Initial support for job queue

ts/util/asyncIterables.ts

@@ -0,0 +1,42 @@
+// Copyright 2021 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+/* eslint-disable max-classes-per-file */
+/* eslint-disable no-await-in-loop */
+/* eslint-disable no-restricted-syntax */
+
+export type MaybeAsyncIterable<T> = Iterable<T> | AsyncIterable<T>;
+
+export function concat<T>(
+  iterables: Iterable<MaybeAsyncIterable<T>>
+): AsyncIterable<T> {
+  return new ConcatAsyncIterable(iterables);
+}
+
+class ConcatAsyncIterable<T> implements AsyncIterable<T> {
+  constructor(private readonly iterables: Iterable<MaybeAsyncIterable<T>>) {}
+
+  async *[Symbol.asyncIterator](): AsyncIterator<T> {
+    for (const iterable of this.iterables) {
+      for await (const value of iterable) {
+        yield value;
+      }
+    }
+  }
+}
+
+export function wrapPromise<T>(
+  promise: Promise<MaybeAsyncIterable<T>>
+): AsyncIterable<T> {
+  return new WrapPromiseAsyncIterable(promise);
+}
+
+class WrapPromiseAsyncIterable<T> implements AsyncIterable<T> {
+  constructor(private readonly promise: Promise<MaybeAsyncIterable<T>>) {}
+
+  async *[Symbol.asyncIterator](): AsyncIterator<T> {
+    for await (const value of await this.promise) {
+      yield value;
+    }
+  }
+}