Pleroma/lib/pleroma/web/activity_pub/transmogrifier.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.Transmogrifier do
  @moduledoc """
  A module to handle coding from internal to wire ActivityPub and back.
  """
  alias Pleroma.Activity
  alias Pleroma.FollowingRelationship
  alias Pleroma.Object
  alias Pleroma.Object.Containment
  alias Pleroma.Repo
  alias Pleroma.User
  alias Pleroma.Web.ActivityPub.ActivityPub
  alias Pleroma.Web.ActivityPub.ObjectValidator
  alias Pleroma.Web.ActivityPub.ObjectValidators.LikeValidator
  alias Pleroma.Web.ActivityPub.Pipeline
  alias Pleroma.Web.ActivityPub.Utils
  alias Pleroma.Web.ActivityPub.Visibility
  alias Pleroma.Web.Federator
  alias Pleroma.Workers.TransmogrifierWorker

  import Ecto.Query

  require Logger
  require Pleroma.Constants

  @doc """
  Modifies an incoming AP object (mastodon format) to our internal format.
  """
  def fix_object(object, options \\ []) do
    object
    |> strip_internal_fields
    |> fix_actor
    |> fix_url
    |> fix_attachments
    |> fix_context
    |> fix_in_reply_to(options)
    |> fix_emoji
    |> fix_tag
    |> fix_content_map
    |> fix_addressing
    |> fix_summary
    |> fix_type(options)
  end

  def fix_summary(%{"summary" => nil} = object) do
    Map.put(object, "summary", "")
  end

  def fix_summary(%{"summary" => _} = object) do
    # summary is present, nothing to do
    object
  end

  def fix_summary(object), do: Map.put(object, "summary", "")

  def fix_addressing_list(map, field) do
    cond do
      is_binary(map[field]) ->
        Map.put(map, field, [map[field]])

      is_nil(map[field]) ->
        Map.put(map, field, [])

      true ->
        map
    end
  end

  def fix_explicit_addressing(
        %{"to" => to, "cc" => cc} = object,
        explicit_mentions,
        follower_collection
      ) do
    explicit_to = Enum.filter(to, fn x -> x in explicit_mentions end)

    explicit_cc = Enum.filter(to, fn x -> x not in explicit_mentions end)

    final_cc =
      (cc ++ explicit_cc)
      |> Enum.reject(fn x -> String.ends_with?(x, "/followers") and x != follower_collection end)
      |> Enum.uniq()

    object
    |> Map.put("to", explicit_to)
    |> Map.put("cc", final_cc)
  end

  def fix_explicit_addressing(object, _explicit_mentions, _followers_collection), do: object

  # if directMessage flag is set to true, leave the addressing alone
  def fix_explicit_addressing(%{"directMessage" => true} = object), do: object

  def fix_explicit_addressing(object) do
    explicit_mentions = Utils.determine_explicit_mentions(object)

    %User{follower_address: follower_collection} =
      object
      |> Containment.get_actor()
      |> User.get_cached_by_ap_id()

    explicit_mentions =
      explicit_mentions ++
        [
          Pleroma.Constants.as_public(),
          follower_collection
        ]

    fix_explicit_addressing(object, explicit_mentions, follower_collection)
  end

  # if as:Public is addressed, then make sure the followers collection is also addressed
  # so that the activities will be delivered to local users.
  def fix_implicit_addressing(%{"to" => to, "cc" => cc} = object, followers_collection) do
    recipients = to ++ cc

    if followers_collection not in recipients do
      cond do
        Pleroma.Constants.as_public() in cc ->
          to = to ++ [followers_collection]
          Map.put(object, "to", to)

        Pleroma.Constants.as_public() in to ->
          cc = cc ++ [followers_collection]
          Map.put(object, "cc", cc)

        true ->
          object
      end
    else
      object
    end
  end

  def fix_implicit_addressing(object, _), do: object

  def fix_addressing(object) do
    {:ok, %User{} = user} = User.get_or_fetch_by_ap_id(object["actor"])
    followers_collection = User.ap_followers(user)

    object
    |> fix_addressing_list("to")
    |> fix_addressing_list("cc")
    |> fix_addressing_list("bto")
    |> fix_addressing_list("bcc")
    |> fix_explicit_addressing()
    |> fix_implicit_addressing(followers_collection)
  end

  def fix_actor(%{"attributedTo" => actor} = object) do
    Map.put(object, "actor", Containment.get_actor(%{"actor" => actor}))
  end

  def fix_in_reply_to(object, options \\ [])

  def fix_in_reply_to(%{"inReplyTo" => in_reply_to} = object, options)
      when not is_nil(in_reply_to) do
    in_reply_to_id = prepare_in_reply_to(in_reply_to)
    object = Map.put(object, "inReplyToAtomUri", in_reply_to_id)
    depth = (options[:depth] || 0) + 1

    if Federator.allowed_thread_distance?(depth) do
      with {:ok, replied_object} <- get_obj_helper(in_reply_to_id, options),
           %Activity{} <- Activity.get_create_by_object_ap_id(replied_object.data["id"]) do
        object
        |> Map.put("inReplyTo", replied_object.data["id"])
        |> Map.put("inReplyToAtomUri", object["inReplyToAtomUri"] || in_reply_to_id)
        |> Map.put("conversation", replied_object.data["context"] || object["conversation"])
        |> Map.put("context", replied_object.data["context"] || object["conversation"])
      else
        e ->
          Logger.error("Couldn't fetch #{inspect(in_reply_to_id)}, error: #{inspect(e)}")
          object
      end
    else
      object
    end
  end

  def fix_in_reply_to(object, _options), do: object

  defp prepare_in_reply_to(in_reply_to) do
    cond do
      is_bitstring(in_reply_to) ->
        in_reply_to

      is_map(in_reply_to) && is_bitstring(in_reply_to["id"]) ->
        in_reply_to["id"]

      is_list(in_reply_to) && is_bitstring(Enum.at(in_reply_to, 0)) ->
        Enum.at(in_reply_to, 0)

      true ->
        ""
    end
  end

  def fix_context(object) do
    context = object["context"] || object["conversation"] || Utils.generate_context_id()

    object
    |> Map.put("context", context)
    |> Map.put("conversation", context)
  end

  defp add_if_present(map, _key, nil), do: map

  defp add_if_present(map, key, value) do
    Map.put(map, key, value)
  end

  def fix_attachments(%{"attachment" => attachment} = object) when is_list(attachment) do
    attachments =
      Enum.map(attachment, fn data ->
        url =
          cond do
            is_list(data["url"]) -> List.first(data["url"])
            is_map(data["url"]) -> data["url"]
            true -> nil
          end

        media_type =
          cond do
            is_map(url) && is_binary(url["mediaType"]) -> url["mediaType"]
            is_binary(data["mediaType"]) -> data["mediaType"]
            is_binary(data["mimeType"]) -> data["mimeType"]
            true -> nil
          end

        href =
          cond do
            is_map(url) && is_binary(url["href"]) -> url["href"]
            is_binary(data["url"]) -> data["url"]
            is_binary(data["href"]) -> data["href"]
          end

        attachment_url =
          %{"href" => href}
          |> add_if_present("mediaType", media_type)
          |> add_if_present("type", Map.get(url || %{}, "type"))

        %{"url" => [attachment_url]}
        |> add_if_present("mediaType", media_type)
        |> add_if_present("type", data["type"])
        |> add_if_present("name", data["name"])
      end)

    Map.put(object, "attachment", attachments)
  end

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

  def fix_attachments(object), do: object

  def fix_url(%{"url" => url} = object) when is_map(url) do
    Map.put(object, "url", url["href"])
  end

  def fix_url(%{"type" => object_type, "url" => url} = object)
      when object_type in ["Video", "Audio"] and is_list(url) do
    first_element = Enum.at(url, 0)

    link_element = Enum.find(url, fn x -> is_map(x) and x["mimeType"] == "text/html" end)

    object
    |> Map.put("attachment", [first_element])
    |> Map.put("url", link_element["href"])
  end

  def fix_url(%{"type" => object_type, "url" => url} = object)
      when object_type != "Video" and is_list(url) do
    first_element = Enum.at(url, 0)

    url_string =
      cond do
        is_bitstring(first_element) -> first_element
        is_map(first_element) -> first_element["href"] || ""
        true -> ""
      end

    Map.put(object, "url", url_string)
  end

  def fix_url(object), do: object

  def fix_emoji(%{"tag" => tags} = object) when is_list(tags) do
    emoji =
      tags
      |> Enum.filter(fn data -> data["type"] == "Emoji" and data["icon"] end)
      |> Enum.reduce(%{}, fn data, mapping ->
        name = String.trim(data["name"], ":")

        Map.put(mapping, name, data["icon"]["url"])
      end)

    # we merge mastodon and pleroma emoji into a single mapping, to allow for both wire formats
    emoji = Map.merge(object["emoji"] || %{}, emoji)

    Map.put(object, "emoji", emoji)
  end

  def fix_emoji(%{"tag" => %{"type" => "Emoji"} = tag} = object) do
    name = String.trim(tag["name"], ":")
    emoji = %{name => tag["icon"]["url"]}

    Map.put(object, "emoji", emoji)
  end

  def fix_emoji(object), do: object

  def fix_tag(%{"tag" => tag} = object) when is_list(tag) do
    tags =
      tag
      |> Enum.filter(fn data -> data["type"] == "Hashtag" and data["name"] end)
      |> Enum.map(fn data -> String.slice(data["name"], 1..-1) end)

    Map.put(object, "tag", tag ++ tags)
  end

  def fix_tag(%{"tag" => %{"type" => "Hashtag", "name" => hashtag} = tag} = object) do
    combined = [tag, String.slice(hashtag, 1..-1)]

    Map.put(object, "tag", combined)
  end

  def fix_tag(%{"tag" => %{} = tag} = object), do: Map.put(object, "tag", [tag])

  def fix_tag(object), do: object

  # content map usually only has one language so this will do for now.
  def fix_content_map(%{"contentMap" => content_map} = object) do
    content_groups = Map.to_list(content_map)
    {_, content} = Enum.at(content_groups, 0)

    Map.put(object, "content", content)
  end

  def fix_content_map(object), do: object

  def fix_type(object, options \\ [])

  def fix_type(%{"inReplyTo" => reply_id, "name" => _} = object, options)
      when is_binary(reply_id) do
    with true <- Federator.allowed_thread_distance?(options[:depth]),
         {:ok, %{data: %{"type" => "Question"} = _} = _} <- get_obj_helper(reply_id, options) do
      Map.put(object, "type", "Answer")
    else
      _ -> object
    end
  end

  def fix_type(object, _), do: object

  defp mastodon_follow_hack(%{"id" => id, "actor" => follower_id}, followed) do
    with true <- id =~ "follows",
         %User{local: true} = follower <- User.get_cached_by_ap_id(follower_id),
         %Activity{} = activity <- Utils.fetch_latest_follow(follower, followed) do
      {:ok, activity}
    else
      _ -> {:error, nil}
    end
  end

  defp mastodon_follow_hack(_, _), do: {:error, nil}

  defp get_follow_activity(follow_object, followed) do
    with object_id when not is_nil(object_id) <- Utils.get_ap_id(follow_object),
         {_, %Activity{} = activity} <- {:activity, Activity.get_by_ap_id(object_id)} do
      {:ok, activity}
    else
      # Can't find the activity. This might a Mastodon 2.3 "Accept"
      {:activity, nil} ->
        mastodon_follow_hack(follow_object, followed)

      _ ->
        {:error, nil}
    end
  end

  # Reduce the object list to find the reported user.
  defp get_reported(objects) do
    Enum.reduce_while(objects, nil, fn ap_id, _ ->
      with %User{} = user <- User.get_cached_by_ap_id(ap_id) do
        {:halt, user}
      else
        _ -> {:cont, nil}
      end
    end)
  end

  def handle_incoming(data, options \\ [])

  # Flag objects are placed ahead of the ID check because Mastodon 2.8 and earlier send them
  # with nil ID.
  def handle_incoming(%{"type" => "Flag", "object" => objects, "actor" => actor} = data, _options) do
    with context <- data["context"] || Utils.generate_context_id(),
         content <- data["content"] || "",
         %User{} = actor <- User.get_cached_by_ap_id(actor),
         # Reduce the object list to find the reported user.
         %User{} = account <- get_reported(objects),
         # Remove the reported user from the object list.
         statuses <- Enum.filter(objects, fn ap_id -> ap_id != account.ap_id end) do
      %{
        actor: actor,
        context: context,
        account: account,
        statuses: statuses,
        content: content,
        additional: %{"cc" => [account.ap_id]}
      }
      |> ActivityPub.flag()
    end
  end

  # disallow objects with bogus IDs
  def handle_incoming(%{"id" => nil}, _options), do: :error
  def handle_incoming(%{"id" => ""}, _options), do: :error
  # length of https:// = 8, should validate better, but good enough for now.
  def handle_incoming(%{"id" => id}, _options) when is_binary(id) and byte_size(id) < 8,
    do: :error

  # TODO: validate those with a Ecto scheme
  # - tags
  # - emoji
  def handle_incoming(
        %{"type" => "Create", "object" => %{"type" => objtype} = object} = data,
        options
      )
      when objtype in ["Article", "Event", "Note", "Video", "Page", "Question", "Answer", "Audio"] do
    actor = Containment.get_actor(data)

    data =
      Map.put(data, "actor", actor)
      |> fix_addressing

    with nil <- Activity.get_create_by_object_ap_id(object["id"]),
         {:ok, %User{} = user} <- User.get_or_fetch_by_ap_id(data["actor"]) do
      object = fix_object(object, options)

      params = %{
        to: data["to"],
        object: object,
        actor: user,
        context: object["conversation"],
        local: false,
        published: data["published"],
        additional:
          Map.take(data, [
            "cc",
            "directMessage",
            "id"
          ])
      }

      with {:ok, created_activity} <- ActivityPub.create(params) do
        reply_depth = (options[:depth] || 0) + 1

        if Federator.allowed_thread_distance?(reply_depth) do
          for reply_id <- replies(object) do
            Pleroma.Workers.RemoteFetcherWorker.enqueue("fetch_remote", %{
              "id" => reply_id,
              "depth" => reply_depth
            })
          end
        end

        {:ok, created_activity}
      end
    else
      %Activity{} = activity -> {:ok, activity}
      _e -> :error
    end
  end

  def handle_incoming(
        %{"type" => "Listen", "object" => %{"type" => "Audio"} = object} = data,
        options
      ) do
    actor = Containment.get_actor(data)

    data =
      Map.put(data, "actor", actor)
      |> fix_addressing

    with {:ok, %User{} = user} <- User.get_or_fetch_by_ap_id(data["actor"]) do
      reply_depth = (options[:depth] || 0) + 1
      options = Keyword.put(options, :depth, reply_depth)
      object = fix_object(object, options)

      params = %{
        to: data["to"],
        object: object,
        actor: user,
        context: nil,
        local: false,
        published: data["published"],
        additional: Map.take(data, ["cc", "id"])
      }

      ActivityPub.listen(params)
    else
      _e -> :error
    end
  end

  def handle_incoming(
        %{"type" => "Follow", "object" => followed, "actor" => follower, "id" => id} = data,
        _options
      ) do
    with %User{local: true} = followed <-
           User.get_cached_by_ap_id(Containment.get_actor(%{"actor" => followed})),
         {:ok, %User{} = follower} <-
           User.get_or_fetch_by_ap_id(Containment.get_actor(%{"actor" => follower})),
         {:ok, activity} <- ActivityPub.follow(follower, followed, id, false) do
      with deny_follow_blocked <- Pleroma.Config.get([:user, :deny_follow_blocked]),
           {_, false} <- {:user_blocked, User.blocks?(followed, follower) && deny_follow_blocked},
           {_, false} <- {:user_locked, User.locked?(followed)},
           {_, {:ok, follower}} <- {:follow, User.follow(follower, followed)},
           {_, {:ok, _}} <-
             {:follow_state_update, Utils.update_follow_state_for_all(activity, "accept")},
           {:ok, _relationship} <- FollowingRelationship.update(follower, followed, "accept") do
        ActivityPub.accept(%{
          to: [follower.ap_id],
          actor: followed,
          object: data,
          local: true
        })
      else
        {:user_blocked, true} ->
          {:ok, _} = Utils.update_follow_state_for_all(activity, "reject")
          {:ok, _relationship} = FollowingRelationship.update(follower, followed, "reject")

          ActivityPub.reject(%{
            to: [follower.ap_id],
            actor: followed,
            object: data,
            local: true
          })

        {:follow, {:error, _}} ->
          {:ok, _} = Utils.update_follow_state_for_all(activity, "reject")
          {:ok, _relationship} = FollowingRelationship.update(follower, followed, "reject")

          ActivityPub.reject(%{
            to: [follower.ap_id],
            actor: followed,
            object: data,
            local: true
          })

        {:user_locked, true} ->
          {:ok, _relationship} = FollowingRelationship.update(follower, followed, "pending")
          :noop
      end

      {:ok, activity}
    else
      _e ->
        :error
    end
  end

  def handle_incoming(
        %{"type" => "Accept", "object" => follow_object, "actor" => _actor, "id" => id} = data,
        _options
      ) do
    with actor <- Containment.get_actor(data),
         {:ok, %User{} = followed} <- User.get_or_fetch_by_ap_id(actor),
         {:ok, follow_activity} <- get_follow_activity(follow_object, followed),
         {:ok, follow_activity} <- Utils.update_follow_state_for_all(follow_activity, "accept"),
         %User{local: true} = follower <- User.get_cached_by_ap_id(follow_activity.data["actor"]),
         {:ok, _relationship} <- FollowingRelationship.update(follower, followed, "accept") do
      ActivityPub.accept(%{
        to: follow_activity.data["to"],
        type: "Accept",
        actor: followed,
        object: follow_activity.data["id"],
        local: false,
        activity_id: id
      })
    else
      _e -> :error
    end
  end

  def handle_incoming(
        %{"type" => "Reject", "object" => follow_object, "actor" => _actor, "id" => id} = data,
        _options
      ) do
    with actor <- Containment.get_actor(data),
         {:ok, %User{} = followed} <- User.get_or_fetch_by_ap_id(actor),
         {:ok, follow_activity} <- get_follow_activity(follow_object, followed),
         {:ok, follow_activity} <- Utils.update_follow_state_for_all(follow_activity, "reject"),
         %User{local: true} = follower <- User.get_cached_by_ap_id(follow_activity.data["actor"]),
         {:ok, _relationship} <- FollowingRelationship.update(follower, followed, "reject"),
         {:ok, activity} <-
           ActivityPub.reject(%{
             to: follow_activity.data["to"],
             type: "Reject",
             actor: followed,
             object: follow_activity.data["id"],
             local: false,
             activity_id: id
           }) do
      {:ok, activity}
    else
      _e -> :error
    end
  end

  @misskey_reactions %{
    "like" => "👍",
    "love" => "❤️",
    "laugh" => "😆",
    "hmm" => "🤔",
    "surprise" => "😮",
    "congrats" => "🎉",
    "angry" => "💢",
    "confused" => "😥",
    "rip" => "😇",
    "pudding" => "🍮",
    "star" => "⭐"
  }

  @doc "Rewrite misskey likes into EmojiReacts"
  def handle_incoming(
        %{
          "type" => "Like",
          "_misskey_reaction" => reaction
        } = data,
        options
      ) do
    data
    |> Map.put("type", "EmojiReact")
    |> Map.put("content", @misskey_reactions[reaction] || reaction)
    |> handle_incoming(options)
  end

  def handle_incoming(%{"type" => "Like"} = data, _options) do
    with {_, {:ok, cast_data_sym}} <-
           {:casting_data,
            data |> LikeValidator.cast_data() |> Ecto.Changeset.apply_action(:insert)},
         cast_data = ObjectValidator.stringify_keys(Map.from_struct(cast_data_sym)),
         :ok <- ObjectValidator.fetch_actor_and_object(cast_data),
         {_, {:ok, cast_data}} <- {:ensure_context_presence, ensure_context_presence(cast_data)},
         {_, {:ok, cast_data}} <-
           {:ensure_recipients_presence, ensure_recipients_presence(cast_data)},
         {_, {:ok, activity, _meta}} <-
           {:common_pipeline, Pipeline.common_pipeline(cast_data, local: false)} do
      {:ok, activity}
    else
      e -> {:error, e}
    end
  end

  def handle_incoming(
        %{
          "type" => "EmojiReact",
          "object" => object_id,
          "actor" => _actor,
          "id" => id,
          "content" => emoji
        } = data,
        _options
      ) do
    with actor <- Containment.get_actor(data),
         {:ok, %User{} = actor} <- User.get_or_fetch_by_ap_id(actor),
         {:ok, object} <- get_obj_helper(object_id),
         {:ok, activity, _object} <-
           ActivityPub.react_with_emoji(actor, object, emoji, activity_id: id, local: false) do
      {:ok, activity}
    else
      _e -> :error
    end
  end

  def handle_incoming(
        %{"type" => "Announce", "object" => object_id, "actor" => _actor, "id" => id} = data,
        _options
      ) do
    with actor <- Containment.get_actor(data),
         {:ok, %User{} = actor} <- User.get_or_fetch_by_ap_id(actor),
         {:ok, object} <- get_embedded_obj_helper(object_id, actor),
         public <- Visibility.is_public?(data),
         {:ok, activity, _object} <- ActivityPub.announce(actor, object, id, false, public) do
      {:ok, activity}
    else
      _e -> :error
    end
  end

  def handle_incoming(
        %{"type" => "Update", "object" => %{"type" => object_type} = object, "actor" => actor_id} =
          data,
        _options
      )
      when object_type in [
             "Person",
             "Application",
             "Service",
             "Organization"
           ] do
    with %User{ap_id: ^actor_id} = actor <- User.get_cached_by_ap_id(object["id"]) do
      {:ok, new_user_data} = ActivityPub.user_data_from_user_object(object)

      actor
      |> User.remote_user_changeset(new_user_data)
      |> User.update_and_set_cache()

      ActivityPub.update(%{
        local: false,
        to: data["to"] || [],
        cc: data["cc"] || [],
        object: object,
        actor: actor_id,
        activity_id: data["id"]
      })
    else
      e ->
        Logger.error(e)
        :error
    end
  end

  # TODO: We presently assume that any actor on the same origin domain as the object being
  # deleted has the rights to delete that object.  A better way to validate whether or not
  # the object should be deleted is to refetch the object URI, which should return either
  # an error or a tombstone.  This would allow us to verify that a deletion actually took
  # place.
  def handle_incoming(
        %{"type" => "Delete", "object" => object_id, "actor" => actor, "id" => id} = data,
        _options
      ) do
    object_id = Utils.get_ap_id(object_id)

    with actor <- Containment.get_actor(data),
         {:ok, %User{} = actor} <- User.get_or_fetch_by_ap_id(actor),
         {:ok, object} <- get_obj_helper(object_id),
         :ok <- Containment.contain_origin(actor.ap_id, object.data),
         {:ok, activity} <-
           ActivityPub.delete(object, local: false, activity_id: id, actor: actor.ap_id) do
      {:ok, activity}
    else
      nil ->
        case User.get_cached_by_ap_id(object_id) do
          %User{ap_id: ^actor} = user ->
            User.delete(user)

          nil ->
            :error
        end

      _e ->
        :error
    end
  end

  def handle_incoming(
        %{
          "type" => "Undo",
          "object" => %{"type" => "Announce", "object" => object_id},
          "actor" => _actor,
          "id" => id
        } = data,
        _options
      ) do
    with actor <- Containment.get_actor(data),
         {:ok, %User{} = actor} <- User.get_or_fetch_by_ap_id(actor),
         {:ok, object} <- get_obj_helper(object_id),
         {:ok, activity, _} <- ActivityPub.unannounce(actor, object, id, false) do
      {:ok, activity}
    else
      _e -> :error
    end
  end

  def handle_incoming(
        %{
          "type" => "Undo",
          "object" => %{"type" => "Follow", "object" => followed},
          "actor" => follower,
          "id" => id
        } = _data,
        _options
      ) do
    with %User{local: true} = followed <- User.get_cached_by_ap_id(followed),
         {:ok, %User{} = follower} <- User.get_or_fetch_by_ap_id(follower),
         {:ok, activity} <- ActivityPub.unfollow(follower, followed, id, false) do
      User.unfollow(follower, followed)
      {:ok, activity}
    else
      _e -> :error
    end
  end

  def handle_incoming(
        %{
          "type" => "Undo",
          "object" => %{"type" => "EmojiReact", "id" => reaction_activity_id},
          "actor" => _actor,
          "id" => id
        } = data,
        _options
      ) do
    with actor <- Containment.get_actor(data),
         {:ok, %User{} = actor} <- User.get_or_fetch_by_ap_id(actor),
         {:ok, activity, _} <-
           ActivityPub.unreact_with_emoji(actor, reaction_activity_id,
             activity_id: id,
             local: false
           ) do
      {:ok, activity}
    else
      _e -> :error
    end
  end

  def handle_incoming(
        %{
          "type" => "Undo",
          "object" => %{"type" => "Block", "object" => blocked},
          "actor" => blocker,
          "id" => id
        } = _data,
        _options
      ) do
    with %User{local: true} = blocked <- User.get_cached_by_ap_id(blocked),
         {:ok, %User{} = blocker} <- User.get_or_fetch_by_ap_id(blocker),
         {:ok, activity} <- ActivityPub.unblock(blocker, blocked, id, false) do
      User.unblock(blocker, blocked)
      {:ok, activity}
    else
      _e -> :error
    end
  end

  def handle_incoming(
        %{"type" => "Block", "object" => blocked, "actor" => blocker, "id" => id} = _data,
        _options
      ) do
    with %User{local: true} = blocked = User.get_cached_by_ap_id(blocked),
         {:ok, %User{} = blocker} = User.get_or_fetch_by_ap_id(blocker),
         {:ok, activity} <- ActivityPub.block(blocker, blocked, id, false) do
      User.unfollow(blocker, blocked)
      User.block(blocker, blocked)
      {:ok, activity}
    else
      _e -> :error
    end
  end

  def handle_incoming(
        %{
          "type" => "Undo",
          "object" => %{"type" => "Like", "object" => object_id},
          "actor" => _actor,
          "id" => id
        } = data,
        _options
      ) do
    with actor <- Containment.get_actor(data),
         {:ok, %User{} = actor} <- User.get_or_fetch_by_ap_id(actor),
         {:ok, object} <- get_obj_helper(object_id),
         {:ok, activity, _, _} <- ActivityPub.unlike(actor, object, id, false) do
      {:ok, activity}
    else
      _e -> :error
    end
  end

  # For Undos that don't have the complete object attached, try to find it in our database.
  def handle_incoming(
        %{
          "type" => "Undo",
          "object" => object
        } = activity,
        options
      )
      when is_binary(object) do
    with %Activity{data: data} <- Activity.get_by_ap_id(object) do
      activity
      |> Map.put("object", data)
      |> handle_incoming(options)
    else
      _e -> :error
    end
  end

  def handle_incoming(
        %{
          "type" => "Move",
          "actor" => origin_actor,
          "object" => origin_actor,
          "target" => target_actor
        },
        _options
      ) do
    with %User{} = origin_user <- User.get_cached_by_ap_id(origin_actor),
         {:ok, %User{} = target_user} <- User.get_or_fetch_by_ap_id(target_actor),
         true <- origin_actor in target_user.also_known_as do
      ActivityPub.move(origin_user, target_user, false)
    else
      _e -> :error
    end
  end

  def handle_incoming(_, _), do: :error

  @spec get_obj_helper(String.t(), Keyword.t()) :: {:ok, Object.t()} | nil
  def get_obj_helper(id, options \\ []) do
    case Object.normalize(id, true, options) do
      %Object{} = object -> {:ok, object}
      _ -> nil
    end
  end

  @spec get_embedded_obj_helper(String.t() | Object.t(), User.t()) :: {:ok, Object.t()} | nil
  def get_embedded_obj_helper(%{"attributedTo" => attributed_to, "id" => object_id} = data, %User{
        ap_id: ap_id
      })
      when attributed_to == ap_id do
    with {:ok, activity} <-
           handle_incoming(%{
             "type" => "Create",
             "to" => data["to"],
             "cc" => data["cc"],
             "actor" => attributed_to,
             "object" => data
           }) do
      {:ok, Object.normalize(activity)}
    else
      _ -> get_obj_helper(object_id)
    end
  end

  def get_embedded_obj_helper(object_id, _) do
    get_obj_helper(object_id)
  end

  def set_reply_to_uri(%{"inReplyTo" => in_reply_to} = object) when is_binary(in_reply_to) do
    with false <- String.starts_with?(in_reply_to, "http"),
         {:ok, %{data: replied_to_object}} <- get_obj_helper(in_reply_to) do
      Map.put(object, "inReplyTo", replied_to_object["external_url"] || in_reply_to)
    else
      _e -> object
    end
  end

  def set_reply_to_uri(obj), do: obj

  @doc """
  Serialized Mastodon-compatible `replies` collection containing _self-replies_.
  Based on Mastodon's ActivityPub::NoteSerializer#replies.
  """
  def set_replies(obj_data) do
    replies_uris =
      with limit when limit > 0 <-
             Pleroma.Config.get([:activitypub, :note_replies_output_limit], 0),
           %Object{} = object <- Object.get_cached_by_ap_id(obj_data["id"]) do
        object
        |> Object.self_replies()
        |> select([o], fragment("?->>'id'", o.data))
        |> limit(^limit)
        |> Repo.all()
      else
        _ -> []
      end

    set_replies(obj_data, replies_uris)
  end

  defp set_replies(obj, []) do
    obj
  end

  defp set_replies(obj, replies_uris) do
    replies_collection = %{
      "type" => "Collection",
      "items" => replies_uris
    }

    Map.merge(obj, %{"replies" => replies_collection})
  end

  def replies(%{"replies" => %{"first" => %{"items" => items}}}) when not is_nil(items) do
    items
  end

  def replies(%{"replies" => %{"items" => items}}) when not is_nil(items) do
    items
  end

  def replies(_), do: []

  # Prepares the object of an outgoing create activity.
  def prepare_object(object) do
    object
    |> set_sensitive
    |> add_hashtags
    |> add_mention_tags
    |> add_emoji_tags
    |> add_attributed_to
    |> prepare_attachments
    |> set_conversation
    |> set_reply_to_uri
    |> set_replies
    |> strip_internal_fields
    |> strip_internal_tags
    |> set_type
  end

  #  @doc
  #  """
  #  internal -> Mastodon
  #  """

  def prepare_outgoing(%{"type" => activity_type, "object" => object_id} = data)
      when activity_type in ["Create", "Listen"] do
    object =
      object_id
      |> Object.normalize()
      |> Map.get(:data)
      |> prepare_object

    data =
      data
      |> Map.put("object", object)
      |> Map.merge(Utils.make_json_ld_header())
      |> Map.delete("bcc")

    {:ok, data}
  end

  def prepare_outgoing(%{"type" => "Announce", "actor" => ap_id, "object" => object_id} = data) do
    object =
      object_id
      |> Object.normalize()

    data =
      if Visibility.is_private?(object) && object.data["actor"] == ap_id do
        data |> Map.put("object", object |> Map.get(:data) |> prepare_object)
      else
        data |> maybe_fix_object_url
      end

    data =
      data
      |> strip_internal_fields
      |> Map.merge(Utils.make_json_ld_header())
      |> Map.delete("bcc")

    {:ok, data}
  end

  # Mastodon Accept/Reject requires a non-normalized object containing the actor URIs,
  # because of course it does.
  def prepare_outgoing(%{"type" => "Accept"} = data) do
    with follow_activity <- Activity.normalize(data["object"]) do
      object = %{
        "actor" => follow_activity.actor,
        "object" => follow_activity.data["object"],
        "id" => follow_activity.data["id"],
        "type" => "Follow"
      }

      data =
        data
        |> Map.put("object", object)
        |> Map.merge(Utils.make_json_ld_header())

      {:ok, data}
    end
  end

  def prepare_outgoing(%{"type" => "Reject"} = data) do
    with follow_activity <- Activity.normalize(data["object"]) do
      object = %{
        "actor" => follow_activity.actor,
        "object" => follow_activity.data["object"],
        "id" => follow_activity.data["id"],
        "type" => "Follow"
      }

      data =
        data
        |> Map.put("object", object)
        |> Map.merge(Utils.make_json_ld_header())

      {:ok, data}
    end
  end

  def prepare_outgoing(%{"type" => _type} = data) do
    data =
      data
      |> strip_internal_fields
      |> maybe_fix_object_url
      |> Map.merge(Utils.make_json_ld_header())

    {:ok, data}
  end

  def maybe_fix_object_url(%{"object" => object} = data) when is_binary(object) do
    with false <- String.starts_with?(object, "http"),
         {:fetch, {:ok, relative_object}} <- {:fetch, get_obj_helper(object)},
         %{data: %{"external_url" => external_url}} when not is_nil(external_url) <-
           relative_object do
      Map.put(data, "object", external_url)
    else
      {:fetch, e} ->
        Logger.error("Couldn't fetch #{object} #{inspect(e)}")
        data

      _ ->
        data
    end
  end

  def maybe_fix_object_url(data), do: data

  def add_hashtags(object) do
    tags =
      (object["tag"] || [])
      |> Enum.map(fn
        # Expand internal representation tags into AS2 tags.
        tag when is_binary(tag) ->
          %{
            "href" => Pleroma.Web.Endpoint.url() <> "/tags/#{tag}",
            "name" => "##{tag}",
            "type" => "Hashtag"
          }

        # Do not process tags which are already AS2 tag objects.
        tag when is_map(tag) ->
          tag
      end)

    Map.put(object, "tag", tags)
  end

  def add_mention_tags(object) do
    {enabled_receivers, disabled_receivers} = Utils.get_notified_from_object(object)
    potential_receivers = enabled_receivers ++ disabled_receivers
    mentions = Enum.map(potential_receivers, &build_mention_tag/1)

    tags = object["tag"] || []
    Map.put(object, "tag", tags ++ mentions)
  end

  defp build_mention_tag(%{ap_id: ap_id, nickname: nickname} = _) do
    %{"type" => "Mention", "href" => ap_id, "name" => "@#{nickname}"}
  end

  def take_emoji_tags(%User{emoji: emoji}) do
    emoji
    |> Enum.flat_map(&Map.to_list/1)
    |> Enum.map(&build_emoji_tag/1)
  end

  # TODO: we should probably send mtime instead of unix epoch time for updated
  def add_emoji_tags(%{"emoji" => emoji} = object) do
    tags = object["tag"] || []

    out = Enum.map(emoji, &build_emoji_tag/1)

    Map.put(object, "tag", tags ++ out)
  end

  def add_emoji_tags(object), do: object

  defp build_emoji_tag({name, url}) do
    %{
      "icon" => %{"url" => url, "type" => "Image"},
      "name" => ":" <> name <> ":",
      "type" => "Emoji",
      "updated" => "1970-01-01T00:00:00Z",
      "id" => url
    }
  end

  def set_conversation(object) do
    Map.put(object, "conversation", object["context"])
  end

  def set_sensitive(object) do
    tags = object["tag"] || []
    Map.put(object, "sensitive", "nsfw" in tags)
  end

  def set_type(%{"type" => "Answer"} = object) do
    Map.put(object, "type", "Note")
  end

  def set_type(object), do: object

  def add_attributed_to(object) do
    attributed_to = object["attributedTo"] || object["actor"]
    Map.put(object, "attributedTo", attributed_to)
  end

  def prepare_attachments(object) do
    attachments =
      (object["attachment"] || [])
      |> Enum.map(fn data ->
        [%{"mediaType" => media_type, "href" => href} | _] = data["url"]
        %{"url" => href, "mediaType" => media_type, "name" => data["name"], "type" => "Document"}
      end)

    Map.put(object, "attachment", attachments)
  end

  def strip_internal_fields(object) do
    object
    |> Map.drop(Pleroma.Constants.object_internal_fields())
  end

  defp strip_internal_tags(%{"tag" => tags} = object) do
    tags = Enum.filter(tags, fn x -> is_map(x) end)

    Map.put(object, "tag", tags)
  end

  defp strip_internal_tags(object), do: object

  def perform(:user_upgrade, user) do
    # we pass a fake user so that the followers collection is stripped away
    old_follower_address = User.ap_followers(%User{nickname: user.nickname})

    from(
      a in Activity,
      where: ^old_follower_address in a.recipients,
      update: [
        set: [
          recipients:
            fragment(
              "array_replace(?,?,?)",
              a.recipients,
              ^old_follower_address,
              ^user.follower_address
            )
        ]
      ]
    )
    |> Repo.update_all([])
  end

  def upgrade_user_from_ap_id(ap_id) do
    with %User{local: false} = user <- User.get_cached_by_ap_id(ap_id),
         {:ok, data} <- ActivityPub.fetch_and_prepare_user_from_ap_id(ap_id),
         {:ok, user} <- update_user(user, data) do
      TransmogrifierWorker.enqueue("user_upgrade", %{"user_id" => user.id})
      {:ok, user}
    else
      %User{} = user -> {:ok, user}
      e -> e
    end
  end

  defp update_user(user, data) do
    user
    |> User.remote_user_changeset(data)
    |> User.update_and_set_cache()
  end

  def maybe_fix_user_url(%{"url" => url} = data) when is_map(url) do
    Map.put(data, "url", url["href"])
  end

  def maybe_fix_user_url(data), do: data

  def maybe_fix_user_object(data), do: maybe_fix_user_url(data)

  defp ensure_context_presence(%{"context" => context} = data) when is_binary(context),
    do: {:ok, data}

  defp ensure_context_presence(%{"object" => object} = data) when is_binary(object) do
    with %{data: %{"context" => context}} when is_binary(context) <- Object.normalize(object) do
      {:ok, Map.put(data, "context", context)}
    else
      _ ->
        {:error, :no_context}
    end
  end

  defp ensure_context_presence(_) do
    {:error, :no_context}
  end

  defp ensure_recipients_presence(%{"to" => [_ | _], "cc" => [_ | _]} = data),
    do: {:ok, data}

  defp ensure_recipients_presence(%{"object" => object} = data) do
    case Object.normalize(object) do
      %{data: %{"actor" => actor}} ->
        data =
          data
          |> Map.put("to", [actor])
          |> Map.put("cc", data["cc"] || [])

        {:ok, data}

      nil ->
        {:error, :no_object}

      _ ->
        {:error, :no_actor}
    end
  end

  defp ensure_recipients_presence(_) do
    {:error, :no_object}
  end
end