@burglekitt/gmt/dist/plain/calculate/getLocaleStartOfWeek.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 { isValidDate } 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`.
 * - Falls back to Monday if the runtime's `weekInfo` data doesn't resolve
 *   a first day for the locale.
 * - Distinct from `startOfDate(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 ISO 8601 date string
 * @param locale BCP 47 locale tag (e.g. "en-US", "fr-FR")
 * @returns ISO 8601 date string for the start of `value`'s locale-relative week, or "" on invalid input
 *
 * @example getLocaleStartOfWeek("2024-02-29", "en-US") // "2024-02-25" (Sunday)
 * @example getLocaleStartOfWeek("2024-02-29", "fr-FR") // "2024-02-26" (Monday)
 * @example getLocaleStartOfWeek("invalid-date", "en-US") // ""
 * @example getLocaleStartOfWeek("2024-02-29", "not-a-locale") // ""
 */
export function getLocaleStartOfWeek(value, locale) {
    if (!isValidDate(value))
        return "";
    const firstDay = getLocaleFirstDayOfWeek(locale);
    if (firstDay === null)
        return "";
    try {
        const source = Temporal.PlainDate.from(value);
        const daysToSubtract = (source.dayOfWeek - firstDay + 7) % 7;
        return source.subtract({ days: daysToSubtract }).toString();
    }
    catch {
        return "";
    }
}