gen_event_repeater.erl

%%%-------------------------------------------------------------------
%%% @author Fernando Benavides <[email protected]>
%%% @copyright (C) 2011 Inaka Networks S.R.L.
%%% @doc It listens and just repeats...
%%% @end
%%%-------------------------------------------------------------------
-module(gen_event_repeater).
-author('Fernando Benavides <[email protected]>').

-behaviour(gen_event).

-export([start/2, start/1, start_link/1, start_link/2]).
-export([init/1, handle_event/2, handle_call/2, handle_info/2, terminate/2, code_change/3]).

-include("elog.hrl").
-include("records.hrl").

-record(state, {dispatcher  :: pid(),
                reference   :: reference()}).
-type state() :: #state{}.

%% ====================================================================
%% External functions
%% ====================================================================
-spec start(pid() | atom() | {global, atom()}) -> {ok, pid()}.
start(Source) ->
  subscribe(Source, gen_event:start()).

-spec start({local, atom()} | {global, atom()}, pid() | atom() | {global, atom()}) -> {ok, pid()}.
start(Name, Source) ->
  subscribe(Source, gen_event:start(Name)).

-spec start_link(pid() | atom() | {global, atom()}) -> {ok, pid()}.
start_link(Source) ->
  subscribe(Source, gen_event:start_link()).

-spec start_link({local, atom()} | {global, atom()}, pid() | atom() | {global, atom()}) -> {ok, pid()}.
start_link(Name, Source) ->
  subscribe(Source, gen_event:start_link(Name)).

%% ====================================================================
%% Server functions
%% ====================================================================
%% @hidden
-spec init(pid()) -> {ok, state()}.
init(Dispatcher) ->
  Ref = erlang:monitor(process, Dispatcher),
  {ok, #state{dispatcher = Dispatcher, reference = Ref}}.

%% @hidden
-spec handle_event(term(), state()) -> {ok, state()}.
handle_event(Event, State) ->
  gen_event:notify(State#state.dispatcher, Event),
  {ok, State}.

%% @hidden
-spec handle_call(term(), state()) -> {ok, ok, state()}.
handle_call(_Call, State) -> {ok, ok, State}.

%% @hidden
-spec handle_info(term(), state()) -> {ok, state()} | remove_handler.
handle_info({'DOWN', Ref, _Type, _Dispatcher, Info}, State = #state{reference = Ref}) ->
  ?WARN("Our dispatcher (~p) died... removing ourselves from the source...~n\t~p~n", [State#state.dispatcher, Info]),
  remove_handler;
handle_info(Info, State) ->
  State#state.dispatcher ! Info,
  {ok, State}.

%% @hidden
-spec terminate(term(), state()) -> ok.
terminate(remove_handler, _State) ->
  ok;
terminate(stop, State) ->
  ?INFO("Source dispatcher stopped. Stopping our own dispatcher too...~n", []),
  gen_event:stop(State#state.dispatcher);
terminate(Reason, State) ->
  ?INFO("Source dispatcher exited (~p). Exiting our own dispatcher too...~n", [Reason]),
  exit(State#state.dispatcher, Reason).

%% @hidden
-spec code_change(term(), state(), term()) -> {ok, state()}.
code_change(_OldVsn, State, _Extra) -> {ok, State}.

%% ====================================================================
%% Private functions
%% ====================================================================
subscribe(Source, {ok, Pid}) ->
  try gen_event:add_handler(Source, {?MODULE, Pid}, Pid) of
    ok -> {ok, Pid}
  catch
    _:Error ->
      ?WARN("gen_event:add_handler error:~n~p~n", [Error]),
      gen_event:stop(Pid),
      throw(Error)
  end;
subscribe(Source, {error, {already_started, Pid}}) ->
  try
    case lists:member({?MODULE, Pid}, gen_event:which_handlers(Source)) of
      true ->
        {ok, Pid};
      false ->
        ok = gen_event:add_handler(Source, {?MODULE, Pid}, Pid),
        {ok, Pid}
    end
  catch
    _:Error ->
      ?WARN("gen_event:add_handler error:~n~p~n", [Error]),
      gen_event:stop(Pid),
      throw(Error)
  end.