%% Copyright (c) 2011 Basho Technologies, Inc.  All Rights Reserved.
%% Copyright (c) 2018 Pivotal Software, Inc.  All rights reserved.
%%
%% This file is provided to you under the Apache License,
%% Version 2.0 (the "License"); you may not use this file
%% except in compliance with the License.  You may obtain
%% a copy of the License at
%%
%%   http://www.apache.org/licenses/LICENSE-2.0
%%
%% Unless required by applicable law or agreed to in writing,
%% software distributed under the License is distributed on an
%% "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
%% KIND, either express or implied.  See the License for the
%% specific language governing permissions and limitations
%% under the License.

%% @doc A simple example for adding a custom event handler (this module)
%% to the `sysmon_handler' application's `system_monitor' event manager.

-module(sysmon_handler_example_handler).

-behaviour(gen_event).

%% API
-export([add_handler/0, get_call_count/0]).

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

-record(state, {
          count = 0 :: integer()
         }).

%%%===================================================================
%%% gen_event callbacks
%%%===================================================================

add_handler() ->
    sysmon_handler_filter:add_custom_handler(?MODULE, []).

get_call_count() ->
    sysmon_handler_filter:call_custom_handler(?MODULE, get_call_count, infinity).

%%%===================================================================
%%% gen_event callbacks
%%%===================================================================

%%--------------------------------------------------------------------
%% @private
%% @doc
%% Whenever a new event handler is added to an event manager,
%% this function is called to initialize the event handler.
%%
%% @spec init(Args) -> {ok, State}
%% @end
%%--------------------------------------------------------------------
init([]) ->
    {ok, #state{}}.

%%--------------------------------------------------------------------
%% @private
%% @doc
%% 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.
%%
%% @spec handle_event(Event, State) ->
%%                          {ok, State} |
%%                          {swap_handler, Args1, State1, Mod2, Args2} |
%%                          remove_handler
%% @end
%%--------------------------------------------------------------------
handle_event(Event, #state{count = Count} = State) ->
    error_logger:info_msg("Example: event ~P\n", [Event, 20]),
    {ok, State#state{count = Count + 1}}.

%%--------------------------------------------------------------------
%% @private
%% @doc
%% 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.
%%
%% @spec handle_call(Request, State) ->
%%                   {ok, Reply, State} |
%%                   {swap_handler, Reply, Args1, State1, Mod2, Args2} |
%%                   {remove_handler, Reply}
%% @end
%%--------------------------------------------------------------------
handle_call(get_call_count, State) ->
    Reply = State#state.count,
    {ok, Reply, State}.

%%--------------------------------------------------------------------
%% @private
%% @doc
%% 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).
%%
%% @spec handle_info(Info, State) ->
%%                         {ok, State} |
%%                         {swap_handler, Args1, State1, Mod2, Args2} |
%%                         remove_handler
%% @end
%%--------------------------------------------------------------------
handle_info(Info, State) ->
    error_logger:info_msg("Example: FYI, handle_info got ~p\n", [Info]),
    {ok, State}.

%%--------------------------------------------------------------------
%% @private
%% @doc
%% 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.
%%
%% @spec terminate(Reason, State) -> void()
%% @end
%%--------------------------------------------------------------------
terminate(Reason, State) ->
    error_logger:info_msg("Example: stopping because ~p, my count ~p\n",
                          [Reason, State#state.count]),
    ok.

%%--------------------------------------------------------------------
%% @private
%% @doc
%% Convert process state when code is changed
%%
%% @spec code_change(OldVsn, State, Extra) -> {ok, NewState}
%% @end
%%--------------------------------------------------------------------
code_change(_OldVsn, State, _Extra) ->
    {ok, State}.

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