source: frontend/node_modules/watchpack/lib/getWatcherManager.js

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

const path = require("path");
const DirectoryWatcher = require("./DirectoryWatcher");

/** @typedef {import("./index").EventMap} EventMap */
/** @typedef {import("./DirectoryWatcher").DirectoryWatcherOptions} DirectoryWatcherOptions */
/** @typedef {import("./DirectoryWatcher").DirectoryWatcherEvents} DirectoryWatcherEvents */
/** @typedef {import("./DirectoryWatcher").FileWatcherEvents} FileWatcherEvents */
/**
 * @template {EventMap} T
 * @typedef {import("./DirectoryWatcher").Watcher<T>} Watcher
 */

class WatcherManager {
        /**
         * @param {DirectoryWatcherOptions=} options options
         */
        constructor(options = {}) {
                this.options = options;
                /** @type {Map<string, DirectoryWatcher>} */
                this.directoryWatchers = new Map();
        }

        /**
         * @param {string} directory a directory
         * @returns {DirectoryWatcher} a directory watcher
         */
        getDirectoryWatcher(directory) {
                const watcher = this.directoryWatchers.get(directory);
                if (watcher === undefined) {
                        const newWatcher = new DirectoryWatcher(this, directory, this.options);
                        this.directoryWatchers.set(directory, newWatcher);
                        newWatcher.on("closed", () => {
                                this.directoryWatchers.delete(directory);
                        });
                        return newWatcher;
                }
                return watcher;
        }

        /**
         * @param {string} file file
         * @param {number=} startTime start time
         * @returns {Watcher<FileWatcherEvents> | null} watcher or null if file has no directory
         */
        watchFile(file, startTime) {
                const directory = path.dirname(file);
                if (directory === file) return null;
                return this.getDirectoryWatcher(directory).watch(file, startTime);
        }

        /**
         * @param {string} directory directory
         * @param {number=} startTime start time
         * @returns {Watcher<DirectoryWatcherEvents>} watcher
         */
        watchDirectory(directory, startTime) {
                return this.getDirectoryWatcher(directory).watch(directory, startTime);
        }
}

const watcherManagers = new WeakMap();

/**
 * @param {DirectoryWatcherOptions} options options
 * @returns {WatcherManager} the watcher manager
 */
module.exports = (options) => {
        const watcherManager = watcherManagers.get(options);
        if (watcherManager !== undefined) return watcherManager;
        const newWatcherManager = new WatcherManager(options);
        watcherManagers.set(options, newWatcherManager);
        return newWatcherManager;
};
module.exports.WatcherManager = WatcherManager;