defmodule SNet.Addr do
  @moduledoc"""
  Helper module for getting our IP addresses.

  Runs an agent that gets our public IPv4 address on the internet and stores it.
  """

  use Agent

  require Logger

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

  def init() do
    Application.ensure_all_started(:inets)
    Application.ensure_all_started(:ssl)
    case :httpc.request('http://api.ipify.org') do
      {:ok, {_, _, body}} ->
        {:ok, addr} = :inet.parse_address body
        Logger.info "Public IP address: #{body}"
        [addr]
      _ ->
        Logger.info "Could not get public IP address"
        []
    end
  end

  @doc"""
  Reteurn the list of IPv4 address for our network interfaces.
  """
  def get_if_inet4 do
    {:ok, ifs} = :inet.getifaddrs
    for {_, opts} <- ifs,
        {:addr, addr} <- opts,
        tuple_size(addr) == 4,
        addr != {127,0,0,1}
    do
      addr
    end
  end

  @doc"""
  Return our public IPv4 address as observed by an external API provider (`ipify.org`)
  """
  def get_pub_inet4 do
    Agent.get(__MODULE__, &(&1))
  end

  @doc"""
  Get all our IPv4 addresses.
  """
  def get_all_inet4 do
    addrset = for x <- get_if_inet4() ++ get_pub_inet4(), into: %MapSet{}, do: x
    MapSet.to_list addrset
  end

  @doc"""
  Determines if an IP address is ours or not.
  """
  def is_local?({:inet, ip, port}) do
    port == Application.get_env(:shard, :port) and (ip == {127,0,0,1} or ip in get_all_inet4())
  end
end