From 5e8aac0e07cf54d527643e9793b92f3c0b3826e2 Mon Sep 17 00:00:00 2001
From: Tusooa Zhu <tusooa@kazv.moe>
Date: Sun, 29 May 2022 13:54:16 -0400
Subject: [PATCH] Record edit history for Note and Question Updates

---
 lib/pleroma/web/activity_pub/side_effects.ex  | 34 +++++++++++++++++
 priv/static/schemas/litepub-0.1.jsonld        |  3 +-
 .../web/activity_pub/side_effects_test.exs    | 37 ++++++++++++++++++-
 3 files changed, 72 insertions(+), 2 deletions(-)

diff --git a/lib/pleroma/web/activity_pub/side_effects.ex b/lib/pleroma/web/activity_pub/side_effects.ex
index aeddf3ed8..c4d56fa20 100644
--- a/lib/pleroma/web/activity_pub/side_effects.ex
+++ b/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})
diff --git a/priv/static/schemas/litepub-0.1.jsonld b/priv/static/schemas/litepub-0.1.jsonld
index 946099a6e..650118475 100644
--- a/priv/static/schemas/litepub-0.1.jsonld
+++ b/priv/static/schemas/litepub-0.1.jsonld
@@ -36,7 +36,8 @@
                 "@id": "as:alsoKnownAs",
                 "@type": "@id"
             },
-            "vcard": "http://www.w3.org/2006/vcard/ns#"
+            "vcard": "http://www.w3.org/2006/vcard/ns#",
+            "formerRepresentations": "litepub:formerRepresentations"
         }
     ]
 }
diff --git a/test/pleroma/web/activity_pub/side_effects_test.exs b/test/pleroma/web/activity_pub/side_effects_test.exs
index f72753116..5c60504d4 100644
--- a/test/pleroma/web/activity_pub/side_effects_test.exs
+++ b/test/pleroma/web/activity_pub/side_effects_test.exs
@@ -153,7 +153,7 @@ defmodule Pleroma.Web.ActivityPub.SideEffectsTest do
       {:ok, update_data, []} = Builder.update(user, updated_note)
       {:ok, update, _meta} = ActivityPub.persist(update_data, local: true)
 
-      %{user: user, object_id: note.id, update_data: update_data, update: update}
+      %{user: user, note: note, object_id: note.id, update_data: update_data, update: update}
     end
 
     test "it updates the note", %{object_id: object_id, update: update} do
@@ -161,6 +161,41 @@ defmodule Pleroma.Web.ActivityPub.SideEffectsTest do
       new_note = Pleroma.Object.get_by_id(object_id)
       assert %{"summary" => "edited summary", "content" => "edited content"} = new_note.data
     end
+
+    test "it records the original note in formerRepresentations", %{
+      note: note,
+      object_id: object_id,
+      update: update
+    } do
+      {:ok, _, _} = SideEffects.handle(update)
+      %{data: new_note} = Pleroma.Object.get_by_id(object_id)
+      assert %{"summary" => "edited summary", "content" => "edited content"} = new_note
+
+      assert [Map.drop(note.data, ["id", "formerRepresentations"])] ==
+               new_note["formerRepresentations"]["orderedItems"]
+
+      assert new_note["formerRepresentations"]["totalItems"] == 1
+    end
+
+    test "it puts the original note at the front of formerRepresentations", %{
+      note: note,
+      object_id: object_id,
+      update: update
+    } do
+      {:ok, _, _} = SideEffects.handle(update)
+      %{data: first_edit} = Pleroma.Object.get_by_id(object_id)
+      {:ok, _, _} = SideEffects.handle(update)
+      %{data: new_note} = Pleroma.Object.get_by_id(object_id)
+      assert %{"summary" => "edited summary", "content" => "edited content"} = new_note
+
+      original_version = Map.drop(note.data, ["id", "formerRepresentations"])
+      first_edit = Map.drop(first_edit, ["id", "formerRepresentations"])
+
+      assert [first_edit, original_version] ==
+               new_note["formerRepresentations"]["orderedItems"]
+
+      assert new_note["formerRepresentations"]["totalItems"] == 2
+    end
   end
 
   describe "EmojiReact objects" do