genserver.ex

defmodule GenServerTpl do
  @moduledoc """
  A GenServer template for a "singleton" process.
  """
  use GenServer

  # Initialization
  def start_link(opts \\ []) do
    GenServer.start_link(__MODULE__, opts, [name: __MODULE__])
  end

  def init(opts) do
    Process.send_after(self(), {:baz, ["spam&eggs"]}, 3_000)
    state = %{
      foo: nil,
      bar: nil,
      baz: nil
    }
    {:ok, state}
  end

  # API
  def foo(value) do
    GenServer.call(__MODULE__, {:foo, [value]})
  end

  def bar(value) do
    GenServer.cast(__MODULE__, {:bar, [value]})
  end

  # Callbacks
  def handle_call({:foo, [value]}, _from, state) do
    resp = "value: #{inspect value}"
    state = %{state|foo: value}
    {:reply, resp, state}
  end

  def handle_cast({:bar, [value]}, state) do
    updated_value = transform_bar(value)
    state = %{state|bar: updated_value}
    {:noreply, state}
  end

  def handle_info({:baz, [value]}, state) do
    state = %{state|baz: value}
    {:noreply, state}
  end

  # Helpers

  defp transform_bar(value) do
    "transformed: #{inspect value}"
  end

end