t which was just deleted.
 */
export class UserContextManagerClass {
  #contextualIdentityListener;
  #userContextIds;

  constructor() {
    lazy.EventEmitter.decorate(this);

    // Map from internal ids (numbers) from the ContextualIdentityService to
    // opaque UUIDs (string).
    this.#userContextIds = new Map();

    // The default user context is always using 0 as internal user context id
    // and should be exposed as "default" instead of a randomly generated id.
    this.#userContextIds.set(DEFAULT_INTERNAL_ID, DEFAULT_CONTEXT_ID);

    // Register other (non-default) public contexts.
    lazy.ContextualIdentityService.getPublicIdentities().forEach(identity =>
      this.#registerIdentity(identity)
    );

    this.#contextualIdentityListener = new lazy.ContextualIdentityListener();
    this.#contextualIdentityListener.on("created", this.#onIdentityCreated);
    this.#contextualIdentityListener.on("deleted", this.#onIdentityDeleted);
    this.#contextualIdentityListener.startListening();
  }

  destroy() {
    this.#contextualIdentityListener.off("created", this.#onIdentityCreated);
    this.#contextualIdentityListener.off("deleted", this.#onIdentityDeleted);
    this.#contextualIdentityListener.destroy();

    this.#userContextIds = null;
  }

  /**
   * Retrieve the user context id corresponding to the default user context.
   *
   * @returns {string}
   *     The default user context id.
   */
  get defaultUserContextId() {
    return DEFAULT_CONTEXT_ID;
  }

  /**
   * Creates a new user context.
   *
   * @param {string} prefix
   *     The prefix to use for the name of the user context.
   *
   * @returns {string}
   *     The user context id of the new user context.
   */
  createContext(prefix = "remote") {
    // Prepare a unique name.
    const name = `${prefix}-${lazy.generateUUID()}`;

    // Create the user context.
    const identity = lazy.ContextualIdentityService.create(name);

    // An id has been set already by the contextual-identity-created observer.
    return this.#userContextIds.get(identity.userContextId);
  }

  /**
   * Retrieve the user context id corresponding to the provided browsing context.
   *
   * @param {BrowsingContext} browsingContext
   *     The browsing context to get the user context id from.
   *
   * @returns {string}
   *     The corresponding user context id.
   *
   * @throws {TypeError}
   *     If `browsingContext` is not a CanonicalBrowsingContext instance.
   */
  getIdByBrowsingContext(browsingContext) {
    if (!CanonicalBrowsingContext.isInstance(browsingContext)) {
      throw new TypeError(
        `Expected browsingContext to be a CanonicalBrowsingContext, got ${browsingContext}`
      );
    }

    return this.getIdByInternalId(
      browsingContext.originAttributes.userContextId
    );
  }

  /**
   * Retrieve the user context id corresponding to the provided internal id.
   *
   * @param {number} internalId
   *     The internal user context id.
   *
   * @returns {string|null}
   *     The corresponding user context id or null if the user context does not
   *     exist.
   */
  getIdByInternalId(internalId) {
    if (this.#userContextIds.has(internalId)) {
      return this.#userContextIds.get(internalId);
    }
    return null;
  }

  /**
   * Retrieve the internal id corresponding to the provided user
   * context id.
   *
   * @param {string} userContextId
   *     The user context id.
   *
   * @returns {number|null}
   *     The internal user context id or null if the user context does not
   *     exist.
   */
  getInternalIdById(userContextId) {
    for (const [internalId, id] of this.#userContextIds) {
      if (userContextId == id) {
        return internalId;
      }
    }
    return null;
  }

  /**
   * Returns an array of tabs related
   * to the provided internal user context id.
   *
   * @param {string} internalId
   *     The internal user context id.
   *
   * @returns {Array<Tab>}
   *     The array of tabs.
   */
  getTabsForUserContext(internalId) {
    return lazy.TabManager.allTabs.filter(tab => {
      return (
        (tab.hasAttribute("usercontextid") &&
          parseInt(tab.getAttribute("usercontextid"), 10) == internalId) ||
        (!tab.hasAttribute("usercontextid") && internalId === 0)
      );
    });
  }

  /**
   * Returns an array of all known user context ids.
   *
   * @returns {Array<string>}
   *     The array of user context ids.
   */
  getUserContextIds() {
    return Array.from(this.#userContextIds.values());
  }

  /**
   * Checks if the provided user context id is known by this UserContextManager.
   *
   * @param {string} userContextId
   *     The id of the user context to check.
   */
  hasUserContextId(userContextId) {
    return this.getUserContextIds().includes(userContextId);
  }

  /**
   * Removes a user context and closes all related container tabs.
   *
   * Note: When closing the related container tabs possible "beforeunload"
   * prompts will be ignored.
   *
   * @param {string} userContextId
   *     The id of the user context to remove.
   * @param {object=} options
   * @param {boolean=} options.closeContextTabs
   *     Pass true if the tabs owned by the user context should also be closed.
   *     Defaults to false.
   */
  removeUserContext(userContextId, options = {}) {
    const { closeContextTabs = false } = options;

    if (!this.hasUserContextId(userContextId)) {
      return;
    }

    const internalId = this.getInternalIdById(userContextId);
    if (closeContextTabs) {
      lazy.ContextualIdentityService.closeContainerTabs(internalId, {
        skipPermitUnload: true,
      });
    }
    lazy.ContextualIdentityService.remove(internalId);
  }

  #onIdentityCreated = (eventName, data) => {
    this.#registerIdentity(data.identity);
  };

  #onIdentityDeleted = (eventName, data) => {
    const userContextId = this.#userContextIds.get(data.identity.userContextId);
    this.#userContextIds.delete(data.identity.userContextId);
    this.emit("user-context-deleted", { userContextId });
  };

  #registerIdentity(identity) {
    const userContextId = lazy.generateUUID();
    this.#userContextIds.set(identity.userContextId, userContextId);
    this.emit("user-context-created", { userContextId });
  }
}

// Expose a shared singleton.
export const UserContextManager = new UserContextManagerClass();
PK