%%--------------------------------------------------------------------
%% Copyright (c) 2012-2017 Feng Lee <feng@emqtt.io>.
%%
%% Licensed 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.
%%--------------------------------------------------------------------

-module(emqttd_broker).

-behaviour(gen_server).

-include("emqttd.hrl").

-include("emqttd_internal.hrl").

%% API Function Exports
-export([start_link/0]).

%% Event API
-export([subscribe/1, notify/2]).

%% Broker API
-export([version/0, uptime/0, datetime/0, sysdescr/0]).

%% Tick API
-export([start_tick/1, stop_tick/1]).

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

-record(state, {started_at, sys_interval, heartbeat, tick_tref, version, sysdescr}).

-define(SERVER, ?MODULE).

-define(BROKER_TAB, mqtt_broker).

%% $SYS Topics of Broker
-define(SYSTOP_BROKERS, [
    version,      % Broker version
    uptime,       % Broker uptime
    datetime,     % Broker local datetime
    sysdescr      % Broker description
]).

%%--------------------------------------------------------------------
%% API
%%--------------------------------------------------------------------

%% @doc Start emqttd broker
-spec(start_link() -> {ok, pid()} | ignore | {error, any()}).
start_link() ->
    gen_server:start_link({local, ?SERVER}, ?MODULE, [], []).

%% @doc Subscribe broker event
-spec(subscribe(EventType :: any()) -> ok).
subscribe(EventType) ->
    gproc:reg({p, l, {broker, EventType}}).
    
%% @doc Notify broker event
-spec(notify(EventType :: any(), Event :: any()) -> ok).
notify(EventType, Event) ->
     gproc:send({p, l, {broker, EventType}}, {notify, EventType, self(), Event}).

%% @doc Get broker version
-spec(version() -> string()).
version() ->
    {ok, Version} = application:get_key(emqttd, vsn), Version.

%% @doc Get broker description
-spec(sysdescr() -> string()).
sysdescr() ->
    {ok, Descr} = application:get_key(emqttd, description), Descr.

%% @doc Get broker uptime
-spec(uptime() -> string()).
uptime() -> gen_server:call(?SERVER, uptime).

%% @doc Get broker datetime
-spec(datetime() -> string()).
datetime() ->
    {{Y, M, D}, {H, MM, S}} = calendar:local_time(),
    lists:flatten(
        io_lib:format(
            "~4..0w-~2..0w-~2..0w ~2..0w:~2..0w:~2..0w", [Y, M, D, H, MM, S])).

%% @doc Start a tick timer
start_tick(Msg) ->
    start_tick(timer:seconds(emqttd:env(broker_sys_interval, 60)), Msg).

start_tick(0, _Msg) ->
    undefined;
start_tick(Interval, Msg) when Interval > 0 ->
    {ok, TRef} = timer:send_interval(Interval, Msg), TRef.

%% @doc Start tick timer
stop_tick(undefined) ->
    ok;
stop_tick(TRef) ->
    timer:cancel(TRef).

%%--------------------------------------------------------------------
%% gen_server callbacks
%%--------------------------------------------------------------------

init([]) ->
    emqttd_time:seed(),
    ets:new(?BROKER_TAB, [set, public, named_table]),
    % Tick
    {ok, #state{started_at = os:timestamp(),
                heartbeat  = start_tick(1000, heartbeat),
                version = list_to_binary(version()),
                sysdescr = list_to_binary(sysdescr()),
                tick_tref  = start_tick(tick)}, hibernate}.

handle_call(uptime, _From, State) ->
    {reply, uptime(State), State};

handle_call(Req, _From, State) ->
    ?UNEXPECTED_REQ(Req, State).

handle_cast(Msg, State) ->
    ?UNEXPECTED_MSG(Msg, State).

handle_info(heartbeat, State) ->
    publish(uptime, list_to_binary(uptime(State))),
    publish(datetime, list_to_binary(datetime())),
    {noreply, State, hibernate};

handle_info(tick, State = #state{version = Version, sysdescr = Descr}) ->
    retain(brokers),
    retain(version,  Version),
    retain(sysdescr, Descr),
    {noreply, State, hibernate};

handle_info(Info, State) ->
    ?UNEXPECTED_INFO(Info, State).

terminate(_Reason, #state{heartbeat = Hb, tick_tref = TRef}) ->
    stop_tick(Hb),
    stop_tick(TRef),
    ok.

code_change(_OldVsn, State, _Extra) ->
    {ok, State}.

%%--------------------------------------------------------------------
%% Internal functions
%%--------------------------------------------------------------------

retain(brokers) ->
    Payload = list_to_binary(string:join([atom_to_list(N) ||
                    N <- emqttd_mnesia:running_nodes()], ",")),
    Msg = emqttd_message:make(broker, <<"$SYS/brokers">>, Payload),
    Msg1 = emqttd_message:set_flag(sys, emqttd_message:set_flag(retain, Msg)),
    emqttd:publish(Msg1).

retain(Topic, Payload) when is_binary(Payload) ->
    Msg = emqttd_message:make(broker, emqttd_topic:systop(Topic), Payload),
    Msg1 = emqttd_message:set_flag(sys, emqttd_message:set_flag(retain, Msg)),
    emqttd:publish(Msg1).

publish(Topic, Payload) when is_binary(Payload) ->
    Msg = emqttd_message:make(broker, emqttd_topic:systop(Topic), Payload),
    emqttd:publish(emqttd_message:set_flag(sys, Msg)).

uptime(#state{started_at = Ts}) ->
    Secs = timer:now_diff(os:timestamp(), Ts) div 1000000,
    lists:flatten(uptime(seconds, Secs)).

uptime(seconds, Secs) when Secs < 60 ->
    [integer_to_list(Secs), " seconds"];
uptime(seconds, Secs) ->
    [uptime(minutes, Secs div 60), integer_to_list(Secs rem 60), " seconds"];
uptime(minutes, M) when M < 60 ->
    [integer_to_list(M), " minutes, "];
uptime(minutes, M) ->
    [uptime(hours, M div 60), integer_to_list(M rem 60), " minutes, "];
uptime(hours, H) when H < 24 ->
    [integer_to_list(H), " hours, "];
uptime(hours, H) ->
    [uptime(days, H div 24), integer_to_list(H rem 24), " hours, "];
uptime(days, D) ->
    [integer_to_list(D), " days,"].