From 468ca0f9b3388878a30f05996d81af0351f943ce Mon Sep 17 00:00:00 2001
From: Bilawal Hameed <bil@spotify.com>
Date: Fri, 3 Jul 2020 16:03:38 +0200
Subject: [PATCH] fix(techdocs): fixed race condition between page loads

---
 .../techdocs/src/reader/components/Reader.tsx | 21 ++++++++-----
 .../techdocs/src/reader/hooks/shadowDom.ts    | 30 ++++++++++++++-----
 2 files changed, 37 insertions(+), 14 deletions(-)

diff --git a/plugins/techdocs/src/reader/components/Reader.tsx b/plugins/techdocs/src/reader/components/Reader.tsx
index 995d9dc99f..bd7ac17a6a 100644
--- a/plugins/techdocs/src/reader/components/Reader.tsx
+++ b/plugins/techdocs/src/reader/components/Reader.tsx
@@ -35,15 +35,22 @@ import { TechDocsPageWrapper } from './TechDocsPageWrapper';
 
 const useFetch = (url: string): AsyncState<string | Error> => {
   const state = useAsync(async () => {
-    const response = await fetch(url);
-    if (response.status === 404) {
-      return new Error('Page not found');
+    const request = await fetch(url);
+    if (request.status === 404) {
+      return [request.url, new Error('Page not found')];
     }
-    const raw = await response.text();
-    return raw;
+    const response = await request.text();
+    return [request.url, response];
   }, [url]);
 
-  return state;
+  const [fetchedUrl, fetchedValue] = state.value ?? [];
+
+  if (url !== fetchedUrl) {
+    // Fixes a race condition between two pages
+    return { loading: true };
+  }
+
+  return Object.assign(state, fetchedValue ? { value: fetchedValue } : {});
 };
 
 const useEnforcedTrailingSlash = (): void => {
@@ -60,7 +67,7 @@ const useEnforcedTrailingSlash = (): void => {
 export const Reader = () => {
   const location = useLocation();
   const { componentId, '*': path } = useParams();
-  const shadowDomRef = useShadowDom();
+  const [ref, shadowRoot] = useShadowDom(componentId, path);
   const navigate = useNavigate();
   const normalizedUrl = new URLFormatter(
     `${docStorageURL}${location.pathname.replace('/docs', '')}`,
diff --git a/plugins/techdocs/src/reader/hooks/shadowDom.ts b/plugins/techdocs/src/reader/hooks/shadowDom.ts
index 5edb8f4e4d..90b287e343 100644
--- a/plugins/techdocs/src/reader/hooks/shadowDom.ts
+++ b/plugins/techdocs/src/reader/hooks/shadowDom.ts
@@ -17,14 +17,30 @@
 import { useEffect, useRef } from 'react';
 import type { RefObject } from 'react';
 
-type IShadowDOMRefObject = RefObject<HTMLDivElement>;
-export const useShadowDom: () => IShadowDOMRefObject = () => {
-  const ref: IShadowDOMRefObject = useRef(null);
+type IUseShadowDOM = (
+  componentId: string,
+  path: string,
+) => [RefObject<HTMLDivElement>, ShadowRoot?];
+
+export const useShadowDom: IUseShadowDOM = (componentId, path) => {
+  const ref = useRef<HTMLDivElement>(null);
 
   useEffect(() => {
-    const divElement = ref.current;
-    divElement?.attachShadow({ mode: 'open' });
-  }, [ref]);
+    const innerDivElement = document.createElement('div');
+    innerDivElement.attachShadow({ mode: 'open' });
 
-  return ref;
+    const outerDivElement = ref.current;
+    outerDivElement?.appendChild(innerDivElement);
+
+    return function cancel() {
+      outerDivElement?.removeChild(innerDivElement);
+    };
+  }, [componentId, path]);
+
+  const shadowRoot =
+    ref.current?.children && ref.current?.children[0].shadowRoot
+      ? ref.current?.children[0].shadowRoot
+      : undefined;
+
+  return [ref, shadowRoot];
 };