Foxnouns.NET/Foxnouns.Backend/Services/Auth/FediverseAuthService.cs

using Foxnouns.Backend.Database;
using Foxnouns.Backend.Database.Models;
using Microsoft.EntityFrameworkCore;
using NodaTime;
using J = System.Text.Json.Serialization.JsonPropertyNameAttribute;

namespace Foxnouns.Backend.Services.Auth;

public partial class FediverseAuthService
{
    private const string NodeInfoRel = "http://nodeinfo.diaspora.software/ns/schema/2.0";

    private readonly ILogger _logger;
    private readonly HttpClient _client;
    private readonly DatabaseContext _db;
    private readonly Config _config;
    private readonly ISnowflakeGenerator _snowflakeGenerator;
    private readonly IClock _clock;

    public FediverseAuthService(
        ILogger logger,
        Config config,
        DatabaseContext db,
        ISnowflakeGenerator snowflakeGenerator,
        IClock clock
    )
    {
        _config = config;
        _db = db;
        _snowflakeGenerator = snowflakeGenerator;
        _clock = clock;
        _logger = logger.ForContext<FediverseAuthService>();
        _client = new HttpClient();
        _client.DefaultRequestHeaders.Remove("User-Agent");
        _client.DefaultRequestHeaders.Remove("Accept");
        _client.DefaultRequestHeaders.Add("User-Agent", $"pronouns.cc/{BuildInfo.Version}");
        _client.DefaultRequestHeaders.Add("Accept", "application/json");
    }

    public async Task<string> GenerateAuthUrlAsync(string instance)
    {
        var app = await GetApplicationAsync(instance);
        return await GenerateAuthUrlAsync(app);
    }

    // thank you, gargron and syuilo, for agreeing on a name for *once* in your lives,
    // and having both mastodon and misskey use "username" in the self user response
    public record FediverseUser(
        [property: J("id")] string Id,
        [property: J("username")] string Username
    );

    public async Task<FediverseApplication> GetApplicationAsync(string instance)
    {
        var app = await _db.FediverseApplications.FirstOrDefaultAsync(a => a.Domain == instance);
        if (app != null)
            return app;

        _logger.Debug("No application for fediverse instance {Instance}, creating it", instance);

        var softwareName = await GetSoftwareNameAsync(instance);

        if (IsMastodonCompatible(softwareName))
        {
            return await CreateMastodonApplicationAsync(instance);
        }

        throw new NotImplementedException();
    }

    private async Task<string> GetSoftwareNameAsync(string instance)
    {
        _logger.Debug("Requesting software name for fediverse instance {Instance}", instance);

        var wellKnownResp = await _client.GetAsync(
            new Uri($"https://{instance}/.well-known/nodeinfo")
        );
        wellKnownResp.EnsureSuccessStatusCode();

        var wellKnown = await wellKnownResp.Content.ReadFromJsonAsync<WellKnownResponse>();
        var nodeInfoUrl = wellKnown?.Links.FirstOrDefault(l => l.Rel == NodeInfoRel)?.Href;
        if (nodeInfoUrl == null)
        {
            throw new FoxnounsError(
                $".well-known/nodeinfo response for instance {instance} was invalid, no nodeinfo link"
            );
        }

        var nodeInfoResp = await _client.GetAsync(nodeInfoUrl);
        nodeInfoResp.EnsureSuccessStatusCode();

        var nodeInfo = await nodeInfoResp.Content.ReadFromJsonAsync<PartialNodeInfo>();
        return nodeInfo?.Software.Name
            ?? throw new FoxnounsError(
                $"Nodeinfo response for instance {instance} was invalid, no software name"
            );
    }

    private async Task<string> GenerateAuthUrlAsync(FediverseApplication app) =>
        app.InstanceType switch
        {
            FediverseInstanceType.MastodonApi => await GenerateMastodonAuthUrlAsync(app),
            FediverseInstanceType.MisskeyApi => throw new NotImplementedException(),
            _ => throw new ArgumentOutOfRangeException(nameof(app), app.InstanceType, null),
        };

    public async Task<FediverseUser> GetRemoteFediverseUserAsync(
        FediverseApplication app,
        string code
    ) =>
        app.InstanceType switch
        {
            FediverseInstanceType.MastodonApi => await GetMastodonUserAsync(app, code),
            FediverseInstanceType.MisskeyApi => throw new NotImplementedException(),
            _ => throw new ArgumentOutOfRangeException(nameof(app), app.InstanceType, null),
        };

    private static readonly string[] MastodonSoftwareNames =
    [
        "mastodon",
        "hometown",
        "akkoma",
        "pleroma",
        "iceshrimp.net",
        "iceshrimp",
        "gotosocial",
        "pixelfed",
    ];

    private static readonly string[] MisskeySoftwareNames =
    [
        "misskey",
        "foundkey",
        "calckey",
        "firefish",
        "sharkey",
    ];

    private static bool IsMastodonCompatible(string softwareName) =>
        MastodonSoftwareNames.Any(n =>
            string.Equals(softwareName, n, StringComparison.InvariantCultureIgnoreCase)
        );

    private static bool IsMisskeyCompatible(string softwareName) =>
        MisskeySoftwareNames.Any(n =>
            string.Equals(softwareName, n, StringComparison.InvariantCultureIgnoreCase)
        );

    private record WellKnownResponse([property: J("links")] WellKnownLink[] Links);

    private record WellKnownLink(
        [property: J("rel")] string Rel,
        [property: J("href")] string Href
    );

    private record PartialNodeInfo([property: J("software")] NodeInfoSoftware Software);

    private record NodeInfoSoftware([property: J("name")] string Name);
}