shrivel

defmodule Shrivel do
  defstruct [:short_url, :long_url, :segment]

  def shorten(long_url) do
    %Shrivel{long_url: long_url}
    |> generate_short_url
  end

  def valid?(url) do
    Regex.match?(
      ~r/
        ^(?:(?:https?|ftp):\/\/)
        (?:\S+(?::\S*)?@)?
        (?:
        (?!(?:10|127)(?:\.\d{1,3}){3})(?!(?:169\.254|192\.168)(?:\.\d{1,3}){2})
        (?!$172\.(?:1[6-9]|2\d|3[0-1])(?:\.\d{1,3}){2})
        (?:[1-9]\d?|1\d\d|2[01]\d|22[0-3])(?:\.(?:1?\d{1,2}|2[0-4]\d|25[0-5])){2}
        (?:\.(?:[1-9]\d?|1\d\d|2[0-4]\d|25[0-4]))
        |(?:(?:[a-z\x{00a1}-\x{ffff}0-9]-*)*[a-z\x{00a1}-\x{ffff}0-9]+)
        (?:\.(?:[a-z\x{00a1}-\x{ffff}0-9]-*)*[a-z\x{00a1}-\x{ffff}0-9]+)*
        (?:\.(?:[a-z\x{00a1}-\x{ffff}]{2,}))\.?)(?::\d{2,5})?(?:[\/?#]\S*)?$
      /ximu,
      url
    )
  end

  defp generate_short_url(shrivel) do
    %{shrivel | short_url: Application.get_env(:shrivel, :host)}
    |> add_segment
  end

  defp add_segment(shrivel) do
    segment = generate_segment
    %{shrivel | short_url: shrivel.short_url <> segment, segment: segment}
  end

  defp generate_segment() do
    length = Application.get_env(:shrivel, :segment_length)
    :crypto.strong_rand_bytes(length) 
    |> Base.url_encode64 
    |> binary_part(0, length)
  end
end