require "erb"
ROOT_PATH = Pathname.new(File.expand_path("../../..", __FILE__))

class TemplateContext
  def initialize(hash)
    hash.each do |key, value|
      singleton_class.send(:define_method, key) { value }
    end
  end

  def get_binding
    binding
  end
end

class Container
  def initialize(data, ip4:, ip6:, dn42_ipv4:, dn42_ipv6:, **options)
    network = @data["network"] || {}
    zone = data["zone"] || {}

    ipv4_subnet = NetAddr::CIDR.create(zone["v4_subnet"] || "192.168.10.0/24")
    ipv6_subnet = NetAddr::CIDR.create(zone["v6_subnet"] || "fd7d:aed0:18aa::/48")

    if subnet = zone["dn42_ipv4_subnet"]
      dn42_ipv4_netmask = NetAddr::CIDR.create(subnet).to_i(:netmask)
    else
      dn42_ipv4_netmask = 24
    end

    if subnet = zone["dn42_ipv6_subnet"]
      dn42_ipv6_netmask = NetAddr::CIDR.create(subnet).to_i(:netmask)
    else
      dn42_ipv6_netmask = 48
    end

    ip4 ||= find_address(ipv4_subnet, collect_subnets(network, "ipv4"))
    ip6 ||= find_address(ipv6_subnet, collect_subnets(network, "ipv6"))
    @opts = options.merge(ipv4: format_address(ip4, ipv4_subnet.to_i(:netmask)),
                          ipv6: format_address(ip6, ipv6_subnet.to_i(:netmask)))
    @opts[:dn42_ipv4] = format_address(dn42_ipv6, dn42_ipv4_netmask)
    @opts[:dn42_ipv6] = format_address(dn42_ipv4, dn42_ipv6_netmask)
  end

  def write_config(config_path)
    context = TemplateContext.new(@opts)
    erb = ERB.new(File.read(ROOT_PATH.join("templates", "config.erb")))
    open(config_path, "w+") do |f|
      f.write(erb.result(context.get_binding))
    end
  end

  private
    def format_address(address, netmask)
      NetAddr::CIDR.create(address, Mask: netmask).desc(IP: true, Short: true)
    end

    def collect_subnets(network, type)
      network.map do |k,v|
        NetAddr::CIDR.create(v[type]) if v[type]
      end.compact!
    end

    def find_address(subnet, assigned_subnets)
      subnet.enumerate(Limit: 1E4, Short: true)[1..1E4].each do |cidr|
        assigned = assigned_subnets.find { |s| s.contains?(cidr) || s == cidr }
        return cidr unless assigned
      end
    end
end