source: frontend/node_modules/webpack/lib/util/Queue.js

/*
        MIT License http://www.opensource.org/licenses/mit-license.php
        Author Tobias Koppers @sokra
*/

"use strict";

/**
 * FIFO queue that keeps items unique by storing them in insertion order inside
 * a `Set`.
 * @template T
 */
class Queue {
        /**
         * Seeds the queue with an optional iterable of initial unique items.
         * @param {Iterable<T>=} items The initial elements.
         */
        constructor(items) {
                /**
                 * @private
                 * @type {Set<T>}
                 */
                this._set = new Set(items);
        }

        /**
         * Returns the number of unique items currently waiting in the queue.
         * @returns {number} The number of elements in this queue.
         */
        get length() {
                return this._set.size;
        }

        /**
         * Enqueues an item, moving nothing if that value is already present.
         * @param {T} item The element to add.
         * @returns {void}
         */
        enqueue(item) {
                this._set.add(item);
        }

        /**
         * Removes and returns the oldest enqueued item.
         * @returns {T | undefined} The head of the queue of `undefined` if this queue is empty.
         */
        dequeue() {
                const result = this._set[Symbol.iterator]().next();
                if (result.done) return;
                this._set.delete(result.value);
                return result.value;
        }
}

module.exports = Queue;