SocialPub/PrivaPub/Infrastructure/Geo/CdnRanges.cs

using MongoDB.Entities;

using PrivaPub.Models.Jobs;

using System.Net;

namespace PrivaPub.Infrastructure.Geo
{
	public interface ICdnRanges
	{
		// the CDN whose published ranges hold the address, or default
		CdnProvider Of(IPAddress address);
		void Replace(CdnRangeSet set);
		Task Load(CancellationToken token);
		// per CDN key: how many ranges are known and when they were downloaded
		IReadOnlyDictionary<string, (int Ranges, DateTime FetchedAt)> Status { get; }
	}

	// The published CDN ranges in memory, rebuilt from the stored CdnRangeSets at start and replaced set by set as
	// CdnUpdater downloads them. A few thousand networks: a linear scan per describe is cheap, and describes are weekly.
	public class CdnRanges : ICdnRanges
	{
		readonly object _gate = new();
		Dictionary<string, (CdnProvider Provider, IPNetwork[] Networks, DateTime FetchedAt)> _sets = new(StringComparer.OrdinalIgnoreCase);

		public IReadOnlyDictionary<string, (int Ranges, DateTime FetchedAt)> Status
		{
			get
			{
				lock (_gate)
					return _sets.ToDictionary(s => s.Key, s => (s.Value.Networks.Length, s.Value.FetchedAt), StringComparer.OrdinalIgnoreCase);
			}
		}

		public CdnProvider Of(IPAddress address)
		{
			if (address == default)
				return default;
			if (address.IsIPv4MappedToIPv6)
				address = address.MapToIPv4();
			Dictionary<string, (CdnProvider Provider, IPNetwork[] Networks, DateTime FetchedAt)> sets;
			lock (_gate)
				sets = _sets;
			foreach (var (provider, networks, _) in sets.Values)
				foreach (var network in networks)
					if (network.BaseAddress.AddressFamily == address.AddressFamily && network.Contains(address))
						return provider;
			return default;
		}

		public void Replace(CdnRangeSet set)
		{
			var provider = CdnCatalog.ByKey(set.Key) ?? new CdnProvider(set.Name, set.Key, Array.Empty<int>(), Array.Empty<CdnList>(), _ => false);
			var networks = set.Ranges.Select(r => IPNetwork.TryParse(r, out var n) ? n : (IPNetwork?)null).Where(n => n != default).Select(n => n!.Value).ToArray();
			lock (_gate)
				_sets = new(_sets, StringComparer.OrdinalIgnoreCase) { [set.Key] = (provider, networks, set.FetchedAt) };
		}

		public async Task Load(CancellationToken token)
		{
			foreach (var set in await DB.Default.Find<CdnRangeSet>().ExecuteAsync(token))
				Replace(set);
		}
	}
}