@burglekitt/gmt/dist/internal/getLocaleWeekYearBounds.js

Temporal-based date and time utilities with timezone support and polyfill integration

import { Temporal } from "@js-temporal/polyfill";
// Week 1 of a locale week-year always contains January's `minimalDays`-th
// day: the week starting on/before Jan 1 has k days in January, where k
// ranges from `minimalDays` (the threshold to still count as week 1) up
// to 7 (a full week starting exactly on Jan 1) — so day `minimalDays` of
// January falls within that range no matter which end it lands on. This
// generalizes ISO 8601's own rule (minimalDays = 4, so week 1 always
// contains Jan 4).
function startOfWeek1(year, firstDay, minimalDays) {
    const anchor = Temporal.PlainDate.from({
        year,
        month: 1,
        day: minimalDays,
    });
    const daysSinceFirstDay = (anchor.dayOfWeek - firstDay + 7) % 7;
    return anchor.subtract({ days: daysSinceFirstDay });
}
/**
 * Resolve the locale week-numbering year `date` belongs to, and the
 * `[start, end)` bounds (in calendar days) of that week-year, given a
 * locale's `firstDay` (1 = Monday .. 7 = Sunday) and `minimalDays` (the
 * minimum January days a week must have to count as week 1) — both from
 * `Intl.Locale.prototype.weekInfo`.
 *
 * Shared by `getLocaleWeekYear` (the year itself) and
 * `getWeeksInLocaleWeekYear` (the week count, derived from `start`/`end`).
 */
export function getLocaleWeekYearBounds(date, firstDay, minimalDays) {
    let weekYear = date.year;
    let start = startOfWeek1(weekYear, firstDay, minimalDays);
    if (Temporal.PlainDate.compare(date, start) < 0) {
        weekYear -= 1;
        start = startOfWeek1(weekYear, firstDay, minimalDays);
    }
    else {
        const nextStart = startOfWeek1(weekYear + 1, firstDay, minimalDays);
        if (Temporal.PlainDate.compare(date, nextStart) >= 0) {
            weekYear += 1;
            start = nextStart;
        }
    }
    const end = startOfWeek1(weekYear + 1, firstDay, minimalDays);
    return { weekYear, start, end };
}