defmodule LSG.Subnet do
  use Agent

  def start_link(_) do
    Agent.start_link(&setup/0, name: __MODULE__)
  end

  def assignations() do
    :dets.select(dets(), [{{:"$1", :"$2"}, [is_binary: :"$2"], [{{:"$1", :"$2"}}]}])
  end

  def find_subnet_for(binary) when is_binary(binary) do
    case :dets.select(dets(), [{{:"$1", :"$2"}, [{:==, :"$2", binary}], [{{:"$1", :"$2"}}]}]) do
      [{subnet, _}] -> subnet
      _ -> nil
    end
  end

  def assign(binary) when is_binary(binary) do
    result = if subnet = find_subnet_for(binary) do
      {:ok, subnet}
    else
      Agent.get_and_update(__MODULE__, fn(dets) ->
        {subnet, _} = available_select(dets)
        :dets.insert(dets, {subnet, binary})
        :dets.sync(dets)
        {{:new, subnet}, dets}
      end)
    end

    case result do
      {:new, subnet} ->
        ip = Pfx.host(subnet, 1)
        set_reverse(binary, ip)
        subnet
      {:ok, subnet} ->
        subnet
    end
  end

  def set_reverse(name, ip, value \\ nil)

  def set_reverse(name, ip, nil) do
    set_reverse(name, ip, "#{name}.users.goulag.org")
  end

  def set_reverse(_, ip, value) do
    ptr_zone = "3.0.0.2.d.f.0.a.2.ip6.arpa"
    ip_fqdn = Pfx.dns_ptr(ip)
    ip_local = String.replace(ip_fqdn, ".#{ptr_zone}", "")
    rev? = String.ends_with?(value, ".users.goulag.org")
    if rev? do
      {:ok, rev_zone} = PowerDNSex.show_zone("users.goulag.org")
      rev_update? = Enum.any?(rev_zone.rrsets, fn(rr) -> rr.name == "#{ip_fqdn}." end)
      record = %{name: "#{value}.", type: "AAAA", ttl: 8600, records: [%{content: ip, disabled: false}]}
      if(rev_update?, do: PowerDNSex.update_record(rev_zone, record), else: PowerDNSex.create_record(rev_zone, record))
    end
    {:ok, zone} = PowerDNSex.show_zone(ptr_zone)
    update? = Enum.any?(zone.rrsets, fn(rr) -> rr.name == "#{ip_fqdn}." end)
    record = %{name: "#{ip_fqdn}.", type: "PTR", ttl: 3600, records: [%{content: "#{value}.", disabled: false}]}
    pdns = if(update?, do: PowerDNSex.update_record(zone, record), else: PowerDNSex.create_record(zone, record))
    :ok
  end

  @doc false
  def dets() do
    (LSG.data_path() <> "/subnets.dets") |> String.to_charlist()
  end

  @doc false
  def setup() do
    {:ok, dets} = :dets.open_file(dets(), [])
    dets
  end

  defp available_select(dets) do
    spec = [{{:"$1", :"$2"}, [is_integer: :"$2"], [{{:"$1", :"$2"}}]}]
    {subnets, _} = :dets.select(dets, spec, 20)
    subnet = subnets
    |> Enum.sort_by(fn({_, last}) -> last end)
    |> List.first()
  end

end