FoxTube/FoxTube/Classes/DownloadAgent.cs

using System;
using System.Collections.Generic;
using System.IO;
using Windows.Storage;
using FoxTube.Classes;
using Newtonsoft.Json;
using Windows.UI.Popups;

namespace FoxTube.Controls
{
    public class DownloadAgent
    {
        public List<DownloadItem> items = new List<DownloadItem>();
        StorageFolder roaming = ApplicationData.Current.RoamingFolder;
        
        public DownloadAgent()
        {
            Initialize();
            Windows.UI.Core.Preview.SystemNavigationManagerPreview.GetForCurrentView().CloseRequested += (s, a) => QuitPrompt();
        }

        public async void Initialize()
        {
            try
            {
                List<DownloadItemContainer> containers = JsonConvert.DeserializeObject<List<DownloadItemContainer>>(await FileIO.ReadTextAsync(await roaming.GetFileAsync("data.json")));

                foreach (DownloadItemContainer i in containers)
                    try { items.Add(new DownloadItem(i)); }
                    catch (FileNotFoundException) { }
            }
            catch { }
        }

        public void Add(string url)
        {
            items.Add(new DownloadItem(url));
        }

        private void Item_DownloadCanceled(object sender, params object[] e)
        {
            items.Remove(sender as DownloadItem);
        }

        public async void QuitPrompt()
        {
            if(items.Find(x => x.InProgress) != null)
            {
                MessageDialog dialog = new MessageDialog("You have some unfinished downloads. Quitting now will erase all downloaded data. Are you sure to continue?", "Some downloads are still pending");

                dialog.Commands.Add(new UICommand("Yes", async (command) =>
                {
                    foreach (DownloadItem i in items.FindAll(x => x.InProgress))
                        i.Cancel();
                    items.RemoveAll(x => x.InProgress);

                    List<DownloadItemContainer> containers = new List<DownloadItemContainer>();
                    foreach (DownloadItem i in items)
                        containers.Add(i.Container);
                    
                    await FileIO.WriteTextAsync(
                        await roaming.CreateFileAsync("data.json", CreationCollisionOption.ReplaceExisting),
                        JsonConvert.SerializeObject(containers));
                }));
                dialog.Commands.Add(new UICommand("No"));

                dialog.DefaultCommandIndex = 1;
                await dialog.ShowAsync();
            }
        }
    }
}