Radicade/Server/Chat/RecentImageReferences.cs

using System.Collections.Concurrent;

namespace RadicadeServer.API
{
	public static class RecentImageReferences
	{
		public static readonly TimeSpan Window = TimeSpan.FromMinutes(10);

		private sealed record Lookup(long ImageId, DateTime At);

		private static readonly ConcurrentDictionary<long, Lookup> ByPlayer = new();

		public static void Remember(long accountId, long imageId)
			=> Remember(accountId, imageId, DateTime.UtcNow);

		public static void Remember(long accountId, long imageId, DateTime at)
		{
			if (accountId <= 0 || imageId <= 0) return;

			Prune(at);
			ByPlayer[accountId] = new Lookup(imageId, at);
		}

		public static bool TryGet(long accountId, out long imageId)
		{
			imageId = 0;
			if (accountId <= 0) return false;
			if (!ByPlayer.TryGetValue(accountId, out var lookup)) return false;
			if (DateTime.UtcNow - lookup.At > Window) return false;

			imageId = lookup.ImageId;
			return true;
		}

		public static void Clear() => ByPlayer.Clear();

		private static void Prune(DateTime now)
		{
			foreach (var pair in ByPlayer)
			{
				if (now - pair.Value.At > Window)
					ByPlayer.TryRemove(pair.Key, out _);
			}
		}
	}
}