decePubClient/Pages/Index.razor

@page "/"
@page "/home"
@page "/index"
@attribute [Authorize]
@inherits LocalizableComponentBase
<Title>@Localizer[Filter.TimelineType is TimelineType.Federation ? "Federated" : Filter.TimelineType.ToString()]</Title>

@* The feed page, the middle and right of three columns (NavMenu is the left): the feed with a tab per kind of feed,
   and the globe, which follows the posts in view (GlobePanel). Below lg the globe is a banner above the feed, closed by
   default on phones. Pages of older posts load as the end comes near (wwwroot/js/feed.js). Newer ones come through
   PrivaPub's streaming API (StreamingService) for the feeds it streams, and are polled every 45 seconds while the page
   is visible otherwise, or while the stream is down; either way they wait behind the "new" button. A deletion or an edit
   the stream tells is applied at once. *@
<div class="flex flex-col lg:grid lg:grid-cols-[minmax(0,1fr)_minmax(320px,42%)] gap-3 md:gap-4 w-full h-full">

	<aside class="@(Filter.ShowGlobe ? "block" : "hidden") lg:block lg:order-last relative h-56 sm:h-64 lg:h-full flex-none min-h-0 rounded-xl neo-raised neo-xs overflow-hidden">
		<GlobePanel @ref="globe" ScrollContainerId="@ScrollId" Posts="posts" />
	</aside>

	<section class="flex flex-col gap-3 min-h-0 flex-1 lg:h-full">
		<FeedTabs Filter="Filter" Groups="groups" Lists="lists" Stats="FeedStats()" IsComposing="isComposing" OnCompose="() => isComposing = !isComposing"
				  OnChanged="ChangeFeed" />

		<div class="relative flex-1 min-h-0 neo-inset neo-xs rounded-xl">
			<div id="@ScrollId" class="absolute inset-0 overflow-y-auto p-3 md:p-4">
				<div class="flex flex-col gap-4">

					@if (isComposing)
					{
						<div class="p-3 md:p-4 rounded-xl neo-raised neo-xs">
							<Composer GroupId="@(Filter.TimelineType is TimelineType.Groups ? Filter.GroupId : null)" OnPublished="Published" />
						</div>
					}

					@if (pending.Count > 0)
					{
						<DButton Size="DSize.Sm" Color="DColor.Primary" class="self-center sticky top-0 z-10" OnClick="ShowPending">
							<i class="ion-md-arrow-up"></i>
							<span>@Localizer["{0} new", pending.Count]</span>
						</DButton>
					}

					@if (Filter.TimelineType is TimelineType.Nearby && position is null)
					{
						<div class="flex flex-col items-center gap-2 text-sm text-center">
							<p>@Localizer["Nearby shows located posts written within their range of you. It needs this device's position, which goes to PrivaPub only."]</p>
							@if (positionError is { Length: > 0 })
							{
								<p class="text-error">@positionError</p>
							}
							<DButton Size="DSize.Sm" OnClick="AskPosition" Disabled="IsDefaultDisabled">
								<i class="ion-md-locate"></i><span>@Localizer["Use my position"]</span>
							</DButton>
						</div>
					}
					else if (IsLoading)
					{
						<p class="flex w-full items-center justify-center gap-2">
							<DLoading Variant="DLoadingVariant.Dots" LabelText="@Localizer["loading"]" />
							@Localizer["loading"]
						</p>
					}
					else if (loadError is { Length: > 0 })
					{
						<DAlert Color="DAlertColor.Error" Variant="DAlertVariant.Soft" class="text-sm">
							<span>@loadError</span>
							<DButton Size="DSize.Sm" OnClick="Reload">@Localizer["Retry"]</DButton>
						</DAlert>
					}
					else if (posts.Count == 0)
					{
						<p class="w-full text-center text-lg" data-feed-empty>
							<i class="ion-ios-remove-circle-outline"></i> @Localizer["Empty"]
						</p>
					}

					@foreach (var post in posts)
					{
						<Content @key="post.Key" Post="post" FilterIn="FilterIn" OnDeleted="Remove" OnReplied="Replied" OnTag="OpenTag" />
					}

					<div id="@SentinelId" class="flex justify-center min-h-8 text-xs opacity-60">
						@if (isLoadingMore)
						{
							<DLoading Size="DSize.Sm" LabelText="@Localizer["loading"]" />
						}
						else if (!IsLoading && posts.Count > 0 && maxId is null)
						{
							<span>@Localizer["That's all."]</span>
						}
					</div>
				</div>
			</div>
		</div>
	</section>

</div>

@code {
	const string ScrollId = "feed-scroll";
	const string SentinelId = "feed-end";
	static readonly TimeSpan PollInterval = TimeSpan.FromSeconds(45);

	[Inject] ILocalStorageService LocalStorage { get; set; }
	[Inject] IJSRuntime JS { get; set; }
	[Inject] TimelineService TimelineService { get; set; }
	[Inject] GroupService GroupService { get; set; }
	[Inject] ListService ListService { get; set; }
	[Inject] StreamingService Streaming { get; set; }
	[Inject] InstanceService InstanceService { get; set; }
	[Inject] RequestStats RequestStats { get; set; }

	FeedFilter Filter { get; set; } = new();
	List<FeedPost> posts = [];
	List<FeedPost> pending = [];
	List<ViewGroup> groups = [];
	List<MastodonList> lists = [];
	string maxId;
	string minId;
	string loadError;
	bool isLoadingMore;
	bool isComposing;
	(double Latitude, double Longitude)? position;
	string positionError;
	string loadedPersonaId;
	FeedQuery lastQuery;
	DateTime? lastPollAt;
	TimeSpan? lastLoadTook;

	GlobePanel globe;
	IJSObjectReference feedModule;
	DotNetObjectReference<Index> reference;
	PeriodicTimer pollTimer;
	CancellationTokenSource pageCancellation = new();
	CancellationTokenSource loadCancellation;

	protected override async Task OnInitializedAsync()
	{
		Streaming.Received += OnStream;
		Filter = await LocalStorage.GetItemAsync<FeedFilter>(nameof(FeedFilter)) ?? new() { ShowGlobe = !CascadingState.Status.IsMobileMedia() };
		if (Filter.TimelineType is TimelineType.Tag && Filter.Tag is not { Length: > 0 })
			Filter.TimelineType = TimelineType.Home;

		if (CascadingState.IsOffline)
		{
			WhenOnline(Reload);
			StartOnlinePolling();
			IsLoading = false;
			return;
		}

		if (CascadingState.PersonaId is null)
		{
			IsLoading = false;
			return;
		}

		await Reload();
	}

	// The persona changed (NavMenu's switcher): everything on the page belongs to the old one.
	protected override async Task OnParametersSetAsync()
	{
		if (CascadingState.PersonaId is null || CascadingState.PersonaId == loadedPersonaId || IsLoading && loadedPersonaId is null)
			return;
		await Reload();
	}

	protected override async Task OnAfterRenderAsync(bool firstRender)
	{
		await base.OnAfterRenderAsync(firstRender);
		if (!firstRender)
			return;

		reference = DotNetObjectReference.Create(this);
		feedModule = await JS.InvokeAsync<IJSObjectReference>("import", "./js/feed.js");
		await feedModule.InvokeVoidAsync("observeEnd", reference, SentinelId, ScrollId);
		pollTimer = new(PollInterval);
		_ = PollNewer(pageCancellation.Token);
	}

	/// <summary>Which of the persona's filters apply to this feed: home's for home and lists, public's for the shared
	/// feeds, none for the persona's own collections (favourites, bookmarks) and conversations.</summary>
	FilterContext? FilterIn => Filter.TimelineType switch
	{
		TimelineType.Home or TimelineType.Lists => FilterContext.Home,
		TimelineType.Local or TimelineType.Federation or TimelineType.Tag or TimelineType.Nearby or TimelineType.Groups => FilterContext.Public,
		TimelineType.Notifications => FilterContext.Notifications,
		_ => null
	};

	FeedQuery Query => new(Filter.TimelineType, CascadingState.PersonaId, Filter.GroupId, groups.FirstOrDefault(g => g.Id == Filter.GroupId)?.IsCommunity == true,
		Filter.Tag, position?.Latitude, position?.Longitude, Filter.ListId);

	/// <summary>Reads the first page of the current feed again, and the persona's groups.</summary>
	async Task Reload()
	{
		loadCancellation?.Cancel();
		loadCancellation = new();
		var cancellationToken = loadCancellation.Token;

		IsLoading = true;
		loadError = default;
		pending = [];
		posts = [];
		maxId = default;
		minId = default;
		StateHasChanged();

		if (CascadingState.PersonaId != loadedPersonaId)
		{
			// a stream is the persona's: another one opens its own
			await Streaming.Stop();
			groups = await GroupService.List(CascadingState.PersonaId, cancellationToken);
			lists = await ListService.All(cancellationToken);
			loadedPersonaId = CascadingState.PersonaId;
		}
		if (Filter.TimelineType is TimelineType.Groups && groups.All(g => g.Id != Filter.GroupId))
			Filter.GroupId = groups.FirstOrDefault()?.Id;
		if (Filter.TimelineType is TimelineType.Lists && lists.All(l => l.Id != Filter.ListId))
			Filter.ListId = lists.FirstOrDefault()?.Id;
		lastQuery = Query;
		if (Filter.TimelineType is TimelineType.Nearby && position is null)
		{
			IsLoading = false;
			return;
		}

		var started = DateTime.UtcNow;
		var result = await TimelineService.Load(Query, cancellationToken: cancellationToken);
		if (cancellationToken.IsCancellationRequested)
			return;
		lastLoadTook = DateTime.UtcNow - started;
		IsLoading = false;
		if (result.IsInvalid)
		{
			if (result.StatusCode is not 410)
				loadError = result.ErrorMessage;
			return;
		}

		var page = (FeedPage)result.Data;
		posts = page.Posts;
		maxId = page.MaxId;
		minId = page.MinId;
		lastPollAt = DateTime.UtcNow;
		await Streaming.Follow(StreamOf(Filter), cancellationToken);
		StateHasChanged();
		await Locate(posts, cancellationToken);
		if (feedModule is not null)
			await feedModule.InvokeVoidAsync("checkEnd");
	}

	/// <summary>Reads the servers of the posts and places the posts on the globe.</summary>
	async Task Locate(List<FeedPost> located, CancellationToken cancellationToken)
	{
		await InstanceService.Resolve(located.Select(p => p.Host).Append(InstanceService.SelfHost), cancellationToken);
		InstanceService.Locate(located, position);
		StateHasChanged();
	}

	[JSInvokable]
	public async Task NearEnd()
	{
		if (IsLoading || isLoadingMore || maxId is null)
			return;

		isLoadingMore = true;
		StateHasChanged();
		var cancellationToken = loadCancellation?.Token ?? default;
		var result = await TimelineService.Load(Query, maxId: maxId, cancellationToken: cancellationToken);
		isLoadingMore = false;
		if (cancellationToken.IsCancellationRequested)
			return;
		if (result.IsInvalid)
		{
			Toast.AddResponseError(result);
			StateHasChanged();
			return;
		}

		var page = (FeedPage)result.Data;
		var known = posts.Select(p => p.Key).ToHashSet();
		var older = page.Posts.Where(p => known.Add(p.Key)).ToList();
		posts.AddRange(older);
		maxId = older.Count == 0 ? null : page.MaxId;
		StateHasChanged();
		await Locate(older, cancellationToken);
		if (feedModule is not null)
			await feedModule.InvokeVoidAsync("checkEnd");
	}

	/// <summary>Asks for posts newer than the newest shown, while the page is visible; they wait behind the "new" button.</summary>
	async Task PollNewer(CancellationToken cancellationToken)
	{
		try
		{
			while (await pollTimer.WaitForNextTickAsync(cancellationToken))
			{
				if (IsLoading || CascadingState.IsOffline || minId is null || Streaming.IsOpen || Filter.TimelineType is TimelineType.Nearby or TimelineType.Direct
					|| Filter.TimelineType is TimelineType.Groups && groups.FirstOrDefault(g => g.Id == Filter.GroupId)?.IsCommunity != true
					|| !await feedModule.InvokeAsync<bool>("isVisible", cancellationToken))
					continue;

				var query = Query;
				var result = await TimelineService.Load(query, minId: pending.FirstOrDefault()?.CursorId ?? minId, cancellationToken: cancellationToken);
				lastPollAt = DateTime.UtcNow;
				if (result.IsInvalid || query != Query)
					continue;

				var known = posts.Concat(pending).Select(p => p.Key).ToHashSet();
				var newer = ((FeedPage)result.Data).Posts.Where(p => known.Add(p.Key)).ToList();
				if (newer.Count == 0)
					continue;

				pending.InsertRange(0, newer);
				await InvokeAsync(StateHasChanged);
			}
		}
		catch (OperationCanceledException)
		{
		}
		catch (JSDisconnectedException)
		{
		}
		catch (Exception ex)
		{
			await CascadingState.ProcessError(ex, $"{nameof(Index)}.{nameof(PollNewer)}", cancellationToken);
		}
	}

	/// <summary>The stream that tells this feed's new posts, or null for a feed PrivaPub does not stream.</summary>
	static StreamSubscription StreamOf(FeedFilter filter) => filter.TimelineType switch
	{
		TimelineType.Home => new("user"),
		TimelineType.Local => new("public:local"),
		TimelineType.Federation => new("public:remote"),
		TimelineType.Notifications => new("user:notification"),
		TimelineType.Tag when filter.Tag is { Length: > 0 } tag => new("hashtag", Tag: tag),
		TimelineType.Lists when filter.ListId is { Length: > 0 } list => new("list", List: list),
		_ => null
	};

	/// <summary>What the stream tells: a new post or notification waits behind the "new" button; a deletion or an edit is
	/// applied where the post is.</summary>
	async Task OnStream(StreamMessage message)
	{
		switch (message.Event)
		{
			case "update" when message.Status is { } status && Filter.TimelineType is not TimelineType.Notifications:
			case "notification" when message.Notification is not null && Filter.TimelineType is TimelineType.Notifications:
				var post = message.Status is { } s ? FeedPost.Of(s) : FeedPost.Of(message.Notification);
				if (posts.Concat(pending).Any(p => p.Key == post.Key))
					return;
				pending.Insert(0, post);
				break;
			case "delete" when message.DeletedId is { } id:
				posts.RemoveAll(p => p.Key == id || p.Status?.Id == id);
				pending.RemoveAll(p => p.Key == id || p.Status?.Id == id);
				break;
			case "status.update" when message.Status is { } edited:
				foreach (var shown in posts.Concat(pending).Where(p => p.Status?.Id == edited.Id))
					shown.Status = edited;
				break;
			default:
				return;
		}
		await InvokeAsync(StateHasChanged);
	}

	async Task ShowPending()
	{
		var shown = pending;
		pending = [];
		posts.InsertRange(0, shown);
		minId = shown.FirstOrDefault()?.CursorId ?? minId;
		await feedModule.InvokeVoidAsync("scrollToTop", ScrollId);
		await Locate(shown, loadCancellation?.Token ?? default);
	}

	/// <summary>Saves the choices; reloads only when they change what the feed shows (not for the globe's toggle).</summary>
	async Task ChangeFeed(FeedFilter filter)
	{
		await LocalStorage.SetItemAsync(nameof(FeedFilter), Filter);
		if (Query == lastQuery)
			return;
		await Reload();
	}

	async Task OpenTag(string tag)
	{
		Filter.Tag = tag;
		Filter.TimelineType = TimelineType.Tag;
		await ChangeFeed(Filter);
	}

	async Task AskPosition()
	{
		positionError = default;
		var answer = await JS.InvokeAsync<GeoAnswer>("feedPosition");
		if (answer?.Latitude is not { } latitude || answer.Longitude is not { } longitude)
		{
			positionError = Localizer["This device did not give its position: {0}", answer?.Error ?? "?"];
			return;
		}

		position = (latitude, longitude);
		await Reload();
	}

	async Task Published(FeedPost post)
	{
		isComposing = false;
		if (post is null)
		{
			if (Filter.TimelineType is TimelineType.Nearby or TimelineType.Groups)
				await Reload();
			return;
		}

		if (Filter.TimelineType is TimelineType.Home or TimelineType.Local || post.Status?.Visibility == "direct" && Filter.TimelineType is TimelineType.Direct)
		{
			posts.Insert(0, post);
			await Locate([post], loadCancellation?.Token ?? default);
		}
	}

	async Task Replied(FeedPost reply)
	{
		if (reply is null || Filter.TimelineType is not (TimelineType.Home or TimelineType.Local))
			return;
		posts.Insert(0, reply);
		await Locate([reply], loadCancellation?.Token ?? default);
	}

	void Remove(FeedPost post)
	{
		posts.RemoveAll(p => p.Key == post.Key || p.Status?.Id == post.Status?.Id);
	}

	IEnumerable<NerdRow> FeedStats()
	{
		yield return NerdRow.Of(Localizer["items"], posts.Count);
		yield return NerdRow.Of(Localizer["waiting"], pending.Count > 0 ? pending.Count : null);
		yield return NerdRow.Of("min_id", minId);
		yield return NerdRow.Of("max_id", maxId ?? (posts.Count > 0 ? Localizer["end"] : null));
		yield return NerdRow.Of(Localizer["first page"], lastLoadTook is { } took ? NerdRow.Duration(took) : null);
		yield return NerdRow.Of(Localizer["polled"], lastPollAt is { } polled ? NerdRow.Duration(DateTime.UtcNow - polled) + " " + Localizer["ago"] : null);
		yield return NerdRow.Of(Localizer["stream"], Streaming.IsOpen ? Localizer["open"] : Localizer["closed, polling"]);
		yield return NerdRow.Of(Localizer["poll every"], NerdRow.Duration(PollInterval));
		yield return NerdRow.Of(Localizer["placed"], posts.Count > 0 ? $"{posts.Count(p => p.Location is not null)}/{posts.Count}" : null);
		if (RequestStats.Latest(1).FirstOrDefault() is { } last)
		{
			yield return NerdRow.Of(Localizer["last request"], $"{last.Method} {last.Route}");
			yield return NerdRow.Of(Localizer["answer"], $"{last.Status} · {last.DurationMs:0} ms · {NerdRow.Bytes(last.Bytes) ?? "?"}");
			yield return NerdRow.Of("X-RateLimit-Remaining", last.RateLimitRemaining);
		}
	}

	public override async ValueTask DisposeAsync()
	{
		Streaming.Received -= OnStream;
		await Streaming.Stop();
		await pageCancellation.CancelAsync();
		pageCancellation.Dispose();
		loadCancellation?.Cancel();
		pollTimer?.Dispose();
		try
		{
			if (feedModule is not null)
			{
				await feedModule.InvokeVoidAsync("dispose");
				await feedModule.DisposeAsync();
			}
		}
		catch (JSDisconnectedException)
		{
		}
		reference?.Dispose();
		await base.DisposeAsync();
	}

	sealed class GeoAnswer
	{
		public double? Latitude { get; set; }
		public double? Longitude { get; set; }
		public string Error { get; set; }
	}
}