55 lines
1.1 KiB
JavaScript
55 lines
1.1 KiB
JavaScript
/*
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MIT License http://www.opensource.org/licenses/mit-license.php
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Author Tobias Koppers @sokra
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*/
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"use strict";
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const createHash = require("../util/createHash");
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/** @typedef {import("../util/Hash")} Hash */
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/**
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* @typedef {Object} HashableObject
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* @property {function(Hash): void} updateHash
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*/
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class LazyHashedEtag {
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/**
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* @param {HashableObject} obj object with updateHash method
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*/
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constructor(obj) {
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this._obj = obj;
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this._hash = undefined;
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}
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/**
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* @returns {string} hash of object
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*/
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toString() {
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if (this._hash === undefined) {
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const hash = createHash("md4");
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this._obj.updateHash(hash);
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this._hash = /** @type {string} */ (hash.digest("base64"));
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}
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return this._hash;
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}
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}
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/** @type {WeakMap<HashableObject, LazyHashedEtag>} */
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const map = new WeakMap();
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/**
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* @param {HashableObject} obj object with updateHash method
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* @returns {LazyHashedEtag} etag
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*/
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const getter = obj => {
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const hash = map.get(obj);
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if (hash !== undefined) return hash;
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const newHash = new LazyHashedEtag(obj);
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map.set(obj, newHash);
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return newHash;
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};
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module.exports = getter;
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