luxon/src/zones/IANAZone.js

Immutable date wrapper

import { formatOffset, parseZoneInfo, isUndefined, objToLocalTS } from "../impl/util.js";
import Zone from "../zone.js";

let dtfCache = {};
function makeDTF(zone) {
  if (!dtfCache[zone]) {
    dtfCache[zone] = new Intl.DateTimeFormat("en-US", {
      hour12: false,
      timeZone: zone,
      year: "numeric",
      month: "2-digit",
      day: "2-digit",
      hour: "2-digit",
      minute: "2-digit",
      second: "2-digit",
      era: "short",
    });
  }
  return dtfCache[zone];
}

const typeToPos = {
  year: 0,
  month: 1,
  day: 2,
  era: 3,
  hour: 4,
  minute: 5,
  second: 6,
};

function hackyOffset(dtf, date) {
  const formatted = dtf.format(date).replace(/\u200E/g, ""),
    parsed = /(\d+)\/(\d+)\/(\d+) (AD|BC),? (\d+):(\d+):(\d+)/.exec(formatted),
    [, fMonth, fDay, fYear, fadOrBc, fHour, fMinute, fSecond] = parsed;
  return [fYear, fMonth, fDay, fadOrBc, fHour, fMinute, fSecond];
}

function partsOffset(dtf, date) {
  const formatted = dtf.formatToParts(date);
  const filled = [];
  for (let i = 0; i < formatted.length; i++) {
    const { type, value } = formatted[i];
    const pos = typeToPos[type];

    if (type === "era") {
      filled[pos] = value;
    } else if (!isUndefined(pos)) {
      filled[pos] = parseInt(value, 10);
    }
  }
  return filled;
}

let ianaZoneCache = {};
/**
 * A zone identified by an IANA identifier, like America/New_York
 * @implements {Zone}
 */
export default class IANAZone extends Zone {
  /**
   * @param {string} name - Zone name
   * @return {IANAZone}
   */
  static create(name) {
    if (!ianaZoneCache[name]) {
      ianaZoneCache[name] = new IANAZone(name);
    }
    return ianaZoneCache[name];
  }

  /**
   * Reset local caches. Should only be necessary in testing scenarios.
   * @return {void}
   */
  static resetCache() {
    ianaZoneCache = {};
    dtfCache = {};
  }

  /**
   * Returns whether the provided string is a valid specifier. This only checks the string's format, not that the specifier identifies a known zone; see isValidZone for that.
   * @param {string} s - The string to check validity on
   * @example IANAZone.isValidSpecifier("America/New_York") //=> true
   * @example IANAZone.isValidSpecifier("Sport~~blorp") //=> false
   * @deprecated For backward compatibility, this forwards to isValidZone, better use `isValidZone()` directly instead.
   * @return {boolean}
   */
  static isValidSpecifier(s) {
    return this.isValidZone(s);
  }

  /**
   * Returns whether the provided string identifies a real zone
   * @param {string} zone - The string to check
   * @example IANAZone.isValidZone("America/New_York") //=> true
   * @example IANAZone.isValidZone("Fantasia/Castle") //=> false
   * @example IANAZone.isValidZone("Sport~~blorp") //=> false
   * @return {boolean}
   */
  static isValidZone(zone) {
    if (!zone) {
      return false;
    }
    try {
      new Intl.DateTimeFormat("en-US", { timeZone: zone }).format();
      return true;
    } catch (e) {
      return false;
    }
  }

  constructor(name) {
    super();
    /** @private **/
    this.zoneName = name;
    /** @private **/
    this.valid = IANAZone.isValidZone(name);
  }

  /**
   * The type of zone. `iana` for all instances of `IANAZone`.
   * @override
   * @type {string}
   */
  get type() {
    return "iana";
  }

  /**
   * The name of this zone (i.e. the IANA zone name).
   * @override
   * @type {string}
   */
  get name() {
    return this.zoneName;
  }

  /**
   * Returns whether the offset is known to be fixed for the whole year:
   * Always returns false for all IANA zones.
   * @override
   * @type {boolean}
   */
  get isUniversal() {
    return false;
  }

  /**
   * Returns the offset's common name (such as EST) at the specified timestamp
   * @override
   * @param {number} ts - Epoch milliseconds for which to get the name
   * @param {Object} opts - Options to affect the format
   * @param {string} opts.format - What style of offset to return. Accepts 'long' or 'short'.
   * @param {string} opts.locale - What locale to return the offset name in.
   * @return {string}
   */
  offsetName(ts, { format, locale }) {
    return parseZoneInfo(ts, format, locale, this.name);
  }

  /**
   * Returns the offset's value as a string
   * @override
   * @param {number} ts - Epoch milliseconds for which to get the offset
   * @param {string} format - What style of offset to return.
   *                          Accepts 'narrow', 'short', or 'techie'. Returning '+6', '+06:00', or '+0600' respectively
   * @return {string}
   */
  formatOffset(ts, format) {
    return formatOffset(this.offset(ts), format);
  }

  /**
   * Return the offset in minutes for this zone at the specified timestamp.
   * @override
   * @param {number} ts - Epoch milliseconds for which to compute the offset
   * @return {number}
   */
  offset(ts) {
    const date = new Date(ts);

    if (isNaN(date)) return NaN;

    const dtf = makeDTF(this.name);
    let [year, month, day, adOrBc, hour, minute, second] = dtf.formatToParts
      ? partsOffset(dtf, date)
      : hackyOffset(dtf, date);

    if (adOrBc === "BC") {
      year = -Math.abs(year) + 1;
    }

    // because we're using hour12 and https://bugs.chromium.org/p/chromium/issues/detail?id=1025564&can=2&q=%2224%3A00%22%20datetimeformat
    const adjustedHour = hour === 24 ? 0 : hour;

    const asUTC = objToLocalTS({
      year,
      month,
      day,
      hour: adjustedHour,
      minute,
      second,
      millisecond: 0,
    });

    let asTS = +date;
    const over = asTS % 1000;
    asTS -= over >= 0 ? over : 1000 + over;
    return (asUTC - asTS) / (60 * 1000);
  }

  /**
   * Return whether this Zone is equal to another zone
   * @override
   * @param {Zone} otherZone - the zone to compare
   * @return {boolean}
   */
  equals(otherZone) {
    return otherZone.type === "iana" && otherZone.name === this.name;
  }

  /**
   * Return whether this Zone is valid.
   * @override
   * @type {boolean}
   */
  get isValid() {
    return this.valid;
  }
}