Add a LaunchDarkly adapter (#10)

* add ld example

* reword

examples/snippets/app/examples/adapter-launchdarkly/adapter.ts

@@ -0,0 +1,71 @@
+import type { Adapter } from '@vercel/flags';
+import { createClient } from '@vercel/edge-config';
+import { init, type LDContext } from '@launchdarkly/vercel-server-sdk';
+
+export type { LDContext };
+
+interface AdapterOptions<ValueType> {
+  defaultValue?: ValueType;
+}
+
+let defaultLaunchDarklyAdapter:
+  | ReturnType<typeof createLaunchDarklyAdapter>
+  | undefined;
+
+function assertEnv(name: string): string {
+  const value = process.env[name];
+  if (!value) {
+    throw new Error(
+      `LaunchDarkly Adapter: Missing ${name} environment variable`,
+    );
+  }
+  return value;
+}
+
+export function createLaunchDarklyAdapter({
+  ldProject,
+  ldClientSideKey,
+  edgeConfigConnectionString,
+}: {
+  ldProject: string;
+  ldClientSideKey: string;
+  edgeConfigConnectionString: string;
+}) {
+  const edgeConfigClient = createClient(edgeConfigConnectionString);
+  const ldClient = init(ldClientSideKey, edgeConfigClient);
+
+  return function launchDarklyAdapter<ValueType>(
+    options: AdapterOptions<ValueType> = {},
+  ): Adapter<ValueType, LDContext> {
+    return {
+      origin(key) {
+        return `https://app.launchdarkly.com/projects/${ldProject}/flags/${key}/`;
+      },
+      async decide({ key, entities }): Promise<ValueType> {
+        await ldClient.waitForInitialization();
+        return ldClient.variation(
+          key,
+          entities!,
+          options.defaultValue,
+        ) as ValueType;
+      },
+    };
+  };
+}
+
+export function launchDarkly<ValueType>(
+  options?: AdapterOptions<ValueType>,
+): Adapter<ValueType, LDContext> {
+  if (!defaultLaunchDarklyAdapter) {
+    const edgeConfigConnectionString = assertEnv('EDGE_CONFIG');
+    const ldClientSideKey = assertEnv('LD_CLIENT_SIDE_KEY');
+    const ldProject = assertEnv('LD_PROJECT_SLUG');
+    defaultLaunchDarklyAdapter = createLaunchDarklyAdapter({
+      ldProject,
+      ldClientSideKey,
+      edgeConfigConnectionString,
+    });
+  }
+
+  return defaultLaunchDarklyAdapter(options);
+}

examples/snippets/app/examples/adapter-launchdarkly/flags.ts

@@ -0,0 +1,12 @@
+import { flag } from '@vercel/flags/next';
+import { launchDarkly } from './adapter';
+
+export const summerSaleFlag = flag({
+  key: 'summer-sale',
+  defaultValue: false,
+  description: 'Whether the summer sale is active',
+  adapter: launchDarkly(),
+  async identify() {
+    return { key: 'uid1' };
+  },
+});

examples/snippets/app/examples/adapter-launchdarkly/page.tsx

@@ -0,0 +1,6 @@
+import { summerSaleFlag } from './flags';
+
+export default async function Page() {
+  const summerSale = await summerSaleFlag();
+  return <div>Flag is on {summerSale ? 'Yes' : 'No'}</div>;
+}

examples/snippets/package.json

@@ -9,6 +9,7 @@
     "start": "next start"
   },
   "dependencies": {
+    "@launchdarkly/vercel-server-sdk": "1.3.21",
     "@radix-ui/react-dialog": "1.1.2",
     "@radix-ui/react-separator": "1.1.0",
     "@radix-ui/react-slot": "1.1.0",