require 'resolv'

def ensure_period(s)
  if s[-1] == '.'
    s
  else
    "#{s}."
  end
end

Facter.add(:dns_zone_serial) do
  confine do
    Facter::Util::Resolution.which('named-checkconf')
  end

  setcode do
    dns = Resolv::DNS.new(nameserver: ['localhost'])
    zones = `named-checkconf -l`
            .split("\n")
            .map { |line| line.split(' ') }
            .filter { |zone| zone.last == 'master' }
    zone_map = {}
    zones.map do |zone|
      z = ensure_period(zone[0])
      zone_map[z] = dns.getresource(z, Resolv::DNS::Resource::IN::SOA).serial
    end
    zone_map
  end
end