decePubClient/Services/OverlayService.cs

using decePubClient.Components.Daisy;

namespace decePubClient.Services
{
	/// <summary>
	/// The overlays open now, newest last (IDOverlayHost): MainLayout closes the newest when the Back button is pressed
	/// while one is open, and all of them when the app goes elsewhere.
	/// </summary>
	public class OverlayService : IDOverlayHost
	{
		readonly List<Entry> open = [];

		public bool HasOpen
		{
			get
			{
				lock (open)
					return open.Count > 0;
			}
		}

		public IDisposable Open(Func<Task> close)
		{
			var entry = new Entry(this, close);
			lock (open)
				open.Add(entry);
			return entry;
		}

		public async Task CloseTop(CancellationToken cancellationToken = default)
		{
			var top = default(Entry);
			lock (open)
				top = open.LastOrDefault();
			if (top is null)
				return;
			top.Dispose();
			await top.Close();
		}

		public async Task CloseAll(CancellationToken cancellationToken = default)
		{
			var all = default(Entry[]);
			lock (open)
			{
				all = [.. open];
				open.Clear();
			}
			foreach (var entry in all.Reverse())
				await entry.Close();
		}

		sealed class Entry(OverlayService owner, Func<Task> close) : IDisposable
		{
			public Func<Task> Close { get; } = close;

			public void Dispose()
			{
				lock (owner.open)
					owner.open.Remove(this);
			}
		}
	}
}