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

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

"use strict";

/**
 * FIFO queue backed by arrays with a reversed dequeue buffer to avoid the cost
 * of repeated `Array#shift` operations.
 * @template T
 */
class ArrayQueue {
        /**
         * Seeds the queue with an optional iterable of items in dequeue order.
         * @param {Iterable<T>=} items The initial elements.
         */
        constructor(items) {
                /**
                 * @private
                 * @type {T[]}
                 */
                this._list = items ? [...items] : [];
                /**
                 * @private
                 * @type {T[]}
                 */
                this._listReversed = [];
        }

        /**
         * Returns the current number of items waiting in either internal buffer.
         * @returns {number} The number of elements in this queue.
         */
        get length() {
                return this._list.length + this._listReversed.length;
        }

        /**
         * Removes all pending items from both internal buffers.
         */
        clear() {
                this._list.length = 0;
                this._listReversed.length = 0;
        }

        /**
         * Appends an item to the tail of the queue.
         * @param {T} item The element to add.
         * @returns {void}
         */
        enqueue(item) {
                this._list.push(item);
        }

        /**
         * Removes and returns the next item in FIFO order, switching to a reversed
         * buffer when that is cheaper than shifting from the front of the array.
         * @returns {T | undefined} The head of the queue of `undefined` if this queue is empty.
         */
        dequeue() {
                if (this._listReversed.length === 0) {
                        if (this._list.length === 0) return;
                        if (this._list.length === 1) return this._list.pop();
                        if (this._list.length < 16) return this._list.shift();
                        const temp = this._listReversed;
                        this._listReversed = this._list;
                        this._listReversed.reverse();
                        this._list = temp;
                }
                return this._listReversed.pop();
        }

        /**
         * Removes the first matching item from whichever internal buffer currently
         * contains it.
         * @param {T} item the item
         * @returns {void}
         */
        delete(item) {
                const i = this._list.indexOf(item);
                if (i >= 0) {
                        this._list.splice(i, 1);
                } else {
                        const i = this._listReversed.indexOf(item);
                        if (i >= 0) this._listReversed.splice(i, 1);
                }
        }

        [Symbol.iterator]() {
                return {
                        next: () => {
                                const item = this.dequeue();
                                if (item) {
                                        return {
                                                done: false,
                                                value: item
                                        };
                                }
                                return {
                                        done: true,
                                        value: undefined
                                };
                        }
                };
        }
}

module.exports = ArrayQueue;