public async Task DeleteAndDownload(List <VkSongModel> toDownload, List <string> toDelete)
        {
            UiSynchronizer.Run(o =>
            {
                var page = (MusicLoaderPage)o.Content;
                if (page == null)
                {
                    return;
                }
                page.LbProgress.Content = "Удаление удаленных песен...";
            });
            var dir = SettingsManager.Get(SettingsRequisites.Directory);

            foreach (var fileName in toDelete)
            {
                File.Delete(Path.Combine(dir, fileName));
            }

            await DownloadSongs(toDownload);

            UiSynchronizer.Run(o =>
            {
                var page = (MusicLoaderPage)o.Content;
                page.LbProgress.Content = "Готово";
                if (page == null)
                {
                    return;
                }
                page.SyncLabels();
            });
        }
        private async Task DownloadBatch(IEnumerable <VkSongModel> batch)
        {
            batch = batch.Take(BatchSize).ToList();
            if (!batch.Any())
            {
                return;
            }
            var jsonContent = "";
            var trying      = 0;

            while (string.IsNullOrEmpty(jsonContent))
            {
                var client  = new RestClient("https://vk.com");
                var request = new RestRequest("al_audio.php", Method.POST);
                request.AddParameter("act", "reload_audio");
                request.AddParameter("al", 1);
                request.AddParameter("ids", string.Join(",", batch.Skip(1).Select(i => i.UniqueId)));

                jsonContent = await SendAlAudioRequest(Sid, request, client);

                if (string.IsNullOrEmpty(jsonContent))
                {
                    trying++;
                    if (trying > 5)
                    {
                        return;
                    }
                    var msg = $"Кажется VK перестал отдавать треки из-за таймаута ({trying}) :( надо подождать 10 сек";
                    UiSynchronizer.Run((o, d) =>
                    {
                        var page = (MusicLoaderPage)o.Content;
                        if (page == null)
                        {
                            return;
                        }
                        page.LbProgress.Content = d;
                    }, msg);
                    await Task.Delay(1000);
                }
            }

            var data = JsonConvert.DeserializeObject <List <object[]> >(jsonContent)
                       .Select(VkSongModel.FromJson)
                       .ToList();

            data.ForEach(x => x.Unmask(Uid));

            var abortSignal = false;

            foreach (var vkSongModel in data)
            {
                if (abortSignal)
                {
                    UiSynchronizer.Run(o =>
                    {
                        var page = (MusicLoaderPage)o.Content;
                        if (page == null)
                        {
                            return;
                        }
                        page.LbProgress.Content = string.Empty;
                        page.ProgressBar.Value  = 0;
                        abortSignal             = page.MarkerToStopDownload;
                    });
                    throw new AbortedException();
                }
                var webClient = new WebClient();
                var filePath  = Path.Combine(Directory, vkSongModel.FileName);
                webClient.DownloadProgressChanged += (sender, args) =>
                {
                    var msg = $"Скачивание {vkSongModel.FileName}";
                    UiSynchronizer.Run((o, d) =>
                    {
                        var page = (MusicLoaderPage)o.Content;
                        if (page == null)
                        {
                            return;
                        }
                        page.LbProgress.Content = d;
                        page.ProgressBar.Value  = args.ProgressPercentage;
                        abortSignal             = page.MarkerToStopDownload;
                    }, msg);
                };
                await webClient.DownloadFileTaskAsync(vkSongModel.Url, filePath);

                UiSynchronizer.Run(o =>
                {
                    var page = (MusicLoaderPage)o.Content;
                    if (page == null)
                    {
                        return;
                    }
                    page.SyncLabels();
                    abortSignal = page.MarkerToStopDownload;
                });
            }
        }