class FileUploaderManager:NSObject
{
    static let shared = FileUploaderManager()

    fileprivate var operations = [Int: AsyncOperation]()

    lazy var session: URLSession = {
        let configuration = URLSessionConfiguration.background(withIdentifier: "bla bla bla")
        configuration.isDiscretionary = false
        configuration.sessionSendsLaunchEvents = true
        //configuration.shouldUseExtendedBackgroundIdleMode = false

        return URLSession(configuration: configuration, delegate: sessionDelegate, delegateQueue: nil)
    }()

    private let queue: OperationQueue =
    {
            let _queue = OperationQueue()
            _queue.maxConcurrentOperationCount = 1
            return _queue
     }()


    var handlers:[String:(() -> Void)?] = [:]


    private override init()
    {
        super.init()
    }
}


extension FileUploaderManager {

    func addUploadable(content:FileContent)
    {
        DispatchQueue.global(qos: .background).async
        {
            self.prepare(content)
       }
    }

    private func prepare(_ content:FileContent)
    {

        let step1Operation = startOperation(content, session)
        let chunksOperation = chunksOperation(content, session, dependencies:step1Operation)
        let commit = lastOperation(content, client, dependencies:chunksOperation)
    }

}


extension FileUploaderManager
{
    @discardableResult
    private func startOperation(_ content:FileContent,_ session:UrlSession) -> AsyncOperation {
        let operation = FirstOperation(...)
        queue.addOperation(operation)
        return operation
    }
}
extension FileUploaderManager
{

    @discardableResult
    private func chunksOperation(_ content:FileContent,_ session:UrlSession _ dependencies:AsyncOperation?) -> [AsyncOperation]
    {
        var all:[AsyncOperation] = []
        content.chunks.forEach { chunk in
            let operation = ChunkOperation(--)
            queue.addOperation(operation)
            all.append(operation)
        }

        return chunks
    }
}


extension FileUploaderManager
{
    @discardableResult
    private func lastOperation(_ content:FileContent,_ session:UrlSession, _ dependencies:[AsyncOperation]?) -> AsyncOperation?
    {
        let last  = LastOperation(....)

        dependencies?.forEach { op in
            last.addDependency(op)
        }

        queue.addOperation(last)

        return commit
    }

}


extension FileUploaderManager :URLSessionDataDelegate {

    func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: Error?) {..}


    func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive response: URLResponse, completionHandler: @escaping (URLSession.ResponseDisposition) -> Void)
    {..}

    func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive data: Data) {... }
}


extension FileUploaderManager: URLSessionDelegate
{
    func urlSessionDidFinishEvents(forBackgroundURLSession session: URLSession) {

	
        DispatchQueue.main.async { [weak self] in
            guard let handler = app[session.configuration.identifier] else {
                    return
            }

            handler?()
      }
    }
}