spawn_link

%%%-------------------------------------------------------------------
%%% File    : eb_withdrawal_handler.erl
%%% Author  : Mitchell Hashimoto <mitchellh@Chip.local>
%%% Description : An event handler to detect withdrawals larger than
%%% a certain amount.
%%%
%%% Created :  7 Sep 2008 by Mitchell Hashimoto <mitchellh@Chip.local>
%%%-------------------------------------------------------------------
-module(eb_withdrawal_handler).

-behaviour(gen_event).

%% API
-export([change_threshold/1]).

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

%%====================================================================
%% API
%%====================================================================
%%--------------------------------------------------------------------
%% Function: change_threshold(Amount) -> {ok, Old, NewThreshold}
%% | {error, Reason}
%% Description: Changes the withdrawal amount threshold during runtime
%%--------------------------------------------------------------------
change_threshold(Amount) ->
  gen_event:call(eb_event_manager, ?MODULE, {change_threshold, Amount}).

%%====================================================================
%% gen_event callbacks
%%====================================================================
%%--------------------------------------------------------------------
%% Function: init(Args) -> {ok, State}
%% Description: Whenever a new event handler is added to an event manager,
%% this function is called to initialize the event handler.
%%--------------------------------------------------------------------
init([]) ->
  {ok, 500}.

%%--------------------------------------------------------------------
%% Function:
%% handle_event(Event, State) -> {ok, State} |
%%                               {swap_handler, Args1, State1, Mod2, Args2} |
%%                               remove_handler
%% Description:Whenever an event manager receives an event sent using
%% gen_event:notify/2 or gen_event:sync_notify/2, this function is called for
%% each installed event handler to handle the event.
%%--------------------------------------------------------------------
handle_event({withdraw, Name, Amount, NewBalance}, State) when Amount >= State ->
  io:format("WITHDRAWAL NOTIFICATION: ~p withdrew ~p leaving ~p left.~n", [Name, Amount, NewBalance]),
  {ok, State};
handle_event(_Event, State) ->
  {ok, State}.

%%--------------------------------------------------------------------
%% Function:
%% handle_call(Request, State) -> {ok, Reply, State} |
%%                                {swap_handler, Reply, Args1, State1,
%%                                  Mod2, Args2} |
%%                                {remove_handler, Reply}
%% Description: Whenever an event manager receives a request sent using
%% gen_event:call/3,4, this function is called for the specified event
%% handler to handle the request.
%%--------------------------------------------------------------------
handle_call({change_threshold, Amount}, State) ->
  io:format("NOTICE: Changing withdrawal threshold from ~p to ~p~n", [State, Amount]),
  {ok, {ok, State, Amount}, Amount};
handle_call(_Request, State) ->
  Reply = ok,
  {ok, Reply, State}.

%%--------------------------------------------------------------------
%% Function:
%% handle_info(Info, State) -> {ok, State} |
%%                             {swap_handler, Args1, State1, Mod2, Args2} |
%%                              remove_handler
%% Description: This function is called for each installed event handler when
%% an event manager receives any other message than an event or a synchronous
%% request (or a system message).
%%--------------------------------------------------------------------
handle_info(_Info, State) ->
  {ok, State}.

%%--------------------------------------------------------------------
%% Function: terminate(Reason, State) -> void()
%% Description:Whenever an event handler is deleted from an event manager,
%% this function is called. It should be the opposite of Module:init/1 and
%% do any necessary cleaning up.
%%--------------------------------------------------------------------
terminate(_Reason, _State) ->
  ok.

%%--------------------------------------------------------------------
%% Function: code_change(OldVsn, State, Extra) -> {ok, NewState}
%% Description: Convert process state when code is changed
%%--------------------------------------------------------------------
code_change(_OldVsn, State, _Extra) ->
  {ok, State}.