IsRebar3 = case application:get_key(rebar, vsn) of
               {ok, VSN} ->
                   [VSN1 | _] = string:tokens(VSN, "-"),
                   [Maj, Min, Patch] = string:tokens(VSN1, "."),
                   (list_to_integer(Maj) >= 3);
               undefined ->
                   lists:keymember(mix, 1, application:loaded_applications())
           end,

case IsRebar3 of
    true ->
        CONFIG;
    false ->
                io:format("la~n", []),

        CONFIG1 = [{eunit_opts, [verbose]},  {plugins, [rebar_gdb_plugin]} | CONFIG],

        ErlOpts = [{d, 'JIFFY_DEV'}],
        Proper = [{proper, ".*", {git, "git://github.com/manopapad/proper.git", "master"}}],

        ConfigPath = filename:dirname(SCRIPT),
        DevMarker = filename:join([ConfigPath, ".jiffy.dev"]),

        case filelib:is_file(DevMarker) of
            true ->
                % Don't override existing dependencies
                CONFIG2 = case lists:keyfind(deps, 1, CONFIG1) of
                    false ->
                        CONFIG1 ++ [{deps, Proper}];
                    {deps, DepsList} ->
                        lists:keyreplace(deps, 1, CONFIG1, {deps, DepsList ++ Proper})
                    end,
                
                case lists:keyfind(erl_opts, 1, CONFIG2) of
                    false ->
                        CONFIG2 ++ [{erl_opts, ErlOpts}];
                    {erl_opts, Opts} ->
                        NewOpts = {erl_opts, Opts ++ ErlOpts},
                        lists:keyreplace(erl_opts, 1, CONFIG2, NewOpts)
                end;
            false ->
                CONFIG1
        end
end.