shrivel

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

  def shorten(url) do
    case valid?(url) do
      {:ok, url} ->
        _shorten(url)
      :error ->
        {:error, "Not a valid URL"}
    end
  end

  def valid?(url) do
    if (is_valid_url?(url)) do
      {:ok, url}
    else
      :error
    end
  end

  def alreadyShort?(long_url, hostString) do
    %{host: long_url_host} = URI.parse(long_url)
    %{host: host} = URI.parse(hostString)

    if (long_url_host === host) do
      {:error, "already shortened"}
    else
      :ok
    end
  end

  defp _shorten(url) do
    result =
      %{long_url: url}
      |> getShortURLHost
      |> add_segment

    {:ok, result}
  end

  defp getShortURLHost(shrivel) do
    Map.put(shrivel, :short_url, Application.get_env(:shrivel, :host))
  end

  defp add_segment(shrivel) do
    segment = generate_segment

    Map.put(shrivel, :segment, segment)
    |> Map.put(:short_url, shrivel.short_url <> 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

  defp is_valid_url?(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
end