GenServer Callbacks examples

hello_server.ex

defmodule HelloServer do
  use GenServer

  ## Server API
  def init(initial_value) do   # initiating the state with the value 1 passed 
    {:ok,initial_value}
  end

  # add the value to the state and returns :ok
  def handle_call({:add,value},_from,state) do
    {:reply, "#{value} add",state + value}
  end

  # returns the state to the caller
  def handle_call(:get,_from,state) do
    :timer.sleep 2000
    {:reply,state,state}
  end
  
  # just reset the state to value 1
  def handle_cast(:reset,state) do
    :timer.sleep 2000
    IO.puts "value has been reset "
    {:noreply,1}
  end

  # This executes periodically
  def handle_info(:work,state) do
    IO.puts " This message prints every after 2 seconds"
    schedule_work()
    {:noreply,state}
  end

  #catch-all clause for the handle_info for handling unkown messages
  def handle_info(_msg, state) do
    IO.puts "unknown message"
    {:noreply, state}
  end

  defp schedule_work() do
    Process.send_after(self(), :work, 2 * 1000) # In 2 seconds
  end

end