#!/usr/bin/env ruby
require 'json'
require 'erb'
require 'netaddr'
require 'fileutils'
require 'pathname'
require 'ostruct'

LXC_ROOT = Pathname.new("/etc/lxc")
ZONE_PATH = LXC_ROOT.join("zones")
TEMPLATE_PATH = LXC_ROOT.join("templates")
CONTAINER_DATA = LXC_ROOT.join("container.json")
LXC_ZONE = ZONE_PATH.join("eve.higgsboson.tk.zone")
DNS_CONTAINER = "dns"

def atomic_write(path, content)
  temp_path = path.to_s + ".tmp"
  File.open(temp_path, 'w+') do |f|
    f.write(content)
  end

  FileUtils.mv(temp_path, path)
end

class ZoneData < OpenStruct
  def get_binding
    binding
  end

  def ip(subnet)
    NetAddr::CIDR.create(subnet).ip(Short: true)
  end

  def pointers(&block)
    subnet_arpa = subnet.arpa
    version = subnet.version

    data["network"].each do |name, data|
      next unless data["ipv#{version}"]
      arpa = NetAddr::CIDR.create(data["ipv#{version}"]).arpa
      addr = arpa[0, arpa.size - subnet_arpa.size - 1]
      yield addr, name
    end
  end
end

def reverse_zone(data, subnet)
  subnet = NetAddr::CIDR.create(subnet)
  zone_data = ZoneData.new(data: data, subnet: subnet).get_binding
  rdns_zone_template = File.read(TEMPLATE_PATH.join("rdns-zone.erb"))
  rdns_path = ZONE_PATH.join(subnet.arpa.gsub(/\.$/, ""))
  template = ERB.new(rdns_zone_template, nil, '-').result(zone_data)
  [rdns_path, template]
end

def main
  json = JSON.load(File.open(CONTAINER_DATA))
  json["zone"]["serial"] += 1

  zone_data = ZoneData.new(data: json)

  lxc_zone_template = File.read(TEMPLATE_PATH.join("lxc-zone.erb"))
  zone = ERB.new(lxc_zone_template, nil, '-').result(zone_data.get_binding)

  atomic_write(LXC_ZONE, zone)
  atomic_write(*reverse_zone(json, json["zone"]["v4_subnet"]))
  atomic_write(*reverse_zone(json, json["zone"]["v6_subnet"]))
  atomic_write(CONTAINER_DATA, JSON.pretty_generate(json))

  system("lxc-attach", "-n", DNS_CONTAINER, "--", "rndc", "reload")
end

main