defmodule RNS.PacketHashStore do
  @moduledoc """
  Stores the hashes of all sent/received packets.
  This is to be sure no packets are received twice, and also limits attacks on announces which could be used to block some paths.
  """

  @spec child_spec(any()) :: map()
  def child_spec(_args) do
    %{
      id: __MODULE__,
      start: {__MODULE__, :start_link, []}
    }
  end

  @spec start_link() :: {:ok, pid()}
  def start_link() do
    pid = spawn_link(__MODULE__, :init, [])
    {:ok, pid}
  end

  # Client
  @doc "Adds a packet hash."
  @spec add(RNS.Packet.hash()) :: :ok
  def add(packet_hash) do
    true = :ets.insert(:packet_hashes, {packet_hash})
    :ok
  end

  @doc "Checks if the packet hash is in the table."
  @spec exists?(RNS.Packet.hash()) :: boolean()
  def exists?(packet_hash) do
    :ets.member(:packet_hashes, packet_hash)
  end

  # Callbacks
  @spec init() :: :ok
  def init() do
    :ets.new(:packet_hashes, [
      {:read_concurrency, true},
      {:write_concurrency, true},
      :public,
      :named_table
    ])

    Process.sleep(:infinity)
  end
end