const express = require('express');
const path = require('path');

const app = express();
const PORT = process.env.PORT || 80;
const BACKEND_URL = process.env.BACKEND_URL;

app.use(express.json());

// Serve static React build
app.use(express.static(path.join(__dirname, 'dist')));

// Proxy endpoint - fetches identity token and forwards to backend
app.post('/api/chat/stream', async (req, res) => {
  try {
    // Fetch identity token from GCP metadata server
    const tokenResponse = await fetch(
      `http://metadata.google.internal/computeMetadata/v1/instance/service-accounts/default/identity?audience=${BACKEND_URL}`,
      { headers: { 'Metadata-Flavor': 'Google' } }
    );
    const identityToken = await tokenResponse.text();

    // Forward request to backend with auth
    const backendResponse = await fetch(`${BACKEND_URL}/chat/stream`, {
      method: 'POST',
      headers: {
        'Content-Type': 'application/json',
        'Authorization': `Bearer ${identityToken}`,
      },
      body: JSON.stringify(req.body),
    });

    // Stream response back to client
    res.setHeader('Content-Type', 'text/event-stream');
    res.setHeader('Cache-Control', 'no-cache');
    res.setHeader('Connection', 'keep-alive');

    const reader = backendResponse.body.getReader();
    const pump = async () => {
      const { done, value } = await reader.read();
      if (done) {
        res.end();
        return;
      }
      res.write(value);
      pump();
    };
    pump();

  } catch (error) {
    console.error('Proxy error:', error);
    res.status(500).json({ error: 'Proxy error' });
  }
});

// SPA fallback - all other routes serve index.html
app.get('/*', (req, res) => {
  res.sendFile(path.join(__dirname, 'dist', 'index.html'));
});

app.listen(PORT, () => {
  console.log(`Server running on port ${PORT}`);
});