Swarm/DysonNetwork.Sphere/ActivityPub/ActivityPubActivityHandler.cs

using DysonNetwork.Shared.Models;
using Microsoft.EntityFrameworkCore;
using NodaTime;
using System.Text.Json;
using DysonNetwork.Shared.Proto;
using ContentMention = DysonNetwork.Shared.Models.ContentMention;
using PostContentType = DysonNetwork.Shared.Models.PostContentType;
using PostReactionAttitude = DysonNetwork.Shared.Models.PostReactionAttitude;
using PostType = DysonNetwork.Shared.Models.PostType;
using PostVisibility = DysonNetwork.Shared.Models.PostVisibility;

namespace DysonNetwork.Sphere.ActivityPub;

public class ActivityPubActivityHandler(
    AppDatabase db,
    ActivityPubSignatureService signatureService,
    ActivityPubDeliveryService deliveryService,
    ActivityPubDiscoveryService discoveryService,
    ILogger<ActivityPubActivityHandler> logger,
    IConfiguration configuration
)
{
    private string Domain => configuration["ActivityPub:Domain"] ?? "localhost";

    private async Task<SnPost?> GetPostByUriAsync(string objectUri)
    {
        var uri = new Uri(objectUri);
        var domain = uri.Host;

        // Remote post
        if (domain != Domain) return await db.Posts.FirstOrDefaultAsync(c => c.FediverseUri == objectUri);

        // Local post, extract ID from path like /posts/{guid}
        var path = uri.AbsolutePath.Trim('/');
        var segments = path.Split('/');
        if (segments is not [.., "posts", _]) return null;
        var idStr = segments[^1];
        if (Guid.TryParse(idStr, out var id))
        {
            return await db.Posts.FirstOrDefaultAsync(p => p.Id == id);
        }

        return null;
    }

    public async Task<bool> HandleIncomingActivityAsync(
        HttpContext context,
        string username,
        Dictionary<string, object> activity
    )
    {
        logger.LogInformation("Incoming activity request. Username: {Username}, Path: {Path}",
            username, context.Request.Path);

        var activityType = activity.GetValueOrDefault("type")?.ToString();
        var activityId = activity.GetValueOrDefault("id")?.ToString();
        var actor = activity.GetValueOrDefault("actor")?.ToString();

        logger.LogInformation("Activity details - Type: {Type}, ID: {Id}, Actor: {Actor}",
            activityType, activityId, actor);

        if (!signatureService.VerifyIncomingRequest(context, out var actorUri))
        {
            logger.LogWarning("Failed to verify signature for incoming activity. Type: {Type}, From: {Actor}",
                activityType, actor);
            return false;
        }

        if (string.IsNullOrEmpty(actorUri))
            return false;

        logger.LogInformation("Signature verified successfully. Handling {Type} from {ActorUri}",
            activityType, actorUri);

        try
        {
            switch (activityType)
            {
                case "Follow":
                    return await HandleFollowAsync(actorUri, activity);
                case "Accept":
                    return await HandleAcceptAsync(actorUri, activity);
                case "Reject":
                    return await HandleRejectAsync(actorUri, activity);
                case "Undo":
                    return await HandleUndoAsync(actorUri, activity);
                case "Create":
                    return await HandleCreateAsync(actorUri, activity);
                case "Like":
                    return await HandleLikeAsync(actorUri, activity);
                case "Announce":
                    return await HandleAnnounceAsync(actorUri, activity);
                case "Delete":
                    return await HandleDeleteAsync(actorUri, activity);
                case "Update":
                    return await HandleUpdateAsync(actorUri, activity);
                default:
                    logger.LogWarning("Unsupported activity type: {Type}. Full activity: {Activity}",
                        activityType, JsonSerializer.Serialize(activity));
                    return false;
            }
        }
        catch (InvalidOperationException err)
        {
            logger.LogError("Failed to handle activity: {Type}, due to {Message}. Full activity: {Activity}",
                activityType, err.Message, JsonSerializer.Serialize(activity));
            return false;
        }
    }

    private async Task<bool> HandleFollowAsync(string actorUri, Dictionary<string, object> activity)
    {
        var objectUri = activity.GetValueOrDefault("object")?.ToString();
        var activityId = activity.GetValueOrDefault("id")?.ToString();

        logger.LogInformation("Handling Follow. Actor: {ActorUri}, Target: {ObjectUri}, ActivityId: {Id}",
            actorUri, objectUri, activityId);

        if (string.IsNullOrEmpty(objectUri))
        {
            logger.LogWarning("Follow activity missing object field");
            return false;
        }

        var actor = await GetOrCreateActorAsync(actorUri);
        // This might be fail, but we assume it works great.
        var targetActor = await GetOrCreateActorAsync(objectUri);

        var existingRelationship = await db.FediverseRelationships
            .FirstOrDefaultAsync(r =>
                r.ActorId == actor.Id &&
                r.TargetActorId == targetActor.Id);

        switch (existingRelationship)
        {
            case { State: RelationshipState.Accepted }:
                logger.LogInformation(
                    "Follow relationship already exists and is accepted. ActorId: {ActorId}, TargetId: {TargetId}",
                    actor.Id, targetActor.Id);
                return true;
            case null:
                existingRelationship = new SnFediverseRelationship
                {
                    ActorId = actor.Id,
                    TargetActorId = targetActor.Id,
                    State = RelationshipState.Accepted,
                    FollowedBackAt = SystemClock.Instance.GetCurrentInstant()
                };
                db.FediverseRelationships.Add(existingRelationship);
                logger.LogInformation(
                    "Created new follow relationship. ActorId: {ActorId}, TargetActorId: {TargetId}",
                    actor.Id, targetActor.Id);
                break;
            default:
                existingRelationship.State = RelationshipState.Accepted;
                existingRelationship.FollowedBackAt = SystemClock.Instance.GetCurrentInstant();
                logger.LogInformation("Updating existing relationship. CurrentState: {State}, NewState: Accepted",
                    existingRelationship.State);
                break;
        }

        await db.SaveChangesAsync();

        await deliveryService.SendAcceptActivityAsync(
            targetActor,
            actorUri,
            activityId ?? ""
        );

        logger.LogInformation("Handled follow from {Actor} to {Target}. RelationshipState: Accepted",
            actorUri, objectUri);
        return true;
    }

    private async Task<bool> HandleAcceptAsync(string actorUri, Dictionary<string, object> activity)
    {
        var objectUri = activity.GetValueOrDefault("object")?.ToString();
        if (string.IsNullOrEmpty(objectUri))
            return false;

        var actor = await GetOrCreateActorAsync(actorUri);

        var relationship = await db.FediverseRelationships
            .Include(r => r.Actor)
            .Include(r => r.TargetActor)
            .FirstOrDefaultAsync(r =>
                r.TargetActorId == actor.Id);

        if (relationship == null)
        {
            // Assume objectUri is the local actor URI that was followed
            var localActor = await db.FediverseActors.FirstOrDefaultAsync(a => a.Uri == objectUri);
            if (localActor == null)
            {
                logger.LogWarning("Local actor not found for accept object: {ObjectUri}", objectUri);
                return false;
            }

            relationship = new SnFediverseRelationship
            {
                ActorId = localActor.Id,
                TargetActorId = actor.Id,
                State = RelationshipState.Accepted,
                FollowedAt = SystemClock.Instance.GetCurrentInstant()
            };
            db.FediverseRelationships.Add(relationship);
        }
        else
        {
            relationship.State = RelationshipState.Accepted;
            relationship.FollowedAt = SystemClock.Instance.GetCurrentInstant();
        }

        await db.SaveChangesAsync();

        logger.LogInformation("Handled accept from {Actor}", actorUri);
        return true;
    }

    private async Task<bool> HandleRejectAsync(string actorUri, Dictionary<string, object> activity)
    {
        var objectUri = activity.GetValueOrDefault("object")?.ToString();
        if (string.IsNullOrEmpty(objectUri))
            return false;

        var actor = await GetOrCreateActorAsync(actorUri);

        var relationship = await db.FediverseRelationships
            .FirstOrDefaultAsync(r =>
                r.TargetActorId == actor.Id);

        if (relationship == null)
        {
            logger.LogWarning("No relationship found for reject");
            return false;
        }

        relationship.State = RelationshipState.Rejected;
        relationship.RejectReason = "Remote rejected follow";

        await db.SaveChangesAsync();

        logger.LogInformation("Handled reject from {Actor}", actorUri);
        return true;
    }

    private async Task<bool> HandleUndoAsync(string actorUri, Dictionary<string, object> activity)
    {
        var objectValue = activity.GetValueOrDefault("object");

        if (objectValue is not Dictionary<string, object> objectDict)
        {
            logger.LogWarning("Unable undo operation, no object found... {Object}", JsonSerializer.Serialize(activity));
            return false;
        }
        
        var objectType = objectDict.GetValueOrDefault("type")?.ToString();
        return objectType switch
        {
            "Follow" => await UndoFollowAsync(actorUri, objectDict.GetValueOrDefault("object")?.ToString()),
            "Like" => await UndoLikeAsync(actorUri, objectDict.GetValueOrDefault("object")?.ToString()),
            "Announce" => await UndoAnnounceAsync(actorUri, objectDict.GetValueOrDefault("object")?.ToString()),
            _ => throw new InvalidOperationException($"Unhandled undo operation for {objectType}")
        };
    }

    private async Task<bool> HandleCreateAsync(string actorUri, Dictionary<string, object> activity)
    {
        var objectValue = activity.GetValueOrDefault("object");
        if (objectValue is not Dictionary<string, object> objectDict)
            return false;

        var objectType = objectDict.GetValueOrDefault("type")?.ToString();
        if (objectType != "Note" && objectType != "Article")
        {
            logger.LogInformation("Skipping non-note content type: {Type}", objectType);
            return true;
        }

        var actor = await GetOrCreateActorAsync(actorUri);

        var contentUri = objectDict.GetValueOrDefault("id")?.ToString();
        if (string.IsNullOrEmpty(contentUri))
            return false;

        var existingContent = await db.Posts
            .FirstOrDefaultAsync(c => c.FediverseUri == contentUri);

        if (existingContent != null)
        {
            logger.LogInformation("Content already exists: {Uri}", contentUri);
            return true;
        }

        var content = new SnPost
        {
            FediverseUri = contentUri,
            FediverseType = objectType == "Article"
                ? FediverseContentType.FediverseArticle
                : FediverseContentType.FediverseNote,
            Title = objectDict.GetValueOrDefault("name")?.ToString(),
            Description = objectDict.GetValueOrDefault("summary")?.ToString(),
            Content = objectDict.GetValueOrDefault("content")?.ToString(),
            ContentType = objectDict.GetValueOrDefault("contentMap") != null
                ? PostContentType.Html
                : PostContentType.Markdown,
            PublishedAt = ParseInstant(objectDict.GetValueOrDefault("published")),
            EditedAt = ParseInstant(objectDict.GetValueOrDefault("updated")),
            ActorId = actor.Id,
            Language = objectDict.GetValueOrDefault("language")?.ToString(),
            Mentions = ParseMentions(objectDict.GetValueOrDefault("tag")),
            Attachments = ParseAttachments(objectDict.GetValueOrDefault("attachment")) ?? [],
            Type = objectType == "Article" ? PostType.Article : PostType.Moment,
            Visibility = PostVisibility.Public,
            Metadata = BuildMetadataFromActivity(objectDict)
        };

        db.Posts.Add(content);
        await db.SaveChangesAsync();

        logger.LogInformation("Created federated content: {Uri}", contentUri);
        return true;
    }

    private async Task<bool> HandleLikeAsync(string actorUri, Dictionary<string, object> activity)
    {
        var objectUri = activity.GetValueOrDefault("object")?.ToString();
        if (string.IsNullOrEmpty(objectUri))
            return false;

        var actor = await GetOrCreateActorAsync(actorUri);
        var content = await GetPostByUriAsync(objectUri);

        if (content == null)
        {
            logger.LogWarning("Content not found for like: {Uri}", objectUri);
            return false;
        }

        var existingReaction = await db.PostReactions
            .FirstOrDefaultAsync(r =>
                r.ActorId == actor.Id &&
                r.PostId == content.Id &&
                r.Symbol == "thumb_up");

        if (existingReaction != null)
        {
            logger.LogInformation("Like already exists");
            return true;
        }

        var reaction = new SnPostReaction
        {
            FediverseUri = activity.GetValueOrDefault("id")?.ToString() ?? Guid.NewGuid().ToString(),
            Symbol = "thumb_up",
            Attitude = PostReactionAttitude.Positive,
            IsLocal = false,
            PostId = content.Id,
            ActorId = actor.Id,
            Actor = actor,
            CreatedAt = SystemClock.Instance.GetCurrentInstant(),
            UpdatedAt = SystemClock.Instance.GetCurrentInstant()
        };

        db.PostReactions.Add(reaction);
        content.Upvotes++;

        await db.SaveChangesAsync();

        logger.LogInformation("Handled like from {Actor}", actorUri);
        return true;
    }

    private async Task<bool> HandleAnnounceAsync(string actorUri, Dictionary<string, object> activity)
    {
        var objectUri = activity.GetValueOrDefault("object")?.ToString();
        if (string.IsNullOrEmpty(objectUri))
            return false;

        var actor = await GetOrCreateActorAsync(actorUri);
        var content = await GetPostByUriAsync(objectUri);

        if (content != null)
        {
            content.BoostCount++;
            await db.SaveChangesAsync();
        }

        logger.LogInformation("Handled announce from {Actor}", actorUri);
        return true;
    }

    private async Task<bool> HandleDeleteAsync(string actorUri, Dictionary<string, object> activity)
    {
        var objectUri = activity.GetValueOrDefault("object")?.ToString();
        if (string.IsNullOrEmpty(objectUri))
            return false;

        var content = await GetPostByUriAsync(objectUri);

        if (content == null) return true;
        content.DeletedAt = SystemClock.Instance.GetCurrentInstant();
        await db.SaveChangesAsync();
        logger.LogInformation("Deleted federated content: {Uri}", objectUri);

        return true;
    }

    private async Task<bool> HandleUpdateAsync(string actorUri, Dictionary<string, object> activity)
    {
        var objectUri = activity.GetValueOrDefault("object")?.ToString();
        if (string.IsNullOrEmpty(objectUri))
            return false;

        var content = await GetPostByUriAsync(objectUri);

        if (content != null)
        {
            content.EditedAt = SystemClock.Instance.GetCurrentInstant();
            content.UpdatedAt = SystemClock.Instance.GetCurrentInstant();
            await db.SaveChangesAsync();
            logger.LogInformation("Updated federated content: {Uri}", objectUri);
        }

        return true;
    }

    private async Task<bool> UndoFollowAsync(string actorUri, string? targetActorUri)
    {
        if (string.IsNullOrEmpty(targetActorUri))
        {
            logger.LogInformation("Undid follow relationship failed, no target actor uri provided.");
            return false;
        }

        var actor = await GetOrCreateActorAsync(actorUri);
        var targetActor = await GetOrCreateActorAsync(targetActorUri);

        var relationship = await db.FediverseRelationships
            .FirstOrDefaultAsync(r => r.ActorId == actor.Id && r.TargetActorId == targetActor.Id);

        if (relationship == null) return true;
        db.Remove(relationship);
        await db.SaveChangesAsync();
        logger.LogInformation("Undid follow relationship");

        return true;
    }

    private async Task<bool> UndoLikeAsync(string actorUri, string? objectUri)
    {
        if (string.IsNullOrEmpty(objectUri))
            return false;

        var actor = await GetOrCreateActorAsync(actorUri);
        var content = await GetPostByUriAsync(objectUri);

        if (content == null)
            return false;

        var reaction = await db.PostReactions
            .FirstOrDefaultAsync(r =>
                r.ActorId == actor.Id &&
                r.PostId == content.Id &&
                r.Symbol == "thumb_up");

        if (reaction != null)
        {
            db.PostReactions.Remove(reaction);
            content.Upvotes--;
            await db.SaveChangesAsync();
        }

        return true;
    }

    private async Task<bool> UndoAnnounceAsync(string actorUri, string? objectUri)
    {
        if (string.IsNullOrEmpty(objectUri))
            return false;

        var content = await GetPostByUriAsync(objectUri);

        if (content != null)
        {
            content.BoostCount = Math.Max(0, content.BoostCount - 1);
            await db.SaveChangesAsync();
        }

        return true;
    }

    private async Task<SnFediverseActor> GetOrCreateActorAsync(string actorUri)
    {
        var actor = await db.FediverseActors
            .FirstOrDefaultAsync(a => a.Uri == actorUri);

        if (actor != null) return actor;

        var instance = await GetOrCreateInstanceAsync(actorUri);
        actor = new SnFediverseActor
        {
            Uri = actorUri,
            Username = ExtractUsernameFromUri(actorUri),
            DisplayName = ExtractUsernameFromUri(actorUri),
            InstanceId = instance.Id
        };
        db.FediverseActors.Add(actor);
        await db.SaveChangesAsync();

        await discoveryService.FetchActorDataAsync(actor);

        return actor;
    }

    private async Task<SnFediverseInstance> GetOrCreateInstanceAsync(string actorUri)
    {
        var domain = ExtractDomainFromUri(actorUri);
        var instance = await db.FediverseInstances
            .FirstOrDefaultAsync(i => i.Domain == domain);

        if (instance == null)
        {
            instance = new SnFediverseInstance
            {
                Domain = domain,
                Name = domain
            };
            db.FediverseInstances.Add(instance);
            await db.SaveChangesAsync();
            await discoveryService.FetchInstanceMetadataAsync(instance);
        }

        return instance;
    }

    private string ExtractUsernameFromUri(string uri)
    {
        return uri.Split('/').Last();
    }

    private string ExtractDomainFromUri(string uri)
    {
        var uriObj = new Uri(uri);
        return uriObj.Host;
    }

    private Instant? ParseInstant(object? value)
    {
        if (value == null)
            return null;

        if (value is Instant instant)
            return instant;

        if (DateTimeOffset.TryParse(value.ToString(), out var dateTimeOffset))
            return Instant.FromDateTimeOffset(dateTimeOffset);

        return null;
    }

    private static List<SnCloudFileReferenceObject>? ParseAttachments(object? value)
    {
        if (value is JsonElement { ValueKind: JsonValueKind.Array } element)
        {
            return element.EnumerateArray()
                .Select(attachment => new SnCloudFileReferenceObject
                {
                    Id = Guid.NewGuid().ToString(),
                    Name = attachment.GetProperty("name").GetString() ?? string.Empty,
                    Url = attachment.GetProperty("url").GetString(),
                    MimeType = attachment.GetProperty("mediaType").GetString(),
                    Width = attachment.GetProperty("width").GetInt32(),
                    Height = attachment.GetProperty("height").GetInt32(),
                    Blurhash = attachment.GetProperty("blurhash").GetString(),
                    FileMeta = new Dictionary<string, object?>(),
                    UserMeta = new Dictionary<string, object?>(),
                    Size = 0,
                    CreatedAt = SystemClock.Instance.GetCurrentInstant(),
                    UpdatedAt = SystemClock.Instance.GetCurrentInstant()
                })
                .ToList();
        }

        return null;
    }

    private static List<ContentMention>? ParseMentions(object? value)
    {
        if (value is JsonElement { ValueKind: JsonValueKind.Array } element)
        {
            return element.EnumerateArray()
                .Where(e => e.GetProperty("type").GetString() == "Mention")
                .Select(mention => new ContentMention
                {
                    Username = mention.GetProperty("name").GetString(),
                    ActorUri = mention.GetProperty("href").GetString()
                })
                .ToList();
        }

        return null;
    }

    private static Dictionary<string, object> BuildMetadataFromActivity(Dictionary<string, object> objectDict)
    {
        var metadata = new Dictionary<string, object>();

        var tagsValue = objectDict.GetValueOrDefault("tag");
        if (tagsValue is JsonElement { ValueKind: JsonValueKind.Array } tagsElement)
        {
            var fediverseTags = tagsElement.EnumerateArray()
                .Where(e => e.GetProperty("type").GetString() == "Hashtag")
                .Select(e => e.GetProperty("name").GetString())
                .ToList();

            if (fediverseTags.Count > 0)
            {
                metadata["fediverseTags"] = fediverseTags;
            }
        }

        var emojiValue = objectDict.GetValueOrDefault("emoji");
        if (emojiValue is not JsonElement { ValueKind: JsonValueKind.Array } emojiElement) return metadata;
        {
            var emojis = emojiElement.EnumerateArray()
                .Select(e => new
                {
                    Shortcode = e.GetProperty("shortcode").GetString(),
                    StaticUrl = e.GetProperty("static_url").GetString(),
                    Url = e.GetProperty("url").GetString()
                })
                .ToList();

            if (emojis.Count > 0)
            {
                metadata["fediverseEmojis"] = emojis;
            }
        }

        return metadata;
    }
}