index.js

var getQuarter = require('../get_quarter/index.js')
var parse = require('../parse/index.js')

/**
 * @category Quarter Helpers
 * @summary Get the number of calendar quarters between the given dates.
 *
 * @description
 * Get the number of calendar quarters between the given dates.
 *
 * @param {Date|String|Number} dateLeft - the later date
 * @param {Date|String|Number} dateRight - the earlier date
 * @returns {Number} the number of calendar quarters
 *
 * @example
 * // How many calendar quarters are between 31 December 2013 and 2 July 2014?
 * var result = differenceInCalendarQuarters(
 *   new Date(2014, 6, 2),
 *   new Date(2013, 11, 31)
 * )
 * //=> 3
 */
function differenceInCalendarQuarters (dirtyDateLeft, dirtyDateRight) {
  var dateLeft = parse(dirtyDateLeft)
  var dateRight = parse(dirtyDateRight)

  var yearDiff = dateLeft.getFullYear() - dateRight.getFullYear()
  var quarterDiff = getQuarter(dateLeft) - getQuarter(dateRight)

  return yearDiff * 4 + quarterDiff
}

module.exports = differenceInCalendarQuarters