@burglekitt/gmt/dist/unix/calculate/startOfQuarterForUnix.js

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

import { Temporal } from "@js-temporal/polyfill";
import { isValidUnixUnit } from "../../unix/validate/isValidUnixUnit.js";
import { getSystemTimeZone } from "../../zoned/get/index.js";
import { isValidTimeZone } from "../../zoned/validate/index.js";
/**
 * Return the start of the quarter for a Unix timestamp.
 *
 * - Converts to ZonedDateTime, calculates quarter start, converts back to epoch.
 * - Q1 returns month 1, Q2 returns month 4, Q3 returns month 7, Q4 returns month 10.
 * - `disambiguation` controls DST gap/overlap resolution when the quarter-start boundary lands on an ambiguous local time: "compatible" (default, matches Temporal's default), "earlier", "later", or "reject" (throws, resulting in null).
 * - `offset` controls whether the source's existing UTC offset is kept when computing the new boundary: "prefer" (Temporal's own default — keeps the source offset whenever still valid, which **makes `disambiguation` inert** in the (rare) common-zone case since quarter boundaries don't fall on DST transitions), "use", "ignore" (**this function's default** — always recomputes from time zone + local time, discarding the stale offset), 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.
 * - Returns null for invalid input.
 *
 * @param value Unix timestamp (number)
 * @param options optional: epochUnit ("seconds" | "milliseconds"), timeZone (IANA), disambiguation ("compatible" | "earlier" | "later" | "reject"), offset ("prefer" | "use" | "ignore" | "reject", default "ignore")
 * @returns Unix epoch number representing the start of the quarter, or null on invalid input
 *
 * @example startOfQuarterForUnix(1706659200000) // 1704067200000
 * @example startOfQuarterForUnix(-86400000) // -25598400001 (Q1 1969 starts Jan 1)
 */
export function startOfQuarterForUnix(value, options) {
    const epochUnit = options?.epochUnit ?? "milliseconds";
    const timeZone = options?.timeZone ?? getSystemTimeZone();
    const disambiguation = options?.disambiguation ?? "compatible";
    const offset = options?.offset ?? "ignore";
    if (!timeZone || !isValidTimeZone(timeZone) || !isValidUnixUnit(epochUnit)) {
        return null;
    }
    if (!Number.isFinite(value) || !Number.isInteger(value)) {
        return null;
    }
    try {
        const instant = Temporal.Instant.fromEpochMilliseconds(epochUnit === "seconds" ? value * 1000 : value);
        const zdt = instant.toZonedDateTimeISO(timeZone);
        const month = zdt.month;
        const quarterStartMonth = Math.floor((month - 1) / 3) * 3 + 1;
        const result = zdt.with({ month: quarterStartMonth, day: 1, hour: 0, minute: 0, second: 0 }, { disambiguation, offset });
        const epoch = epochUnit === "seconds"
            ? Math.floor(result.epochMilliseconds / 1000)
            : result.epochMilliseconds;
        return epoch;
    }
    catch {
        return null;
    }
}