module Reversed

# File lib/reversed.rb, line 6
def self.lookup(ip, timeout: 5, nameservers: nil)
  ip = ip.to_s
  unless ip.empty?
    begin
      # ensure valid ip
      ip = IPAddr.new(ip)
    rescue IPAddr::InvalidAddressError
      raise ArgumentError, "Invalid IP"
    end

    options = {
      retry_number: 3,
      udp_timeout: timeout
    }
    options[:nameservers] = nameservers if nameservers
    begin
      resolver = Net::DNS::Resolver.new(options).search(ip.reverse, Net::DNS::PTR)
      answer = resolver.answer.first || resolver.authority.first
      if answer && !answer.value.empty?
        answer.value.split(" ").first[0..-2]
      end
    rescue Net::DNS::Resolver::NoResponseError
      nil
    rescue Errno::EAFNOSUPPORT
      options[:use_tcp] = true
      options[:tcp_timeout] = timeout
      retry
    end
  end
end