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import toDate from '../toDate/index'
import differenceInCalendarDays from '../differenceInCalendarDays/index'
import requiredArgs from '../_lib/requiredArgs/index'
// Like `compareAsc` but uses local time not UTC, which is needed
// for accurate equality comparisons of UTC timestamps that end up
// having the same representation in local time, e.g. one hour before
// DST ends vs. the instant that DST ends.
function compareLocalAsc(dateLeft: Date, dateRight: Date): number {
const diff =
dateLeft.getFullYear() - dateRight.getFullYear() ||
dateLeft.getMonth() - dateRight.getMonth() ||
dateLeft.getDate() - dateRight.getDate() ||
dateLeft.getHours() - dateRight.getHours() ||
dateLeft.getMinutes() - dateRight.getMinutes() ||
dateLeft.getSeconds() - dateRight.getSeconds() ||
dateLeft.getMilliseconds() - dateRight.getMilliseconds()
if (diff < 0) {
return -1
} else if (diff > 0) {
return 1
// Return 0 if diff is 0; return NaN if diff is NaN
} else {
return diff
}
}
/**
* @name differenceInDays
* @category Day Helpers
* @summary Get the number of full days between the given dates.
*
* @description
* Get the number of full day periods between two dates. Fractional days are
* truncated towards zero.
*
* One "full day" is the distance between a local time in one day to the same
* local time on the next or previous day. A full day can sometimes be less than
* or more than 24 hours if a daylight savings change happens between two dates.
*
* To ignore DST and only measure exact 24-hour periods, use this instead:
* `Math.floor(differenceInHours(dateLeft, dateRight)/24)|0`.
*
*
* ### v2.0.0 breaking changes:
*
* - [Changes that are common for the whole library](https://github.com/date-fns/date-fns/blob/master/docs/upgradeGuide.md#Common-Changes).
*
* @param {Date|Number} dateLeft - the later date
* @param {Date|Number} dateRight - the earlier date
* @returns {Number} the number of full days according to the local timezone
* @throws {TypeError} 2 arguments required
*
* @example
* // How many full days are between
* // 2 July 2011 23:00:00 and 2 July 2012 00:00:00?
* const result = differenceInDays(
* new Date(2012, 6, 2, 0, 0),
* new Date(2011, 6, 2, 23, 0)
* )
* //=> 365
* // How many full days are between
* // 2 July 2011 23:59:00 and 3 July 2011 00:01:00?
* const result = differenceInDays(
* new Date(2011, 6, 3, 0, 1),
* new Date(2011, 6, 2, 23, 59)
* )
* //=> 0
* // How many full days are between
* // 1 March 2020 0:00 and 1 June 2020 0:00 ?
* // Note: because local time is used, the
* // result will always be 92 days, even in
* // time zones where DST starts and the
* // period has only 92*24-1 hours.
* const result = differenceInDays(
* new Date(2020, 5, 1),
* new Date(2020, 2, 1)
* )
//=> 92
*/
export default function differenceInDays(
dirtyDateLeft: Date | number,
dirtyDateRight: Date | number
): number {
requiredArgs(2, arguments)
const dateLeft = toDate(dirtyDateLeft)
const dateRight = toDate(dirtyDateRight)
const sign = compareLocalAsc(dateLeft, dateRight)
const difference = Math.abs(differenceInCalendarDays(dateLeft, dateRight))
dateLeft.setDate(dateLeft.getDate() - sign * difference)
// Math.abs(diff in full days - diff in calendar days) === 1 if last calendar day is not full
// If so, result must be decreased by 1 in absolute value
const isLastDayNotFull = Number(
compareLocalAsc(dateLeft, dateRight) === -sign
)
const result = sign * (difference - isLastDayNotFull)
// Prevent negative zero
return result === 0 ? 0 : result
}
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