defmodule Newsletter do
  def read_emails(path), do: File.read!(path) |> String.split("\n", trim: true)
  def open_log(path), do: File.open!(path, [:write])
  def log_sent_email(pid, email), do: IO.puts(pid, email)
  def close_log(pid), do: File.close(pid)

  def send_newsletter(emails_path, log_path, send_fun) do
    pid = open_log(log_path)

    read_emails(emails_path)
    |> Enum.each(&(send_fun.(&1) == :ok and log_sent_email(pid, &1)))

    close_log(pid)
  end
end