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

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

"use strict";

/**
 * intersect creates Set containing the intersection of elements between all sets
 * @template T
 * @param {Set<T>[]} sets an array of sets being checked for shared elements
 * @returns {Set<T>} returns a new Set containing the intersecting items
 */
const intersect = (sets) => {
        if (sets.length === 0) return new Set();
        if (sets.length === 1) return new Set(sets[0]);
        let minSize = Infinity;
        let minIndex = -1;
        for (let i = 0; i < sets.length; i++) {
                const size = sets[i].size;
                if (size < minSize) {
                        minIndex = i;
                        minSize = size;
                }
        }
        const current = new Set(sets[minIndex]);
        for (let i = 0; i < sets.length; i++) {
                if (i === minIndex) continue;
                const set = sets[i];
                for (const item of current) {
                        if (!set.has(item)) {
                                current.delete(item);
                        }
                }
        }
        return current;
};

/**
 * Checks if a set is the subset of another set
 * @template T
 * @param {Set<T>} bigSet a Set which contains the original elements to compare against
 * @param {Set<T>} smallSet the set whose elements might be contained inside of bigSet
 * @returns {boolean} returns true if smallSet contains all elements inside of the bigSet
 */
const isSubset = (bigSet, smallSet) => {
        if (bigSet.size < smallSet.size) return false;
        for (const item of smallSet) {
                if (!bigSet.has(item)) return false;
        }
        return true;
};

/**
 * Returns found item.
 * @template T
 * @param {Set<T>} set a set
 * @param {(set: T) => boolean} fn selector function
 * @returns {T | undefined} found item
 */
const find = (set, fn) => {
        for (const item of set) {
                if (fn(item)) return item;
        }
};

/**
 * Returns first item.
 * @template T
 * @param {Set<T> | ReadonlySet<T>} set a set
 * @returns {T | undefined} first item
 */
const first = (set) => {
        const entry = set.values().next();
        return entry.done ? undefined : entry.value;
};

/**
 * Returns combined set, may be identical to a or b.
 * @template T
 * @param {Set<T>} a first
 * @param {Set<T>} b second
 * @returns {Set<T>} combined set, may be identical to a or b
 */
const combine = (a, b) => {
        if (b.size === 0) return a;
        if (a.size === 0) return b;
        const set = new Set(a);
        for (const item of b) set.add(item);
        return set;
};

module.exports.combine = combine;
module.exports.find = find;
module.exports.first = first;
module.exports.intersect = intersect;
module.exports.isSubset = isSubset;