defmodule Electric.Publisher do
  @doc """
  Calls many GenServers asynchronously with the same message and waits
  for their responses before returning.

  Returns `:ok` once all GenServers have responded or have died.

  There is no timeout so if the GenServers do not respond or die, this
  function will block indefinitely.
  """
  def publish(pids, message) do
    # Based on OTP GenServer.call, see:
    # https://github.com/erlang/otp/blob/090c308d7c925e154240685174addaa516ea2f69/lib/stdlib/src/gen.erl#L243
    pids
    |> Enum.map(fn pid ->
      ref = Process.monitor(pid)
      send(pid, {:"$gen_call", {self(), ref}, message})
      ref
    end)
    |> Enum.each(fn ref ->
      receive do
        {^ref, _reply} ->
          Process.demonitor(ref, [:flush])
          :ok

        {:DOWN, ^ref, _, _, _reason} ->
          :ok
      end
    end)
  end
end