Source: formatRelative/index.js

import differenceInCalendarDays from '../differenceInCalendarDays/index'
import format from '../format/index'
import defaultLocale from '../locale/en-US/index'
import subMilliseconds from '../subMilliseconds/index'
import toDate from '../toDate/index'
import getTimezoneOffsetInMilliseconds from '../_lib/getTimezoneOffsetInMilliseconds/index'
import requiredArgs from '../_lib/requiredArgs/index'

/**
 * @name formatRelative
 * @category Common Helpers
 * @summary Represent the date in words relative to the given base date.
 *
 * @description
 * Represent the date in words relative to the given base date.
 *
 * | Distance to the base date | Result                    |
 * |---------------------------|---------------------------|
 * | Previous 6 days           | last Sunday at 04:30 AM   |
 * | Last day                  | yesterday at 04:30 AM     |
 * | Same day                  | today at 04:30 AM         |
 * | Next day                  | tomorrow at 04:30 AM      |
 * | Next 6 days               | Sunday at 04:30 AM        |
 * | Other                     | 12/31/2017                |
 *
 * ### 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} date - the date to format
 * @param {Date|Number} baseDate - the date to compare with
 * @param {Object} [options] - an object with options.
 * @param {Locale} [options.locale=defaultLocale] - the locale object. See [Locale]{@link https://date-fns.org/docs/Locale}
 * @param {0|1|2|3|4|5|6} [options.weekStartsOn=0] - the index of the first day of the week (0 - Sunday)
 * @returns {String} the date in words
 * @throws {TypeError} 2 arguments required
 * @throws {RangeError} `date` must not be Invalid Date
 * @throws {RangeError} `baseDate` must not be Invalid Date
 * @throws {RangeError} `options.weekStartsOn` must be between 0 and 6
 * @throws {RangeError} `options.locale` must contain `localize` property
 * @throws {RangeError} `options.locale` must contain `formatLong` property
 * @throws {RangeError} `options.locale` must contain `formatRelative` property
 */
export default function formatRelative(dirtyDate, dirtyBaseDate, dirtyOptions) {
  requiredArgs(2, arguments)

  var date = toDate(dirtyDate)
  var baseDate = toDate(dirtyBaseDate)

  var options = dirtyOptions || {}
  var locale = options.locale || defaultLocale

  if (!locale.localize) {
    throw new RangeError('locale must contain localize property')
  }

  if (!locale.formatLong) {
    throw new RangeError('locale must contain formatLong property')
  }

  if (!locale.formatRelative) {
    throw new RangeError('locale must contain formatRelative property')
  }

  var diff = differenceInCalendarDays(date, baseDate)

  if (isNaN(diff)) {
    throw new RangeError('Invalid time value')
  }

  var token
  if (diff < -6) {
    token = 'other'
  } else if (diff < -1) {
    token = 'lastWeek'
  } else if (diff < 0) {
    token = 'yesterday'
  } else if (diff < 1) {
    token = 'today'
  } else if (diff < 2) {
    token = 'tomorrow'
  } else if (diff < 7) {
    token = 'nextWeek'
  } else {
    token = 'other'
  }

  var utcDate = subMilliseconds(date, getTimezoneOffsetInMilliseconds(date))
  var utcBaseDate = subMilliseconds(
    baseDate,
    getTimezoneOffsetInMilliseconds(baseDate)
  )
  var formatStr = locale.formatRelative(token, utcDate, utcBaseDate, options)
  return format(date, formatStr, options)
}