typealias ImageCacheLoaderCompletionHandler = ((UIImage) -> ())

class ImageCacheLoader {

    var task: URLSessionDownloadTask!
    var session: URLSession!
    var cache: NSCache<NSString, UIImage>!

    init() {
        session = URLSession.shared
        task = URLSessionDownloadTask()
        self.cache = NSCache()
    }

    func obtainImageWithPath(imagePath: String, completionHandler: @escaping ImageCacheLoaderCompletionHandler) {
        if let image = self.cache.object(forKey: imagePath as NSString) {
            DispatchQueue.main.async {
                completionHandler(image)
            }
        } else {
            /* You need placeholder image in your assets,
               if you want to display a placeholder to user */
            let placeholder = UIImage(bundleImageName: "Contact List/CreateGroupActionIcon")!
            DispatchQueue.main.async {
                completionHandler(placeholder)
            }
            let url: URL! = URL(string: imagePath)
            task = session.downloadTask(with: url, completionHandler: { (location, response, error) in
                if let location = location {
                    if let data = try? Data(contentsOf: location) {
                        let img: UIImage! = UIImage(data: data)
                        self.cache.setObject(img, forKey: imagePath as NSString)
                        DispatchQueue.main.async {
                            completionHandler(img)
                        }
                    }
                }
            })
            task.resume()
        }
    }
}