Move all items to src folder

MAILPOET-6215

packages/js/email-editor/src/engine/components/template-select/async.ts

@@ -0,0 +1,46 @@
+/**
+ * WordPress dependencies
+ */
+import { useEffect, useState, flushSync } from '@wordpress/element';
+// @ts-expect-error TS7016 Could not find a declaration file for module '@wordpress/priority-queue'
+import { createQueue } from '@wordpress/priority-queue';
+
+const blockPreviewQueue = createQueue();
+
+/**
+ * Renders a component at the next idle time.
+ * @param {*} props
+ */
+export function Async({ children, placeholder }) {
+  const [shouldRender, setShouldRender] = useState(false);
+
+  // In the future, we could try to use startTransition here, but currently
+  // react will batch all transitions, which means all previews will be
+  // rendered at the same time.
+  // https://react.dev/reference/react/startTransition#caveats
+  // > If there are multiple ongoing Transitions, React currently batches them
+  // > together. This is a limitation that will likely be removed in a future
+  // > release.
+
+  useEffect(() => {
+    const context = {};
+    blockPreviewQueue.add(context, () => {
+      // Synchronously run all renders so it consumes timeRemaining.
+      // See https://github.com/WordPress/gutenberg/pull/48238
+      flushSync(() => {
+        setShouldRender(true);
+      });
+    });
+    return () => {
+      blockPreviewQueue.cancel(context);
+    };
+  }, []);
+
+  if (!shouldRender) {
+    // eslint-disable-next-line @typescript-eslint/no-unsafe-return
+    return placeholder;
+  }
+
+  // eslint-disable-next-line @typescript-eslint/no-unsafe-return
+  return children;
+}