defmodule MvWeb.Plugs.JoinFormEnabled do
  @moduledoc """
  For GET /join: returns 404 when the join form is disabled in settings.
  No-op for other paths.
  """
  import Plug.Conn

  alias Mv.Membership

  def init(opts), do: opts

  def call(conn, _opts) do
    if join_path?(conn), do: maybe_404(conn), else: conn
  end

  defp join_path?(conn) do
    conn.request_path == "/join" and conn.method == "GET"
  end

  defp maybe_404(conn) do
    case Membership.get_settings() do
      {:ok, %{join_form_enabled: true}} -> conn
      _ -> send_404(conn)
    end
  end

  # Same body as default ErrorHTML 404 (no custom error templates in this app).
  defp send_404(conn) do
    conn
    |> put_resp_content_type("text/html")
    |> send_resp(404, "Not Found")
    |> halt()
  end
end