%%%-------------------------------------------------------------------
%%% @author anlicheng
%%% @copyright (C) 2024, <COMPANY>
%%% @doc
%%%
%%% @end
%%% Created : 09. 4月 2024 17:37
%%%-------------------------------------------------------------------
-module(dns_server).
-author("anlicheng").
-include("sdlan.hrl").
-include("sdlan_pb.hrl").

-behaviour(gen_server).

%% API
-export([start_link/2]).
-export([get_name/1]).

%% gen_server callbacks
-export([init/1, handle_call/3, handle_cast/2, handle_info/2, terminate/2, code_change/3]).

-define(SERVER, ?MODULE).

-record(state, {
    socket
}).

%%%===================================================================
%%% API
%%%===================================================================

-spec get_name(Id :: integer()) -> atom().
get_name(Id) when is_integer(Id) ->
    list_to_atom("dns_server:" ++ integer_to_list(Id)).

%% @doc Spawns the server and registers the local name (unique)
-spec(start_link(Name :: atom(), Port :: integer()) ->
    {ok, Pid :: pid()} | ignore | {error, Reason :: term()}).
start_link(Name, Port) when is_atom(Name), is_integer(Port) ->
    gen_server:start_link({local, Name}, ?MODULE, [Port], []).

%%%===================================================================
%%% gen_server callbacks
%%%===================================================================

%% @private
%% @doc Initializes the server
-spec(init(Args :: term()) ->
    {ok, State :: #state{}} | {ok, State :: #state{}, timeout() | hibernate} |
    {stop, Reason :: term()} | ignore).
init([Port]) ->
    %% 需要提高进程的调度优先级
    erlang:process_flag(priority, high),
    Opts = [
        binary,
        {reuseaddr, true},
        {reuseport, true},
        {active, true},
        {recbuf, 5 * 1024 * 1024},
        {sndbuf, 5 * 1024 * 1024}
    ],
    {ok, Socket} = gen_udp:open(Port, Opts),
    inet_udp:controlling_process(Socket, self()),

    logger:debug("[sdlan_stun] start at port: ~p", [Port]),
    {ok, #state{socket = Socket}}.

%% @private
%% @doc Handling call messages
-spec(handle_call(Request :: term(), From :: {pid(), Tag :: term()},
    State :: #state{}) ->
    {reply, Reply :: term(), NewState :: #state{}} |
    {reply, Reply :: term(), NewState :: #state{}, timeout() | hibernate} |
    {noreply, NewState :: #state{}} |
    {noreply, NewState :: #state{}, timeout() | hibernate} |
    {stop, Reason :: term(), Reply :: term(), NewState :: #state{}} |
    {stop, Reason :: term(), NewState :: #state{}}).
handle_call(_Request, _From, State = #state{}) ->
    {reply, ok, State}.

%% @private
%% @doc Handling cast messages
-spec(handle_cast(Request :: term(), State :: #state{}) ->
    {noreply, NewState :: #state{}} |
    {noreply, NewState :: #state{}, timeout() | hibernate} |
    {stop, Reason :: term(), NewState :: #state{}}).
%% 当前node下的转发，基于进程间的通讯
handle_cast(_Request, State) ->
    {noreply, State}.

%% @private
%% @doc Handling all non call/cast messages
-spec(handle_info(Info :: timeout() | term(), State :: #state{}) ->
    {noreply, NewState :: #state{}} |
    {noreply, NewState :: #state{}, timeout() | hibernate} |
    {stop, Reason :: term(), NewState :: #state{}}).
handle_info({udp, Sock, Ip, Port, IpPacket}, State = #state{socket = Sock}) ->
    case dns_resolver:resolve(IpPacket) of
        {ok, RespIpPacket} ->
            gen_udp:send(Sock, Ip, Port, RespIpPacket);
        {error, Reason} ->
            logger:debug("[dns_server] resolve dns query error: ~p", [Reason])
    end,
    {noreply, State};
handle_info(Info, State) ->
    logger:error("[sdlan_stun] get a unknown message: ~p, channel will closed", [Info]),
    {noreply, State}.

%% @private
%% @doc This function is called by a gen_server when it is about to
%% terminate. It should be the opposite of Module:init/1 and do any
%% necessary cleaning up. When it returns, the gen_server terminates
%% with Reason. The return value is ignored.
-spec(terminate(Reason :: (normal | shutdown | {shutdown, term()} | term()),
    State :: #state{}) -> term()).
terminate(_Reason, _State = #state{}) ->
    ok.

%% @private
%% @doc Convert process state when code is changed
-spec(code_change(OldVsn :: term() | {down, term()}, State :: #state{},
    Extra :: term()) ->
    {ok, NewState :: #state{}} | {error, Reason :: term()}).
code_change(_OldVsn, State = #state{}, _Extra) ->
    {ok, State}.

%%%===================================================================
%%% Internal functions
%%%===================================================================