# Retell AI Configuration
RETELL_API_KEY=key_xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
RETELL_AGENT_ID=agent_xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

# Frontend can override agent ID (optional)
VITE_RETELL_AGENT_ID=agent_xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

app.post('/api/retell/create-web-call', async (req, res) => {
  try {
    const { agentId } = req.body;
    const retellApiKey = process.env.RETELL_API_KEY;

    if (!retellApiKey) {
      return res.status(500).json({
        error: 'RETELL_API_KEY not configured on server',
      });
    }

    const effectiveAgentId = agentId || process.env.RETELL_AGENT_ID;

    if (!effectiveAgentId) {
      return res.status(400).json({
        error: 'No agent ID provided',
      });
    }

    // Call Retell API
    const retellResponse = await fetch('https://api.retellai.com/v2/create-web-call', {
      method: 'POST',
      headers: {
        'Authorization': `Bearer ${retellApiKey}`,
        'Content-Type': 'application/json',
      },
      body: JSON.stringify({
        agent_id: effectiveAgentId,
      }),
    });

    if (!retellResponse.ok) {
      const errorBody = await retellResponse.text();
      return res.status(retellResponse.status).json({
        error: `Retell API error: ${retellResponse.status}`,
        details: errorBody,
      });
    }

    const data = await retellResponse.json();

    // Return access token to client
    return res.json({
      callId: data.call_id,
      accessToken: data.access_token,  // Short-lived, safe to send to client
      agentId: data.agent_id,
    });
  } catch (error: any) {
    return res.status(500).json({
      error: error.message || 'Internal server error',
    });
  }
});

npm install retell-client-js-sdk

import { RetellWebClient } from 'retell-client-js-sdk';

const retellClient = new RetellWebClient();

// Set up event listeners
retellClient.on('call_started', () => {
  console.log('Call started');
  setCallState('active');
});

retellClient.on('call_ended', () => {
  console.log('Call ended');
  setCallState('ended');
});

retellClient.on('agent_start_talking', () => {
  setAgentTalking(true);
});

retellClient.on('agent_stop_talking', () => {
  setAgentTalking(false);
});

retellClient.on('update', (update) => {
  // Live transcript
  if (update.transcript) {
    const entries = update.transcript.map((t, i) => ({
      id: `t-${i}`,
      role: t.role === 'agent' ? 'agent' : 'user',
      text: t.content,
      timestamp: new Date(),
    }));
    setTranscript(entries);
  }
});

retellClient.on('error', (error) => {
  console.error('Call error:', error);
  setErrorMessage(error.message);
});

// Start call
const startCall = async () => {
  // Get access token from backend
  const response = await fetch(`${API_BASE}/api/retell/create-web-call`, {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify({ agentId: 'agent_xxxxx' }),
  });

  const { callId, accessToken } = await response.json();
  setCallId(callId);

  // Start WebRTC call
  await retellClient.startCall({ accessToken });
};

// End call
const endCall = () => {
  retellClient.stopCall();
};

You: "My dog is bleeding from his leg and won't stop!"

Expected Luna Response:
"This sounds like an emergency. I'm going to connect you with our veterinarian right away. Please stay on the line."

Expected System Behavior:
- Triage level = 'emergency'
- Urgency score = 9
- Push notification sent to on-call vet
- UI shows red emergency badge

app.post('/api/retell/webhook', (req, res) => {
  const event = req.body;
  console.log('[Retell Webhook]', event.event, event.call?.call_id);

  switch (event.event) {
    case 'call_started':
      console.log('Call started:', event.call?.call_id);
      // Log to database, send notification, etc.
      break;

    case 'call_ended':
      console.log('Call ended:', event.call?.call_id);
      // Save final transcript, triage data, etc.
      break;

    case 'call_analyzed':
      console.log('Call analyzed:', event.call?.call_id);
      // Post-processing: sentiment analysis, quality scoring
      break;

    default:
      console.log('Unknown event:', event.event);
  }

  res.json({ received: true });
});