fix: defer MongoDB connection until runtime

proto/src/lib/mongodb.test.ts

@@ -32,6 +32,7 @@ const originalEnv = process.env
 
 describe('MongoDB Connection (Unit Tests)', () => {
   beforeEach(() => {
+    jest.resetModules()
     process.env = {
       ...originalEnv,
       MONGODB_URI: 'mongodb://localhost:27017/test',
@@ -58,9 +59,8 @@ describe('MongoDB Connection (Unit Tests)', () => {
       // Clear module cache to force re-import
       jest.resetModules()
       
-      expect(() => {
-        require('./mongodb')
-      }).toThrow('Please add MONGODB_URI to your environment variables')
+      const { getClientPromise } = require('./mongodb')
+      expect(() => getClientPromise()).toThrow('Please add MONGODB_URI to your environment variables')
       
       // Restore environment
       process.env.MONGODB_URI = originalMongodbUri
@@ -70,9 +70,9 @@ describe('MongoDB Connection (Unit Tests)', () => {
   describe('Database connection', () => {
     it('should create MongoClient with correct URI and options', async () => {
       // Import after setting up the mock
-      const { clientPromise } = await import('./mongodb')
+      const { getClientPromise } = await import('./mongodb')
 
-      await clientPromise
+      await getClientPromise()
 
       expect(MockedMongoClient).toHaveBeenCalledWith(
         process.env.MONGODB_URI,
@@ -131,10 +131,10 @@ describe('MongoDB Connection (Unit Tests)', () => {
 
   describe('Connection reuse and caching', () => {
     it('should reuse the same MongoClient instance for multiple calls', async () => {
-      const { clientPromise } = await import('./mongodb')
+      const { getClientPromise } = await import('./mongodb')
 
-      const client1 = await clientPromise
-      const client2 = await clientPromise
+      const client1 = await getClientPromise()
+      const client2 = await getClientPromise()
 
       // Should be the same client instance
       expect(client1).toBe(client2)

proto/src/lib/mongodb.ts

@@ -1,39 +1,41 @@
 import { MongoClient, Db, Collection, Document } from 'mongodb'
 
-if (!process.env.MONGODB_URI) {
-  throw new Error('Please add MONGODB_URI to your environment variables')
-}
-
-const uri = process.env.MONGODB_URI
 const options = {
   maxPoolSize: 10,
   serverSelectionTimeoutMS: 5000,
   socketTimeoutMS: 45000,
 }
 
-let client: MongoClient
-let clientPromise: Promise<MongoClient>
+let clientPromise: Promise<MongoClient> | undefined
 
-// In development mode, use a global variable so that the client is not recreated between hot reloads
-if (process.env.NODE_ENV === 'development') {
-  // @ts-expect-error - Global variable for development hot reload
-  if (!global._mongoClientPromise) {
-    client = new MongoClient(uri, options)
-    // @ts-expect-error - Global variable for development hot reload
-    global._mongoClientPromise = client.connect()
+function createClientPromise(): Promise<MongoClient> {
+  const uri = process.env.MONGODB_URI
+  if (!uri) {
+    throw new Error('Please add MONGODB_URI to your environment variables')
   }
-  // @ts-expect-error - Global variable for development hot reload
-  clientPromise = global._mongoClientPromise
-} else {
-  // In production mode, it's best to not use a global variable
-  client = new MongoClient(uri, options)
-  clientPromise = client.connect()
+
+  return new MongoClient(uri, options).connect()
 }
 
-export default clientPromise
+export function getClientPromise(): Promise<MongoClient> {
+  // In development mode, use a global variable so that the client is not recreated between hot reloads.
+  // The connection is intentionally created lazily: `next build` must not require runtime secrets.
+  if (process.env.NODE_ENV === 'development') {
+    // @ts-expect-error - Global variable for development hot reload
+    if (!global._mongoClientPromise) {
+      // @ts-expect-error - Global variable for development hot reload
+      global._mongoClientPromise = createClientPromise()
+    }
+    // @ts-expect-error - Global variable for development hot reload
+    return global._mongoClientPromise
+  }
+
+  clientPromise ??= createClientPromise()
+  return clientPromise
+}
 
 export async function getDb(): Promise<Db> {
-  const client = await clientPromise
+  const client = await getClientPromise()
   return client.db(process.env.MONGODB_DB || 'mozdit')
 }