private boolean isNumeric(String str) {
        for(char ch : str.toCharArray()) {
            if(!Character.isDigit(ch)) {
                return false;
            }
        }

        return true;
    }

    private long parseTime(String timeString, String timeMode) throws CommandException {
        if(!isNumeric(timeString)) {
            throw new CommandException(Lang.COMMAND_ERROR_TIMEFORMAT);
        }
        if(timeMode.length() > 1) {
            throw new CommandException(Lang.COMMAND_ERROR_TIMEFORMAT);
        }

        int sec = Integer.parseInt(timeString) * 60;

        char unit = timeMode.charAt(0);
        switch (unit) {
            case 'h':
                sec *= 60;
                break;
            case 'd':
                sec *= (60 * 24);
                break;
            case 'w':
                sec *= (7 * 60 * 24);
                break;
            case 'm':
                sec *= (30 * 60 * 24);
                break;
            default:
                throw new CommandException(Lang.COMMAND_ERROR_TIMEFORMAT);
        }

        return sec * 1000L;
    }