From 8b7deca0349556cf3d6151298a959e57472c83ce Mon Sep 17 00:00:00 2001
From: Dominik Ferber <dominik.ferber@gmail.com>
Date: Fri, 14 Feb 2025 07:19:10 +0200
Subject: [PATCH] add flags context

---
 .../app/examples/flag-context/flags.ts        | 26 ++++++++++
 .../app/examples/flag-context/layout.tsx      | 16 +++++++
 .../app/examples/flag-context/page.tsx        | 47 +++++++++++++++++++
 packages/flags/src/react/index.tsx            | 27 +++++++++++
 4 files changed, 116 insertions(+)
 create mode 100644 examples/snippets/app/examples/flag-context/flags.ts
 create mode 100644 examples/snippets/app/examples/flag-context/layout.tsx
 create mode 100644 examples/snippets/app/examples/flag-context/page.tsx

diff --git a/examples/snippets/app/examples/flag-context/flags.ts b/examples/snippets/app/examples/flag-context/flags.ts
new file mode 100644
index 0000000..c7e9bda
--- /dev/null
+++ b/examples/snippets/app/examples/flag-context/flags.ts
@@ -0,0 +1,26 @@
+import type { ReadonlyRequestCookies } from '@vercel/flags';
+import { flag, dedupe } from '@vercel/flags/next';
+
+interface Entities {
+  user?: { id: string };
+}
+
+const identify = dedupe(
+  ({ cookies }: { cookies: ReadonlyRequestCookies }): Entities => {
+    const userId = cookies.get('dashboard-user-id')?.value;
+    return { user: userId ? { id: userId } : undefined };
+  },
+);
+
+export const dashboardFlag = flag<boolean, Entities>({
+  key: 'dashboard-flag',
+  identify,
+  description: 'Flag used on the Dashboard Pages example',
+  decide({ entities }) {
+    if (!entities?.user) return false;
+    // Allowed users could be loaded from Edge Config or elsewhere
+    const allowedUsers = ['user1'];
+
+    return allowedUsers.includes(entities.user.id);
+  },
+});
diff --git a/examples/snippets/app/examples/flag-context/layout.tsx b/examples/snippets/app/examples/flag-context/layout.tsx
new file mode 100644
index 0000000..67ba610
--- /dev/null
+++ b/examples/snippets/app/examples/flag-context/layout.tsx
@@ -0,0 +1,16 @@
+import { FlagContextProvider } from '@vercel/flags/react';
+import { dashboardFlag } from './flags';
+
+export default async function Layout({
+  children,
+}: {
+  children: React.ReactNode;
+}) {
+  const dashboard = await dashboardFlag();
+
+  return (
+    <FlagContextProvider values={{ [dashboardFlag.key]: dashboard }}>
+      {children}
+    </FlagContextProvider>
+  );
+}
diff --git a/examples/snippets/app/examples/flag-context/page.tsx b/examples/snippets/app/examples/flag-context/page.tsx
new file mode 100644
index 0000000..8449714
--- /dev/null
+++ b/examples/snippets/app/examples/flag-context/page.tsx
@@ -0,0 +1,47 @@
+'use client';
+
+import { Button } from '@/components/ui/button';
+import { useFlagContext } from '@vercel/flags/react';
+import { DemoFlag } from '@/components/demo-flag';
+import { useRouter } from 'next/navigation';
+import type { FlagValuesType } from '@vercel/flags';
+
+export default function Page() {
+  const dashboard = useFlagContext<boolean>('dashboard-flag');
+  const router = useRouter();
+  return (
+    <>
+      <DemoFlag name="dashboard-flag" value={dashboard} />
+      <div className="flex gap-2">
+        <Button
+          onClick={() => {
+            document.cookie = 'dashboard-user-id=user1; path=/';
+            router.refresh();
+          }}
+          variant="outline"
+        >
+          Act as a flagged in user
+        </Button>
+        <Button
+          onClick={() => {
+            document.cookie = 'dashboard-user-id=user2; path=/';
+            router.refresh();
+          }}
+          variant="outline"
+        >
+          Act as a regular user
+        </Button>
+        <Button
+          onClick={() => {
+            document.cookie =
+              'dashboard-user-id=; path=/; expires=Thu, 01 Jan 1970 00:00:00 GMT';
+            router.refresh();
+          }}
+          variant="outline"
+        >
+          Clear cookie
+        </Button>
+      </div>
+    </>
+  );
+}
diff --git a/packages/flags/src/react/index.tsx b/packages/flags/src/react/index.tsx
index bf81339..ba0092c 100644
--- a/packages/flags/src/react/index.tsx
+++ b/packages/flags/src/react/index.tsx
@@ -1,3 +1,5 @@
+'use client';
+
 import React from 'react';
 import type { FlagDefinitionsType, FlagValuesType } from '../types';
 import { safeJsonStringify } from '../lib/safe-json-stringify';
@@ -42,3 +44,28 @@ export function FlagValues({
     />
   );
 }
+
+const emptyValues: FlagValuesType = {};
+const FlagContext = React.createContext<FlagValuesType>(emptyValues);
+
+export function FlagContextProvider<T>({
+  children,
+  values,
+}: {
+  children: React.ReactNode;
+  values: FlagValuesType;
+}) {
+  return <FlagContext.Provider value={values}>{children}</FlagContext.Provider>;
+}
+
+export function useFlagContext<T>(): T;
+export function useFlagContext<T>(key: string): T;
+export function useFlagContext<T>(key?: string): T {
+  const values = React.useContext(FlagContext);
+
+  if (values === emptyValues) {
+    throw new Error('FlagContextProvider not found');
+  }
+
+  return typeof key === 'string' ? (values[key] as T) : (values as T);
+}