@burglekitt/gmt/dist/plain/interval/mergeIntervalsDate.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 { isValidDateInterval } from "./validate/index.js";
/**
 * Collapse a list of date intervals into the minimum set of non-overlapping intervals.
 *
 * - List-form generalization of `intervalUnionDate`, which is pairwise only.
 * - Intervals are merged when they overlap or share an endpoint exactly (adjacent intervals,
 *   e.g. `aEnd === bStart`, ARE merged — same rule as `intervalUnionDate`).
 * - Order of the input list does not matter; the result is sorted by start.
 * - Returns `[]` for an empty list.
 * - Returns `[]` when `intervals` is not an array, when any element is not a
 *   `{ start, end }` record of valid ISO PlainDate strings, or when any element has
 *   `start > end`.
 * - Accepts GMT calendar-annotated PlainDate strings — E5 (issue #78). Since the result is
 *   date *values*, every `start`/`end` across the whole list must carry the *same* calendar tag
 *   (or all be bare ISO); any mismatch returns `[]` (E5 decision of record D4).
 *
 * @param intervals array of `{ start, end }` records, optionally calendar-annotated
 * @returns the minimum set of non-overlapping `{ start, end }` records, sorted by start, or `[]` on invalid input / mismatched calendars
 *
 * @example mergeIntervalsDate([{ start: "2024-01-01", end: "2024-01-10" }, { start: "2024-01-05", end: "2024-01-15" }]) // [{ start: "2024-01-01", end: "2024-01-15" }]
 * @example mergeIntervalsDate([{ start: "2024-01-01", end: "2024-01-10" }, { start: "2024-01-10", end: "2024-01-20" }]) // [{ start: "2024-01-01", end: "2024-01-20" }] (adjacent, merged)
 * @example mergeIntervalsDate([{ start: "2024-01-01", end: "2024-01-05" }, { start: "2024-01-10", end: "2024-01-15" }]) // [{ start: "2024-01-01", end: "2024-01-05" }, { start: "2024-01-10", end: "2024-01-15" }] (disjoint)
 * @example mergeIntervalsDate([]) // []
 * @example mergeIntervalsDate([{ start: "2024-01-10", end: "2024-01-01" }]) // []
 */
export function mergeIntervalsDate(intervals) {
    if (!Array.isArray(intervals) || intervals.length === 0) {
        return [];
    }
    if (!intervals.every((interval) => interval &&
        typeof interval === "object" &&
        isValidDateInterval(interval.start, interval.end))) {
        return [];
    }
    const calendar = calendarOfAllDateValues(intervals.flatMap((interval) => [interval.start, interval.end]));
    if (!calendar) {
        return [];
    }
    try {
        const parsed = intervals.map((interval) => ({
            start: parseCalendarDateValue(interval.start),
            end: parseCalendarDateValue(interval.end),
        }));
        parsed.sort((a, b) => Temporal.PlainDate.compare(a.start, b.start));
        const merged = [];
        for (const interval of parsed) {
            const last = merged[merged.length - 1];
            if (last && Temporal.PlainDate.compare(interval.start, last.end) <= 0) {
                if (Temporal.PlainDate.compare(interval.end, last.end) > 0) {
                    last.end = interval.end;
                }
            }
            else {
                merged.push({ start: interval.start, end: interval.end });
            }
        }
        return merged.map((interval) => ({
            start: formatDateInCalendar(interval.start, calendar),
            end: formatDateInCalendar(interval.end, calendar),
        }));
    }
    catch {
        return [];
    }
}