decePubClient/Pages/ExpandMessage.razor

@page "/expand/{statusId}"
@attribute [Authorize]
@inherits LocalizableComponentBase
<Title>@Localizer["Thread"]</Title>

@* A post with its thread (/api/v1/statuses/{id}/context): the posts it answers above, the post, the answers below.
   The cards do their own actions; a reply or a deletion updates the thread here. The persona's thread filters apply
   to the posts around the one it opened, never to that one. Opening a remote thread makes PrivaPub read its replies
   from their servers, so the thread is read twice more, a few seconds later, and what was found joins it. *@
<section class="block relative w-full h-full neo-inset neo-xs rounded-xl">
	<div class="flex flex-col gap-4 p-4 md:p-5 w-full h-full absolute overflow-y-auto">

		<div class="flex items-center gap-2">
			<DButton Size="DSize.Sm" OnClick="Back" title="@Localizer["Back"]">
				<i class="ion-md-arrow-back"></i>
			</DButton>
			<h1 class="font-bold">@Localizer["Thread"]</h1>
		</div>

		@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 (current is null)
		{
			<p class="w-full text-center text-lg">
				<i class="ion-ios-remove-circle-outline"></i> @Localizer["This message doesn't exist."]
			</p>
		}
		else
		{
			@foreach (var post in ancestors)
			{
				<Content @key="post.Key" Post="post" CssContainer="ml-6 w-auto" FilterIn="FilterContext.Thread" OnDeleted="Remove" OnReplied="Replied" OnTag="OpenTag" />
			}

			<Content @key="current.Key" Post="current" Highlighted="true" IncludeExpand="false" OnDeleted="Remove" OnReplied="Replied" OnTag="OpenTag" />

			@foreach (var post in descendants)
			{
				<Content @key="post.Key" Post="post" CssContainer="ml-6 w-auto" FilterIn="FilterContext.Thread" OnDeleted="Remove" OnReplied="Replied" OnTag="OpenTag" />
			}
		}
	</div>
</section>

@code {
	[Inject] StatusService StatusService { get; set; }
	[Inject] InstanceService InstanceService { get; set; }
	[Inject] ILocalStorageService LocalStorage { get; set; }
	[Inject] IJSRuntime JS { get; set; }

	[Parameter] public string StatusId { get; set; }

	// when the thread is read again, after PrivaPub has had time to fetch the replies held on other servers
	static readonly TimeSpan[] Rereads = [TimeSpan.FromSeconds(4), TimeSpan.FromSeconds(15)];

	FeedPost current;
	List<FeedPost> ancestors = [];
	List<FeedPost> descendants = [];
	string loadedId;
	CancellationTokenSource rereading;

	protected override async Task OnParametersSetAsync()
	{
		if (StatusId == loadedId)
			return;
		loadedId = StatusId;

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

		await LoadData();
	}

	async Task LoadData()
	{
		rereading?.Cancel();
		rereading?.Dispose();
		rereading = null;
		IsLoading = true;
		var status = await StatusService.Get(StatusId);
		if (status is null)
		{
			current = null;
			IsLoading = false;
			return;
		}

		var context = await StatusService.Context(status.Id);
		current = FeedPost.Of(status);
		ancestors = [.. (context?.Ancestors ?? []).Select(FeedPost.Of)];
		descendants = [.. (context?.Descendants ?? []).Select(FeedPost.Of)];
		IsLoading = false;

		var all = ancestors.Append(current).Concat(descendants).ToList();
		await InstanceService.Resolve(all.Select(p => p.Host).Append(InstanceService.SelfHost));
		InstanceService.Locate(all);

		if (new[] { current, ancestors.FirstOrDefault() }.Any(p => p is not null && p.Host != InstanceService.SelfHost))
		{
			rereading = new();
			_ = Reread(status.Id, rereading.Token);
		}
	}

	// the answers PrivaPub found since, in the thread's order; the cards already shown stay as they are, and one the
	// thread no longer lists (a reply just made, not yet in it) stays at the end
	async Task Reread(string statusId, CancellationToken cancellationToken)
	{
		foreach (var pause in Rereads)
		{
			try
			{
				await Task.Delay(pause, cancellationToken);
			}
			catch (OperationCanceledException)
			{
				return;
			}
			var context = await StatusService.Context(statusId, cancellationToken);
			if (cancellationToken.IsCancellationRequested || context is null)
				return;
			var shown = descendants.ToDictionary(p => p.Key);
			var found = context.Descendants.Where(s => !shown.ContainsKey(s.Id)).Select(FeedPost.Of).ToList();
			if (found.Count == 0)
				continue;
			var listed = context.Descendants.Select(s => s.Id).ToHashSet();
			descendants = [.. context.Descendants.Select(s => shown.GetValueOrDefault(s.Id) ?? found.First(p => p.Key == s.Id)),
				.. descendants.Where(p => !listed.Contains(p.Key))];
			await InstanceService.Resolve(found.Select(p => p.Host));
			InstanceService.Locate(found);
			await InvokeAsync(StateHasChanged);
		}
	}

	void Remove(FeedPost post)
	{
		if (post.Key == current?.Key)
		{
			current = null;
			return;
		}
		ancestors.RemoveAll(p => p.Key == post.Key);
		descendants.RemoveAll(p => p.Key == post.Key);
	}

	async Task Replied(FeedPost reply)
	{
		if (reply is null)
			return;
		descendants.Add(reply);
		await InstanceService.Resolve([reply.Host]);
		InstanceService.Locate([reply]);
	}

	async Task OpenTag(string tag)
	{
		var filter = await LocalStorage.GetItemAsync<FeedFilter>(nameof(FeedFilter)) ?? new();
		filter.Tag = tag;
		filter.TimelineType = TimelineType.Tag;
		await LocalStorage.SetItemAsync(nameof(FeedFilter), filter);
		Navigation.NavigateTo("");
	}

	async Task Back() => await JS.InvokeVoidAsync("history.back");

	public override async ValueTask DisposeAsync()
	{
		if (rereading is not null)
		{
			await rereading.CancelAsync();
			rereading.Dispose();
		}
		await base.DisposeAsync();
	}
}