AP.NET/ActivityStore.cs

using ActivityPub.Utils;
using Microsoft.AspNetCore.Mvc;
using System.ComponentModel;
using KristofferStrube.ActivityStreams;
using OneOf;

namespace ActivityPub;
using Activity = OneOf<Activity, IntransitiveActiviy>;

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(KristofferStrube.ActivityStreams.Object 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) {
    List<Uri> recipients = runDelivery ? ExtractRecipients(newActivity) : new List<Uri>();

    string id = NewId;
    string uriId = this.Url.AbsoluteRouteUrl(ActivityStoreType == ActivityStoreType.Inbox ? "GetInboxById" : "GetOutboxById", new { id }).ToLower();
    newActivity.Switch(
      _ => { _.Id = uriId; _.Bto = _.Bcc = null; },
      _ => { _.Id = uriId; _.Bto = _.Bcc = null; }
    );
    if (runSideEffects) newActivity = RunSideEffect(newActivity);

    _activities[id] = newActivity;

    if (runDelivery) RunDelivery(newActivity, recipients);

    return newActivity;
  }

  ///// <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(IntransitiveActiviy newActivity, bool runSideEffects = true, bool runDelivery = true) {
  //  string id = NewId;
  //  newActivity.Id = this.Url.AbsoluteRouteUrl(ActivityStoreType == ActivityStoreType.Inbox ? "GetInboxById" : "GetOutboxById", new { id }).ToLower();
  //  if (runSideEffects) newActivity = RunSideEffect(newActivity);

  //  List<Uri> recipients = runDelivery ? ExtractRecipients(newActivity) : new List<Uri>();
  //  newActivity.Bto = newActivity.Bcc = null;

  //  _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) {
    string? type = newActivity.Match(
      _ => _.Type?.FirstOrDefault(),
      _ => _.Type?.FirstOrDefault()
    );
    switch (type) {
      case "Create":
      case "Update":
      case "Delete":
      case "Follow":
      case "Add":
      case "Remove":
      case "Like":
      case "Dislike":
      case "Block":
        
        if (!newActivity.IsT0 || newActivity.AsT0.Object == null) throw new ArgumentException($"'{type}' Activities require an 'Object' property");
        break;
      default: break;
    }
    return true;
  }

  private Activity RunSideEffect(Activity newActivity) {
    string? type = newActivity.Match(
      _ => _.Type?.FirstOrDefault(),
      _ => _.Type?.FirstOrDefault()
    );
    switch (type) {
      case "Create":
        KristofferStrube.ActivityStreams.Object? newObject = newActivity.AsT0.Object.FirstOrDefault() as KristofferStrube.ActivityStreams.Object;
        if (newObject == null) throw new ArgumentException("'Create' Activities require an 'Object' property");
        newActivity.AsT0.Object = new List<IObjectOrLink> { (IObjectOrLink)ObjectStore.InsertObject(newObject) };
        break;

      case "Update":
      case "Delete":
      case "Follow":
      case "Add":
      case "Remove":
      case "Like":
      case "Dislike":
      case "Block":
      case "Undo":

      case "Accept":
      case "Announce":
      case "Arrive":
      case "Flag":
      case "Ignore":
      case "Invite":
      case "Join":
      case "Leave":
      case "Listen":
      case "Move":
      case "Offer":
      case "Question":
      case "Reject":
      case "Read":
      case "TentativeReject":
      case "TentativeAccept":
      case "Travel":
      case "View":
        throw new NotImplementedException();
      default:
        throw new InvalidEnumArgumentException($"Invalid Activity Type '{type}'");
    }

    return newActivity;
  }

}