@burglekitt/gmt/dist/plain/interval/intervalUnionDate.js

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

import { Temporal } from "@js-temporal/polyfill";
import { calendarOfAllDateValues, formatDateInCalendar, parseCalendarDateValue, } from "../../internal/index.js";
import { isValidCalendarDate } from "../validate/index.js";
/**
 * Return the combined span of two date intervals, or null when they are disjoint.
 *
 * - Uses `Temporal.PlainDate.compare` for comparison.
 * - Overlapping intervals return their merged span.
 * - Adjacent intervals (e.g. `aEnd === bStart`) share one instant and ARE merged.
 * - Returns `null` if either interval is invalid (`start > end`).
 * - Returns `null` on invalid input (wrong type, malformed strings).
 * - Accepts GMT calendar-annotated PlainDate strings — E5 (issue #78). Since the result is a
 *   date *value*, all four arguments must carry the *same* calendar tag (or all be bare ISO);
 *   a mismatch returns `null` rather than guessing an output calendar (E5 decision of record
 *   D4). The output's tag is re-derived from the merged span, never copied from an input.
 *
 * @param aStart ISO 8601 date string for the first interval start, optionally calendar-annotated
 * @param aEnd ISO 8601 date string for the first interval end, optionally calendar-annotated
 * @param bStart ISO 8601 date string for the second interval start, optionally calendar-annotated
 * @param bEnd ISO 8601 date string for the second interval end, optionally calendar-annotated
 * @returns `{ start, end }` with the merged span, or null on invalid input / disjoint intervals / mismatched calendars
 *
 * @example intervalUnionDate("2024-01-01", "2024-06-30", "2024-04-01", "2024-12-31") // { start: "2024-01-01", end: "2024-12-31" }
 * @example intervalUnionDate("2024-01-01", "2024-06-30", "2024-06-30", "2024-12-31") // { start: "2024-01-01", end: "2024-12-31" }
 * @example intervalUnionDate("2024-01-01", "2024-06-30", "2024-07-01", "2024-12-31") // null
 * @example intervalUnionDate("invalid", "2024-06-30", "2024-04-01", "2024-12-31") // null
 * @example intervalUnionDate("5785-01-01[u-ca=hebrew]", "2024-06-30", "2024-04-01", "2024-12-31") // null (mismatched calendars)
 */
export function intervalUnionDate(aStart, aEnd, bStart, bEnd) {
    if (typeof aStart !== "string" ||
        typeof aEnd !== "string" ||
        typeof bStart !== "string" ||
        typeof bEnd !== "string") {
        return null;
    }
    if (!isValidCalendarDate(aStart) ||
        !isValidCalendarDate(aEnd) ||
        !isValidCalendarDate(bStart) ||
        !isValidCalendarDate(bEnd)) {
        return null;
    }
    const calendar = calendarOfAllDateValues([aStart, aEnd, bStart, bEnd]);
    if (!calendar) {
        return null;
    }
    try {
        const aS = parseCalendarDateValue(aStart);
        const aE = parseCalendarDateValue(aEnd);
        const bS = parseCalendarDateValue(bStart);
        const bE = parseCalendarDateValue(bEnd);
        if (Temporal.PlainDate.compare(aS, aE) > 0) {
            return null;
        }
        if (Temporal.PlainDate.compare(bS, bE) > 0) {
            return null;
        }
        if (Temporal.PlainDate.compare(aE, bS) < 0 ||
            Temporal.PlainDate.compare(bE, aS) < 0) {
            return null;
        }
        const start = Temporal.PlainDate.compare(aS, bS) <= 0 ? aS : bS;
        const end = Temporal.PlainDate.compare(aE, bE) >= 0 ? aE : bE;
        return {
            start: formatDateInCalendar(start, calendar),
            end: formatDateInCalendar(end, calendar),
        };
    }
    catch {
        return null;
    }
}