54 lines
1.9 KiB
JavaScript
54 lines
1.9 KiB
JavaScript
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import { compareAsc } from "./compareAsc.mjs";
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import { differenceInCalendarISOWeekYears } from "./differenceInCalendarISOWeekYears.mjs";
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import { subISOWeekYears } from "./subISOWeekYears.mjs";
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import { toDate } from "./toDate.mjs";
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/**
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* @name differenceInISOWeekYears
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* @category ISO Week-Numbering Year Helpers
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* @summary Get the number of full ISO week-numbering years between the given dates.
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*
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* @description
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* Get the number of full ISO week-numbering years between the given dates.
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*
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* ISO week-numbering year: http://en.wikipedia.org/wiki/ISO_week_date
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*
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* @typeParam DateType - The `Date` type, the function operates on. Gets inferred from passed arguments. Allows to use extensions like [`UTCDate`](https://github.com/date-fns/utc).
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*
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* @param dateLeft - The later date
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* @param dateRight - The earlier date
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*
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* @returns The number of full ISO week-numbering years
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*
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* @example
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* // How many full ISO week-numbering years are between 1 January 2010 and 1 January 2012?
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* const result = differenceInISOWeekYears(
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* new Date(2012, 0, 1),
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* new Date(2010, 0, 1)
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* )
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* //=> 1
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*/
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export function differenceInISOWeekYears(dateLeft, dateRight) {
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let _dateLeft = toDate(dateLeft);
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const _dateRight = toDate(dateRight);
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const sign = compareAsc(_dateLeft, _dateRight);
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const difference = Math.abs(
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differenceInCalendarISOWeekYears(_dateLeft, _dateRight),
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);
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_dateLeft = subISOWeekYears(_dateLeft, sign * difference);
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// Math.abs(diff in full ISO years - diff in calendar ISO years) === 1
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// if last calendar ISO year is not full
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// If so, result must be decreased by 1 in absolute value
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const isLastISOWeekYearNotFull = Number(
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compareAsc(_dateLeft, _dateRight) === -sign,
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);
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const result = sign * (difference - isLastISOWeekYearNotFull);
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// Prevent negative zero
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return result === 0 ? 0 : result;
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}
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// Fallback for modularized imports:
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export default differenceInISOWeekYears;
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