Handle "Move" activity

lib/pleroma/following_relationship.ex

@@ -107,4 +107,28 @@ defmodule Pleroma.FollowingRelationship do
       [user.follower_address | following]
     end
   end
+
+  def move_following(origin, target) do
+    following_relationships =
+      __MODULE__
+      |> where(following_id: ^origin.id)
+      |> preload([:follower])
+      |> limit(50)
+      |> Repo.all()
+
+    case following_relationships do
+      [] ->
+        :ok
+
+      following_relationships ->
+        Enum.each(following_relationships, fn following_relationship ->
+          Repo.transaction(fn ->
+            Repo.delete(following_relationship)
+            User.follow(following_relationship.follower, target)
+          end)
+        end)
+
+        move_following(origin, target)
+    end
+  end
 end

lib/pleroma/web/activity_pub/activity_pub.ex

@@ -514,6 +514,30 @@ defmodule Pleroma.Web.ActivityPub.ActivityPub do
     end
   end
 
+  def move(%User{} = origin, %User{} = target, local \\ true) do
+    params = %{
+      "type" => "Move",
+      "actor" => origin.ap_id,
+      "object" => origin.ap_id,
+      "target" => target.ap_id
+    }
+
+    with true <- origin.ap_id in target.also_known_as,
+         {:ok, activity} <- insert(params, local) do
+      maybe_federate(activity)
+
+      BackgroundWorker.enqueue("move_following", %{
+        "origin_id" => origin.id,
+        "target_id" => target.id
+      })
+
+      {:ok, activity}
+    else
+      false -> {:error, "Target account must have the origin in `alsoKnownAs`"}
+      err -> err
+    end
+  end
+
   defp fetch_activities_for_context_query(context, opts) do
     public = [Pleroma.Constants.as_public()]
 

lib/pleroma/web/activity_pub/transmogrifier.ex

@@ -785,6 +785,24 @@ defmodule Pleroma.Web.ActivityPub.Transmogrifier do
     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

lib/pleroma/web/activity_pub/visibility.ex

@@ -14,6 +14,7 @@ defmodule Pleroma.Web.ActivityPub.Visibility do
   @spec is_public?(Object.t() | Activity.t() | map()) :: boolean()
   def is_public?(%Object{data: %{"type" => "Tombstone"}}), do: false
   def is_public?(%Object{data: data}), do: is_public?(data)
+  def is_public?(%Activity{data: %{"type" => "Move"}}), do: true
   def is_public?(%Activity{data: data}), do: is_public?(data)
   def is_public?(%{"directMessage" => true}), do: false
   def is_public?(data), do: Utils.label_in_message?(Pleroma.Constants.as_public(), data)

lib/pleroma/workers/background_worker.ex

@@ -71,4 +71,11 @@ defmodule Pleroma.Workers.BackgroundWorker do
     activity = Activity.get_by_id(activity_id)
     Pleroma.Web.RichMedia.Helpers.perform(:fetch, activity)
   end
+
+  def perform(%{"op" => "move_following", "origin_id" => origin_id, "target_id" => target_id}, _) do
+    origin = User.get_cached_by_id(origin_id)
+    target = User.get_cached_by_id(target_id)
+
+    Pleroma.FollowingRelationship.move_following(origin, target)
+  end
 end