feat: doc search infra (#7166)

detail in `packages/common/infra/src/sync/indexer/README.md`

packages/common/infra/src/utils/exhaustmap-with-trailing.ts

@@ -0,0 +1,41 @@
+import {
+  asyncScheduler,
+  defer,
+  exhaustMap,
+  finalize,
+  type Observable,
+  type ObservableInput,
+  type OperatorFunction,
+  scheduled,
+  Subject,
+  throttle,
+} from 'rxjs';
+
+/**
+ * Like exhaustMap, but also includes the trailing value emitted from the source observable while waiting for the preceding inner observable to complete
+ *
+ * Original code adapted from https://github.com/ReactiveX/rxjs/issues/5004
+ * @param {function<T, K>(value: T, ?index: number): ObservableInput<K>} project - A function that, when applied to an item emitted by the
+ * source Observable, returns a projected Observable.
+ */
+export function exhaustMapWithTrailing<T, R>(
+  project: (value: T, index: number) => ObservableInput<R>
+): OperatorFunction<T, R> {
+  return (source$): Observable<R> =>
+    defer(() => {
+      const release$ = new Subject<void>();
+      return source$.pipe(
+        throttle(() => release$, {
+          leading: true,
+          trailing: true,
+        }),
+        exhaustMap((value, index) =>
+          scheduled(project(value, index), asyncScheduler).pipe(
+            finalize(() => {
+              release$.next();
+            })
+          )
+        )
+      );
+    });
+}