AP.NET/ActivityStore.cs

using ActivityPub.Utils;
using Microsoft.AspNetCore.Mvc;
using KristofferStrube.ActivityStreams;

using Object = KristofferStrube.ActivityStreams.Object;

namespace ActivityPub;

public enum ActivityStoreType {
  Inbox,
  Outbox
}

public class ActivityStore {
  private static Dictionary<string, Activity> _outbox = new();
  private static Dictionary<string, Activity> _inbox = new();
  private Dictionary<string, Activity> _activities { get => ActivityStoreType == ActivityStoreType.Inbox ? _inbox : _outbox; }
  private IUrlHelper Url { get; set; }
  private ObjectStore ObjectStore { get; set; }

  /// <summary>
  /// The type (inbox or outbox) of this ActivityStore instance
  /// </summary>
  public ActivityStoreType ActivityStoreType { get; private set; }

  /// <summary>
  /// Default Constructor
  /// </summary>
  /// <param name="url">A url helper to construct id urls</param>
  /// <param name="activityStoreType">The typee (inbox or outbox) of this ActivityStore</param>
  public ActivityStore(IUrlHelper url, ActivityStoreType activityStoreType) {
    this.Url = url;
    this.ObjectStore = new ObjectStore(url);
    this.ActivityStoreType = activityStoreType;
  }

  /// <summary>
  /// Gets a new Id for an Activity
  /// </summary>
  public string NewId {
    get {
      long idTime = DateTimeOffset.UtcNow.ToUnixTimeMilliseconds();
      while (_activities.ContainsKey(Base36.ToString(idTime))) idTime++;
      return Base36.ToString(idTime);
    }
  }

  /// <summary>
  /// Wraps an Object in a Create Activity
  /// </summary>
  /// <param name="newObject">The object to create</param>
  /// <returns>The create Activity, with the object inside.</returns>
  public Create WrapObjectInCreate(IObject newObject) {
    Create newActivity = new Create() { // new create activity
      Actor = newObject.AttributedTo,
      To = newObject.To,
      Cc = newObject.Cc,
      Bto = newObject.Bto,
      Bcc = newObject.Bcc,
      Audience = newObject.Audience,
      AttributedTo = newObject.AttributedTo,
      Name = newObject.Name?.FirstOrDefault() == null ? null : new List<string> { $"Create {newObject.Name.First()}" },
    };
    newActivity.Object = new List<IObjectOrLink> { newObject };

    return newActivity;
  }

  /// <summary>
  /// Gets an activity by Id
  /// </summary>
  /// <param name="id">The Id to find</param>
  /// <returns>The activity with the corresponding id, or null if not found</returns>
  public Activity? GetById(string id) {
    foreach (KeyValuePair<string, Activity> kvp in _activities) {
      if (kvp.Key == id) return kvp.Value;
    }
    return null;
  }

  /// <summary>
  /// Gets All activities
  /// </summary>
  /// <returns>A lit of all activities</returns>
  public List<Activity> GetAll() {
    return _activities.Values.ToList();
  }

  /// <summary>
  /// Inserts an activity into the data store
  /// </summary>
  /// <param name="newActivity">The Activity to create</param>
  /// <param name="runSideEffects">A boolean indicating whether side effects should be run (default true)</param>
  /// <param name="runDelivery">A boolean indicating whether delivery tasks should be run (default true)</param>
  /// <returns>The newly inserted activity</returns>
  public Activity InsertActivity(Activity newActivity, bool runSideEffects = true, bool runDelivery = true) {

    string id = NewId;
    string uriId = this.Url.AbsoluteRouteUrl(ActivityStoreType == ActivityStoreType.Inbox ? "GetInboxById" : "GetOutboxById", new { id }).ToLower();
    List<Uri> recipients = runDelivery ? ExtractRecipients(newActivity) : new List<Uri>();
    newActivity.Id = uriId;
    newActivity.Bto = newActivity.Bcc = null;

    if (runSideEffects) newActivity = RunSideEffect(newActivity);

    _activities[id] = newActivity;

    if (runDelivery) RunDelivery(newActivity, recipients);

    return newActivity;
  }

  /// <summary>
  /// Extract a list of recipients for an activity.
  /// clients must be aware that the server will only forward new Activities to addressees in the to, bto, cc, bcc, and audience fields. 
  /// </summary>
  /// <param name="newActivity">The activity to extract recipients from</param>
  /// <returns>A list of Uris representing inboxes to post to</returns>
  private List<Uri> ExtractRecipients(Activity newActivity) {
    List<Uri> recipients = new();
    // TODO: recipients.Add(newActivity.To)
    // TODO: recipients.Add(newActivity.Bto)
    // TODO: recipients.Add(newActivity.Cc)
    // TODO: recipients.Add(newActivity.Bcc)
    // TODO: recipients.Add(newActivity.Audience)
    // TODO: Filter out duplicates
    // TODO: Populate lists (e.g. followers)
    // TODO: Again, filter out duplicates
    // TODO: change (remove?) public collection
    return recipients;
  }

  private void RunDelivery(Activity newActivity, List<Uri> recipients) {
    foreach (Uri recipient in recipients) {
      // TODO: send a Http request to each recipient
      // it should be a POST request with the Activity as the body
    }
  }

  /// <summary>
  /// Validates an activity
  /// </summary>
  /// <param name="newActivity">the activity to validate</param>
  /// <returns>True on successful validation</returns>
  /// <exception cref="ArgumentException">Thown if the activity is invalid</exception>
  public bool ValidateActivity(Activity newActivity) {
    if (!(newActivity is IntransitiveActivity) && newActivity.Object?.FirstOrDefault() == null) 
      throw new ArgumentException($"'{newActivity.Type?.FirstOrDefault()}' Activities require an 'Object' property");
    return true;
  }

  private Activity RunSideEffect(Activity newActivity) {
    
    if (newActivity is IntransitiveActivity) {
      // intransitive activities go here
      IntransitiveActivity activity = (IntransitiveActivity)newActivity;
      if (activity is Arrive)          return Arrive((Arrive)activity);
      else if (activity is Travel)          return Travel((Travel)activity);
      // else if (activity is Question)             return Question((Question)activity); // TODO: Temporary until question is intransitory again
      else throw new InvalidOperationException($"Activity type '{activity.Type?.FirstOrDefault()}' is unrecognized");

    }
    else {
      Activity activity = newActivity;

           if (activity is Create)          return Create((Create)activity);
      else if (activity is Update)          return Update((Update)activity);
      else if (activity is Delete)          return Delete((Delete)activity);
      else if (activity is Follow)          return Follow((Follow)activity);
      else if (activity is Add)             return Add((Add)activity);
      else if (activity is Remove)          return Remove((Remove)activity);
      else if (activity is Like)            return Like((Like)activity);
      else if (activity is Dislike)         return Dislike((Dislike)activity);
      else if (activity is Block)           return Block((Block)activity);
      else if (activity is Undo)            return Undo((Undo)activity);
      else if (activity is Accept)          return Accept((Accept)activity);
      else if (activity is Announce)        return Announce((Announce)activity);
      else if (activity is Flag)            return Flag((Flag)activity);
      else if (activity is Ignore)          return Ignore((Ignore)activity);
      else if (activity is Invite)          return Invite((Invite)activity);
      else if (activity is Join)            return Join((Join)activity);
      else if (activity is Leave)           return Leave((Leave)activity);
      else if (activity is Listen)          return Listen((Listen)activity);
      else if (activity is Move)            return Move((Move)activity);
      else if (activity is Offer)           return Offer((Offer)activity);
      else if (activity is Reject)          return Reject((Reject)activity);
      else if (activity is Read)            return Read((Read)activity);
      else if (activity is TentativeReject) return TentativeReject((TentativeReject)activity);
      else if (activity is TentativeAccept) return TentativeAccept((TentativeAccept)activity);
      else if (activity is View)            return View((View)activity);
      else if (activity is Question) return Question((Question)activity); // TODO: Temporary until question is intransitory again
      else throw new InvalidOperationException($"Activity type '{activity.Type?.FirstOrDefault()}' is unrecognized");
    }
  }

  private Create Create(Create activity) {
    Object? newObject = activity.Object?.FirstOrDefault() as Object;
    if (newObject == null) throw new ArgumentException("'Create' Activities require an 'Object' property");
    activity.Object = new List<IObjectOrLink> { ObjectStore.InsertObject(newObject) };
    return activity;
  }

  private Update Update(Update activity) {
    throw new NotImplementedException();
  }

  private Delete Delete(Delete activity) {
    throw new NotImplementedException();
  }

  private Follow Follow(Follow activity) {
    throw new NotImplementedException();
  }

  private Add Add(Add activity) {
    throw new NotImplementedException();
  }

  private Remove Remove(Remove activity) {
    throw new NotImplementedException();
  }

  private Like Like(Like activity) {
    throw new NotImplementedException();
  }

  private Dislike Dislike(Dislike activity) {
    throw new NotImplementedException();
  }

  private Block Block(Block activity) {
    throw new NotImplementedException();
  }

  private Undo Undo(Undo activity) {
    throw new NotImplementedException();
  }

  private Accept Accept(Accept activity) {
    throw new NotImplementedException();
  }

  private Announce Announce(Announce activity) {
    throw new NotImplementedException();
  }

  private Flag Flag(Flag activity) {
    throw new NotImplementedException();
  }

  private Ignore Ignore(Ignore activity) {
    throw new NotImplementedException();
  }

  private Invite Invite(Invite activity) {
    throw new NotImplementedException();
  }

  private Join Join(Join activity) {
    throw new NotImplementedException();
  }

  private Leave Leave(Leave activity) {
    throw new NotImplementedException();
  }

  private Listen Listen(Listen activity) {
    throw new NotImplementedException();
  }

  private Move Move(Move activity) {
    throw new NotImplementedException();
  }

  private Offer Offer(Offer activity) {
    throw new NotImplementedException();
  }

  private Reject Reject(Reject activity) {
    throw new NotImplementedException();
  }

  private Read Read(Read activity) {
    throw new NotImplementedException();
  }

  private TentativeReject TentativeReject(TentativeReject activity) {
    throw new NotImplementedException();
  }

  private TentativeAccept TentativeAccept(TentativeAccept activity) {
    throw new NotImplementedException();
  }

  private View View(View activity) {
    throw new NotImplementedException();
  }

  private Question Question(Question activity) {
    throw new NotImplementedException();
  }

  private Arrive Arrive(Arrive activity) {
    throw new NotImplementedException();
  }

  private Travel Travel(Travel activity) {
    throw new NotImplementedException();
  }
}