SocialPub/PrivaPub/Federation/Moderation/DomainBlocks.cs

using MongoDB.Entities;

using PrivaPub.Models.Federation;

namespace PrivaPub.Federation.Moderation
{
	public interface IDomainBlocks
	{
		DomainBlock Find(string host);
		bool IsSuspended(string host);
		Task Reload(CancellationToken token);
	}

	public class DomainBlocks : IDomainBlocks
	{
		static readonly TimeSpan Staleness = TimeSpan.FromMinutes(5);

		readonly ILogger<DomainBlocks> _logger;
		IReadOnlyDictionary<string, DomainBlock> _blocks = new Dictionary<string, DomainBlock>();
		DateTime _loadedAt = DateTime.MinValue;
		int _reloading;

		public DomainBlocks(ILogger<DomainBlocks> logger)
		{
			_logger = logger;
		}

		public static string Normalise(string domain) => domain?.Trim().Trim('.').ToLowerInvariant();

		public DomainBlock Find(string host)
		{
			RefreshIfStale();
			host = Normalise(host);
			var blocks = _blocks;
			while (!string.IsNullOrEmpty(host))
			{
				if (blocks.TryGetValue(host, out var block))
					return block;
				var dot = host.IndexOf('.');
				host = dot < 0 ? default : host[(dot + 1)..];
			}
			return default;
		}

		public bool IsSuspended(string host) => Find(host)?.Severity == DomainBlockSeverity.Suspend;

		public async Task Reload(CancellationToken token)
		{
			var blocks = await DB.Default.Find<DomainBlock>().ExecuteAsync(token);
			_blocks = blocks.Where(b => !string.IsNullOrEmpty(b.Domain))
				.GroupBy(b => Normalise(b.Domain))
				.ToDictionary(g => g.Key, g => g.First());
			_loadedAt = DateTime.UtcNow;
		}

		void RefreshIfStale()
		{
			if (DateTime.UtcNow - _loadedAt < Staleness || Interlocked.Exchange(ref _reloading, 1) == 1)
				return;
			_ = Task.Run(async () =>
			{
				try
				{
					await Reload(CancellationToken.None);
				}
				catch (Exception ex)
				{
					_logger.LogWarning(ex, "Domain blocks could not be reloaded");
				}
				finally
				{
					Interlocked.Exchange(ref _reloading, 0);
				}
			});
		}
	}
}