if Code.ensure_loaded?(Ecto) do
  defmodule EView.Changeset.Validators.Email do
    @moduledoc """
    This helper validates emails by complex regex pattern.
    """
    import Ecto.Changeset

    @email_regex Regex.compile!(
                   ~S((?:[a-z0-9!#$%&'*+\/=?^_`{|}~-]+(?:\.[a-z0-9!#$%&'*+\/=?^_`{|}~-]+\)*|") <>
                     ~S((?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21\x23-\x5b\x5d-\x7f]|\\[\x01-\x09\x0b\x0c\x0e-\x7f]\)*"\)) <>
                     ~S(@(?:(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9]\)?\.\)+[a-z0-9](?:[a-z0-9-]*[a-z0-9]\)?) <>
                     ~S(|\[(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?\)\.\){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?) <>
                     ~S(|[a-z0-9-]*[a-z0-9]:(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21-\x5a\x53-\x7f]) <>
                     ~S(|\\[\x01-\x09\x0b\x0c\x0e-\x7f]\)+\)\]\))
                 )

    def validate_email(changeset, field, opts \\ []) do
      validate_change(changeset, field, {:email, @email_regex}, fn _, value ->
        if value =~ @email_regex, do: [], else: [{field, {message(opts, "is not a valid email"), [validation: :email]}}]
      end)
    end

    defp message(opts, key \\ :message, default) do
      Keyword.get(opts, key, default)
    end
  end
end