//
//
//  Created by Guilherme Leite Colares on 07/10/2019.
//  Copyright © 2019 Guilherme Leite Colares.

import UIKit

class ImageLoader {
    var cache = NSCache<NSString, UIImage>()

    class var sharedLoader : ImageLoader {
        struct Static {
            static let instance : ImageLoader = ImageLoader()
        }
        return Static.instance
    }

    func imageForUrl(_ urlString: String, completionHandler:@escaping (_ image: UIImage?, _ url: String) -> ()) {
        let urlStringConvert = urlString.addingPercentEncoding( withAllowedCharacters: .urlQueryAllowed)!
        let url = URL(string: urlStringConvert )

        DispatchQueue.global(qos: .background).async {
            let data = self.cache.object(forKey: urlString as NSString)
            if let image = data {
                DispatchQueue.main.async {
                    completionHandler(image, urlString)
                }
                return
            }

            let downloadTask: URLSessionDataTask = URLSession.shared.dataTask(with: url!, completionHandler: { (data, response, error) in
                if error != nil {
                    completionHandler(nil, urlString)
                    return
                }

                if data != nil {
                    let image = UIImage(data: data!)
                    self.cache.setObject(image!, forKey: urlString as NSString)
                    DispatchQueue.main.async(execute: {
                        completionHandler(image, urlString)
                    })
                    return
                }
            })
            downloadTask.resume()
        }


    }
}