private static int weekDayValue(String weekDay) {
        weekDay = weekDay.toLowerCase();
        switch (weekDay) {
            case "mon":
            case "monday":
                return 1;
            case "tue":
            case "tuesday":
                return 2;
            case "wed":
            case "wednesday":
                return 3;
            case "thu":
            case "thursday":
                return 4;
            case "fri":
            case "friday":
                return 5;
            case "sat":
            case "saturday":
                return 6;
            case "sun":
            case "sunday":
                return 7;
            default:
                throw new IllegalArgumentException("Unknown weekday:" + weekDay);
        }
    }
https://stackoverflow.com/questions/33942544/how-to-skip-weekends-while-adding-days-to-localdate-in-java-8/33943576
exts/jphp-zend-ext/src/main/java/org/develnext/jphp/zend/ext/standard/date/Adjusters.java