39 lines
1.5 KiB
JavaScript
39 lines
1.5 KiB
JavaScript
"use strict";
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Object.defineProperty(exports, "__esModule", { value: true });
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exports.getPreviousMonth = getPreviousMonth;
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/**
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* Returns the previous month the user can navigate to, based on the given
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* options.
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*
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* The previous month is not always the previous calendar month:
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*
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* - If it is before the `calendarStartMonth`, it returns `undefined`.
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* - If paged navigation is enabled, it skips back by the number of displayed
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* months.
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*
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* @param firstDisplayedMonth The first month currently displayed in the
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* calendar.
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* @param calendarStartMonth The earliest month the user can navigate to.
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* @param options Navigation options, including `numberOfMonths` and
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* `pagedNavigation`.
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* @param dateLib The date library to use for date manipulation.
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* @returns The previous month, or `undefined` if navigation is not possible.
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*/
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function getPreviousMonth(firstDisplayedMonth, calendarStartMonth, options, dateLib) {
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if (options.disableNavigation) {
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return undefined;
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}
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const { pagedNavigation, numberOfMonths } = options;
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const { startOfMonth, addMonths, differenceInCalendarMonths } = dateLib;
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const offset = pagedNavigation ? (numberOfMonths ?? 1) : 1;
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const month = startOfMonth(firstDisplayedMonth);
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if (!calendarStartMonth) {
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return addMonths(month, -offset);
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}
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const monthsDiff = differenceInCalendarMonths(month, calendarStartMonth);
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if (monthsDiff <= 0) {
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return undefined;
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}
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return addMonths(month, -offset);
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}
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