feat(server): job system (#10134)

packages/backend/server/src/base/event/scanner.ts

@@ -0,0 +1,71 @@
+import { Injectable } from '@nestjs/common';
+import { once } from 'lodash-es';
+
+import { ModuleScanner } from '../nestjs';
+import {
+  type EventName,
+  type EventOptions,
+  getEventHandlerMetadata,
+} from './def';
+
+@Injectable()
+export class EventHandlerScanner {
+  constructor(private readonly scanner: ModuleScanner) {}
+
+  scan = once(() => {
+    const handlers: Array<{
+      event: EventName;
+      handler: (payload: any) => any;
+      opts?: EventOptions;
+    }> = [];
+    const providers = this.scanner.getAtInjectables();
+
+    providers.forEach(wrapper => {
+      const { instance, name } = wrapper;
+      if (!instance || wrapper.isAlias) {
+        return;
+      }
+
+      const methods = this.scanner.getAllMethodNames(instance);
+
+      methods.forEach(method => {
+        const fn = instance[method];
+
+        let defs = getEventHandlerMetadata(instance[method]);
+
+        if (defs.length === 0) {
+          return;
+        }
+
+        const signature = `${name}.${method}`;
+
+        if (typeof fn !== 'function') {
+          throw new Error(`Event handler [${signature}] is not a function.`);
+        }
+
+        if (!wrapper.isDependencyTreeStatic()) {
+          throw new Error(
+            `Provider [${name}] could not be RequestScoped or TransientScoped injectable if it contains event handlers.`
+          );
+        }
+
+        defs.forEach(({ event, opts }) => {
+          handlers.push({
+            event,
+            handler: (payload: any) => {
+              // NOTE(@forehalo):
+              //   we might create spies on the event handlers when testing,
+              //   avoid reusing `fn` variable to fail the spies or stubs
+              return instance[method].bind(instance)(payload);
+            },
+            opts: {
+              name: signature,
+              ...opts,
+            },
+          });
+        });
+      });
+    });
+    return handlers;
+  });
+}