feat(hook): add a hook such that it's easier to use company-specific subclasses

Author: djMax

__tests__/fake-serv/src/index.ts

@@ -1,6 +1,7 @@
 import { RestApiErrorResponse, RestApiSuccessResponse } from 'rest-api-support';
 
 import type { Service, ServiceLocals } from '../../../src/types';
+import { useService } from '../../../src';
 
 export interface FakeServLocals extends ServiceLocals {
   services: {
@@ -11,16 +12,21 @@ export interface FakeServLocals extends ServiceLocals {
 }
 
 export function service(): Service<FakeServLocals> {
+  const base = useService<FakeServLocals>();
   return {
-    start(app) {
+    ...base,
+    async start(app) {
+      await base.start(app);
       app.locals.services.fakeServ = {
         get_something() { throw new Error('Should not be called.'); },
       };
     },
-    onRequest(req, res) {
+    async onRequest(req, res) {
+      await base.onRequest?.(req, res);
       res.locals.rawBody = true;
     },
-    async healthy() {
+    async healthy(app) {
+      await base.healthy?.(app);
       return new Promise((accept) => {
         setTimeout(accept, 1000);
       });

src/hook.ts

@@ -0,0 +1,35 @@
+import type { RequestLocals, Service, ServiceLocals } from './types';
+
+/**
+ * Your service should call this function and then "inherit"
+ * the behavior in a functional way. So,
+ *
+ * const myServiceFn = () => {
+ *   const baseService = useService<YourService>();
+ *   return {
+ *     ...baseService,
+ *     async start(app) {
+ *       await baseService.start(app);
+ *       // your start stuff goes here
+ *     },
+ *     async onRequest(req, res) {
+ *       // This might throw (auth for example), so don't catch it
+ *       await baseService?.onRequest(req, res);
+ *     },
+ *   }
+ * }
+ *
+ * @returns Service<SLocals, RLocals>
+ */
+export function useService<
+  SLocals extends ServiceLocals = ServiceLocals,
+  RLocals extends RequestLocals = RequestLocals,
+>(baseService?: Service<SLocals, RLocals>): Service<SLocals, RLocals> {
+  return {
+    async start(app) {
+      await baseService?.start(app);
+      // Do nothing. This hook exists mainly to reduce change required
+      // to adopt your specific companies base service.
+    },
+  };
+}

src/index.ts

@@ -6,3 +6,4 @@ export * from './env';
 export * from './config';
 export * from './error';
 export * from './bootstrap';
+export * from './hook';