Record edit history for Note and Question Updates

lib/pleroma/web/activity_pub/side_effects.ex

@@ -410,6 +410,26 @@ defmodule Pleroma.Web.ActivityPub.SideEffects do
     {:ok, object, meta}
   end
 
+  defp history_for_object(object) do
+    with history <- Map.get(object, "formerRepresentations"),
+         true <- is_map(history),
+         "OrderedCollection" <- Map.get(history, "type"),
+         true <- is_list(Map.get(history, "orderedItems")),
+         true <- is_integer(Map.get(history, "totalItems")) do
+      history
+    else
+      _ -> history_skeleton()
+    end
+  end
+
+  defp history_skeleton do
+    %{
+      "type" => "OrderedCollection",
+      "totalItems" => 0,
+      "orderedItems" => []
+    }
+  end
+
   @updatable_object_types ["Note", "Question"]
   # We do not allow poll options to be changed, but the poll description can be.
   @updatable_fields [
@@ -431,6 +451,19 @@ defmodule Pleroma.Web.ActivityPub.SideEffects do
     orig_object_data = orig_object.data
 
     if orig_object_data["type"] in @updatable_object_types do
+      # Put edit history
+      # Note that we may have got the edit history by first fetching the object
+      history = history_for_object(orig_object_data)
+
+      latest_history_item =
+        orig_object_data
+        |> Map.drop(["id", "formerRepresentations"])
+
+      new_history =
+        history
+        |> Map.put("orderedItems", [latest_history_item | history["orderedItems"]])
+        |> Map.put("totalItems", history["totalItems"] + 1)
+
       updated_object_data =
         @updatable_fields
         |> Enum.reduce(
@@ -443,6 +476,7 @@ defmodule Pleroma.Web.ActivityPub.SideEffects do
             end
           end
         )
+        |> Map.put("formerRepresentations", new_history)
 
       orig_object
       |> Object.change(%{data: updated_object_data})