decePubClient/LayerComponents/LocalizableComponentBase.cs

using decePubClient.Services;

using Microsoft.AspNetCore.Components;

namespace decePubClient.LayerComponents
{
	/// <summary>
	/// Base of every page and app component (b2b.next's WidmannComponentBase). It gives them the cascading state, the
	/// localizer, navigation and toasts, the loading flag and the disable rule, and the offline helpers: a page that
	/// finds the app offline registers its fetch with WhenOnline, starts StartOnlinePolling and stops loading; the
	/// job runs once when the app is back online.
	/// </summary>
	public class LocalizableComponentBase : ComponentBase, IAsyncDisposable
	{
		[CascadingParameter] protected CascadingState CascadingState { get; set; }
		[Inject] public CoalescingStringLocalizer Localizer { get; set; }
		[Inject] protected NavigationManager Navigation { get; set; }
		[Inject] protected ToastService Toast { get; set; }

		/// <summary>Work to run once after the next render, e.g. JS interop that needs the rendered DOM.</summary>
		protected List<Func<Task>> AfterRenderAsyncJobs = [];

		/// <summary>True until the component's first load completes; set it to false at the end of OnInitializedAsync.</summary>
		protected bool IsLoading { get; set; } = true;

		/// <summary>What every Disabled= binding starts from: loading, or no connection.</summary>
		protected bool IsDefaultDisabled => IsLoading || CascadingState.IsOffline;

		readonly List<Func<Task>> onOnlineJobs = [];
		PeriodicTimer pollingTimer;
		CancellationTokenSource pollingCancellation;
		bool disposed;

		protected override async Task OnAfterRenderAsync(bool firstRender)
		{
			if (AfterRenderAsyncJobs.Count == 0)
				return;

			var jobs = AfterRenderAsyncJobs.ToList();
			AfterRenderAsyncJobs.Clear();
			foreach (var job in jobs)
				await job();
		}

		/// <summary>Runs the job once, the next time the app is online (needs StartOnlinePolling).</summary>
		protected void WhenOnline(Func<Task> job) => onOnlineJobs.Add(job);

		/// <summary>Checks every interval (10 seconds by default) whether the app is back online to run the WhenOnline jobs.</summary>
		protected void StartOnlinePolling(TimeSpan? interval = null)
		{
			if (pollingTimer is not null)
				return;

			pollingCancellation = new();
			pollingTimer = new(interval ?? TimeSpan.FromSeconds(10));
			_ = PollOnline(pollingCancellation.Token);
		}

		async Task PollOnline(CancellationToken cancellationToken)
		{
			try
			{
				while (await pollingTimer.WaitForNextTickAsync(cancellationToken))
				{
					if (CascadingState.IsOffline || onOnlineJobs.Count == 0)
						continue;

					var jobs = onOnlineJobs.ToList();
					onOnlineJobs.Clear();
					foreach (var job in jobs)
					{
						try
						{
							await InvokeAsync(job);
						}
						catch (Exception ex)
						{
							await CascadingState.ProcessError(ex, $"{GetType().Name}.{nameof(PollOnline)}", cancellationToken);
						}
					}

					await InvokeAsync(StateHasChanged);
				}
			}
			catch (OperationCanceledException)
			{
			}
		}

		public virtual async ValueTask DisposeAsync()
		{
			if (disposed)
				return;

			disposed = true;
			if (pollingCancellation is not null)
			{
				await pollingCancellation.CancelAsync();
				pollingCancellation.Dispose();
			}

			pollingTimer?.Dispose();
			onOnlineJobs.Clear();
			GC.SuppressFinalize(this);
		}
	}
}