docs(headless-react): add standalone provider in sample (#4674)

Add missing provider on PDP

https://coveord.atlassian.net/browse/KIT-3739

---------

Co-authored-by: Alex Prudhomme <78121423+alexprudhomme@users.noreply.github.com>

packages/samples/headless-ssr-commerce/app/products/[productId]/page.tsx

@@ -1,6 +1,8 @@
 import * as externalCartAPI from '@/actions/external-cart-api';
 import ContextDropdown from '@/components/context-dropdown';
 import ProductPage from '@/components/pages/product-page';
+import StandaloneProvider from '@/components/providers/standalone-provider';
+import StandaloneSearchBox from '@/components/standalone-search-box';
 import {searchEngineDefinition} from '@/lib/commerce-engine';
 import {NextJsNavigatorContext} from '@/lib/navigatorContextProvider';
 import {defaultContext} from '@/utils/context';
@@ -34,17 +36,21 @@ export default async function ProductDescriptionPage({
     },
   });
   return (
-    <>
+    <StandaloneProvider
+      staticState={staticState}
+      navigatorContext={navigatorContext.marshal}
+    >
       <h2>Product description page</h2>
       <ContextDropdown />
+      <StandaloneSearchBox />
       <Suspense fallback={<p>Loading...</p>}>
         <ProductPage
           staticState={staticState}
           navigatorContext={navigatorContext.marshal}
           productId={params.productId}
         />
       </Suspense>
-    </>
+    </StandaloneProvider>
   );
 }
 

packages/samples/headless-ssr-commerce/components/providers/standalone-provider.tsx

@@ -0,0 +1,72 @@
+'use client';
+
+import {
+  StandaloneHydratedState,
+  StandaloneStaticState,
+  standaloneEngineDefinition,
+} from '@/lib/commerce-engine';
+import {NavigatorContext} from '@coveo/headless-react/ssr-commerce';
+import {PropsWithChildren, useEffect, useState} from 'react';
+
+interface StandalonePageProps {
+  staticState: StandaloneStaticState;
+  navigatorContext: NavigatorContext;
+}
+
+export default function StandaloneProvider({
+  staticState,
+  navigatorContext,
+  children,
+}: PropsWithChildren<StandalonePageProps>) {
+  const [hydratedState, setHydratedState] = useState<
+    StandaloneHydratedState | undefined
+  >(undefined);
+
+  // Setting the navigator context provider also in client-side before hydrating the application
+  standaloneEngineDefinition.setNavigatorContextProvider(
+    () => navigatorContext
+  );
+
+  useEffect(() => {
+    standaloneEngineDefinition
+      .hydrateStaticState({
+        searchAction: staticState.searchAction,
+        controllers: {
+          cart: {
+            initialState: {items: staticState.controllers.cart.state.items},
+          },
+          context: staticState.controllers.context.state,
+        },
+      })
+      .then(({engine, controllers}) => {
+        setHydratedState({engine, controllers});
+
+        // Refreshing recommendations in the browser after hydrating the state in the client-side
+        // Recommendation refresh in the server is not supported yet.
+        // controllers.popularBoughtRecs.refresh();
+      });
+  }, [staticState]);
+
+  if (hydratedState) {
+    return (
+      <standaloneEngineDefinition.HydratedStateProvider
+        engine={hydratedState.engine}
+        controllers={hydratedState.controllers}
+      >
+        {/* // TODO: KIT-3701: Type 'React.ReactNode' is not assignable to type 'import(".../node_modules/@types/react/index").ReactNode'.
+  Type 'bigint' is not assignable to type 'ReactNode'.*/}
+        <>{children}</>
+      </standaloneEngineDefinition.HydratedStateProvider>
+    );
+  } else {
+    return (
+      <standaloneEngineDefinition.StaticStateProvider
+        controllers={staticState.controllers}
+      >
+        {/* // TODO: KIT-3701: Type 'React.ReactNode' is not assignable to type 'import(".../node_modules/@types/react/index").ReactNode'.
+  Type 'bigint' is not assignable to type 'ReactNode'.*/}
+        <>{children}</>
+      </standaloneEngineDefinition.StaticStateProvider>
+    );
+  }
+}