webpack/lib/cache/getLazyHashedEtag.js

Packs CommonJs/AMD modules for the browser. Allows to split your codebase into multiple bundles, which can be loaded on demand. Support loaders to preprocess files, i.e. json, jsx, es7, css, less, ... and your custom stuff.

/*
	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 {typeof import("../util/Hash")} HashConstructor */

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

class LazyHashedEtag {
	/**
	 * @param {HashableObject} obj object with updateHash method
	 * @param {string | HashConstructor} hashFunction the hash function to use
	 */
	constructor(obj, hashFunction = "md4") {
		this._obj = obj;
		this._hash = undefined;
		this._hashFunction = hashFunction;
	}

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

/** @type {Map<string | HashConstructor, WeakMap<HashableObject, LazyHashedEtag>>} */
const mapStrings = new Map();

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

/**
 * @param {HashableObject} obj object with updateHash method
 * @param {string | HashConstructor} hashFunction the hash function to use
 * @returns {LazyHashedEtag} etag
 */
const getter = (obj, hashFunction = "md4") => {
	let innerMap;
	if (typeof hashFunction === "string") {
		innerMap = mapStrings.get(hashFunction);
		if (innerMap === undefined) {
			const newHash = new LazyHashedEtag(obj, hashFunction);
			innerMap = new WeakMap();
			innerMap.set(obj, newHash);
			mapStrings.set(hashFunction, innerMap);
			return newHash;
		}
	} else {
		innerMap = mapObjects.get(hashFunction);
		if (innerMap === undefined) {
			const newHash = new LazyHashedEtag(obj, hashFunction);
			innerMap = new WeakMap();
			innerMap.set(obj, newHash);
			mapObjects.set(hashFunction, innerMap);
			return newHash;
		}
	}
	const hash = innerMap.get(obj);
	if (hash !== undefined) return hash;
	const newHash = new LazyHashedEtag(obj, hashFunction);
	innerMap.set(obj, newHash);
	return newHash;
};

module.exports = getter;