source: trip-planner-front/node_modules/webpack/lib/util/createHash.js

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

"use strict";

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

const BULK_SIZE = 2000;

// We are using an object instead of a Map as this will stay static during the runtime
// so access to it can be optimized by v8
const digestCaches = {};

class BulkUpdateDecorator extends Hash {
        /**
         * @param {Hash | function(): Hash} hashOrFactory function to create a hash
         * @param {string=} hashKey key for caching
         */
        constructor(hashOrFactory, hashKey) {
                super();
                this.hashKey = hashKey;
                if (typeof hashOrFactory === "function") {
                        this.hashFactory = hashOrFactory;
                        this.hash = undefined;
                } else {
                        this.hashFactory = undefined;
                        this.hash = hashOrFactory;
                }
                this.buffer = "";
        }

        /**
         * Update hash {@link https://nodejs.org/api/crypto.html#crypto_hash_update_data_inputencoding}
         * @param {string|Buffer} data data
         * @param {string=} inputEncoding data encoding
         * @returns {this} updated hash
         */
        update(data, inputEncoding) {
                if (
                        inputEncoding !== undefined ||
                        typeof data !== "string" ||
                        data.length > BULK_SIZE
                ) {
                        if (this.hash === undefined) this.hash = this.hashFactory();
                        if (this.buffer.length > 0) {
                                this.hash.update(this.buffer);
                                this.buffer = "";
                        }
                        this.hash.update(data, inputEncoding);
                } else {
                        this.buffer += data;
                        if (this.buffer.length > BULK_SIZE) {
                                if (this.hash === undefined) this.hash = this.hashFactory();
                                this.hash.update(this.buffer);
                                this.buffer = "";
                        }
                }
                return this;
        }

        /**
         * Calculates the digest {@link https://nodejs.org/api/crypto.html#crypto_hash_digest_encoding}
         * @param {string=} encoding encoding of the return value
         * @returns {string|Buffer} digest
         */
        digest(encoding) {
                let digestCache;
                const buffer = this.buffer;
                if (this.hash === undefined) {
                        // short data for hash, we can use caching
                        const cacheKey = `${this.hashKey}-${encoding}`;
                        digestCache = digestCaches[cacheKey];
                        if (digestCache === undefined) {
                                digestCache = digestCaches[cacheKey] = new Map();
                        }
                        const cacheEntry = digestCache.get(buffer);
                        if (cacheEntry !== undefined) return cacheEntry;
                        this.hash = this.hashFactory();
                }
                if (buffer.length > 0) {
                        this.hash.update(buffer);
                }
                const digestResult = this.hash.digest(encoding);
                const result =
                        typeof digestResult === "string" ? digestResult : digestResult.toString();
                if (digestCache !== undefined) {
                        digestCache.set(buffer, result);
                }
                return result;
        }
}

/* istanbul ignore next */
class DebugHash extends Hash {
        constructor() {
                super();
                this.string = "";
        }

        /**
         * Update hash {@link https://nodejs.org/api/crypto.html#crypto_hash_update_data_inputencoding}
         * @param {string|Buffer} data data
         * @param {string=} inputEncoding data encoding
         * @returns {this} updated hash
         */
        update(data, inputEncoding) {
                if (typeof data !== "string") data = data.toString("utf-8");
                if (data.startsWith("debug-digest-")) {
                        data = Buffer.from(data.slice("debug-digest-".length), "hex").toString();
                }
                this.string += `[${data}](${new Error().stack.split("\n", 3)[2]})\n`;
                return this;
        }

        /**
         * Calculates the digest {@link https://nodejs.org/api/crypto.html#crypto_hash_digest_encoding}
         * @param {string=} encoding encoding of the return value
         * @returns {string|Buffer} digest
         */
        digest(encoding) {
                return "debug-digest-" + Buffer.from(this.string).toString("hex");
        }
}

let crypto = undefined;

/**
 * Creates a hash by name or function
 * @param {string | typeof Hash} algorithm the algorithm name or a constructor creating a hash
 * @returns {Hash} the hash
 */
module.exports = algorithm => {
        if (typeof algorithm === "function") {
                return new BulkUpdateDecorator(() => new algorithm());
        }
        switch (algorithm) {
                // TODO add non-cryptographic algorithm here
                case "debug":
                        return new DebugHash();
                default:
                        if (crypto === undefined) crypto = require("crypto");
                        return new BulkUpdateDecorator(
                                () => crypto.createHash(algorithm),
                                algorithm
                        );
        }
};