How To Download Multiple Files Sequentially using NSURLSession downloadTask in Swift

DownloadManager.swift

mport Foundation


    class DownloadManager {

        var delegate: HavingWebView?
        var gotFirstAndEnough = true
        var finalURL: NSURL?{
            didSet{
                if finalURL != nil {
                    if let s = self.contentOfURL{
                        self.delegate?.webView.loadHTMLString(s, baseURL: nil)
                    }
                }
            }
        }
        var lastRequestBeginning: NSDate?

        var myLinks = [String](){
            didSet{
                self.handledLink = self.myLinks.count
            }
        }

        var contentOfURL: String?

        var handledLink = 0 {
            didSet{
                if handledLink == 0 {
                    self.finalURL = nil
                    print("🔴🔶🔴🔶🔶🔴🔶🔴🔶🔴🔶🔴")
                } else {
                    if self.finalURL == nil {
                        if let nextURL = NSURL(string: self.myLinks[self.handledLink-1]) {
                            self.loadAsync(nextURL)
                        }
                    }
                }
            }
        }

        func loadAsync(url: NSURL) {
            let sessionConfig = NSURLSessionConfiguration.ephemeralSessionConfiguration()
            let session = NSURLSession(configuration: sessionConfig, delegate: nil, delegateQueue: NSOperationQueue.mainQueue())
            let request = NSMutableURLRequest(URL: url, cachePolicy: NSURLRequestCachePolicy.ReloadIgnoringCacheData, timeoutInterval: 15.0)
            request.HTTPMethod = "GET"
            print("🚀")
            self.lastRequestBeginning = NSDate()
            print("Requet began:    \(self.lastRequestBeginning )")
            let task = session.dataTaskWithRequest(request, completionHandler: { (data: NSData?, response: NSURLResponse?, error: NSError?) -> Void in
                if (error == nil) {
                    if let response = response as? NSHTTPURLResponse {
                        print("\(response)")
                        if response.statusCode == 200 {
                            if let content = String(data: data!, encoding: NSUTF8StringEncoding) {
                                self.contentOfURL = content
                            }
                            self.finalURL =  url
                        }
                    }
                }
                else {
                    print("Failure: \(error!.localizedDescription)");
                }

                let elapsed = NSDate().timeIntervalSinceDate(self.lastRequestBeginning!)
                print("trying \(url) takes \(elapsed)")
                print("🏁   Request finished")
                print("____________________________________________")
                self.handledLink -= 1
            })
            task.resume()
        }
    }

ViewController.swift

protocol HavingWebView {
    var webView: UIWebView! {get set}
}


class ViewController: UIViewController, HavingWebView {

    @IBOutlet weak var webView: UIWebView!

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        let dm = DownloadManager()
        dm.delegate = self
        dm.myLinks =  ["https://medium.com/the-mission/consider-the-present-and-future-value-of-your-decisions-b20fb72f5e#.a12uiiz11",
                       "https://medium.com/@prianka.kariat/ios-10-notifications-with-attachments-and-much-more-169a7405ddaf#.svymi6230",
                       "https://myerotica.com/jingle-bell-fuck-the-twins-5a48782bf5f1#.mjqz821yo",
                       "https://blog.medium.com/39-reasons-we-wont-soon-forget-2016-154ac95683af#.cmb37i58b",
                       "https://backchannel.com/in-2017-your-coworkers-will-live-everywhere-ae14979b5255#.wmi6hxk9p"]
    }



}