defmodule Arithmetic.Worker do
    use GenServer

    ### Client API ###
    def start() do
        GenServer.start(__MODULE__, nil)
    end

    def square(pid, x) do
      GenServer.call(pid, {:square, x})
    end

    def sqrt(pid, x) do
      GenServer.call(pid, {:sqrt, x})
    end

    ### Server Impl ###
    @impl true
    def init(_arg) do
        {:ok, nil}
    end

    @impl true
    def handle_call({:square, x}, _from, state) do
      {:reply, x * x, state}
    end

    @impl true
    def handle_call({:sqrt, x}, _from, state) do
      {:reply, (if x < 0, do: :error, else: :math.sqrt(x)), state}
    end
end