defmodule Shard.Identity do
  use Agent
  require Salty.Sign.Ed25519, as: Sign
  require Logger

  @identity_db [Application.get_env(:shard, :data_path), "identity_db"] |> Path.join |> String.to_atom

  def start_link(_) do
    Agent.start_link(__MODULE__, :init, [], name: __MODULE__)
  end

  def init() do
    :dets.start
    {:ok, @identity_db} = :dets.open_file @identity_db, type: :set

    case :dets.match @identity_db, :"$1" do
      [] ->
        Logger.info "Generating keypair..."
        {pk, sk} = gen_keypair(Application.get_env(:shard, :peer_id_suffix))
        nick_suffix = pk
                      |> binary_part(0, 3)
                      |> Base.encode16
                      |> String.downcase
        nick = "Anon" <> nick_suffix
        :dets.insert @identity_db, {pk, sk, nick}
        %{
          keypair:  {pk, sk},
          nickname: nick
        }
      [[{pk, sk, nick}] | _] ->
        %{
          keypair:  {pk, sk},
          nickname: nick
        }
    end
  end

  defp gen_keypair(suffix, n \\ 0) do
    {:ok, pk, sk} = Sign.keypair
    if rem(n, 10000) == 0 do
      Logger.info "#{n}... expected #{:math.pow(256, byte_size(suffix))}"
    end
    if :binary.longest_common_suffix([pk, suffix]) == byte_size(suffix) do
      {pk, sk}
    else
      gen_keypair(suffix, n+1)
    end
  end

  def get_keypair() do
    Agent.get(__MODULE__, &(&1.keypair))
  end

  def get_nickname() do
    Agent.get(__MODULE__, &(&1.nickname))
  end

  def set_nickname(newnick) do
    Agent.update(__MODULE__, fn state ->
      {pk, sk} = state.keypair
      :dets.insert @identity_db, {pk, sk, newnick}
      %{state | nickname: newnick}
    end)
  end
end