refactor: separate elements logic into a standalone package (#9285)

packages/common/src/promise-pool.ts

@@ -0,0 +1,50 @@
+import Pool from "es6-promise-pool";
+
+// extending the missing types
+// relying on the [Index, T] to keep a correct order
+type TPromisePool<T, Index = number> = Pool<[Index, T][]> & {
+  addEventListener: (
+    type: "fulfilled",
+    listener: (event: { data: { result: [Index, T] } }) => void,
+  ) => (event: { data: { result: [Index, T] } }) => void;
+  removeEventListener: (
+    type: "fulfilled",
+    listener: (event: { data: { result: [Index, T] } }) => void,
+  ) => void;
+};
+
+export class PromisePool<T> {
+  private readonly pool: TPromisePool<T>;
+  private readonly entries: Record<number, T> = {};
+
+  constructor(
+    source: IterableIterator<Promise<void | readonly [number, T]>>,
+    concurrency: number,
+  ) {
+    this.pool = new Pool(
+      source as unknown as () => void | PromiseLike<[number, T][]>,
+      concurrency,
+    ) as TPromisePool<T>;
+  }
+
+  public all() {
+    const listener = (event: { data: { result: void | [number, T] } }) => {
+      if (event.data.result) {
+        // by default pool does not return the results, so we are gathering them manually
+        // with the correct call order (represented by the index in the tuple)
+        const [index, value] = event.data.result;
+        this.entries[index] = value;
+      }
+    };
+
+    this.pool.addEventListener("fulfilled", listener);
+
+    return this.pool.start().then(() => {
+      setTimeout(() => {
+        this.pool.removeEventListener("fulfilled", listener);
+      });
+
+      return Object.values(this.entries);
+    });
+  }
+}