Method addDays

base/src/main/java/net/time4j/PlainDate.java:2052–2087

(
        PlainDate date,
        long amount
    )

    }

    private static PlainDate addDays(
        PlainDate date,
        long amount
    ) {

        long dom = MathUtils.safeAdd(date.dayOfMonth, amount);
        Weekday weekday = null;
        boolean hasDOW = (date.weekday != null);

        if (hasDOW) {
            if (amount == 1) {
                weekday = date.weekday.next();
            } else if (amount == 7) {
                weekday = date.weekday;
            }
        }

        if ((dom >= 1) && (dom <= 28)) {
            if (hasDOW && (weekday == null)) {
                weekday = date.weekday.roll((int) amount);
            }
            return PlainDate.create(date.year, date.month, (int) dom, weekday, false);
        }

        long doy = MathUtils.safeAdd(date.getDayOfYear(), amount);

        if ((doy >= 1) && (doy <= 365)) {
            if (hasDOW && (weekday == null)) {
                weekday = date.weekday.roll((int) amount);
            }
            return PlainDate.ofYearDay(date.year, (int) doy, weekday);
        }

        return TRANSFORMER.transform(MathUtils.safeAdd(date.getDaysSinceUTC(), amount));

    }

    private static void fill(
        Map<String, Object> map,