Unify the logic of updating objects

lib/pleroma/object/fetcher.ex

@@ -50,7 +50,14 @@ defmodule Pleroma.Object.Fetcher do
           Pleroma.Constants.status_updatable_fields()
           |> Enum.any?(fn field -> Map.get(old_data, field) != Map.get(new_data, field) end)
 
-        new_data |> Object.maybe_update_history(old_data, changed?)
+        %{updated_object: updated_object} =
+          new_data
+          |> Object.Updater.maybe_update_history(old_data,
+            updated: changed?,
+            use_history_in_new_object?: false
+          )
+
+        updated_object
       else
         new_data
       end

lib/pleroma/object/updater.ex

@@ -0,0 +1,157 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2022 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.Object.Updater do
+  require Pleroma.Constants
+
+  def update_content_fields(orig_object_data, updated_object) do
+    Pleroma.Constants.status_updatable_fields()
+    |> Enum.reduce(
+      %{data: orig_object_data, updated: false},
+      fn field, %{data: data, updated: updated} ->
+        updated = updated or Map.get(updated_object, field) != Map.get(orig_object_data, field)
+
+        data =
+          if Map.has_key?(updated_object, field) do
+            Map.put(data, field, updated_object[field])
+          else
+            Map.drop(data, [field])
+          end
+
+        %{data: data, updated: updated}
+      end
+    )
+  end
+
+  def maybe_history(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
+      _ -> nil
+    end
+  end
+
+  def history_for(object) do
+    with history when not is_nil(history) <- maybe_history(object) do
+      history
+    else
+      _ -> history_skeleton()
+    end
+  end
+
+  defp history_skeleton do
+    %{
+      "type" => "OrderedCollection",
+      "totalItems" => 0,
+      "orderedItems" => []
+    }
+  end
+
+  def maybe_update_history(
+        updated_object,
+        orig_object_data,
+        opts
+      ) do
+    updated = opts[:updated]
+    use_history_in_new_object? = opts[:use_history_in_new_object?]
+
+    if not updated do
+      %{updated_object: updated_object, used_history_in_new_object?: false}
+    else
+      # Put edit history
+      # Note that we may have got the edit history by first fetching the object
+      {new_history, used_history_in_new_object?} =
+        with true <- use_history_in_new_object?,
+             updated_history when not is_nil(updated_history) <- maybe_history(updated_object) do
+          {updated_history, true}
+        else
+          _ ->
+            history = history_for(orig_object_data)
+
+            latest_history_item =
+              orig_object_data
+              |> Map.drop(["id", "formerRepresentations"])
+
+            updated_history =
+              history
+              |> Map.put("orderedItems", [latest_history_item | history["orderedItems"]])
+              |> Map.put("totalItems", history["totalItems"] + 1)
+
+            {updated_history, false}
+        end
+
+      updated_object =
+        updated_object
+        |> Map.put("formerRepresentations", new_history)
+
+      %{updated_object: updated_object, used_history_in_new_object?: used_history_in_new_object?}
+    end
+  end
+
+  defp maybe_update_poll(to_be_updated, updated_object) do
+    choice_key = fn data ->
+      if Map.has_key?(data, "anyOf"), do: "anyOf", else: "oneOf"
+    end
+
+    with true <- to_be_updated["type"] == "Question",
+         key <- choice_key.(updated_object),
+         true <- key == choice_key.(to_be_updated),
+         orig_choices <- to_be_updated[key] |> Enum.map(&Map.drop(&1, ["replies"])),
+         new_choices <- updated_object[key] |> Enum.map(&Map.drop(&1, ["replies"])),
+         true <- orig_choices == new_choices do
+      # Choices are the same, but counts are different
+      to_be_updated
+      |> Map.put(key, updated_object[key])
+    else
+      # Choices (or vote type) have changed, do not allow this
+      _ -> to_be_updated
+    end
+  end
+
+  # This calculates the data to be sent as the object of an Update.
+  # new_data's formerRepresentations is not considered.
+  # formerRepresentations is added to the returned data.
+  def make_update_object_data(original_data, new_data, date) do
+    %{data: updated_data, updated: updated} =
+      original_data
+      |> update_content_fields(new_data)
+
+    if not updated do
+      updated_data
+    else
+      %{updated_object: updated_data} =
+        updated_data
+        |> maybe_update_history(original_data, updated: updated, use_history_in_new_object?: false)
+
+      updated_data
+      |> Map.put("updated", date)
+    end
+  end
+
+  # This calculates the data of the new Object from an Update.
+  # new_data's formerRepresentations is considered.
+  def make_new_object_data_from_update_object(original_data, new_data) do
+    %{data: updated_data, updated: updated} =
+      original_data
+      |> update_content_fields(new_data)
+
+    %{updated_object: updated_data, used_history_in_new_object?: used_history_in_new_object?} =
+      updated_data
+      |> maybe_update_history(original_data, updated: updated, use_history_in_new_object?: false)
+
+    updated_data =
+      updated_data
+      |> maybe_update_poll(new_data)
+
+    %{
+      updated_data: updated_data,
+      updated: updated,
+      used_history_in_new_object?: used_history_in_new_object?
+    }
+  end
+end