import type { RequestHandler } from 'express';
import { createGoogleGenerativeAI } from '@ai-sdk/google';
import { streamText } from 'ai';
import type { CoreMessage } from 'ai';
import { verifySignature, streamResponse } from '@layercode/node-server-sdk';
import { Readable } from 'node:stream'; // Node.js 18+ only
const google = createGoogleGenerativeAI({
apiKey: process.env.GOOGLE_GENERATIVE_AI_API_KEY,
});
const sessionMessages: Record<string, CoreMessage[]> = {};
const SYSTEM_PROMPT =
"You are a helpful conversation assistant. You should respond to the user's message in a conversational manner. Your output will be spoken by a TTS model. You should respond in a way that is easy for the TTS model to speak and sound natural.";
const WELCOME_MESSAGE = 'Welcome to Layercode. How can I help you today?';
export const onRequestPost: RequestHandler = async (req, res) => {
const requestBody = req.body;
const signature = req.header('layercode-signature') || '';
const secret = process.env.LAYERCODE_WEBHOOK_SECRET || '';
const payload = JSON.stringify(requestBody);
const isValid = verifySignature({ payload, signature, secret });
if (!isValid) {
console.error('Invalid signature', signature, secret, payload);
res.status(401).send('Unauthorized');
return;
}
console.log('Request body received from Layercode', requestBody);
const { session_id, text, type } = requestBody;
let messages = sessionMessages[session_id] || [];
messages.push({ role: 'user', content: [{ type: 'text', text }] });
let response;
if (type === 'session.start') {
response = streamResponse(requestBody, async ({ stream }: { stream: any }) => {
stream.tts(WELCOME_MESSAGE);
messages.push({
role: 'assistant',
content: [{ type: 'text', text: WELCOME_MESSAGE }],
});
stream.end();
});
} else {
response = streamResponse(requestBody, async ({ stream }: { stream: any }) => {
try {
const { textStream } = streamText({
model: google('gemini-2.0-flash-001'),
system: SYSTEM_PROMPT,
messages,
onFinish: async ({ response }: { response: any }) => {
messages.push(...response.messages);
console.log('Current message history for session', session_id, JSON.stringify(messages, null, 2));
sessionMessages[session_id] = messages;
},
});
stream.data({
textToBeShown: 'Hello, how can I help you today?',
});
await stream.ttsTextStream(textStream);
} catch (err) {
console.error('Handler error:', err);
} finally {
console.log('Stream ended');
stream.end();
}
});
}
// Set headers and status
response.headers.forEach((value, key) => res.setHeader(key, value));
res.status(response.status);
if (response.body) {
const nodeStream = Readable.fromWeb(response.body as any);
nodeStream.pipe(res);
} else {
res.end();
}
};