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

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

"use strict";

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

const namespaceStartCharCode = "@".charCodeAt(0);

module.exports = class JoinRequestPartPlugin {
        /**
         * @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);
                resolver
                        .getHook(this.source)
                        .tapAsync(
                                "JoinRequestPartPlugin",
                                (request, resolveContext, callback) => {
                                        const req = request.request || "";
                                        let i = req.indexOf("/", 3);

                                        if (i >= 0 && req.charCodeAt(2) === namespaceStartCharCode) {
                                                i = req.indexOf("/", i + 1);
                                        }

                                        /** @type {string} */
                                        let moduleName;
                                        /** @type {string} */
                                        let remainingRequest;
                                        /** @type {boolean} */
                                        let fullySpecified;
                                        if (i < 0) {
                                                moduleName = req;
                                                remainingRequest = ".";
                                                fullySpecified = false;
                                        } else {
                                                moduleName = req.slice(0, i);
                                                remainingRequest = "." + req.slice(i);
                                                fullySpecified = /** @type {boolean} */ (request.fullySpecified);
                                        }
                                        /** @type {ResolveRequest} */
                                        const obj = {
                                                ...request,
                                                path: resolver.join(
                                                        /** @type {string} */
                                                        (request.path),
                                                        moduleName
                                                ),
                                                relativePath:
                                                        request.relativePath &&
                                                        resolver.join(request.relativePath, moduleName),
                                                request: remainingRequest,
                                                fullySpecified
                                        };
                                        resolver.doResolve(target, obj, null, resolveContext, callback);
                                }
                        );
        }
};