/**
 * Copyright © Volker Schukai and all contributing authors, {{copyRightYear}}. All rights reserved.
 * Node module: @schukai/monster
 *
 * This source code is licensed under the GNU Affero General Public License version 3 (AGPLv3).
 * The full text of the license can be found at: https://www.gnu.org/licenses/agpl-3.0.en.html
 *
 * For those who do not wish to adhere to the AGPLv3, a commercial license is available.
 * Acquiring a commercial license allows you to use this software without complying with the AGPLv3 terms.
 * For more information about purchasing a commercial license, please contact Volker Schukai.
 *
 * SPDX-License-Identifier: AGPL-3.0
 */

import { Queue } from "./queue.mjs";
import { instanceSymbol, internalSymbol } from "../constants.mjs";
import { ObserverList } from "./observerlist.mjs";

export { ObservableQueue };

/**
 * An observable queue is a list of items that are processed one after another (first in, first out).
 *
 * `Queue.add()` and `Queue.clear()` notify all observers.
 *
 * @fragments /fragments/libraries/types/observablequeue/
 *
 * @example /examples/libraries/types/observablequeue/simple/ Observe queue changes while items are added
 * @since 3.3.0
 * @copyright Volker Schukai
 * @summary A FIFO queue that notifies observers whenever its contents change.
 */
class ObservableQueue extends Queue {
	/**
	 *
	 */
	constructor() {
		super();
		this[internalSymbol] = {
			observers: new ObserverList(),
		};
	}

	/**
	 * This method is called by the `instanceof` operator.
	 * @return {symbol}
	 */
	static get [instanceSymbol]() {
		return Symbol.for("@schukai/monster/types/observablequeue");
	}

	/**
	 * Add a new element to the end of the queue.
	 *
	 * @param {*} value
	 * @return {Queue}
	 */
	add(value) {
		super.add(value);
		this.notifyObservers();
		return this;
	}

	/**
	 * remove all entries
	 *
	 * @return {Queue}
	 */
	clear() {
		super.clear();
		this.notifyObservers();
		return this;
	}

	/**
	 * Attach a new observer
	 *
	 * @param {Observer} observer
	 * @return {ProxyObserver}
	 */
	attachObserver(observer) {
		this[internalSymbol].observers.attach(observer);
		return this;
	}

	/**
	 * Detach a observer
	 *
	 * @param {Observer} observer
	 * @return {ProxyObserver}
	 */
	detachObserver(observer) {
		this[internalSymbol].observers.detach(observer);
		return this;
	}

	/**
	 * Notify all observer
	 *
	 * @return {Promise}
	 */
	notifyObservers() {
		return this[internalSymbol].observers.notify(this);
	}

	/**
	 * @param {Observer} observer
	 * @return {boolean}
	 */
	containsObserver(observer) {
		return this[internalSymbol].observers.contains(observer);
	}
}
