def handle_call({:become_admin, %{user: user_uuid, password: password}}, _from, state) do
    cond do
      state.password != password ->
        {:reply, %{status: :error, message: "invalid password"}, state}
      !Map.has_key?(state.users, user_uuid) ->
        {:reply, %{status: :error, message: "invalid user"}, state}
      true ->
        state = put_in(state.users[user_uuid].is_admin?, true)
        {:reply, %{status: :ok, message: state.users}, state}
    end
  end

  def handle_call({:user_promote, %{admin: admin, user_uuid: user_uuid}}, _from, state) do
    cond do
      !Map.has_key?(state.users, admin) || !state.users[admin].is_admin? ->
        {:reply, %{status: :error, message: "invalid admin"}, state}
      true ->
        handle_call({:become_admin, %{user: user_uuid, password: state.password}}, {}, state)
    end
  end