I have a very simple plug that sets the subdomain layout based on the Endpoint subdomain.

defmodule MyApp.Plug.Subdomain do
  import Plug.Conn
  alias MyApp.Endpoint

  def init(opts), do: opts

  def call(conn, _) do
    subdomain = get_subdomain(conn.host)

    # Check here, does this #{subdomain}.eex layout file exist?

    conn
    |> assign(:subdomain_layout, subdomain)
  end

  @spec get_subdomain(String.t()) :: String.t()
  defp get_subdomain(host) do
    String.replace(host, ~r/.?#{Endpoint.host()}/, "")
  end
end

How can I check if the layout file exists in the folder? Can I use File.exists??