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

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

"use strict";

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

/**
 * StringXor class provides methods for performing
 * [XOR operations](https://en.wikipedia.org/wiki/Exclusive_or) on strings. In this context
 * we operating on the character codes of two strings, which are represented as
 * [Buffer](https://nodejs.org/api/buffer.html) objects.
 *
 * We use [StringXor in webpack](https://github.com/webpack/webpack/commit/41a8e2ea483a544c4ccd3e6217bdfb80daffca39)
 * to create a hash of the current state of the compilation. By XOR'ing the Module hashes, it
 * doesn't matter if the Module hashes are sorted or not. This is useful because it allows us to avoid sorting the
 * Module hashes.
 *
 * @example
 * ```js
 * const xor = new StringXor();
 * xor.add('hello');
 * xor.add('world');
 * console.log(xor.toString());
 * ```
 *
 * @example
 * ```js
 * const xor = new StringXor();
 * xor.add('foo');
 * xor.add('bar');
 * const hash = createHash('sha256');
 * hash.update(xor.toString());
 * console.log(hash.digest('hex'));
 * ```
 */
class StringXor {
	constructor() {
		/** @type {Buffer|undefined} */
		this._value = undefined;
	}

	/**
	 * Adds a string to the current StringXor object.
	 *
	 * @param {string} str string
	 * @returns {void}
	 */
	add(str) {
		const len = str.length;
		const value = this._value;
		if (value === undefined) {
			/**
			 * We are choosing to use Buffer.allocUnsafe() because it is often faster than Buffer.alloc() because
			 * it allocates a new buffer of the specified size without initializing the memory.
			 */
			const newValue = (this._value = Buffer.allocUnsafe(len));
			for (let i = 0; i < len; i++) {
				newValue[i] = str.charCodeAt(i);
			}
			return;
		}
		const valueLen = value.length;
		if (valueLen < len) {
			const newValue = (this._value = Buffer.allocUnsafe(len));
			let i;
			for (i = 0; i < valueLen; i++) {
				newValue[i] = value[i] ^ str.charCodeAt(i);
			}
			for (; i < len; i++) {
				newValue[i] = str.charCodeAt(i);
			}
		} else {
			for (let i = 0; i < len; i++) {
				value[i] = value[i] ^ str.charCodeAt(i);
			}
		}
	}

	/**
	 * Returns a string that represents the current state of the StringXor object. We chose to use "latin1" encoding
	 * here because "latin1" encoding is a single-byte encoding that can represent all characters in the
	 * [ISO-8859-1 character set](https://en.wikipedia.org/wiki/ISO/IEC_8859-1). This is useful when working
	 * with binary data that needs to be represented as a string.
	 *
	 * @returns {string} Returns a string that represents the current state of the StringXor object.
	 */
	toString() {
		const value = this._value;
		return value === undefined ? "" : value.toString("latin1");
	}

	/**
	 * Updates the hash with the current state of the StringXor object.
	 *
	 * @param {Hash} hash Hash instance
	 */
	updateHash(hash) {
		const value = this._value;
		if (value !== undefined) hash.update(value);
	}
}

module.exports = StringXor;