@burglekitt/gmt/dist/zoned/calculate/getLocaleZonedStartOfWeek.js

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

import { Temporal } from "@js-temporal/polyfill";
import { getLocaleFirstDayOfWeek } from "../../internal/index.js";
import { isValidZonedDateTime } from "../validate/index.js";
/**
 * Return the start of the week containing `value`, using `locale`'s
 * first day of week (e.g. en-US: Sunday, fr-FR: Monday).
 *
 * - Resolves the locale's first day of week via
 *   `Intl.Locale.prototype.weekInfo`, then resets the local time-of-day to
 *   midnight.
 * - Falls back to Monday if the runtime's `weekInfo` data doesn't resolve
 *   a first day for the locale.
 * - `disambiguation` controls DST gap/overlap resolution when the
 *   midnight reset lands on an ambiguous local time: "compatible"
 *   (default, matches Temporal's default), "earlier", "later", or
 *   "reject" (throws, resulting in "").
 * - `offset` controls whether the source's existing UTC offset is kept
 *   when resetting to midnight: "prefer" (Temporal's own default — keeps
 *   the source offset whenever still valid, which **makes
 *   `disambiguation` inert** for almost every case here), "use", "ignore"
 *   (**this function's default** — always recomputes from time zone +
 *   local time, discarding the stale offset; this is what makes
 *   `disambiguation` actually take effect), or "reject" (throws if the
 *   source offset is invalid for the new fields, independent of
 *   `disambiguation`). Leave `offset` at its default unless you
 *   specifically need Temporal's raw `.with()` semantics.
 * - Distinct from `startOfZoned(value, "week", { weekStartsOn })`, which
 *   takes an explicit ISO-biased `weekStartsOn` option instead of deriving
 *   it from a locale.
 * - Returns "" if `value` or `locale` is invalid.
 *
 * @param value zoned ISO 8601 datetime string
 * @param locale BCP 47 locale tag (e.g. "en-US", "fr-FR")
 * @param options optional: fractionalSecondDigits (number), disambiguation ("compatible" | "earlier" | "later" | "reject"), offset ("prefer" | "use" | "ignore" | "reject", default "ignore")
 * @returns zoned ISO 8601 string for the start of `value`'s locale-relative week, or "" on invalid input
 *
 * @example getLocaleZonedStartOfWeek("2024-02-29T12:00:00+00:00[UTC]", "en-US") // "2024-02-25T00:00:00+00:00[UTC]" (Sunday)
 * @example getLocaleZonedStartOfWeek("2024-02-29T12:00:00+00:00[UTC]", "fr-FR") // "2024-02-26T00:00:00+00:00[UTC]" (Monday)
 * @example getLocaleZonedStartOfWeek("invalid", "en-US") // ""
 * @example getLocaleZonedStartOfWeek("2024-02-29T12:00:00+00:00[UTC]", "not-a-locale") // ""
 */
export function getLocaleZonedStartOfWeek(value, locale, optionsArg) {
    const fractionalSecondDigits = optionsArg?.fractionalSecondDigits ?? 0;
    const disambiguation = optionsArg?.disambiguation ?? "compatible";
    const offset = optionsArg?.offset ?? "ignore";
    if (!isValidZonedDateTime(value))
        return "";
    const firstDay = getLocaleFirstDayOfWeek(locale);
    if (firstDay === null)
        return "";
    try {
        const source = Temporal.ZonedDateTime.from(value);
        const daysToSubtract = (source.dayOfWeek - firstDay + 7) % 7;
        const startOfWeekDate = source.subtract({ days: daysToSubtract });
        const result = startOfWeekDate.with({
            hour: 0,
            minute: 0,
            second: 0,
            millisecond: 0,
            microsecond: 0,
            nanosecond: 0,
        }, { disambiguation, offset });
        return result.toString({ fractionalSecondDigits });
    }
    catch {
        return "";
    }
}