defmodule LucasNumbers do
  @moduledoc """
  Lucas numbers are an infinite sequence of numbers which build progressively
  which hold a strong correlation to the golden ratio (φ or ϕ)

  E.g.: 2, 1, 3, 4, 7, 11, 18, 29, ...
  """

  def generate(count) when is_integer(count) and count > 0 do
    {2, 1}
    |> Stream.iterate(fn {a, b} -> {b, a + b} end)
    |> Stream.map(&elem(&1, 0))
    |> Enum.take(count)
  end

  def generate(_count), do: raise(ArgumentError, "count must be specified as an integer >= 1")
end