-module(load_test_lager).

-define(PRINT_MSG(Format, Args), io:format(Format, Args)).
-define(DEBUG_MSG(Format, Args), lager:debug(Format, Args)).
-define(INFO_MSG(Format, Args), lager:info(Format, Args)).
-define(WARNING_MSG(Format, Args), lager:warning(Format, Args)).
-define(ERROR_MSG(Format, Args), lager:error(Format, Args)).

% stacktrace

-ifdef(OTP_RELEASE). %% this implies 21 or higher
    -define(EXCEPTION(Class, Reason, Stacktrace), Class:Reason:Stacktrace).
    -define(GET_STACK(Stacktrace), Stacktrace).
-else.
    -define(EXCEPTION(Class, Reason, _), Class:Reason).
    -define(GET_STACK(_), erlang:get_stacktrace()).
-endif.

-export([
    bench/2
]).

bench(Number, Concurrency) ->
    application:ensure_all_started(lager),
    gen_event:delete_handler(lager_event, lager_console_backend, []),
    ok = lager:set_loglevel(lager_file_backend, "log/applog.log", warning),

    Self = self(),
    List = lists:seq(1, Concurrency),
    LoopNumbers = Number div Concurrency,

    Fun = fun() ->
        try
            ?INFO_MSG("hello world", [])
        catch
            ?EXCEPTION(Class, Error, Stack) ->
                io:format("received error class: ~p error: ~p stack: ~p ~n", [Class, Error, ?GET_STACK(Stack)])
        end
    end,

    A = os:timestamp(),
    Pids = [spawn_link(fun() -> loop(LoopNumbers, Fun), Self ! {self(), done} end) || _ <- List],
    [receive {Pid, done} -> ok end || Pid <- Pids],
    B = os:timestamp(),

    print(Number, A, B).

print(Num, A, B) ->
    Microsecs = timer:now_diff(B, A),
    Time = Microsecs div Num,
    PerSec = case Time of
                 0 ->
                     "N/A";
                 _ ->
                     1000000 div Time
             end,

    io:format("### ~p ms ~p req/sec ~n", [Microsecs div 1000, PerSec]).

loop(0, _Fun) ->
    ok;
loop(Nr, Fun) ->
    Fun(),
    loop(Nr-1, Fun).