decePubClient/Services/InstanceService.cs

using System.Text.Json.Nodes;

using Blazored.LocalStorage;

using decePubClient.Extensions;
using decePubClient.Helpers;
using decePubClient.Models;
using decePubClient.Models.Mastodon;

namespace decePubClient.Services
{
	/// <summary>
	/// What PrivaPub knows about the servers the feed shows (/api/privapub/v1/instances, up to 40 at once), cached in
	/// memory and localStorage for a day, and where each feed item is drawn. A post is placed, best first: at its own
	/// place (Pixelfed), at its event's venue, at the reader for a located post, at its author's server (0.1°), or at a
	/// point in the server's country when PrivaPub located it only to a country. A CDN-fronted server has no place: its
	/// posts join their CDN's group. A server's weekly history and a CDN's page are read on demand, once per session.
	/// </summary>
	public class InstanceService(IHttpService httpService, ILocalStorageService localStorage, AppConfiguration appConfiguration, ILoggingService logger)
	{
		const int MaxHostsPerRead = 40;
		const string StorageKey = "ServerInfos";
		static readonly TimeSpan Lifetime = TimeSpan.FromDays(1);
		static readonly TimeSpan UnknownLifetime = TimeSpan.FromHours(1);

		readonly Dictionary<string, ServerInfo> servers = new(StringComparer.OrdinalIgnoreCase);
		readonly Dictionary<string, List<InstanceWeek>> histories = new(StringComparer.OrdinalIgnoreCase);
		readonly Dictionary<string, CdnDetail> cdns = new(StringComparer.OrdinalIgnoreCase);
		bool loaded;
		string selfHost;

		/// <summary>
		/// PrivaPub's own host, the point every arc starts from: the host of the signed-in persona's account (CascadingState
		/// sets it), since the API may be reached under another name; the API's host until then.
		/// </summary>
		public string SelfHost
		{
			get => selfHost ?? appConfiguration.ApiHost;
			set => selfHost = value;
		}

		public ServerInfo Known(string host) => host is not null && servers.TryGetValue(host, out var server) && !server.Unknown ? server : null;

		public async Task<ServerInfo> Self(CancellationToken cancellationToken = default)
		{
			await Resolve([SelfHost], cancellationToken);
			return Known(SelfHost);
		}

		/// <summary>Reads the servers not known yet (or known for too long) from PrivaPub.</summary>
		public async Task Resolve(IEnumerable<string> hosts, CancellationToken cancellationToken = default)
		{
			await Load(cancellationToken);
			var now = DateTime.UtcNow;
			var wanted = hosts.Where(host => host is { Length: > 0 }).Distinct(StringComparer.OrdinalIgnoreCase)
				.Where(host => !servers.TryGetValue(host, out var server) || now - server.FetchedAt > (server.Unknown ? UnknownLifetime : Lifetime))
				.ToList();
			if (wanted.Count == 0)
				return;

			foreach (var chunk in wanted.Chunk(MaxHostsPerRead))
			{
				using var response = await httpService.GetAnon(APIs.PrivaPub.GET_Instances, [.. chunk.Select(host => $"host[]={Uri.EscapeDataString(host)}")],
					cancellationToken: cancellationToken);
				if (!response.IsSuccessStatusCode)
					continue;

				var described = await response.MastodonReadFromJsonAsync<List<InstanceDescription>>(cancellationToken) ?? [];
				foreach (var host in chunk)
					servers[host] = described.FirstOrDefault(d => string.Equals(d.Host, host, StringComparison.OrdinalIgnoreCase)) is { } description
						? ToServerInfo(description, now)
						: new() { Host = host, FetchedAt = now, Unknown = true };
			}
			await Save(cancellationToken);
		}

		public List<InstanceWeek> KnownHistory(string host) => host is not null ? histories.GetValueOrDefault(host) : null;

		public CdnDetail KnownCdn(string key) => key is not null ? cdns.GetValueOrDefault(key) : null;

		/// <summary>The server's weekly snapshots, newest first; empty when PrivaPub has none.</summary>
		public async Task<List<InstanceWeek>> History(string host, CancellationToken cancellationToken = default)
		{
			if (host is null)
				return [];
			if (KnownHistory(host) is { } known)
				return known;

			using var response = await httpService.GetAnon(APIs.PrivaPub.GET_M_InstanceHistory(host), [$"weeks=52"], cancellationToken: cancellationToken);
			var history = response.IsSuccessStatusCode ? await response.MastodonReadFromJsonAsync<List<InstanceWeek>>(cancellationToken) ?? [] : [];
			histories[host] = history;
			return history;
		}

		/// <summary>A CDN's servers and its weeks, or null when PrivaPub does not know it.</summary>
		public async Task<CdnDetail> Cdn(string key, CancellationToken cancellationToken = default)
		{
			if (key is null)
				return null;
			if (KnownCdn(key) is { } known)
				return known;

			using var response = await httpService.GetAnon(APIs.PrivaPub.GET_M_Cdn(key), [$"weeks=12"], cancellationToken: cancellationToken);
			if (!response.IsSuccessStatusCode)
				return null;
			var cdn = await response.MastodonReadFromJsonAsync<CdnDetail>(cancellationToken);
			if (cdn is not null)
				cdns[key] = cdn;
			return cdn;
		}

		/// <summary>Places each post; nearYou is the reader's position, for located posts.</summary>
		public void Locate(IEnumerable<FeedPost> posts, (double Latitude, double Longitude)? nearYou = default)
		{
			foreach (var post in posts)
				post.Location = Locate(post, nearYou);
		}

		FeedLocation Locate(FeedPost post, (double Latitude, double Longitude)? nearYou)
		{
			if (post.Status?.Privapub?.Place is { Latitude: { } placeLatitude, Longitude: { } placeLongitude } place)
				return new(placeLatitude, placeLongitude, LocationSource.Place, JoinLabel(place.Name, place.Country), 1);

			if (post.Status?.Privapub?.Event?.Places.FirstOrDefault(p => p.Latitude is not null && p.Longitude is not null) is { } venue)
				return new(venue.Latitude!.Value, venue.Longitude!.Value, LocationSource.Event, venue.Name ?? venue.Address, 1);

			if (post.Located && nearYou is { } reader)
				return new(reader.Latitude, reader.Longitude, LocationSource.NearYou, null, post.RangeKm ?? 5);

			var geo = Known(post.Host)?.Geo;
			if (geo?.Cdn is { Length: > 0 } cdn)
				return new(0, 0, LocationSource.Cdn, cdn, 0, geo.CdnDomain ?? cdn.ToLowerInvariant(), geo.BeforeCdn);

			if (geo is { Latitude: { } latitude, Longitude: { } longitude })
				return new(latitude, longitude, LocationSource.Server, JoinLabel(geo.City, CountryName(geo.Country)), 11);

			if (CountryPoints.Of(geo?.Country) is { } country)
				return new(country.Latitude, country.Longitude, LocationSource.Country, CountryName(geo.Country), 500);

			return null;
		}

		/// <summary>
		/// The country's English name, or the code when .NET does not know it. Not DisplayName: in the browser it falls back
		/// to the country's own language ("日本").
		/// </summary>
		public static string CountryName(string countryCode)
		{
			if (countryCode is not { Length: 2 })
				return countryCode;
			try
			{
				return new System.Globalization.RegionInfo(countryCode).EnglishName;
			}
			catch (ArgumentException)
			{
				return countryCode;
			}
		}

		static string JoinLabel(params string[] parts) => string.Join(", ", parts.Where(part => !string.IsNullOrWhiteSpace(part)));

		static ServerInfo ToServerInfo(InstanceDescription description, DateTime fetchedAt) => new()
		{
			Host = description.Host,
			Software = description.Software,
			Version = description.Version,
			NodeName = description.NodeName,
			OpenRegistrations = description.OpenRegistrations,
			Users = Number(description.NodeInfo, "usage", "users", "total"),
			ActiveMonth = Number(description.NodeInfo, "usage", "users", "activeMonth"),
			LocalPosts = Number(description.NodeInfo, "usage", "localPosts"),
			Geo = description.Geo,
			ConsecutiveFailures = description.Delivery?.ConsecutiveFailures ?? 0,
			LastSuccessAt = description.Delivery?.LastSuccessAt,
			LastFailureAt = description.Delivery?.LastFailureAt,
			DescribedAt = description.DescribedAt,
			DescriptionError = description.DescriptionError,
			FetchedAt = fetchedAt
		};

		static long? Number(JsonNode node, params string[] path)
		{
			foreach (var step in path)
				node = node is JsonObject obj ? obj[step] : null;
			return node is JsonValue value && value.TryGetValue<long>(out var number) ? number : null;
		}

		async Task Load(CancellationToken cancellationToken)
		{
			if (loaded)
				return;
			loaded = true;
			try
			{
				foreach (var server in await localStorage.GetItemAsync<List<ServerInfo>>(StorageKey, cancellationToken) ?? [])
					servers.TryAdd(server.Host, server);
			}
			catch (Exception ex)
			{
				await logger.ProcessWarning(ex.Message, $"{nameof(InstanceService)}.{nameof(Load)}", cancellationToken);
			}
		}

		async Task Save(CancellationToken cancellationToken)
		{
			try
			{
				var fresh = servers.Values.Where(server => DateTime.UtcNow - server.FetchedAt <= Lifetime).ToList();
				await localStorage.SetItemAsync(StorageKey, fresh, cancellationToken);
			}
			catch (Exception ex)
			{
				await logger.ProcessWarning(ex.Message, $"{nameof(InstanceService)}.{nameof(Save)}", cancellationToken);
			}
		}
	}
}