var cameraSystemState: DJICameraSystemState?
var isPlayback: Bool = false

// My download function
func downloadMediaPhoto(iDs: [String]) {
        print("iDs count: \(iDs.count)")
        let camera = self.fetchCamera()
        camera?.delegate = self
        var images: [Data] = []
        var imageData = Data()

        // 0. show hub
        showDownloadingHub()

        // 1. switch to playback mode
        camera?.setMode(.mediaDownload, withCompletion: { [unowned self] (error) in
            guard error == nil else {
                print("3. \(String(describing: error))")
                Alerts.showAlert("3. \(String(describing: error?.localizedDescription))", completion: nil)
                self.gotoUpLoadingVcIfNeeded()
                return
            }

            var countDownTimeOut = 0
            repeat {
                sleep(1)
                countDownTimeOut += 1
                print("Waiting playback mode")
            } while (self.isPlayback == false && countDownTimeOut < 60)

            if countDownTimeOut >= 60 {
                Alerts.showAlert("Disconnected to Aircraft!", completion: nil)
                self.hideDownloadingHub()
                camera?.setMode(.shootPhoto, withCompletion: nil)
                self.gotoUpLoadingVcIfNeeded()
            }

            runOnGlobalThread {

                let downloadGroup = DispatchGroup()

                // 3. check selected file
                for (index, id) in iDs.enumerated() {
                    var isDownloadFile = true

                    // 4. downloadSelectedFile
                    camera?.playbackManager?.downloadSelectedFiles(preparation: { (fileName, fileType, fileSize, skip) in
                        print("fileName: \(String(describing: fileName)) | fileType: \(fileType) | fileSize: \(fileSize) | skip: \(skip)")
                        imageData = Data()

                    }, process: { (data, _) in
                        if let data = data {
                            imageData.append(data)
                        }
                    }, fileCompletion: {
                        images.append(imageData)
                        DispatchQueue.global(qos: DispatchQoS.QoSClass.default).async {
                            downloadGroup.enter()
                            self.saveImage(imageData: imageData, id: id, fullRes: true)
                            downloadGroup.leave()
                        }

                    }, overallCompletion: { (error) in
                        print("4. \(String(describing: error))")
                        if error != nil {
                            Alerts.showAlert("4. \(String(describing: error?.localizedDescription))", completion: nil)
                        }

                        if index < iDs.count - 1 {
                            camera?.playbackManager?.goToPreviousSinglePreviewPage()
                            isDownloadFile = false
                        } else if index == iDs.count - 1 {
                            isDownloadFile = false
                        }
                    })

                    repeat {
                        sleep(1)
                    } while (isDownloadFile)
                }

                downloadGroup.notify(queue: DispatchQueue.main) {
                    self.hideDownloadingHub()
                    camera?.setMode(.shootPhoto, withCompletion: nil)
                    self.gotoUpLoadingVcIfNeeded()
                }
            }
        })
    }

// MARK: - DJICameraDelegate
extension StreamingVC: DJICameraDelegate {
    func camera(_ camera: DJICamera, didUpdate systemState: DJICameraSystemState) {
        self.cameraSystemState = systemState
        isPlayback = (systemState.mode == .playback) || (systemState.mode == .mediaDownload)
    }
}