18F/identity-idp

# frozen_string_literal: true

require 'resolv'

# Class to help normalize email addresses for services like Gmail that let users
# add extra things after a +
class EmailNormalizer
  attr_reader :email

  # @param [#to_s] email
  def initialize(email)
    @email = Mail::Address.new(email.to_s)
  end

  # @return [String]
  def normalized_email
    if gmail?
      before_plus, _after_plus = email.local.split('+', 2)
      [before_plus.tr('.', ''), email.domain].join('@')
    else
      email.to_s
    end
  end

  private

  def gmail?
    email.domain == 'gmail.com' || google_mx_record?
  end

  def google_mx_record?
    return false if ENV['RAILS_OFFLINE']
    return false if email.domain.blank? || !email.domain.to_s.ascii_only?

    mx_records(email.domain).any? { |domain| domain.end_with?('google.com') }
  end

  def mx_records(domain)
    Resolv::DNS.open do |dns|
      dns.getresources(domain, Resolv::DNS::Resource::IN::MX).
        map { |r| r.exchange.to_s }
    end
  end
end