akkoma/lib/pleroma/web/activity_pub/utils.ex

# Pleroma: A lightweight social networking server
# Copyright © 2017-2020 Pleroma Authors <https://pleroma.social/>
# SPDX-License-Identifier: AGPL-3.0-only

defmodule Pleroma.Web.ActivityPub.Utils do
  alias Ecto.Changeset
  alias Ecto.UUID
  alias Pleroma.Activity
  alias Pleroma.Notification
  alias Pleroma.Object
  alias Pleroma.Repo
  alias Pleroma.User
  alias Pleroma.Web
  alias Pleroma.Web.ActivityPub.ActivityPub
  alias Pleroma.Web.ActivityPub.Visibility
  alias Pleroma.Web.AdminAPI.AccountView
  alias Pleroma.Web.Endpoint
  alias Pleroma.Web.Router.Helpers

  import Ecto.Query

  require Logger
  require Pleroma.Constants

  @supported_object_types [
    "Article",
    "Note",
    "Event",
    "Video",
    "Page",
    "Question",
    "Answer",
    "Audio"
  ]
  @strip_status_report_states ~w(closed resolved)
  @supported_report_states ~w(open closed resolved)
  @valid_visibilities ~w(public unlisted private direct)

  # Some implementations send the actor URI as the actor field, others send the entire actor object,
  # so figure out what the actor's URI is based on what we have.
  def get_ap_id(%{"id" => id} = _), do: id
  def get_ap_id(id), do: id

  def normalize_params(params) do
    Map.put(params, "actor", get_ap_id(params["actor"]))
  end

  @spec determine_explicit_mentions(map()) :: [any]
  def determine_explicit_mentions(%{"tag" => tag}) when is_list(tag) do
    Enum.flat_map(tag, fn
      %{"type" => "Mention", "href" => href} -> [href]
      _ -> []
    end)
  end

  def determine_explicit_mentions(%{"tag" => tag} = object) when is_map(tag) do
    object
    |> Map.put("tag", [tag])
    |> determine_explicit_mentions()
  end

  def determine_explicit_mentions(_), do: []

  @spec label_in_collection?(any(), any()) :: boolean()
  defp label_in_collection?(ap_id, coll) when is_binary(coll), do: ap_id == coll
  defp label_in_collection?(ap_id, coll) when is_list(coll), do: ap_id in coll
  defp label_in_collection?(_, _), do: false

  @spec label_in_message?(String.t(), map()) :: boolean()
  def label_in_message?(label, params),
    do:
      [params["to"], params["cc"], params["bto"], params["bcc"]]
      |> Enum.any?(&label_in_collection?(label, &1))

  @spec unaddressed_message?(map()) :: boolean()
  def unaddressed_message?(params),
    do:
      [params["to"], params["cc"], params["bto"], params["bcc"]]
      |> Enum.all?(&is_nil(&1))

  @spec recipient_in_message(User.t(), User.t(), map()) :: boolean()
  def recipient_in_message(%User{ap_id: ap_id} = recipient, %User{} = actor, params),
    do:
      label_in_message?(ap_id, params) || unaddressed_message?(params) ||
        User.following?(recipient, actor)

  defp extract_list(target) when is_binary(target), do: [target]
  defp extract_list(lst) when is_list(lst), do: lst
  defp extract_list(_), do: []

  def maybe_splice_recipient(ap_id, params) do
    need_splice? =
      !label_in_collection?(ap_id, params["to"]) &&
        !label_in_collection?(ap_id, params["cc"])

    if need_splice? do
      cc_list = extract_list(params["cc"])
      Map.put(params, "cc", [ap_id | cc_list])
    else
      params
    end
  end

  def make_json_ld_header do
    %{
      "@context" => [
        "https://www.w3.org/ns/activitystreams",
        "#{Web.base_url()}/schemas/litepub-0.1.jsonld",
        %{
          "@language" => "und"
        }
      ]
    }
  end

  def make_date do
    DateTime.utc_now() |> DateTime.to_iso8601()
  end

  def generate_activity_id do
    generate_id("activities")
  end

  def generate_context_id do
    generate_id("contexts")
  end

  def generate_object_id do
    Helpers.o_status_url(Endpoint, :object, UUID.generate())
  end

  def generate_id(type) do
    "#{Web.base_url()}/#{type}/#{UUID.generate()}"
  end

  def get_notified_from_object(%{"type" => type} = object) when type in @supported_object_types do
    fake_create_activity = %{
      "to" => object["to"],
      "cc" => object["cc"],
      "type" => "Create",
      "object" => object
    }

    get_notified_from_object(fake_create_activity)
  end

  def get_notified_from_object(object) do
    Notification.get_notified_from_activity(%Activity{data: object}, false)
  end

  def create_context(context) do
    context = context || generate_id("contexts")

    # Ecto has problems accessing the constraint inside the jsonb,
    # so we explicitly check for the existed object before insert
    object = Object.get_cached_by_ap_id(context)

    with true <- is_nil(object),
         changeset <- Object.context_mapping(context),
         {:ok, inserted_object} <- Repo.insert(changeset) do
      inserted_object
    else
      _ ->
        object
    end
  end

  @doc """
  Enqueues an activity for federation if it's local
  """
  @spec maybe_federate(any()) :: :ok
  def maybe_federate(%Activity{local: true} = activity) do
    if Pleroma.Config.get!([:instance, :federating]) do
      Pleroma.Web.Federator.publish(activity)
    end

    :ok
  end

  def maybe_federate(_), do: :ok

  @doc """
  Adds an id and a published data if they aren't there,
  also adds it to an included object
  """
  @spec lazy_put_activity_defaults(map(), boolean) :: map()
  def lazy_put_activity_defaults(map, fake? \\ false)

  def lazy_put_activity_defaults(map, true) do
    map
    |> Map.put_new("id", "pleroma:fakeid")
    |> Map.put_new_lazy("published", &make_date/0)
    |> Map.put_new("context", "pleroma:fakecontext")
    |> Map.put_new("context_id", -1)
    |> lazy_put_object_defaults(true)
  end

  def lazy_put_activity_defaults(map, _fake?) do
    %{data: %{"id" => context}, id: context_id} = create_context(map["context"])

    map
    |> Map.put_new_lazy("id", &generate_activity_id/0)
    |> Map.put_new_lazy("published", &make_date/0)
    |> Map.put_new("context", context)
    |> Map.put_new("context_id", context_id)
    |> lazy_put_object_defaults(false)
  end

  # Adds an id and published date if they aren't there.
  #
  @spec lazy_put_object_defaults(map(), boolean()) :: map()
  defp lazy_put_object_defaults(%{"object" => map} = activity, true)
       when is_map(map) do
    object =
      map
      |> Map.put_new("id", "pleroma:fake_object_id")
      |> Map.put_new_lazy("published", &make_date/0)
      |> Map.put_new("context", activity["context"])
      |> Map.put_new("context_id", activity["context_id"])
      |> Map.put_new("fake", true)

    %{activity | "object" => object}
  end

  defp lazy_put_object_defaults(%{"object" => map} = activity, _)
       when is_map(map) do
    object =
      map
      |> Map.put_new_lazy("id", &generate_object_id/0)
      |> Map.put_new_lazy("published", &make_date/0)
      |> Map.put_new("context", activity["context"])
      |> Map.put_new("context_id", activity["context_id"])

    %{activity | "object" => object}
  end

  defp lazy_put_object_defaults(activity, _), do: activity

  @doc """
  Inserts a full object if it is contained in an activity.
  """
  def insert_full_object(%{"object" => %{"type" => type} = object_data} = map)
      when is_map(object_data) and type in @supported_object_types do
    with {:ok, object} <- Object.create(object_data) do
      map = Map.put(map, "object", object.data["id"])

      {:ok, map, object}
    end
  end

  def insert_full_object(map), do: {:ok, map, nil}

  #### Like-related helpers

  @doc """
  Returns an existing like if a user already liked an object
  """
  @spec get_existing_like(String.t(), map()) :: Activity.t() | nil
  def get_existing_like(actor, %{data: %{"id" => id}}) do
    actor
    |> Activity.Queries.by_actor()
    |> Activity.Queries.by_object_id(id)
    |> Activity.Queries.by_type("Like")
    |> limit(1)
    |> Repo.one()
  end

  @doc """
  Returns like activities targeting an object
  """
  def get_object_likes(%{data: %{"id" => id}}) do
    id
    |> Activity.Queries.by_object_id()
    |> Activity.Queries.by_type("Like")
    |> Repo.all()
  end

  @spec make_like_data(User.t(), map(), String.t()) :: map()
  def make_like_data(
        %User{ap_id: ap_id} = actor,
        %{data: %{"actor" => object_actor_id, "id" => id}} = object,
        activity_id
      ) do
    object_actor = User.get_cached_by_ap_id(object_actor_id)

    to =
      if Visibility.is_public?(object) do
        [actor.follower_address, object.data["actor"]]
      else
        [object.data["actor"]]
      end

    cc =
      (object.data["to"] ++ (object.data["cc"] || []))
      |> List.delete(actor.ap_id)
      |> List.delete(object_actor.follower_address)

    %{
      "type" => "Like",
      "actor" => ap_id,
      "object" => id,
      "to" => to,
      "cc" => cc,
      "context" => object.data["context"]
    }
    |> maybe_put("id", activity_id)
  end

  def make_emoji_reaction_data(user, object, emoji, activity_id) do
    make_like_data(user, object, activity_id)
    |> Map.put("type", "EmojiReact")
    |> Map.put("content", emoji)
  end

  @spec update_element_in_object(String.t(), list(any), Object.t(), integer() | nil) ::
          {:ok, Object.t()} | {:error, Ecto.Changeset.t()}
  def update_element_in_object(property, element, object, count \\ nil) do
    length =
      count ||
        length(element)

    data =
      Map.merge(
        object.data,
        %{"#{property}_count" => length, "#{property}s" => element}
      )

    object
    |> Changeset.change(data: data)
    |> Object.update_and_set_cache()
  end

  @spec add_emoji_reaction_to_object(Activity.t(), Object.t()) ::
          {:ok, Object.t()} | {:error, Ecto.Changeset.t()}

  def add_emoji_reaction_to_object(
        %Activity{data: %{"content" => emoji, "actor" => actor}},
        object
      ) do
    reactions = get_cached_emoji_reactions(object)

    new_reactions =
      case Enum.find_index(reactions, fn [candidate, _] -> emoji == candidate end) do
        nil ->
          reactions ++ [[emoji, [actor]]]

        index ->
          List.update_at(
            reactions,
            index,
            fn [emoji, users] -> [emoji, Enum.uniq([actor | users])] end
          )
      end

    count = emoji_count(new_reactions)

    update_element_in_object("reaction", new_reactions, object, count)
  end

  def emoji_count(reactions_list) do
    Enum.reduce(reactions_list, 0, fn [_, users], acc -> acc + length(users) end)
  end

  def remove_emoji_reaction_from_object(
        %Activity{data: %{"content" => emoji, "actor" => actor}},
        object
      ) do
    reactions = get_cached_emoji_reactions(object)

    new_reactions =
      case Enum.find_index(reactions, fn [candidate, _] -> emoji == candidate end) do
        nil ->
          reactions

        index ->
          List.update_at(
            reactions,
            index,
            fn [emoji, users] -> [emoji, List.delete(users, actor)] end
          )
          |> Enum.reject(fn [_, users] -> Enum.empty?(users) end)
      end

    count = emoji_count(new_reactions)
    update_element_in_object("reaction", new_reactions, object, count)
  end

  def get_cached_emoji_reactions(object) do
    if is_list(object.data["reactions"]) do
      object.data["reactions"]
    else
      []
    end
  end

  @spec add_like_to_object(Activity.t(), Object.t()) ::
          {:ok, Object.t()} | {:error, Ecto.Changeset.t()}
  def add_like_to_object(%Activity{data: %{"actor" => actor}}, object) do
    [actor | fetch_likes(object)]
    |> Enum.uniq()
    |> update_likes_in_object(object)
  end

  @spec remove_like_from_object(Activity.t(), Object.t()) ::
          {:ok, Object.t()} | {:error, Ecto.Changeset.t()}
  def remove_like_from_object(%Activity{data: %{"actor" => actor}}, object) do
    object
    |> fetch_likes()
    |> List.delete(actor)
    |> update_likes_in_object(object)
  end

  defp update_likes_in_object(likes, object) do
    update_element_in_object("like", likes, object)
  end

  defp fetch_likes(object) do
    if is_list(object.data["likes"]) do
      object.data["likes"]
    else
      []
    end
  end

  #### Follow-related helpers

  @doc """
  Updates a follow activity's state (for locked accounts).
  """
  @spec update_follow_state_for_all(Activity.t(), String.t()) :: {:ok, Activity | nil}
  def update_follow_state_for_all(
        %Activity{data: %{"actor" => actor, "object" => object}} = activity,
        state
      ) do
    "Follow"
    |> Activity.Queries.by_type()
    |> Activity.Queries.by_actor(actor)
    |> Activity.Queries.by_object_id(object)
    |> where(fragment("data->>'state' = 'pending'"))
    |> update(set: [data: fragment("jsonb_set(data, '{state}', ?)", ^state)])
    |> Repo.update_all([])

    activity = Activity.get_by_id(activity.id)

    {:ok, activity}
  end

  def update_follow_state(
        %Activity{} = activity,
        state
      ) do
    new_data = Map.put(activity.data, "state", state)
    changeset = Changeset.change(activity, data: new_data)

    with {:ok, activity} <- Repo.update(changeset) do
      {:ok, activity}
    end
  end

  @doc """
  Makes a follow activity data for the given follower and followed
  """
  def make_follow_data(
        %User{ap_id: follower_id},
        %User{ap_id: followed_id} = _followed,
        activity_id
      ) do
    %{
      "type" => "Follow",
      "actor" => follower_id,
      "to" => [followed_id],
      "cc" => [Pleroma.Constants.as_public()],
      "object" => followed_id,
      "state" => "pending"
    }
    |> maybe_put("id", activity_id)
  end

  def fetch_latest_follow(%User{ap_id: follower_id}, %User{ap_id: followed_id}) do
    "Follow"
    |> Activity.Queries.by_type()
    |> where(actor: ^follower_id)
    # this is to use the index
    |> Activity.Queries.by_object_id(followed_id)
    |> order_by([activity], fragment("? desc nulls last", activity.id))
    |> limit(1)
    |> Repo.one()
  end

  def fetch_latest_undo(%User{ap_id: ap_id}) do
    "Undo"
    |> Activity.Queries.by_type()
    |> where(actor: ^ap_id)
    |> order_by([activity], fragment("? desc nulls last", activity.id))
    |> limit(1)
    |> Repo.one()
  end

  def get_latest_reaction(internal_activity_id, %{ap_id: ap_id}, emoji) do
    %{data: %{"object" => object_ap_id}} = Activity.get_by_id(internal_activity_id)

    "EmojiReact"
    |> Activity.Queries.by_type()
    |> where(actor: ^ap_id)
    |> where([activity], fragment("?->>'content' = ?", activity.data, ^emoji))
    |> Activity.Queries.by_object_id(object_ap_id)
    |> order_by([activity], fragment("? desc nulls last", activity.id))
    |> limit(1)
    |> Repo.one()
  end

  #### Announce-related helpers

  @doc """
  Retruns an existing announce activity if the notice has already been announced
  """
  @spec get_existing_announce(String.t(), map()) :: Activity.t() | nil
  def get_existing_announce(actor, %{data: %{"id" => ap_id}}) do
    "Announce"
    |> Activity.Queries.by_type()
    |> where(actor: ^actor)
    # this is to use the index
    |> Activity.Queries.by_object_id(ap_id)
    |> Repo.one()
  end

  @doc """
  Make announce activity data for the given actor and object
  """
  # for relayed messages, we only want to send to subscribers
  def make_announce_data(
        %User{ap_id: ap_id} = user,
        %Object{data: %{"id" => id}} = object,
        activity_id,
        false
      ) do
    %{
      "type" => "Announce",
      "actor" => ap_id,
      "object" => id,
      "to" => [user.follower_address],
      "cc" => [],
      "context" => object.data["context"]
    }
    |> maybe_put("id", activity_id)
  end

  def make_announce_data(
        %User{ap_id: ap_id} = user,
        %Object{data: %{"id" => id}} = object,
        activity_id,
        true
      ) do
    %{
      "type" => "Announce",
      "actor" => ap_id,
      "object" => id,
      "to" => [user.follower_address, object.data["actor"]],
      "cc" => [Pleroma.Constants.as_public()],
      "context" => object.data["context"]
    }
    |> maybe_put("id", activity_id)
  end

  def make_undo_data(
        %User{ap_id: actor, follower_address: follower_address},
        %Activity{
          data: %{"id" => undone_activity_id, "context" => context},
          actor: undone_activity_actor
        },
        activity_id \\ nil
      ) do
    %{
      "type" => "Undo",
      "actor" => actor,
      "object" => undone_activity_id,
      "to" => [follower_address, undone_activity_actor],
      "cc" => [Pleroma.Constants.as_public()],
      "context" => context
    }
    |> maybe_put("id", activity_id)
  end

  @spec add_announce_to_object(Activity.t(), Object.t()) ::
          {:ok, Object.t()} | {:error, Ecto.Changeset.t()}
  def add_announce_to_object(
        %Activity{data: %{"actor" => actor}},
        object
      ) do
    unless actor |> User.get_cached_by_ap_id() |> User.invisible?() do
      announcements = take_announcements(object)

      with announcements <- Enum.uniq([actor | announcements]) do
        update_element_in_object("announcement", announcements, object)
      end
    else
      {:ok, object}
    end
  end

  def add_announce_to_object(_, object), do: {:ok, object}

  @spec remove_announce_from_object(Activity.t(), Object.t()) ::
          {:ok, Object.t()} | {:error, Ecto.Changeset.t()}
  def remove_announce_from_object(%Activity{data: %{"actor" => actor}}, object) do
    with announcements <- List.delete(take_announcements(object), actor) do
      update_element_in_object("announcement", announcements, object)
    end
  end

  defp take_announcements(%{data: %{"announcements" => announcements}} = _)
       when is_list(announcements),
       do: announcements

  defp take_announcements(_), do: []

  #### Unfollow-related helpers

  def make_unfollow_data(follower, followed, follow_activity, activity_id) do
    %{
      "type" => "Undo",
      "actor" => follower.ap_id,
      "to" => [followed.ap_id],
      "object" => follow_activity.data
    }
    |> maybe_put("id", activity_id)
  end

  #### Block-related helpers
  @spec fetch_latest_block(User.t(), User.t()) :: Activity.t() | nil
  def fetch_latest_block(%User{ap_id: blocker_id}, %User{ap_id: blocked_id}) do
    "Block"
    |> Activity.Queries.by_type()
    |> where(actor: ^blocker_id)
    # this is to use the index
    |> Activity.Queries.by_object_id(blocked_id)
    |> order_by([activity], fragment("? desc nulls last", activity.id))
    |> limit(1)
    |> Repo.one()
  end

  def make_block_data(blocker, blocked, activity_id) do
    %{
      "type" => "Block",
      "actor" => blocker.ap_id,
      "to" => [blocked.ap_id],
      "object" => blocked.ap_id
    }
    |> maybe_put("id", activity_id)
  end

  #### Create-related helpers

  def make_create_data(params, additional) do
    published = params.published || make_date()

    %{
      "type" => "Create",
      "to" => params.to |> Enum.uniq(),
      "actor" => params.actor.ap_id,
      "object" => params.object,
      "published" => published,
      "context" => params.context
    }
    |> Map.merge(additional)
  end

  #### Listen-related helpers
  def make_listen_data(params, additional) do
    published = params.published || make_date()

    %{
      "type" => "Listen",
      "to" => params.to |> Enum.uniq(),
      "actor" => params.actor.ap_id,
      "object" => params.object,
      "published" => published,
      "context" => params.context
    }
    |> Map.merge(additional)
  end

  #### Flag-related helpers
  @spec make_flag_data(map(), map()) :: map()
  def make_flag_data(%{actor: actor, context: context, content: content} = params, additional) do
    %{
      "type" => "Flag",
      "actor" => actor.ap_id,
      "content" => content,
      "object" => build_flag_object(params),
      "context" => context,
      "state" => "open"
    }
    |> Map.merge(additional)
  end

  def make_flag_data(_, _), do: %{}

  defp build_flag_object(%{account: account, statuses: statuses} = _) do
    [account.ap_id] ++ build_flag_object(%{statuses: statuses})
  end

  defp build_flag_object(%{statuses: statuses}) do
    Enum.map(statuses || [], &build_flag_object/1)
  end

  defp build_flag_object(act) when is_map(act) or is_binary(act) do
    id =
      case act do
        %Activity{} = act -> act.data["id"]
        act when is_map(act) -> act["id"]
        act when is_binary(act) -> act
      end

    case Activity.get_by_ap_id_with_object(id) do
      %Activity{} = activity ->
        %{
          "type" => "Note",
          "id" => activity.data["id"],
          "content" => activity.object.data["content"],
          "published" => activity.object.data["published"],
          "actor" =>
            AccountView.render("show.json", %{
              user: User.get_by_ap_id(activity.object.data["actor"])
            })
        }

      _ ->
        %{"id" => id, "deleted" => true}
    end
  end

  defp build_flag_object(_), do: []

  #### Report-related helpers
  def get_reports(params, page, page_size) do
    params =
      params
      |> Map.put("type", "Flag")
      |> Map.put("skip_preload", true)
      |> Map.put("preload_report_notes", true)
      |> Map.put("total", true)
      |> Map.put("limit", page_size)
      |> Map.put("offset", (page - 1) * page_size)

    ActivityPub.fetch_activities([], params, :offset)
  end

  def update_report_state(%Activity{} = activity, state)
      when state in @strip_status_report_states do
    {:ok, stripped_activity} = strip_report_status_data(activity)

    new_data =
      activity.data
      |> Map.put("state", state)
      |> Map.put("object", stripped_activity.data["object"])

    activity
    |> Changeset.change(data: new_data)
    |> Repo.update()
  end

  def update_report_state(%Activity{} = activity, state) when state in @supported_report_states do
    new_data = Map.put(activity.data, "state", state)

    activity
    |> Changeset.change(data: new_data)
    |> Repo.update()
  end

  def update_report_state(activity_ids, state) when state in @supported_report_states do
    activities_num = length(activity_ids)

    from(a in Activity, where: a.id in ^activity_ids)
    |> update(set: [data: fragment("jsonb_set(data, '{state}', ?)", ^state)])
    |> Repo.update_all([])
    |> case do
      {^activities_num, _} -> :ok
      _ -> {:error, activity_ids}
    end
  end

  def update_report_state(_, _), do: {:error, "Unsupported state"}

  def strip_report_status_data(activity) do
    [actor | reported_activities] = activity.data["object"]

    stripped_activities =
      Enum.map(reported_activities, fn
        act when is_map(act) -> act["id"]
        act when is_binary(act) -> act
      end)

    new_data = put_in(activity.data, ["object"], [actor | stripped_activities])

    {:ok, %{activity | data: new_data}}
  end

  def update_activity_visibility(activity, visibility) when visibility in @valid_visibilities do
    [to, cc, recipients] =
      activity
      |> get_updated_targets(visibility)
      |> Enum.map(&Enum.uniq/1)

    object_data =
      activity.object.data
      |> Map.put("to", to)
      |> Map.put("cc", cc)

    {:ok, object} =
      activity.object
      |> Object.change(%{data: object_data})
      |> Object.update_and_set_cache()

    activity_data =
      activity.data
      |> Map.put("to", to)
      |> Map.put("cc", cc)

    activity
    |> Map.put(:object, object)
    |> Activity.change(%{data: activity_data, recipients: recipients})
    |> Repo.update()
  end

  def update_activity_visibility(_, _), do: {:error, "Unsupported visibility"}

  defp get_updated_targets(
         %Activity{data: %{"to" => to} = data, recipients: recipients},
         visibility
       ) do
    cc = Map.get(data, "cc", [])
    follower_address = User.get_cached_by_ap_id(data["actor"]).follower_address
    public = Pleroma.Constants.as_public()

    case visibility do
      "public" ->
        to = [public | List.delete(to, follower_address)]
        cc = [follower_address | List.delete(cc, public)]
        recipients = [public | recipients]
        [to, cc, recipients]

      "private" ->
        to = [follower_address | List.delete(to, public)]
        cc = List.delete(cc, public)
        recipients = List.delete(recipients, public)
        [to, cc, recipients]

      "unlisted" ->
        to = [follower_address | List.delete(to, public)]
        cc = [public | List.delete(cc, follower_address)]
        recipients = recipients ++ [follower_address, public]
        [to, cc, recipients]

      _ ->
        [to, cc, recipients]
    end
  end

  def get_existing_votes(actor, %{data: %{"id" => id}}) do
    actor
    |> Activity.Queries.by_actor()
    |> Activity.Queries.by_type("Create")
    |> Activity.with_preloaded_object()
    |> where([a, object: o], fragment("(?)->>'inReplyTo' = ?", o.data, ^to_string(id)))
    |> where([a, object: o], fragment("(?)->>'type' = 'Answer'", o.data))
    |> Repo.all()
  end

  def maybe_put(map, _key, nil), do: map
  def maybe_put(map, key, value), do: Map.put(map, key, value)
end