defmodule ValidUrl do
  @moduledoc """
  The base module of ValidUrl.

  It exposes a single function, `validate`.
  """

  @docp """
  Regex to validate URLs.
  Adapted from https://gist.github.com/dperini/729294.
  """
  @link_regex Regex.compile!(
    "^" <>
      # protocol identifier
      "(?:(?:https?|ftp)://)" <>
      # user:pass authentication
      "(?:\\S+(?::\\S*)?@)?" <>
      "(?:" <>
        # IP address exclusion
        # private & local networks
        "(?!(?: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})" <>
        # IP address dotted notation octets
        # excludes loopback network 0.0.0.0
        # excludes reserved space >= 224.0.0.0
        # excludes network & broacast addresses
        # (first & last IP address of each class)
        "(?:[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]))" <>
      "|" <>
        # host name
        "(?:(?:[a-z\\x{00a1}-\\x{ffff}0-9]-*)*[a-z\\x{00a1}-\\x{ffff}0-9]+)" <>
        # domain name
        "(?:\\.(?:[a-z\\x{00a1}-\\x{ffff}0-9]-*)*[a-z\\x{00a1}-\\x{ffff}0-9]+)*" <>
        # TLD identifier
        "(?:\\.(?:[a-z\\x{00a1}-\\x{ffff}]{2,}))" <>
        # TLD may end with dot
        "\\.?" <>
      ")" <>
      # port number
      "(?::\\d{2,5})?" <>
      # resource path
      "(?:[/?#]\\S*)?" <>
    "$", "iu"
  )

  @doc """
  Test whether a string is a valid URL.

  Regular expression-based.  Adapted from [https://gist.github.com/dperini/729294](https://gist.github.com/dperini/729294).

  Args:

  * `url` - The URL to validate, string

  Returns a boolean.
  """
  def validate(url) do
    Regex.match?(@link_regex, url)
  end
end