Discord-History-Tracker/app/Desktop/Main/Pages/DownloadsPageModel.cs

using System;
using System.Collections.ObjectModel;
using System.Reactive.Linq;
using System.Threading.Tasks;
using Avalonia.ReactiveUI;
using CommunityToolkit.Mvvm.ComponentModel;
using DHT.Desktop.Common;
using DHT.Desktop.Main.Controls;
using DHT.Server;
using DHT.Server.Data.Aggregations;
using DHT.Server.Data.Filters;
using DHT.Server.Download;
using DHT.Utils.Logging;
using DHT.Utils.Tasks;

namespace DHT.Desktop.Main.Pages;

sealed partial class DownloadsPageModel : ObservableObject, IDisposable {
	private static readonly Log Log = Log.ForType<DownloadsPageModel>();

	[ObservableProperty(Setter = Access.Private)]
	private bool isToggleDownloadButtonEnabled = true;

	public string ToggleDownloadButtonText => IsDownloading ? "Stop Downloading" : "Start Downloading";

	[ObservableProperty(Setter = Access.Private)]
	[NotifyPropertyChangedFor(nameof(IsRetryFailedOnDownloadsButtonEnabled))]
	private bool isRetryingFailedDownloads = false;

	[ObservableProperty(Setter = Access.Private)]
	[NotifyPropertyChangedFor(nameof(IsRetryFailedOnDownloadsButtonEnabled))]
	private bool hasFailedDownloads;

	public bool IsRetryFailedOnDownloadsButtonEnabled => !IsRetryingFailedDownloads && HasFailedDownloads;

	[ObservableProperty(Setter = Access.Private)]
	private string downloadMessage = "";

	public DownloadItemFilterPanelModel FilterModel { get; }

	private readonly StatisticsRow statisticsPending = new ("Pending");
	private readonly StatisticsRow statisticsDownloaded = new ("Downloaded");
	private readonly StatisticsRow statisticsFailed = new ("Failed");
	private readonly StatisticsRow statisticsSkipped = new ("Skipped");

	public ObservableCollection<StatisticsRow> StatisticsRows { get; }

	public bool IsDownloading => state.Downloader.IsDownloading;

	private readonly State state;
	private readonly ThrottledTask<DownloadStatusStatistics> downloadStatisticsTask;
	private readonly IDisposable downloadItemCountSubscription;
	
	private IDisposable? finishedItemsSubscription;
	private DownloadItemFilter? currentDownloadFilter;

	public DownloadsPageModel() : this(State.Dummy) {}

	public DownloadsPageModel(State state) {
		this.state = state;

		FilterModel = new DownloadItemFilterPanelModel(state);
		
		StatisticsRows = [
			statisticsPending,
			statisticsDownloaded,
			statisticsFailed,
			statisticsSkipped
		];

		downloadStatisticsTask = new ThrottledTask<DownloadStatusStatistics>(Log, UpdateStatistics, TaskScheduler.FromCurrentSynchronizationContext());
		downloadItemCountSubscription = state.Db.Downloads.TotalCount.ObserveOn(AvaloniaScheduler.Instance).Subscribe(OnDownloadCountChanged);

		RecomputeDownloadStatistics();
	}

	public void Dispose() {
		finishedItemsSubscription?.Dispose();
		
		downloadItemCountSubscription.Dispose();
		downloadStatisticsTask.Dispose();

		FilterModel.Dispose();
	}

	private void OnDownloadCountChanged(long newDownloadCount) {
		RecomputeDownloadStatistics();
	}

	public async Task OnClickToggleDownload() {
		IsToggleDownloadButtonEnabled = false;

		if (IsDownloading) {
			await state.Downloader.Stop();
			await state.Db.Downloads.MoveDownloadingItemsBackToQueue();

			finishedItemsSubscription?.Dispose();
			finishedItemsSubscription = null;
			
			currentDownloadFilter = null;
		}
		else {
			await state.Db.Downloads.MoveDownloadingItemsBackToQueue();
			
			var finishedItems = await state.Downloader.Start(currentDownloadFilter = FilterModel.CreateFilter());
			finishedItemsSubscription = finishedItems.ObserveOn(AvaloniaScheduler.Instance).Subscribe(OnItemFinished);
		}

		RecomputeDownloadStatistics();

		OnPropertyChanged(nameof(ToggleDownloadButtonText));
		OnPropertyChanged(nameof(IsDownloading));
		IsToggleDownloadButtonEnabled = true;
	}

	private void OnItemFinished(DownloadItem item) {
		RecomputeDownloadStatistics();
	}

	public async Task OnClickRetryFailedDownloads() {
		IsRetryingFailedDownloads = true;

		try {
			await state.Db.Downloads.RetryFailed();
			RecomputeDownloadStatistics();
		} catch (Exception e) {
			Log.Error(e);
		} finally {
			IsRetryingFailedDownloads = false;
		}
	}

	private void RecomputeDownloadStatistics() {
		downloadStatisticsTask.Post(cancellationToken => state.Db.Downloads.GetStatistics(currentDownloadFilter ?? new DownloadItemFilter(), cancellationToken));
	}

	private void UpdateStatistics(DownloadStatusStatistics statusStatistics) {
		statisticsPending.Items = statusStatistics.PendingCount;
		statisticsPending.Size = statusStatistics.PendingTotalSize;
		statisticsPending.HasFilesWithUnknownSize = statusStatistics.PendingWithUnknownSizeCount > 0;

		statisticsDownloaded.Items = statusStatistics.SuccessfulCount;
		statisticsDownloaded.Size = statusStatistics.SuccessfulTotalSize;
		statisticsDownloaded.HasFilesWithUnknownSize = statusStatistics.SuccessfulWithUnknownSizeCount > 0;

		statisticsFailed.Items = statusStatistics.FailedCount;
		statisticsFailed.Size = statusStatistics.FailedTotalSize;
		statisticsFailed.HasFilesWithUnknownSize = statusStatistics.FailedWithUnknownSizeCount > 0;
		
		statisticsSkipped.Items = statusStatistics.SkippedCount;
		statisticsSkipped.Size = statusStatistics.SkippedTotalSize;
		statisticsSkipped.HasFilesWithUnknownSize = statusStatistics.SkippedWithUnknownSizeCount > 0;

		HasFailedDownloads = statusStatistics.FailedCount > 0;
	}

	[ObservableObject]
	public sealed partial class StatisticsRow(string state) {
		public string State { get; } = state;

		[ObservableProperty]
		private int items;

		[ObservableProperty]
		[NotifyPropertyChangedFor(nameof(SizeText))]
		private ulong? size;
		
		[ObservableProperty]
		[NotifyPropertyChangedFor(nameof(SizeText))]
		private bool hasFilesWithUnknownSize;

		public string SizeText {
			get {
				if (size == null) {
					return "-";
				}
				else if (hasFilesWithUnknownSize) {
					return "\u2265 " + BytesValueConverter.Convert(size.Value);
				}
				else {
					return BytesValueConverter.Convert(size.Value);
				}
			}
		}
	}
}