date-fns/src/_lib/setUTCDay/index.js


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import toInteger from '../toInteger/index'
import toDate from '../../toDate/index'
import requiredArgs from '../requiredArgs/index'

// This function will be a part of public API when UTC function will be implemented.
// See issue: https://github.com/date-fns/date-fns/issues/376
export default function setUTCDay(dirtyDate, dirtyDay, dirtyOptions) {
  requiredArgs(2, arguments)

  var options = dirtyOptions || {}
  var locale = options.locale
  var localeWeekStartsOn =
    locale && locale.options && locale.options.weekStartsOn
  var defaultWeekStartsOn =
    localeWeekStartsOn == null ? 0 : toInteger(localeWeekStartsOn)
  var weekStartsOn =
    options.weekStartsOn == null
      ? defaultWeekStartsOn
      : toInteger(options.weekStartsOn)

  // Test if weekStartsOn is between 0 and 6 _and_ is not NaN
  if (!(weekStartsOn >= 0 && weekStartsOn <= 6)) {
    throw new RangeError('weekStartsOn must be between 0 and 6 inclusively')
  }

  var date = toDate(dirtyDate)
  var day = toInteger(dirtyDay)

  var currentDay = date.getUTCDay()

  var remainder = day % 7
  var dayIndex = (remainder + 7) % 7

  var diff = (dayIndex < weekStartsOn ? 7 : 0) + day - currentDay

  date.setUTCDate(date.getUTCDate() + diff)
  return date
}