class Logger:
    class __Logger:
        def __init__(self, file_name):
            self.file_name = file_name

        def __write_log(self, level, message):
            with open(self.file_name, 'a') as log_file:
                log_file.write('[{0}] {1}\n'.format(level, message))

        def critical(self, message):
            self.__write_log('CRITICAL', message)

        def error(self, message):
            self.__write_log('ERROR', message)

        def warning(self, message):
            self.__write_log('WARNING', message)

        def info(self, message):
            self.__write_log('INFO', message)

        def debug(self, message):
            self.__write_log('DEBUG', message)

    instance = None

    def __new__(cls, *args, **kwargs):
        if not Logger.instance:
            Logger.instance = __Logger(*args, **kwargs)
        return Logger.instance

    def __getattr__(self, item):
        return getattr(self.instance, item)

    def __setattr__(self, key, value):
        return setattr(self.instance, key, value)