defmodule AccessToken do
  @moduledoc """
  Access token generator.
  """

  @default_length 64

  @doc """
  Generates a random access token with URL and filename safe alphabet.

      iex> AccessToken.generate()
      "MPjl2Y5AkvtP30rFb3ABRwkYNWsuRhJXkRQLhjaweqsC7H4fg8H2UmY5RpOkbO05"
      iex> AccessToken.generate(20)
      "XpT7OoqccDKg8Oa14B5w"

  """
  @spec generate(integer) :: String.t()
  def generate(length \\ @default_length) do
    :crypto.strong_rand_bytes(length)
    |> Base.url_encode64(padding: false)
    |> String.slice(0, length)
  end
end