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

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

"use strict";

const TupleSet = require("./TupleSet");

/**
 * FIFO queue for tuples that preserves uniqueness by delegating membership
 * tracking to `TupleSet`.
 * @template T
 * @template V
 */
class TupleQueue {
        /**
         * Seeds the queue with an optional iterable of tuples to visit.
         * @param {Iterable<[T, V, ...EXPECTED_ANY]>=} items The initial elements.
         */
        constructor(items) {
                /**
                 * @private
                 * @type {TupleSet<T, V>}
                 */
                this._set = new TupleSet(items);
                /**
                 * @private
                 * @type {Iterator<[T, V, ...EXPECTED_ANY]>}
                 */
                this._iterator = this._set[Symbol.iterator]();
        }

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

        /**
         * Enqueues a tuple if it is not already present in the underlying set.
         * @param {[T, V, ...EXPECTED_ANY]} item The element to add.
         * @returns {void}
         */
        enqueue(...item) {
                this._set.add(...item);
        }

        /**
         * Removes and returns the next queued tuple, rebuilding the iterator when
         * the underlying tuple set has changed since the last full pass.
         * @returns {[T, V, ...EXPECTED_ANY] | undefined} The head of the queue of `undefined` if this queue is empty.
         */
        dequeue() {
                const result = this._iterator.next();
                if (result.done) {
                        if (this._set.size > 0) {
                                this._iterator = this._set[Symbol.iterator]();
                                const value =
                                        /** @type {[T, V, ...EXPECTED_ANY]} */
                                        (this._iterator.next().value);
                                this._set.delete(...value);
                                return value;
                        }
                        return;
                }
                this._set.delete(.../** @type {[T, V, ...EXPECTED_ANY]} */ (result.value));
                return result.value;
        }
}

module.exports = TupleQueue;