lager_app improvement

lager_app.erl

%%
%% ...
%%

start(_StartType, _StartArgs) ->
    %% until lager is completely started, allow all messages to go through
    lager_mochiglobal:put(loglevel, {?DEBUG, []}),
    {ok, Pid} = lager_sup:start_link(),
    Handlers = case application:get_env(lager, handlers) of
        undefined ->
            [{lager_console_backend, info},
                {lager_file_backend, [{"log/error.log", error, 10485760, "", 5},
                        {"log/console.log", info, 10485760, "", 5}]}];
        {ok, Val} ->
            {Date, Time} = lager_util:format_time(),
            Node = erlang:atom_to_list(node()),
            Raw_file_backends = proplists:get_value(lager_file_backend, Val),
            Rest_backends = proplists:delete(lager_file_backend, Val),
            File_backends = lists:map(
                fun
                    ({File,Level,Size,Rotate,Index}) ->
                    {
                        re:replace(
                            re:replace(
                                re:replace(File, "~[{]node[(][)][}]", Node, [{return, list}]),
                            "~[{]date[(][)][}]", Date, [{return, list}]),
                        "~[{]time[(][)][}]", Time, [{return, list}]),
                        Level,
                        Size,
                        Rotate,
                        Index
                    };
                    (X)-> X
                end,
                Raw_file_backends
            ),
            [{lager_file_backend, File_backends}|Rest_backends]
    end,

    %% handlers failing to start are handled in the handler_watcher
    _ = [supervisor:start_child(lager_handler_watcher_sup, [lager_event, Module, Config]) ||
        {Module, Config} <- expand_handlers(Handlers)],

    %% mask the messages we have no use for
    MinLog = lager:minimum_loglevel(lager:get_loglevels()),
    {_, Traces} = lager_mochiglobal:get(loglevel),
    lager_mochiglobal:put(loglevel, {MinLog, Traces}),

    SavedHandlers = case application:get_env(lager, error_logger_redirect) of
        {ok, false} ->
            [];
        _ ->
            case supervisor:start_child(lager_handler_watcher_sup, [error_logger, error_logger_lager_h, []]) of
              {ok, _} ->
                %% Should we allow user to whitelist handlers to not be removed?
                [begin error_logger:delete_report_handler(X), X end ||
                  X <- gen_event:which_handlers(error_logger) -- [error_logger_lager_h]];
              {error, _} ->
                []
            end
    end,

    {ok, Pid, SavedHandlers}.

%%
%% ...
%%

mynode.config

[
    %% ...

    %% What handlers to install with what arguments
    {lager, [
        {handlers, [
            {lager_console_backend, info},
            {lager_file_backend, [
                {"priv/logs/~{node()}/~{date()}/~{time()}/debug.log",   debug,      10485760, "$D0", 5},
                {"priv/logs/~{node()}/~{date()}/~{time()}/info.log",    info,       10485760, "$D0", 5},
                {"priv/logs/~{node()}/~{date()}/~{time()}/notice.log",  notice,     10485760, "$D0", 5},
                {"priv/logs/~{node()}/~{date()}/warning.log",           warning,    10485760, "$D0", 5},
                {"priv/logs/~{node()}/~{date()}/error.log",             error,      10485760, "$D0", 5},
                {"priv/logs/~{node()}/critical.log",                    critical,   10485760, "$D0", 5},
                {"priv/logs/~{node()}/alert.log",                       alert,      10485760, "$D0", 5},
                {"priv/logs/emergency.log",                             emergency,  10485760, "$D0", 5}
            ]}
        ]},
        %% Whether to write a crash log, and where. Undefined means no crash logger.
        {crash_log, "priv/logs/crash.log"},
        %% Maximum size in bytes of events in the crash log - defaults to 65536
        {crash_log_msg_size, 65536},
        %% Maximum size of the crash log in bytes, before its rotated, set
        %% to 0 to disable rotation - default is 0
        {crash_log_size, 10485760},
        %% What time to rotate the crash log - default is no time
        %% rotation. See the README for a description of this format.
        {crash_log_date, "$D0"},
        %% Number of rotated crash logs to keep, 0 means keep only the
        %% current one - default is 0
        {crash_log_count, 5},
        %% Whether to redirect error_logger messages into lager - defaults to true
        {error_logger_redirect, true}
    ]},
    %% ...
]