update cached client

__tests__/mongoClient.test.ts

@@ -0,0 +1,58 @@
+/** @jest-environment node */
+import { getClient, resetClient } from '@utils/mongodb/mongoClient.mjs';
+import { MongoClient } from 'mongodb';
+
+describe('getClient', () => {
+  beforeEach(async () => {
+    await resetClient();
+    jest.restoreAllMocks();
+  });
+
+  it('should throw an error if MONGODB_URI is missing', async () => {
+    const originalUri = process.env.MONGODB_URI;
+    delete process.env.MONGODB_URI;
+
+    await resetClient();
+
+    await expect(getClient()).rejects.toThrow(
+      'Missing MONGODB_URI environment variable.'
+    );
+
+    process.env.MONGODB_URI = originalUri;
+  });
+
+  it('should return the same instance on multiple calls', async () => {
+    const mockDb = { db: jest.fn() };
+    const spy = jest
+      .spyOn(MongoClient.prototype, 'connect')
+      .mockResolvedValue(mockDb as any);
+
+    const c1 = await getClient();
+    const c2 = await getClient();
+
+    expect(c1).toBe(c2);
+    expect(spy).toHaveBeenCalledTimes(1);
+  });
+
+  it('should dedupe concurrent callers using cachedPromise', async () => {
+    const mockDb = { db: jest.fn() };
+    const spy = jest
+      .spyOn(MongoClient.prototype, 'connect')
+      .mockResolvedValue(mockDb as any);
+    const [c1, c2] = await Promise.all([getClient(), getClient()]);
+    expect(c1).toBe(c2);
+    expect(spy).toHaveBeenCalledTimes(1);
+  });
+
+  it('should retry after a failed connection', async () => {
+    const spy = jest
+      .spyOn(MongoClient.prototype, 'connect')
+      .mockRejectedValueOnce(new Error('Network Fail'))
+      .mockResolvedValueOnce({ db: jest.fn() } as any);
+
+    await expect(getClient()).rejects.toThrow('Network Fail');
+
+    await expect(getClient()).resolves.toBeDefined();
+    expect(spy).toHaveBeenCalledTimes(2);
+  });
+});

app/(api)/_utils/mongodb/mongoClient.mjs

@@ -1,15 +1,41 @@
 import { MongoClient } from 'mongodb';
 
-const uri = process.env.MONGODB_URI;
 let cachedClient = null;
+let cachedPromise = null;
 
 export async function getClient() {
+  const uri = process.env.MONGODB_URI;
+  if (!uri) {
+    throw new Error('Missing MONGODB_URI environment variable.');
+  }
+
   if (cachedClient) {
     return cachedClient;
   }
-  const client = new MongoClient(uri);
-  cachedClient = client;
-  return cachedClient;
+
+  if (!cachedPromise) {
+    const client = new MongoClient(uri);
+    cachedPromise = client
+      .connect()
+      .then((connectedClient) => {
+        cachedClient = connectedClient;
+        return connectedClient;
+      })
+      .catch((error) => {
+        client.close().catch(() => {});
+        cachedPromise = null;
+        cachedClient = null;
+        throw error;
+      });
+  }
+
+  return cachedPromise;
+}
+
+// Helper function for testing
+export async function resetClient() {
+  cachedClient = null;
+  cachedPromise = null;
 }
 
 export async function getDatabase() {