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

let singleton = null;

/**
 * Represents the local zone for this JavaScript environment.
 * @implements {Zone}
 */
export default class SystemZone extends Zone {
  /**
   * Get a singleton instance of the local zone
   * @return {SystemZone}
   */
  static get instance() {
    if (singleton === null) {
      singleton = new SystemZone();
    }
    return singleton;
  }

  /** @override **/
  get type() {
    return "system";
  }

  /** @override **/
  get name() {
    return new Intl.DateTimeFormat().resolvedOptions().timeZone;
  }

  /** @override **/
  get isUniversal() {
    return false;
  }

  /** @override **/
  offsetName(ts, { format, locale }) {
    return parseZoneInfo(ts, format, locale);
  }

  /** @override **/
  formatOffset(ts, format) {
    return formatOffset(this.offset(ts), format);
  }

  /** @override **/
  offset(ts) {
    return -new Date(ts).getTimezoneOffset();
  }

  /** @override **/
  equals(otherZone) {
    return otherZone.type === "system";
  }

  /** @override **/
  get isValid() {
    return true;
  }
}