Iceshrimp.NET/Iceshrimp.Backend/Core/Services/UserProfileMentionsResolver.cs

using System.Diagnostics.CodeAnalysis;
using System.Runtime.CompilerServices;
using Iceshrimp.Backend.Core.Configuration;
using Iceshrimp.Backend.Core.Database.Tables;
using Iceshrimp.Backend.Core.Extensions;
using Iceshrimp.Backend.Core.Federation.ActivityStreams.Types;
using Iceshrimp.Backend.Core.Helpers.LibMfm.Conversion;
using Iceshrimp.MfmSharp;
using Microsoft.Extensions.Options;
using static Iceshrimp.Backend.Core.Federation.ActivityPub.UserResolver;

namespace Iceshrimp.Backend.Core.Services;

using MentionTuple = (List<Note.MentionedUser> mentions,
	Dictionary<(string usernameLower, string webDomain), string> splitDomainMapping);

public class UserProfileMentionsResolver(
	ActivityPub.UserResolver userResolver,
	IOptions<Config.InstanceSection> config
) : IScopedService
{
	public async Task<MentionTuple> ResolveMentionsAsync(ASActor actor, string? host)
	{
		var fields = actor.Attachments?.OfType<ASField>()
		                  .Where(p => p is { Name: not null, Value: not null })
		                  .ToList()
		             ?? [];

		if (fields is not { Count: > 0 } && (actor.MkSummary ?? actor.Summary) == null) return ([], []);
		var parsedFields = fields.SelectMany<ASField, string?>(p => [p.Name, p.Value])
		                         .Select(MfmConverter.ExtractMentionsFromHtml);

		var parsedBio = actor.MkSummary == null ? MfmConverter.ExtractMentionsFromHtml(actor.Summary) : [];

		var userUris     = parsedFields.Prepend(parsedBio).SelectMany(p => p).ToList();
		var mentionNodes = new List<MfmMentionNode>();

		if (actor.MkSummary != null)
		{
			var nodes = MfmParser.Parse(actor.MkSummary.ReplaceLineEndings("\n"));
			mentionNodes = EnumerateMentions(nodes);
		}

		var users = await mentionNodes
		                  .DistinctBy(p => p.Acct)
		                  .Select(p => userResolver.ResolveOrNullAsync(GetQuery(p.User, p.Host ?? host),
		                                                               ResolveFlags.Acct))
		                  .AwaitAllNoConcurrencyAsync();

		users.AddRange(await userUris
		                     .Distinct()
		                     .Select(p => userResolver.ResolveOrNullAsync(p, EnforceUriFlags))
		                     .AwaitAllNoConcurrencyAsync());

		var mentions = users.NotNull()
		                    .DistinctBy(p => p.Id)
		                    .Select(p => new Note.MentionedUser
		                    {
			                    Host     = p.Host,
			                    Uri      = p.Uri ?? p.GetPublicUri(config.Value),
			                    Url      = p.IsRemoteUser ? p.UserProfile?.Url : p.GetPublicUrl(config.Value),
			                    Username = p.Username
		                    })
		                    .ToList();

		var splitDomainMapping = users.Where(p => p is { IsRemoteUser: true, Uri: not null })
		                              .Cast<User>()
		                              .Where(p => new Uri(p.Uri!).Host != p.Host)
		                              .DistinctBy(p => p.Host)
		                              .ToDictionary(p => (p.UsernameLower, new Uri(p.Uri!).Host), p => p.Host!);

		return (mentions, splitDomainMapping);
	}

	public async Task<List<Note.MentionedUser>> ResolveMentionsAsync(
		UserProfile.Field[]? fields, string? bio, string? host
	)
	{
		if (fields is not { Length: > 0 } && bio == null) return [];
		var input = (fields ?? [])
		            .SelectMany<UserProfile.Field, string>(p => [p.Name, p.Value])
		            .Prepend(bio)
		            .Where(p => p != null)
		            .Cast<string>()
		            .ToList();

		var nodes        = input.SelectMany(p => MfmParser.Parse(p.ReplaceLineEndings("\n"))).ToArray();
		var mentionNodes = EnumerateMentions(nodes);
		var users = await mentionNodes
		                  .DistinctBy(p => p.Acct)
		                  .Select(p => userResolver.ResolveOrNullAsync(GetQuery(p.User, p.Host ?? host),
		                                                               ResolveFlags.Acct))
		                  .AwaitAllNoConcurrencyAsync();

		return users.NotNull()
		            .DistinctBy(p => p.Id)
		            .Select(p => new Note.MentionedUser
		            {
			            Host     = p.Host,
			            Uri      = p.Uri ?? p.GetPublicUri(config.Value),
			            Url      = p.IsRemoteUser ? p.UserProfile?.Url : p.GetPublicUrl(config.Value),
			            Username = p.Username
		            })
		            .ToList();
	}

	[SuppressMessage("ReSharper", "ReturnTypeCanBeEnumerable.Local",
	                 Justification = "Roslyn inspection says this hurts performance")]
	private static List<MfmMentionNode> EnumerateMentions(Span<IMfmNode> nodes)
	{
		var list = new List<MfmMentionNode>();

		foreach (var node in nodes)
		{
			if (node is MfmMentionNode mention)
				list.Add(mention);
			else
				list.AddRange(EnumerateMentions(node.Children));
		}

		return list;
	}
	
	[SuppressMessage("ReSharper", "ReturnTypeCanBeEnumerable.Local",
	                 Justification = "Roslyn inspection says this hurts performance")]
	[OverloadResolutionPriority(1)]
	private static List<MfmMentionNode> EnumerateMentions(Span<IMfmInlineNode> nodes)
	{
		var list = new List<MfmMentionNode>();

		foreach (var node in nodes)
		{
			if (node is MfmMentionNode mention)
				list.Add(mention);
			else
				list.AddRange(EnumerateMentions(node.Children));
		}

		return list;
	}
}