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

lib/decentralised_book_index/metadata.ex

@@ -149,6 +149,7 @@ defmodule DecentralisedBookIndex.Metadata do
       define :get_publisher_by_id, args: [:id], action: :by_id
       define :search_publisher, action: :search, args: [:name]
       define :update_publisher, action: :update
+      define :assign_publisher_dbi_server, args: [:dbi_server_id], action: :assign_dbi_server_id
       define :destroy_publisher, action: :destroy
     end
   end

lib/decentralised_book_index/metadata/publisher.ex

@@ -56,6 +56,10 @@ defmodule DecentralisedBookIndex.Metadata.Publisher do
       accept [:name]
     end
 
+    update :assign_dbi_server_id do
+      accept [:dbi_server_id]
+    end
+
     update :sync do
       accept [:name, :inserted_at, :updated_at, :dbi_server_id]
     end

lib/decentralised_book_index/sync/sync/publisher_sync.ex

@@ -5,21 +5,23 @@ defmodule DecentralisedBookIndex.Sync.PublisherSync do
   def create_update(attrs, server_id) do
     case Metadata.get_publisher_by_id(attrs.id) do
       {:ok, publisher} ->
-        attrs =
-          attrs
-          |> Map.delete(:id)
-          |> Map.put(:dbi_server_id, server_id)
+        if not is_local(publisher) and is_new(attrs, publisher) do
+          attrs =
+            attrs
+            |> Map.delete(:id)
+            |> Map.put_new(:dbi_server_id, server_id)
 
-        publisher
-        |> Ash.Changeset.for_update(:sync, attrs)
-        |> Ash.update!(authorize?: false)
+          publisher
+          |> Ash.Changeset.for_update(:sync, attrs)
+          |> Ash.update!(authorize?: false)
+        end
 
         :ok
 
       {:error, %Ash.Error.Query.NotFound{}} ->
         attrs =
           attrs
-          |> Map.put(:dbi_server_id, server_id)
+          |> Map.put_new(:dbi_server_id, server_id)
 
         Publisher
         |> Ash.Changeset.for_create(:sync_create, attrs)
@@ -28,4 +30,17 @@ defmodule DecentralisedBookIndex.Sync.PublisherSync do
         :ok
     end
   end
+
+  defp is_local(publisher) do
+    is_nil(publisher.dbi_server_id)
+  end
+
+  defp is_new(new_publisher, publisher) do
+    with {:ok, datetime, _offset} <- DateTime.from_iso8601(new_publisher[:updated_at]) do
+      DateTime.after?(datetime, publisher.updated_at)
+    else
+      {:error, reason} ->
+        false
+    end
+  end
 end