fix: defer MongoClient init to request time to fix build crash

src/app/api/cohort/route.ts

@@ -1,19 +1,40 @@
-// app/api/cohort/route.ts
 import { NextResponse } from 'next/server';
 import { MongoClient } from 'mongodb';
 
+let cachedClient: MongoClient | null = null;
 
-const uri = process.env.MONGO_URI!;
-const client = new MongoClient(uri);
-const dbName = 'cohortDB';
-const collectionName = 'cohortData';
+async function getClient(): Promise<MongoClient> {
+  if (cachedClient) return cachedClient;
+
+  const uri = process.env.MONGO_URI;
+  if (!uri) {
+    throw new Error('MONGO_URI environment variable is not set');
+  }
+
+  const client = new MongoClient(uri);
+  await client.connect();
+  cachedClient = client;
+  return client;
+}
+
+const DB_NAME = 'cohortDB';
+const COLLECTION_NAME = 'cohortData';
 
 export async function GET() {
   try {
-    await client.connect();
-    const data = await client.db(dbName).collection(collectionName).find({}).toArray();
+    const client = await getClient();
+    const data = await client
+      .db(DB_NAME)
+      .collection(COLLECTION_NAME)
+      .find({})
+      .toArray();
+
     return NextResponse.json(data);
   } catch (error) {
-    return NextResponse.json({ error: 'Failed to fetch data' }, { status: 500 });
+    console.error('Failed to fetch cohort data:', error);
+    return NextResponse.json(
+      { error: error instanceof Error ? error.message : 'Failed to fetch data' },
+      { status: 500 }
+    );
   }
-}
+}