Vereinfacht: update existing contact when found by email

Before saving contact_id to member, sync current data to the
existing contact so Vereinfacht stays up to date.

lib/mv/vereinfacht/vereinfacht.ex

@@ -36,21 +36,49 @@ defmodule Mv.Vereinfacht do
 
   defp do_sync_member(member) do
     if present_contact_id?(member.vereinfacht_contact_id) do
-      case Client.update_contact(member.vereinfacht_contact_id, member) do
-        {:ok, _} -> :ok
-        {:error, reason} -> {:error, reason}
-      end
+      sync_existing_contact(member)
     else
-      case Client.create_contact(member) do
-        {:ok, contact_id} ->
-          save_contact_id(member, contact_id)
+      ensure_contact_then_save(member)
+    end
+  end
 
-        {:error, reason} ->
-          {:error, reason}
+  defp sync_existing_contact(member) do
+    case Client.update_contact(member.vereinfacht_contact_id, member) do
+      {:ok, _} -> :ok
+      {:error, reason} -> {:error, reason}
+    end
+  end
+
+  defp ensure_contact_then_save(member) do
+    case get_or_create_contact_id(member) do
+      {:ok, contact_id} -> save_contact_id(member, contact_id)
+      {:error, _} = err -> err
+    end
+  end
+
+  # Before create: find by email to avoid duplicate contacts (idempotency).
+  # When an existing contact is found, update it with current member data.
+  defp get_or_create_contact_id(member) do
+    email = member |> Map.get(:email) |> to_string() |> String.trim()
+
+    if email == "" do
+      Client.create_contact(member)
+    else
+      case Client.find_contact_by_email(email) do
+        {:ok, existing_id} -> update_existing_contact_and_return_id(existing_id, member)
+        {:error, :not_found} -> Client.create_contact(member)
+        {:error, _} = err -> err
       end
     end
   end
 
+  defp update_existing_contact_and_return_id(contact_id, member) do
+    case Client.update_contact(contact_id, member) do
+      {:ok, _} -> {:ok, contact_id}
+      {:error, _} = err -> err
+    end
+  end
+
   defp save_contact_id(member, contact_id) do
     system_actor = SystemActor.get_system_actor()
     opts = Helpers.ash_actor_opts(system_actor)