source: imaps-frontend/node_modules/enhanced-resolve/lib/SymlinkPlugin.js

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

"use strict";

const forEachBail = require("./forEachBail");
const getPaths = require("./getPaths");
const { getType, PathType } = require("./util/path");

/** @typedef {import("./Resolver")} Resolver */
/** @typedef {import("./Resolver").ResolveRequest} ResolveRequest */
/** @typedef {import("./Resolver").ResolveStepHook} ResolveStepHook */

module.exports = class SymlinkPlugin {
        /**
         * @param {string | ResolveStepHook} source source
         * @param {string | ResolveStepHook} target target
         */
        constructor(source, target) {
                this.source = source;
                this.target = target;
        }

        /**
         * @param {Resolver} resolver the resolver
         * @returns {void}
         */
        apply(resolver) {
                const target = resolver.ensureHook(this.target);
                const fs = resolver.fileSystem;
                resolver
                        .getHook(this.source)
                        .tapAsync("SymlinkPlugin", (request, resolveContext, callback) => {
                                if (request.ignoreSymlinks) return callback();
                                const pathsResult = getPaths(/** @type {string} */ (request.path));
                                const pathSegments = pathsResult.segments;
                                const paths = pathsResult.paths;

                                let containsSymlink = false;
                                let idx = -1;
                                forEachBail(
                                        paths,
                                        /**
                                         * @param {string} path path
                                         * @param {(err?: null|Error, result?: null|number) => void} callback callback
                                         * @returns {void}
                                         */
                                        (path, callback) => {
                                                idx++;
                                                if (resolveContext.fileDependencies)
                                                        resolveContext.fileDependencies.add(path);
                                                fs.readlink(path, (err, result) => {
                                                        if (!err && result) {
                                                                pathSegments[idx] = /** @type {string} */ (result);
                                                                containsSymlink = true;
                                                                // Shortcut when absolute symlink found
                                                                const resultType = getType(result.toString());
                                                                if (
                                                                        resultType === PathType.AbsoluteWin ||
                                                                        resultType === PathType.AbsolutePosix
                                                                ) {
                                                                        return callback(null, idx);
                                                                }
                                                        }
                                                        callback();
                                                });
                                        },
                                        /**
                                         * @param {null|Error} [err] error
                                         * @param {null|number} [idx] result
                                         * @returns {void}
                                         */
                                        (err, idx) => {
                                                if (!containsSymlink) return callback();
                                                const resultSegments =
                                                        typeof idx === "number"
                                                                ? pathSegments.slice(0, idx + 1)
                                                                : pathSegments.slice();
                                                const result = resultSegments.reduceRight((a, b) => {
                                                        return resolver.join(a, b);
                                                });
                                                /** @type {ResolveRequest} */
                                                const obj = {
                                                        ...request,
                                                        path: result
                                                };
                                                resolver.doResolve(
                                                        target,
                                                        obj,
                                                        "resolved symlink to " + result,
                                                        resolveContext,
                                                        callback
                                                );
                                        }
                                );
                        });
        }
};