Update Author to sync only a new non-local data.

lib/decentralised_book_index/metadata.ex

@@ -98,6 +98,7 @@ defmodule DecentralisedBookIndex.Metadata do
       define :search_author, action: :search, args: [:name]
       define :update_author, action: :update
       define :assign_author_avatar_image, args: [:avatar_url], action: :assign_avatar_image
+      define :assign_author_dbi_server, args: [:dbi_server_id], action: :assign_dbi_server_id
       define :destroy_author, action: :destroy
     end
 

lib/decentralised_book_index/metadata/author.ex

@@ -195,6 +195,10 @@ defmodule DecentralisedBookIndex.Metadata.Author do
     update :assign_avatar_image do
       accept [:avatar_url]
     end
+
+    update :assign_dbi_server_id do
+      accept [:dbi_server_id]
+    end
   end
 
   policies do

lib/decentralised_book_index/sync/sync/author_sync.ex

@@ -8,15 +8,17 @@ defmodule DecentralisedBookIndex.Sync.AuthorSync do
 
     case Metadata.get_author_by_id(attrs.id) do
       {:ok, author} ->
-        attrs =
-          attrs
-          |> Map.delete(:id)
-          |> update_registry(registry_info)
-          |> Map.put(:dbi_server_id, server_id)
+        if not is_local(author) and is_new(attrs, author) do
+          attrs =
+            attrs
+            |> Map.delete(:id)
+            |> update_registry(registry_info)
+            |> Map.put_new(:dbi_server_id, server_id)
 
-        author
-        |> Ash.Changeset.for_update(:sync, attrs)
-        |> Ash.update!(authorize?: false)
+          author
+          |> Ash.Changeset.for_update(:sync, attrs)
+          |> Ash.update!(authorize?: false)
+        end
 
         :ok
 
@@ -24,7 +26,7 @@ defmodule DecentralisedBookIndex.Sync.AuthorSync do
         attrs =
           attrs
           |> update_registry(registry_info)
-          |> Map.put(:dbi_server_id, server_id)
+          |> Map.put_new(:dbi_server_id, server_id)
 
         Author
         |> Ash.Changeset.for_create(:sync_create, attrs)
@@ -58,4 +60,17 @@ defmodule DecentralisedBookIndex.Sync.AuthorSync do
         |> Map.delete(:author_alias_registry_id)
     end
   end
+
+  defp is_local(author) do
+    is_nil(author.dbi_server_id)
+  end
+
+  defp is_new(new_author, author) do
+    with {:ok, datetime, _offset} <- DateTime.from_iso8601(new_author[:updated_at]) do
+      DateTime.after?(datetime, author.updated_at)
+    else
+      {:error, reason} ->
+        false
+    end
+  end
 end