Express: Add middlewareFactory(deps)(middleware)

README.md

@@ -16,6 +16,7 @@ npm i @quickcase/node-toolkit
 * [Case Access](#case-access)
 * [Definition](#definition)
 * [Document](#document)
+* [Express](#express)
 * [Field](#field)
 * [HTTP Client](#http-client)
 * [OAuth2](#oauth2)
@@ -442,6 +443,45 @@ docDownload:
 */
 ```
 
+### Express
+
+Utilities for [ExpressJS](https://expressjs.com/) v4.x.x.
+
+#### middlewareFactory(dependencySuppliers)(middlewareSupplier)(req, res, next)
+
+Decorator for an Express middleware which dynamically instantiates request-based dependencies and underlying middleware upon processing of a request.
+
+##### Arguments
+
+| Name | Type | Description |
+|------|------|-------------|
+| dependencySuppliers | object | Required. Map of named dependency supplier functions which take the request object as an input |
+| middlewareSupplier | function | Function that will be passed the initialised dependencies and return an initialised Express middleware. |
+
+##### Returns
+
+ExpressJS middleware function.
+
+##### Example
+
+```js
+import {middlewareFactory} from '@quickcase/node-toolkit';
+import express from 'express';
+
+const router = express.Router();
+
+const dependencySuppliers = {
+  tokenProvider: (req) => () => Promise.resolve(req.accessToken),
+  service: (req) => {...},
+};
+
+const middlewareSupplier = ({tokenProvider, service}) => (req, res) => {
+  // use initialised `tokenProvider` and `service`...
+};
+
+router.get('/', middlewareFactory(dependencySuppliers)(middlewareSupplier));
+```
+
 ### Field
 
 #### isNo(value)

main.js

@@ -3,6 +3,7 @@ export * from './modules/case';
 export * from './modules/case-access';
 export * from './modules/definition';
 export * from './modules/document';
+export * from './modules/express';
 export * from './modules/field';
 export * from './modules/http-client';
 export * from './modules/oauth2';

modules/express.js

@@ -0,0 +1,19 @@
+/**
+ * Decorator for an Express middleware which dynamically instantiates request-based
+ * dependencies and underlying middleware upon processing of a request.
+ * @param {object} dependencySuppliers Dictionary of named dependency suppliers.
+ *  Each supplier will be invoked with the instance of the current Express request.
+ *  Each dependency supplied will be provided to the middleware under the same name.
+ * @param {function} middlewareSupplier Function that will be passed
+ *  the initialised dependencies and return an initialised Express middleware.
+ * @return {ExpressMiddleware} Express middleware function which will invoke the
+ *  initialised middleware when called.
+ */
+export const middlewareFactory = (dependencySuppliers) => (middlewareSupplier) => (req, res, next) => {
+  const dependencies = Object.entries(dependencySuppliers)
+                             .reduce((acc, [key, factory]) => {
+                               acc[key] = factory(req);
+                               return acc;
+                             }, {});
+  middlewareSupplier(dependencies)(req, res, next);
+};

modules/express.test.js

@@ -0,0 +1,23 @@
+import {middlewareFactory} from './express';
+
+describe('middlewareFactory', () => {
+  const ACCESS_TOKEN = 'ey123';
+  const ROLES = ['role1', 'role2'];
+
+  test('should create middleware with initialised dependencies', (done) => {
+    const middleware = ({tokenSupplier, roles}) => (req, res, next) => {
+      expect(tokenSupplier()).toEqual(ACCESS_TOKEN);
+      expect(roles).toEqual(ROLES);
+      done();
+    };
+    const req = {
+      accessToken: ACCESS_TOKEN,
+      roles: ROLES,
+    };
+
+    middlewareFactory({
+      tokenSupplier: (req) => () => req.accessToken,
+      roles: (req) => req.roles,
+    })(middleware)(req);
+  });
+});