webpack/lib/util/StackedMap.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 TOMBSTONE = Symbol("tombstone");
const UNDEFINED_MARKER = Symbol("undefined");

/**
 * @template T
 * @typedef {T | undefined} Cell<T>
 */

/**
 * @template T
 * @typedef {T | typeof TOMBSTONE | typeof UNDEFINED_MARKER} InternalCell<T>
 */

/**
 * @template K
 * @template V
 * @param {[K, InternalCell<V>]} pair the internal cell
 * @returns {[K, Cell<V>]} its “safe” representation
 */
const extractPair = pair => {
	const key = pair[0];
	const val = pair[1];
	if (val === UNDEFINED_MARKER || val === TOMBSTONE) {
		return [key, undefined];
	} else {
		return /** @type {[K, Cell<V>]} */ (pair);
	}
};

/**
 * @template K
 * @template V
 */
class StackedMap {
	/**
	 * @param {Map<K, InternalCell<V>>[]=} parentStack an optional parent
	 */
	constructor(parentStack) {
		/** @type {Map<K, InternalCell<V>>} */
		this.map = new Map();
		/** @type {Map<K, InternalCell<V>>[]} */
		this.stack = parentStack === undefined ? [] : parentStack.slice();
		this.stack.push(this.map);
	}

	/**
	 * @param {K} item the key of the element to add
	 * @param {V} value the value of the element to add
	 * @returns {void}
	 */
	set(item, value) {
		this.map.set(item, value === undefined ? UNDEFINED_MARKER : value);
	}

	/**
	 * @param {K} item the item to delete
	 * @returns {void}
	 */
	delete(item) {
		if (this.stack.length > 1) {
			this.map.set(item, TOMBSTONE);
		} else {
			this.map.delete(item);
		}
	}

	/**
	 * @param {K} item the item to test
	 * @returns {boolean} true if the item exists in this set
	 */
	has(item) {
		const topValue = this.map.get(item);
		if (topValue !== undefined) {
			return topValue !== TOMBSTONE;
		}
		if (this.stack.length > 1) {
			for (let i = this.stack.length - 2; i >= 0; i--) {
				const value = this.stack[i].get(item);
				if (value !== undefined) {
					this.map.set(item, value);
					return value !== TOMBSTONE;
				}
			}
			this.map.set(item, TOMBSTONE);
		}
		return false;
	}

	/**
	 * @param {K} item the key of the element to return
	 * @returns {Cell<V>} the value of the element
	 */
	get(item) {
		const topValue = this.map.get(item);
		if (topValue !== undefined) {
			return topValue === TOMBSTONE || topValue === UNDEFINED_MARKER
				? undefined
				: topValue;
		}
		if (this.stack.length > 1) {
			for (let i = this.stack.length - 2; i >= 0; i--) {
				const value = this.stack[i].get(item);
				if (value !== undefined) {
					this.map.set(item, value);
					return value === TOMBSTONE || value === UNDEFINED_MARKER
						? undefined
						: value;
				}
			}
			this.map.set(item, TOMBSTONE);
		}
		return undefined;
	}

	_compress() {
		if (this.stack.length === 1) return;
		this.map = new Map();
		for (const data of this.stack) {
			for (const pair of data) {
				if (pair[1] === TOMBSTONE) {
					this.map.delete(pair[0]);
				} else {
					this.map.set(pair[0], pair[1]);
				}
			}
		}
		this.stack = [this.map];
	}

	asArray() {
		this._compress();
		return Array.from(this.map.keys());
	}

	asSet() {
		this._compress();
		return new Set(this.map.keys());
	}

	asPairArray() {
		this._compress();
		return Array.from(this.map.entries(), extractPair);
	}

	asMap() {
		return new Map(this.asPairArray());
	}

	get size() {
		this._compress();
		return this.map.size;
	}

	createChild() {
		return new StackedMap(this.stack);
	}
}

module.exports = StackedMap;