defmodule Drempel.Backoff do
  @moduledoc """
  Backoff functions for Drempel
  """

  @doc """
  Backoff function based on exponential growth.
  """
  def exponential_backoff(x) when x > 14 do
    exponential_backoff(14)
  end

  def exponential_backoff(x) do
    (:erlang.bsl(1, x) - 1) * 1_000
  end

  @doc """
  Backoff function based on geometric growth.
  """
  def geometric_backoff(x) do
    2 * x * 1_000
  end

  @doc """
  Example tabled backoff function.
  """
  def table_backoff(0), do: 0 * 1_000
  def table_backoff(1), do: 1 * 1_000
  def table_backoff(2), do: 2 * 1_000
  def table_backoff(3), do: 5 * 1_000
  def table_backoff(4), do: 10 * 1_000
  def table_backoff(5), do: 15 * 1_000
  def table_backoff(6), do: 30 * 1_000
  def table_backoff(7), do: 1 * 60 * 1_000
  def table_backoff(8), do: 2 * 60 * 1_000
  def table_backoff(9), do: 5 * 60 * 1_000
  def table_backoff(10), do: 10 * 60 * 1_000
  def table_backoff(11), do: 15 * 60 * 1_000
  def table_backoff(12), do: 30 * 60 * 1_000
  def table_backoff(13), do: 1 * 60 * 60 * 1_000
  def table_backoff(14), do: 2 * 60 * 60 * 1_000
  def table_backoff(_), do: 4 * 60 * 60 * 1_000
end