send_after.ex

defmodule SendAfter do
  def send_after(pid, message, nanoseconds) do
    {_, os_name} = :os.type()
    increment =
      if os_name == :Windows do
        # monotonic time for Windows in miliseconds, in Linux and MacOS it's nanoseconds
        # so we'll need to convert to miliseconds for windows
        nanoseconds / 1_000_000
      else
        nanoseconds
      end
      
    start_time = :erlang.monotonic_time()
    end_time = start_time + increment
    Task.async(fn -> wait_and_send(end_time, pid, message) end)
  end
  
  def wait_and_send(end_time, pid, message) do
    if :erlang.monotonic_time() >= end_time do
      send(pid, message)
    else
      wait_and_send(end_time, pid, message)
    end
  end
end