src/routes/conversation/+server.ts

import type { RequestHandler } from './$types';
import { collections } from '$lib/server/database';
import { ObjectId } from 'mongodb';

export const POST: RequestHandler = async (input) => {
	const res = await collections.conversations.insertOne({
		_id: new ObjectId(),
		title:
			'Untitled ' +
			((await collections.conversations.countDocuments({ sessionId: input.locals.sessionId })) + 1),
		messages: [],
		createdAt: new Date(),
		updatedAt: new Date(),
		sessionId: input.locals.sessionId
	});

	return new Response(
		JSON.stringify({
			conversationId: res.insertedId.toString()
		}),
		{ headers: { 'Content-Type': 'application/json' } }
	);
};