source: trip-planner-front/node_modules/webpack/lib/cache/getLazyHashedEtag.js@ 8d391a1

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

"use strict";

const createHash = require("../util/createHash");

/** @typedef {import("../util/Hash")} Hash */

/**
 * @typedef {Object} HashableObject
 * @property {function(Hash): void} updateHash
 */

class LazyHashedEtag {
        /**
         * @param {HashableObject} obj object with updateHash method
         */
        constructor(obj) {
                this._obj = obj;
                this._hash = undefined;
        }

        /**
         * @returns {string} hash of object
         */
        toString() {
                if (this._hash === undefined) {
                        const hash = createHash("md4");
                        this._obj.updateHash(hash);
                        this._hash = /** @type {string} */ (hash.digest("base64"));
                }
                return this._hash;
        }
}

/** @type {WeakMap<HashableObject, LazyHashedEtag>} */
const map = new WeakMap();

/**
 * @param {HashableObject} obj object with updateHash method
 * @returns {LazyHashedEtag} etag
 */
const getter = obj => {
        const hash = map.get(obj);
        if (hash !== undefined) return hash;
        const newHash = new LazyHashedEtag(obj);
        map.set(obj, newHash);
        return newHash;
};

module.exports = getter;