src/index.js

const express = require('express');
const helmet = require('helmet');
const cors = require('cors');
const rateLimit = require('express-rate-limit');
const { GoogleGenerativeAI } = require('@google/generative-ai');
const Database = require('better-sqlite3');

const app = express();
const PORT = process.env.PORT || 7860;

// Security
app.use(helmet());
app.use(cors());
app.use(express.json());

// Rate limiting
const limiter = rateLimit({
  windowMs: 15 * 60 * 1000, // 15 minutes
  max: 100, // Limit each IP to 100 requests per windowMs
  message: { error: { type: 'rate_limit_error', message: 'Too many requests' }}
});
app.use('/anthropic', limiter);

// Database for usage tracking
const db = new Database(':memory:');
db.exec(`CREATE TABLE IF NOT EXISTS usage ( id INTEGER PRIMARY KEY AUTOINCREMENT, api_key TEXT, input_tokens INTEGER, output_tokens INTEGER, timestamp DATETIME DEFAULT CURRENT_TIMESTAMP )`);

// Gemini client
const genAI = new GoogleGenerativeAI(process.env.GEMINI_API_KEY || '');

// Auth middleware
const authenticate = (req, res, next) => {
  const apiKey = req.headers['x-api-key'];
  if (!apiKey || apiKey !== process.env.PROXY_API_KEY) {
    return res.status(401).json({
      error: { type: 'authentication_error', message: 'Invalid API key' }
    });
  }
  req.apiKey = apiKey;
  next();
};

// Health check
app.get('/health', (req, res) => {
  res.json({ status: 'healthy', timestamp: new Date().toISOString() });
});

// Models endpoint
app.get('/anthropic/v1/models', authenticate, (req, res) => {
  res.json({
    data: [
      {
        id: 'claude-3-5-sonnet-20241022',
        name: 'Claude 3.5 Sonnet',
        type: 'model'
      }
    ]
  });
});

// Messages endpoint
app.post('/anthropic/v1/messages', authenticate, async (req, res) => {
  try {
    const { messages, max_tokens = 1024, stream = false } = req.body;

    if (!messages || !Array.isArray(messages)) {
      return res.status(400).json({
        error: { type: 'invalid_request_error', message: 'messages is required' }
      });
    }

    // Convert to Gemini format
    const prompt = messages.map(m => `${m.role}: ${m.content}`).join('\n');

    const model = genAI.getGenerativeModel({ model: 'gemini-2.0-flash-exp' });

    if (stream) {
      res.setHeader('Content-Type', 'text/event-stream');
      res.setHeader('Cache-Control', 'no-cache');
      res.setHeader('Connection', 'keep-alive');
      
      const result = await model.generateContentStream(prompt);
      
      for await (const chunk of result.stream) {
        const text = chunk.text();
        res.write(`event: content_block_delta\n`);
        res.write(`data: ${JSON.stringify({
          type: 'content_block_delta',
          delta: { type: 'text_delta', text }
        })}\n\n`);
      }
      
      res.write(`event: message_stop\n`);
      res.write(`data: {}\n\n`);
      res.end();
    } else {
      const result = await model.generateContent(prompt);
      const text = result.response.text();
      
      // Track usage
      const inputTokens = Math.ceil(prompt.length / 4);
      const outputTokens = Math.ceil(text.length / 4);
      
      db.prepare('INSERT INTO usage (api_key, input_tokens, output_tokens) VALUES (?, ?, ?)')
        .run(req.apiKey, inputTokens, outputTokens);
      
      res.json({
        id: `msg_${Date.now()}`,
        type: 'message',
        role: 'assistant',
        content: [{ type: 'text', text }],
        model: 'claude-3-5-sonnet-20241022',
        stop_reason: 'end_turn',
        usage: {
          input_tokens: inputTokens,
          output_tokens: outputTokens
        }
      });
    }
  } catch (error) {
    console.error('Error:', error);
    res.status(500).json({
      error: { type: 'api_error', message: error.message }
    });
  }
});

app.listen(PORT, () => {
  console.log(`🚀 Server running on port ${PORT}`);
  console.log(`📊 Health: http://localhost:${PORT}/health`);
});