var startOfWeek = require('../start_of_week/index.js')
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var MILLISECONDS_IN_MINUTE = 60000
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var MILLISECONDS_IN_WEEK = 604800000
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/**
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* @category Week Helpers
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* @summary Get the number of calendar weeks between the given dates.
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*
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* @description
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* Get the number of calendar weeks between the given dates.
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*
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* @param {Date|String|Number} dateLeft - the later date
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* @param {Date|String|Number} dateRight - the earlier date
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* @param {Object} [options] - the object with options
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* @param {Number} [options.weekStartsOn=0] - the index of the first day of the week (0 - Sunday)
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* @returns {Number} the number of calendar weeks
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*
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* @example
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* // How many calendar weeks are between 5 July 2014 and 20 July 2014?
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* var result = differenceInCalendarWeeks(
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* new Date(2014, 6, 20),
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* new Date(2014, 6, 5)
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* )
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* //=> 3
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*
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* @example
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* // If the week starts on Monday,
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* // how many calendar weeks are between 5 July 2014 and 20 July 2014?
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* var result = differenceInCalendarWeeks(
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* new Date(2014, 6, 20),
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* new Date(2014, 6, 5),
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* {weekStartsOn: 1}
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* )
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* //=> 2
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*/
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function differenceInCalendarWeeks (dirtyDateLeft, dirtyDateRight, dirtyOptions) {
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var startOfWeekLeft = startOfWeek(dirtyDateLeft, dirtyOptions)
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var startOfWeekRight = startOfWeek(dirtyDateRight, dirtyOptions)
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var timestampLeft = startOfWeekLeft.getTime() -
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startOfWeekLeft.getTimezoneOffset() * MILLISECONDS_IN_MINUTE
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var timestampRight = startOfWeekRight.getTime() -
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startOfWeekRight.getTimezoneOffset() * MILLISECONDS_IN_MINUTE
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// Round the number of days to the nearest integer
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// because the number of milliseconds in a week is not constant
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// (e.g. it's different in the week of the daylight saving time clock shift)
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return Math.round((timestampLeft - timestampRight) / MILLISECONDS_IN_WEEK)
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}
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module.exports = differenceInCalendarWeeks
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