// api/generate.js — Vercel serverless proxy for Anthropic API
// The API key lives in Vercel's environment variables, never in the browser.

export default async function handler(req, res) {
  // Only allow POST
  if (req.method !== 'POST') {
    return res.status(405).json({ error: 'Method not allowed' });
  }

  // Basic rate-limit guard: reject if no body or missing required fields
  const { messages, system } = req.body || {};
  if (!messages || !Array.isArray(messages) || messages.length === 0) {
    return res.status(400).json({ error: 'Missing or invalid messages' });
  }

  const apiKey = process.env.ANTHROPIC_API_KEY;
  if (!apiKey) {
    console.error('ANTHROPIC_API_KEY not set in environment variables');
    return res.status(500).json({ error: 'Server configuration error' });
  }

  try {
    const anthropicBody = {
      model: 'claude-sonnet-4-6',
      max_tokens: 4096,
      messages: messages,
    };

    // Pass through the system prompt if provided
    if (system) {
      anthropicBody.system = system;
    }

    const response = await fetch('https://api.anthropic.com/v1/messages', {
      method: 'POST',
      headers: {
        'Content-Type': 'application/json',
        'x-api-key': apiKey,
        'anthropic-version': '2023-06-01',
      },
      body: JSON.stringify(anthropicBody),
    });

    const data = await response.json();

    if (!response.ok) {
      console.error('Anthropic API error:', data);
      return res.status(response.status).json({
        error: data.error?.message || 'Anthropic API error',
      });
    }

    return res.status(200).json(data);
  } catch (err) {
    console.error('Proxy error:', err);
    return res.status(500).json({ error: 'Internal server error' });
  }
}