%%%-------------------------------------------------------------------
%%% @author anlicheng
%%% @copyright (C) 2025, <COMPANY>
%%% @doc
%%%
%%% @end
%%% Created : 17. 8月 2025 00:26
%%%-------------------------------------------------------------------
-module(iot_name_server).
-author("anlicheng").

-behaviour(gen_server).

%% API
-export([start_link/0]).
-export([whereis_alias/1, register/2]).

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

-define(SERVER, ?MODULE).
-define(TAB, iot_name_server).

-record(state, {
    %% #{Pid => Name}
    pid_names = #{},
    refs = []
}).

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

-spec register(Name :: atom(), Pid :: pid()) -> ok.
register(Name, Pid) when is_atom(Name), is_pid(Pid) ->
    gen_server:call(?SERVER, {register, Name, Pid}).

-spec whereis_alias(Name :: atom()) -> undefined | pid().
whereis_alias(Name) when is_atom(Name) ->
    case ets:lookup(?TAB, Name) of
        [] ->
            undefined;
        [{Name, Pid}|_] ->
            case is_process_alive(Pid) of
                true ->
                    Pid;
                false ->
                    undefined
            end
    end.

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

%%%===================================================================
%%% 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([]) ->
    %% 初始化存储
    ets:new(?TAB, [named_table, ordered_set, public, {keypos, 1}]),
    {ok, #state{}}.

%% @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({register, Name, Pid}, _From, State = #state{refs = Refs, pid_names = PidNames}) ->
    true = ets:insert(?TAB, {Name, Pid}),
    MRef = erlang:monitor(process, Pid),
    {reply, ok, State#state{refs = [MRef|Refs], pid_names = maps:put(Pid, Name, PidNames)}}.

%% @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{}}).
handle_cast(_Request, State = #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({'DOWN', MRef, process, Pid, Reason}, State = #state{refs = Refs, pid_names = PidNames}) ->
    % lager:debug("[iot_name_server] pid: ~p, down with reason: ~p", [Reason]),
    case lists:member(MRef, Refs) of
        true ->
            case maps:take(Pid, PidNames) of
                error ->
                    {noreply, State#state{refs = lists:delete(MRef, Refs)}};
                {Name, NPidNames} ->
                    true = ets:delete(?TAB, Name),
                    {noreply, State#state{pid_names = NPidNames, refs = lists:delete(MRef, Refs)}}
            end;
        false ->
            {noreply, State}
    end.

%% @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
%%%===================================================================