awesome-typescript-loader/src/paths-plugin.ts

import { setupTs, readConfigFile } from './instance';
import { LoaderConfig } from './interfaces';
import * as path from 'path';
import * as _ from 'lodash';
import * as ts from 'typescript';

const ModulesInRootPlugin: new (a: string, b: string, c: string) => ResolverPlugin
    = require('enhanced-resolve/lib/ModulesInRootPlugin');

const createInnerCallback: CreateInnerCallback = require('enhanced-resolve/lib/createInnerCallback');
const getInnerRequest: getInnerRequest = require('enhanced-resolve/lib/getInnerRequest');

type CreateInnerCallback = (callback: Callback, options: Callback, message?: string, messageOptional?: string) => Callback;
type getInnerRequest = (resolver: Resolver, request: Request) => string;

export interface Request {
    request?: Request;
    relativePath: string;
}

export interface Callback {
    (err?: Error, result?: any): void;

    log?: any;
    stack?: any;
    missing?: any;
}

export type ResolverCallback = (request: Request, callback: Callback) => void;

export interface ResolverPlugin {
    apply(resolver: Resolver): void;
}

export interface Resolver {
    apply(plugin: ResolverPlugin): void;
    plugin(source: string, cb: ResolverCallback);
    doResolve(target: string, req: Request, desc: string, Callback);
    join(relativePath: string, innerRequest: Request): Request;
}

export interface Mapping {
    onlyModule: boolean;
    alias: string;
    aliasPattern: RegExp;
    target: string;
}

function escapeRegExp(str) {
  return str.replace(/[\-\[\]\/\{\}\(\)\*\+\?\.\\\^\$\|]/g, "\\$&");
}

export interface PathPluginOptions {
    context?: string;
}

export class PathPlugin implements ResolverPlugin {
    source: string;
    target: string;
    ts: typeof ts;
    configFilePath: string;
    options: ts.CompilerOptions;

    baseUrl: string;
    mappings: Mapping[];
    absoluteBaseUrl: string;

    constructor(config: LoaderConfig & ts.CompilerOptions & PathPluginOptions = {} as any) {
        this.source = 'described-resolve';
        this.target = 'resolve';

        this.ts = setupTs(config.compiler).tsImpl;

        let context = config.context || process.cwd();
        let { configFilePath, compilerConfig } = readConfigFile(context, config, {}, this.ts);

        this.options = compilerConfig.options;
        this.configFilePath = configFilePath;

        this.baseUrl = this.options.baseUrl;
        this.absoluteBaseUrl = path.resolve(
            path.dirname(this.configFilePath),
            this.baseUrl || '.'
        );

        this.mappings = [];
        let paths = this.options.paths || {};
        Object.keys(paths).forEach(alias => {
            let onlyModule = alias.indexOf('*') === -1;
            let excapedAlias = escapeRegExp(alias);
            let targets = paths[alias];
            targets.forEach(target => {
                let aliasPattern: RegExp;
                if (onlyModule) {
                    aliasPattern = new RegExp(`^${excapedAlias}$`);
                } else {
                    let withStarCapturing = excapedAlias.replace('\\*', '(.*)');
                    aliasPattern = new RegExp(`^${withStarCapturing}`);
                }

                this.mappings.push({
                    onlyModule,
                    alias,
                    aliasPattern,
                    target: target
                });
            });
        });
    }

    apply(resolver: Resolver) {
        let { baseUrl, mappings } = this;

        if (baseUrl) {
            resolver.apply(new ModulesInRootPlugin("module", this.absoluteBaseUrl, "resolve"));
        }

        mappings.forEach(mapping => {
            resolver.plugin(this.source, this.createPlugin(resolver, mapping));
        });
    }

    createPlugin(resolver: Resolver, mapping: Mapping) {
        return (request, callback) => {
            let innerRequest = getInnerRequest(resolver, request);
            if (!innerRequest) {
                return callback();
            }

            let match = innerRequest.match(mapping.aliasPattern);
            if (!match) {
                return callback();
            }

            let newRequestStr = mapping.target;
            if (!mapping.onlyModule) {
                newRequestStr = newRequestStr.replace('*', match[1]);
            }

            if (newRequestStr[0] === '.') {
                newRequestStr = path.resolve(this.absoluteBaseUrl, newRequestStr);
            }

            let newRequest = _.extend({}, request, {
                request: newRequestStr
            }) as Request;

            return resolver.doResolve(
                this.target,
                newRequest,
                "aliased with mapping '" + innerRequest  + "': '" + mapping.alias + "' to '" + newRequestStr + "'",
                createInnerCallback(
                    function(err, result) {
                        if (arguments.length > 0) {
                            return callback(err, result);
                        }

                        // don't allow other aliasing or raw request
                        callback(null, null);
                    },
                    callback
                )
            );
        };
    }
}