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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";

const Factory = require("enhanced-resolve").ResolverFactory;
const { HookMap, SyncHook, SyncWaterfallHook } = require("tapable");
const {
	cachedCleverMerge,
	removeOperations,
	resolveByProperty
} = require("./util/cleverMerge");

/** @typedef {import("enhanced-resolve").ResolveContext} ResolveContext */
/** @typedef {import("enhanced-resolve").ResolveOptions} ResolveOptions */
/** @typedef {import("enhanced-resolve").ResolveRequest} ResolveRequest */
/** @typedef {import("enhanced-resolve").Resolver} Resolver */
/** @typedef {import("../declarations/WebpackOptions").ResolveOptions} WebpackResolveOptions */
/** @typedef {import("../declarations/WebpackOptions").ResolvePluginInstance} ResolvePluginInstance */

/** @typedef {WebpackResolveOptions & {dependencyType?: string, resolveToContext?: boolean }} ResolveOptionsWithDependencyType */
/**
 * @typedef {object} WithOptions
 * @property {function(Partial): ResolverWithOptions} withOptions create a resolver with additional/different options
 */

/** @typedef {Resolver & WithOptions} ResolverWithOptions */

// need to be hoisted on module level for caching identity
const EMPTY_RESOLVE_OPTIONS = {};

/**
 * @param {ResolveOptionsWithDependencyType} resolveOptionsWithDepType enhanced options
 * @returns {ResolveOptions} merged options
 */
const convertToResolveOptions = resolveOptionsWithDepType => {
	const { dependencyType, plugins, ...remaining } = resolveOptionsWithDepType;

	// check type compat
	/** @type {Partial} */
	const partialOptions = {
		...remaining,
		plugins:
			plugins &&
			/** @type {ResolvePluginInstance[]} */ (
				plugins.filter(item => item !== "...")
			)
	};

	if (!partialOptions.fileSystem) {
		throw new Error(
			"fileSystem is missing in resolveOptions, but it's required for enhanced-resolve"
		);
	}
	// These weird types validate that we checked all non-optional properties
	const options =
		/** @type {Partial & Pick} */ (
			partialOptions
		);

	return removeOperations(
		resolveByProperty(options, "byDependency", dependencyType),
		// Keep the `unsafeCache` because it can be a `Proxy`
		["unsafeCache"]
	);
};

/**
 * @typedef {object} ResolverCache
 * @property {WeakMap} direct
 * @property {Map} stringified
 */

module.exports = class ResolverFactory {
	constructor() {
		this.hooks = Object.freeze({
			/** @type {HookMap>} */
			resolveOptions: new HookMap(
				() => new SyncWaterfallHook(["resolveOptions"])
			),
			/** @type {HookMap>} */
			resolver: new HookMap(
				() => new SyncHook(["resolver", "resolveOptions", "userResolveOptions"])
			)
		});
		/** @type {Map} */
		this.cache = new Map();
	}

	/**
	 * @param {string} type type of resolver
	 * @param {ResolveOptionsWithDependencyType=} resolveOptions options
	 * @returns {ResolverWithOptions} the resolver
	 */
	get(type, resolveOptions = EMPTY_RESOLVE_OPTIONS) {
		let typedCaches = this.cache.get(type);
		if (!typedCaches) {
			typedCaches = {
				direct: new WeakMap(),
				stringified: new Map()
			};
			this.cache.set(type, typedCaches);
		}
		const cachedResolver = typedCaches.direct.get(resolveOptions);
		if (cachedResolver) {
			return cachedResolver;
		}
		const ident = JSON.stringify(resolveOptions);
		const resolver = typedCaches.stringified.get(ident);
		if (resolver) {
			typedCaches.direct.set(resolveOptions, resolver);
			return resolver;
		}
		const newResolver = this._create(type, resolveOptions);
		typedCaches.direct.set(resolveOptions, newResolver);
		typedCaches.stringified.set(ident, newResolver);
		return newResolver;
	}

	/**
	 * @param {string} type type of resolver
	 * @param {ResolveOptionsWithDependencyType} resolveOptionsWithDepType options
	 * @returns {ResolverWithOptions} the resolver
	 */
	_create(type, resolveOptionsWithDepType) {
		/** @type {ResolveOptionsWithDependencyType} */
		const originalResolveOptions = { ...resolveOptionsWithDepType };

		const resolveOptions = convertToResolveOptions(
			this.hooks.resolveOptions.for(type).call(resolveOptionsWithDepType)
		);
		const resolver = /** @type {ResolverWithOptions} */ (
			Factory.createResolver(resolveOptions)
		);
		if (!resolver) {
			throw new Error("No resolver created");
		}
		/** @type {WeakMap, ResolverWithOptions>} */
		const childCache = new WeakMap();
		resolver.withOptions = options => {
			const cacheEntry = childCache.get(options);
			if (cacheEntry !== undefined) return cacheEntry;
			const mergedOptions = cachedCleverMerge(originalResolveOptions, options);
			const resolver = this.get(type, mergedOptions);
			childCache.set(options, resolver);
			return resolver;
		};
		this.hooks.resolver
			.for(type)
			.call(resolver, resolveOptions, originalResolveOptions);
		return resolver;
	}
};