// Netlify Function: POST /api/ai — server-side AI proxy for Sasquatch.
//
// Why this exists: a `VITE_*` API key is compiled into the client bundle and is
// therefore public. This function keeps the OpenRouter key server-side (Netlify
// env var OPENROUTER_API_KEY) so it never ships to the browser/APK.
//
// Safety: only `:free` OpenRouter models are allowed, so even an abused endpoint
// cannot spend credits — the worst case is exhausting the free quota (the app
// then falls back to the keyless Pollinations provider).
//
// Request body (OpenAI chat shape):
//   { model, messages, max_tokens?, stream? }
// When stream:true, OpenRouter's SSE is passed straight through.

// Netlify's AI Gateway injects OPENROUTER_API_KEY + OPENROUTER_BASE_URL into
// Functions (server-side only), so no key is managed or shipped by us. If you
// later set your OWN OPENROUTER_API_KEY in the project env, Netlify stops
// injecting both, and this falls back to the public OpenRouter endpoint — so it
// works either way.
const OPENROUTER_BASE = (process.env.OPENROUTER_BASE_URL || 'https://openrouter.ai/api/v1').replace(
  /\/+$/,
  '',
);
const OPENROUTER_URL = `${OPENROUTER_BASE}/chat/completions`;

// Models Sasquatch may request. Curated on purpose: the client sends the model
// slug, so an allowlist stops anyone using this endpoint as an open proxy for
// arbitrary (potentially expensive) models. These are fast, cheap, capable slugs
// served through Netlify's AI Gateway.
const ALLOWED_MODELS = new Set([
  'meta-llama/llama-3.3-70b-instruct',
  'deepseek/deepseek-chat-v3-0324',
  'x-ai/grok-4.5',
  'moonshotai/kimi-k2',
  'qwen/qwen-2.5-72b-instruct',
  'mistralai/mistral-nemo',
  'meta-llama/llama-3.1-8b-instruct',
]);

// Origins allowed to call the proxy (web + local dev + Capacitor native).
const ALLOWED_ORIGINS = new Set([
  'https://skate-spots.org',
  'http://localhost:8080',
  'http://localhost:5173',
  'capacitor://localhost',
  'http://localhost',
  'https://localhost',
]);

// Best-effort in-memory throttle. Serverless instances are ephemeral, so this is
// a blunt abuse damper, not a hard guarantee.
const WINDOW_MS = 60_000;
const LIMIT = 20;
const hits = new Map();

function corsHeaders(origin) {
  return {
    'Access-Control-Allow-Origin': ALLOWED_ORIGINS.has(origin) ? origin : 'https://skate-spots.org',
    'Access-Control-Allow-Methods': 'POST, OPTIONS',
    'Access-Control-Allow-Headers': 'Content-Type',
    Vary: 'Origin',
  };
}

function json(body, status, headers) {
  return new Response(JSON.stringify(body), {
    status,
    headers: { ...headers, 'Content-Type': 'application/json' },
  });
}

export default async function handler(request) {
  const origin = request.headers.get('origin') || '';
  const headers = corsHeaders(origin);

  if (request.method === 'OPTIONS') return new Response(null, { status: 204, headers });
  if (request.method !== 'POST') return json({ error: 'Method not allowed' }, 405, headers);

  const key = process.env.OPENROUTER_API_KEY;
  if (!key) return json({ error: 'AI proxy not configured' }, 503, headers);

  // Throttle per client IP (Netlify sets x-nf-client-connection-ip).
  const ip =
    request.headers.get('x-nf-client-connection-ip') ||
    request.headers.get('x-forwarded-for') ||
    'unknown';
  const now = Date.now();
  const recent = (hits.get(ip) ?? []).filter((t) => now - t < WINDOW_MS);
  if (recent.length >= LIMIT) return json({ error: 'Too many requests' }, 429, headers);
  recent.push(now);
  hits.set(ip, recent);

  let body;
  try {
    body = await request.json();
  } catch {
    return json({ error: 'Invalid JSON' }, 400, headers);
  }

  const model = String(body.model ?? '');
  if (!ALLOWED_MODELS.has(model)) return json({ error: 'Model not allowed' }, 400, headers);

  const messages = Array.isArray(body.messages) ? body.messages.slice(-20) : [];
  const maxTokens = Math.min(Number(body.max_tokens) || 400, 800);
  const stream = body.stream === true;

  let upstream;
  try {
    upstream = await fetch(OPENROUTER_URL, {
      method: 'POST',
      headers: {
        Authorization: `Bearer ${key}`,
        'Content-Type': 'application/json',
        'HTTP-Referer': 'https://skate-spots.org',
        'X-Title': 'SkateSpots',
      },
      body: JSON.stringify({ model, messages, max_tokens: maxTokens, stream }),
      signal: AbortSignal.timeout(30_000),
    });
  } catch (err) {
    return json({ error: `Upstream failed: ${String(err)}` }, 502, headers);
  }

  // Pass OpenRouter's response straight through (JSON or SSE).
  const passthrough = { ...headers };
  const contentType = upstream.headers.get('content-type');
  if (contentType) passthrough['Content-Type'] = contentType;

  return new Response(upstream.body, { status: upstream.status, headers: passthrough });
}

// Netlify Functions v2 routing — serve this at /api/ai.
export const config = { path: '/api/ai' };