// 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 talks to models server-side (Netlify's AI
// Gateway injects the credentials) so no key ever ships to the browser/APK.
//
// Access: the model list is a curated allowlist so this can't be used as an open
// proxy. Set SASQUATCH_REQUIRE_PRO=1 to additionally require a valid NIP-98 auth
// header (`x-sasquatch-auth`) plus proof of an active Sasquatch Pro pass
// (`x-sasquatch-pro` = a provider-authored zap receipt). Off by default so the
// client can be updated before enforcement is switched on.
//
// Request body (OpenAI chat shape):
//   { model, messages, max_tokens?, stream? }
// When stream:true, the upstream SSE is passed straight through.
import { verifyEvent } from 'nostr-tools';

// 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',
]);

// ── Sasquatch Pro enforcement (env-gated) ────────────────────────────────────
const REQUIRE_PRO = process.env.SASQUATCH_REQUIRE_PRO === '1';
const PLATFORM_PRO_ADDRESS = 'skatespots@minibits.cash';
/** Primary platform pubkey — zap requests must tag it; owners always pass. */
const PLATFORM_PUBKEY = '20e7c953439e66f3882ab96fe0faa8ba246d6fb12c03b0cb4e2dc4623b8bcb21';
const PLATFORM_OWNER_PUBKEYS = new Set([
  PLATFORM_PUBKEY,
  'caba497f7beda0650d6b78ab211216e4d2ebabeec9ca6eb2a05cee8e55c6871b',
]);
const DAY_SECONDS = 86_400;
/** Tier days ↔ sats. Keep in sync with PRO_TIERS in src/lib/sasquatchPro.ts. */
const PRO_TIERS = [
  { days: 7, sats: 2000 },
  { days: 30, sats: 5000 },
  { days: 90, sats: 12000 },
  { days: 365, sats: 36000 },
];

let providerPubkeyCache;
/** Resolve the platform's LNURL provider pubkey (zap receipts must be theirs). */
async function getProProviderPubkey() {
  if (providerPubkeyCache !== undefined) return providerPubkeyCache;
  try {
    const [user, domain] = PLATFORM_PRO_ADDRESS.split('@');
    const res = await fetch(`https://${domain}/.well-known/lnurlp/${user}`, {
      signal: AbortSignal.timeout(6000),
    });
    const j = await res.json();
    providerPubkeyCache = j.nostrPubkey || null;
  } catch {
    providerPubkeyCache = null;
  }
  return providerPubkeyCache;
}

function decodeB64Json(value) {
  try {
    return JSON.parse(Buffer.from(value, 'base64').toString('utf8'));
  } catch {
    return null;
  }
}
function tagVal(tags, name) {
  return tags?.find((t) => t[0] === name)?.[1];
}
/** Satoshis from a BOLT11 amount. The receipt is provider-signed, so we only
 *  need the amount (not full invoice validation). */
function satsFromBolt11(pr) {
  const m = /^lnbc(\d+)([munp]?)/i.exec(String(pr).toLowerCase());
  if (!m) return 0;
  const n = Number(m[1]);
  const mult = { m: 1e-3, u: 1e-6, n: 1e-9, p: 1e-12 }[m[2]] ?? 1;
  return Math.round(n * mult * 1e8);
}

/** Verify a NIP-98 auth header → pubkey, or null. A generous window lets one
 *  signature act as a session (so Amber doesn't pop per request). */
function verifyNip98(authHeader) {
  if (!authHeader) return null;
  const ev = decodeB64Json(authHeader);
  if (!ev || ev.kind !== 27235) return null;
  const method = tagVal(ev.tags, 'method');
  if (method && method !== 'POST') return null;
  const u = tagVal(ev.tags, 'u') ?? '';
  if (u && !u.endsWith('/api/ai')) return null;
  if (Math.abs(Date.now() / 1000 - ev.created_at) > 12 * 3600) return null;
  try {
    return verifyEvent(ev) ? ev.pubkey : null;
  } catch {
    return null;
  }
}

/** Verify a Pro pass (provider-authored zap receipt bound to the caller, paying
 *  the platform ≥ the smallest tier) → proUntil (unix sec), or null. */
async function verifyPro(receiptHeader, userPubkey) {
  if (!receiptHeader) return null;
  const receipt = decodeB64Json(receiptHeader);
  if (!receipt || receipt.kind !== 9735) return null;
  const providerPubkey = await getProProviderPubkey();
  if (!providerPubkey || receipt.pubkey !== providerPubkey) return null;
  try {
    if (!verifyEvent(receipt)) return null;
  } catch {
    return null;
  }

  const desc = tagVal(receipt.tags, 'description');
  if (!desc) return null;
  let zapReq;
  try {
    zapReq = JSON.parse(desc);
  } catch {
    return null;
  }
  if (!zapReq || zapReq.pubkey !== userPubkey) return null;
  try {
    if (!verifyEvent(zapReq)) return null;
  } catch {
    return null;
  }
  if (!zapReq.tags?.some((t) => t[0] === 'p' && t[1] === PLATFORM_PUBKEY)) return null;

  let paidSats = satsFromBolt11(tagVal(receipt.tags, 'bolt11'));
  if (!paidSats) {
    const msat = Number(tagVal(zapReq.tags, 'amount'));
    if (Number.isFinite(msat) && msat > 0) paidSats = Math.floor(msat / 1000);
  }
  const tier = [...PRO_TIERS].sort((a, b) => b.sats - a.sats).find((t) => paidSats >= t.sats);
  if (!tier) return null;
  return receipt.created_at + tier.days * DAY_SECONDS;
}

// 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);

  // Pro gate (env-gated): require a NIP-98-signed identity and, unless the
  // caller is a platform owner, an active Pro pass.
  if (REQUIRE_PRO) {
    const pubkey = verifyNip98(request.headers.get('x-sasquatch-auth'));
    if (!pubkey) return json({ error: 'auth required' }, 401, headers);
    if (!PLATFORM_OWNER_PUBKEYS.has(pubkey)) {
      const proUntil = await verifyPro(request.headers.get('x-sasquatch-pro'), pubkey);
      if (!proUntil || proUntil < Math.floor(Date.now() / 1000)) {
        return json({ error: 'pro required' }, 402, 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' };