contentViewBlurStyle)
        }
    }


    /// Delegate of the VKPopupView
    open var delegate: VKPopupViewDelegate?

    /// Set the animation duration for show and hide
    /// - Note: Default is `0.4` seconds
    open var animationSpeed: TimeInterval = 0.4

    /// Constant of the content frame
    /// - Attention: Please use it as constant for all your content views
    open static let contentFrame = CGRect(x: 0, y: 0, width: 300, height: 300)

    // MARK: Private properties
    // Views

    /// Background overlay view
    fileprivate var viewOverlay     = UIVisualEffectView()

    /// Container of the content view
    fileprivate var containerView   = UIVisualEffectView()

    /// Title label
    /// - Note: It will not show up in `title` is `nil`
    fileprivate var labelTitle      = UILabel()

    // Sizes
    /// Initial frame from where `VKPopupView` will fade in and fade out
    fileprivate var initialFrame: CGRect!

    /// Default frame which is used when `initialFrame` is `nil`
    fileprivate var zeroFrame = CGRect(x: UIScreen.main.bounds.midX, y: UIScreen.main.bounds.midY, width: 0, height: 0)

    /// Frame used when `VKPopupView` is shown
    fileprivate lazy var finalFrame: CGRect =
        {
            var size: CGFloat = 300
            let x: CGFloat = self.viewOverlay.bounds.midX - size / 2
            let y: CGFloat = self.viewOverlay.bounds.midY - size / 2

            return CGRect(x: x, y: y, width: size, height: size)
    }()

    // MARK: Init

    /// Init VKPopupView and set 'backgrundStyle' and 'contentViewStyle' properties
    ///
    /// - Parameters:
    ///   - backgroundStyle: Set 'backgroundStyle' value
    ///   - contentViewStyle: Set 'contentViewStyle' value
    ///
    /// Example:
    ///
    ///     let popup = VKPopup(backgroundStyle: .dark, contentViewStyle: .light)
    /// ___
    public convenience init(backgroundStyle: UIBlurEffectStyle = .light, contentViewStyle: UIBlurEffectStyle = .extraLight)
    {
        self.init()
        self.backgroundBlurStyle  = backgroundStyle
        self.contentViewBlurStyle = contentViewStyle
    }
}