index.ts

import { toDate } from '../toDate/index.js'
import { tzPattern } from '../_lib/tzPattern/index.js'
import { tzParseTimezone } from '../_lib/tzParseTimezone/index.js'
import { newDateUTC } from '../_lib/newDateUTC/index.js'
import { ToDateOptionsWithTZ } from '../index.js'

/**
 * @name fromZonedTime
 * @category Time Zone Helpers
 * @summary Get the UTC date/time from a date representing local time in a given time zone
 *
 * @description
 * Returns a date instance with the UTC time of the provided date of which the values
 * represented the local time in the time zone specified. In other words, if the input
 * date represented local time in time zone, the timestamp of the output date will
 * give the equivalent UTC of that local time regardless of the current system time zone.
 *
 * @param date the date with values representing the local time
 * @param timeZone the time zone of this local time, can be an offset or IANA time zone
 * @param options the object with options. See [Options]{@link https://date-fns.org/docs/Options}
 * @param {0|1|2} [options.additionalDigits=2] - passed to `toDate`. See [toDate]{@link https://date-fns.org/docs/toDate}
 * @throws {TypeError} 2 arguments required
 * @throws {RangeError} `options.additionalDigits` must be 0, 1 or 2
 *
 * @example
 * // In June 10am in Los Angeles is 5pm UTC
 * const result = fromZonedTime(new Date(2014, 5, 25, 10, 0, 0), 'America/Los_Angeles')
 * //=> 2014-06-25T17:00:00.000Z
 */
export function fromZonedTime(
  date: Date | string | number,
  timeZone: string,
  options?: ToDateOptionsWithTZ
): Date {
  if (typeof date === 'string' && !date.match(tzPattern)) {
    return toDate(date, { ...options, timeZone })
  }

  date = toDate(date, options)

  const utc = newDateUTC(
    date.getFullYear(),
    date.getMonth(),
    date.getDate(),
    date.getHours(),
    date.getMinutes(),
    date.getSeconds(),
    date.getMilliseconds()
  ).getTime()

  const offsetMilliseconds = tzParseTimezone(timeZone, new Date(utc))

  return new Date(utc + offsetMilliseconds)
}