UIView+Blurable.swift

// Modified version of the extension found in https://github.com/FlexMonkey/Blurable

extension UIView {
    func asImage() -> UIImage {
        let format = UIGraphicsImageRendererFormat()
        format.scale = 1.0
        let renderer = UIGraphicsImageRenderer(size: bounds.size, format: format)
        return renderer.image { ctx in
            layer.render(in: ctx.cgContext)
        }
    }
    
    func blur(blurRadius: CGFloat) {
        guard let blur = CIFilter(name: "CIGaussianBlur") else { return }
        
        let image = self.blurViewImage
  
        blur.setValue(CIImage(image: image), forKey: kCIInputImageKey)
        blur.setValue(blurRadius, forKey: kCIInputRadiusKey)
        
        let ciContext  = CIImage.ciContext
        
        guard let result = blur.value(forKey: kCIOutputImageKey) as? CIImage else { return }
        
        let boundingRect = CGRect(x: 0, y: 0, width: frame.width, height: frame.height)
        
        guard let cgImage = ciContext.createCGImage(result, from: boundingRect) else { return}

        let filteredImage = UIImage(cgImage: cgImage)
        
        let blurOverlay = BlurOverlay()
        blurOverlay.backgroundColor = .clear
        blurOverlay.frame = boundingRect
        blurOverlay.image = filteredImage
        blurOverlay.contentMode = .scaleAspectFill
        blurOverlay.frame.origin = frame.origin

        UIView.transition(from: self, to: blurOverlay, duration: 0, options: UIView.AnimationOptions.curveEaseIn, completion: nil)
        
        objc_setAssociatedObject(self, &BlurableKey.blurable, blurOverlay, objc_AssociationPolicy.OBJC_ASSOCIATION_RETAIN)
    }
    
    func removeBlur() {
        guard let blurOverlay = objc_getAssociatedObject(self, &BlurableKey.blurable) as? BlurOverlay else { return }
        
        self.frame.origin = blurOverlay.frame.origin
        UIView.transition(from: blurOverlay, to: self, duration: 0.2, options: UIView.AnimationOptions.curveEaseIn, completion: nil)
        
        objc_setAssociatedObject(self, &BlurableKey.blurable, nil, objc_AssociationPolicy.OBJC_ASSOCIATION_RETAIN)
    }
    
    func removeBlurAndDeallocateBlurImage() {
        removeBlur()
        objc_setAssociatedObject(self, &BlurableKey.blurViewImage, nil, objc_AssociationPolicy.OBJC_ASSOCIATION_RETAIN)
    }
    
    var isBlurred: Bool {
        return objc_getAssociatedObject(self, &BlurableKey.blurable) is BlurOverlay
    }
    
    var blurViewImage: UIImage {
        get {
            if let image = objc_getAssociatedObject(self, &BlurableKey.blurViewImage) as? UIImage {
                return image
            } else {
                let image = self.asImage()
                objc_setAssociatedObject(self, &BlurableKey.blurViewImage, image, objc_AssociationPolicy.OBJC_ASSOCIATION_RETAIN)
                return image
            }
        }
    }
}

class BlurOverlay: UIImageView {}

struct BlurableKey {
    static var blurable = "blurable"
    static var blurViewImage = "blurViewImage"
}