defmodule Kaffe.PartitionSelector do
  @doc """
  Cycle current from 0 to total-1.

  ## Examples

      iex> Kaffe.PartitionSelector.round_robin(nil, 3)
      0

      iex> Kaffe.PartitionSelector.round_robin(0, 3)
      1

      iex> Kaffe.PartitionSelector.round_robin(1, 3)
      2

      iex> Kaffe.PartitionSelector.round_robin(2, 3)
      0

  """
  def round_robin(current, total) do
    if current < total - 1 do
      current + 1
    else
      0
    end
  end

  def random(total) when total >= 1 do
    :rand.uniform(total) - 1
  end

  def md5(key, total) do
    :crypto.hash(:md5, key)
    |> :binary.bin_to_list()
    |> Enum.sum()
    |> rem(total)
  end
end