refact

lib/service/online_service.rb

@@ -0,0 +1,10 @@
+# frozen_string_literal: true
+
+class OnlineService
+  def initialize(repo) = @repo = repo
+
+  def add(session_id, username) = @repo.add(session_id, username)
+  def remove(session_id)        = @repo.remove(session_id)
+  def count                     = @repo.count
+  def user_list                 = @repo.snapshot.sort.map { |_, name| name }
+end