defmodule Calculator do
  use GenServer

  def init(val) do
    {:ok, val}
  end

  def handle_cast({:add, num}, state) do
    {:noreply, state + num}
  end

  def handle_cast({:sub, num}, state) do
    {:noreply, state - num}
  end

  def handle_cast({:mult, num}, state) do
    {:noreply, state * num}
  end

  def handle_cast({:div, num}, state) do
    {:noreply, div(state, num)}
  end

  def handle_call(:get_result, _ , state) do
    {:reply, state, state}
  end

  def start(num \\ 0) do
    GenServer.start(Calculator, num)
  end

  def add(pid, num) do
    GenServer.cast(pid, {:add, num})
    GenServer.call(pid, :get_result)
  end

  def sub(pid, num) do
    GenServer.cast(pid, {:sub, num})
    GenServer.call(pid, :get_result)
  end

  def mult(pid, num) do
    GenServer.cast(pid, {:mult, num})
    GenServer.call(pid, :get_result)
  end

  def divi(pid, num) do
    GenServer.cast(pid, {:div, num})
    GenServer.call(pid, :get_result)
  end
end