/* ============================================================================
 * p2p-hub.js — live presence + WebRTC signalling for P2P devices, and the
 * availability payload (docs/p2p-architecture.md flows 4–5).
 *
 *   /ws/p2p   (credentials never go in the URL — proxies log URLs)
 *     you → server  {type:'auth', device, secret}             first message, within 10 s
 *     server → you  {type:'hello', peer}                      after auth
 *     you → peer    {type:'signal', to:<peer>, data}          relayed as
 *     server → peer {type:'signal', from:<your peer>, data}
 *     server → you  {type:'error', error}
 *   Server-initiated messages (plan 018) go through hub.send(deviceId, msg).
 *
 * "Online" lives only in memory: a server restart forgets it, a closed
 * socket drops it. Holder ROWS are persistent (p2p_holders) — the payload
 * reports both: `online` (now) and `lastVerifiedAt` / `stale` (history).
 * Peers are addressed by an opaque id (peerIdOf), never by device id.
 * ========================================================================== */
import { createHash, timingSafeEqual } from 'node:crypto';

const sha = (s) => createHash('sha256').update(String(s)).digest('hex');
const same = (a, b) => { const x = Buffer.from(String(a)), y = Buffer.from(String(b)); return x.length === y.length && timingSafeEqual(x, y); };
export const peerIdOf = (deviceId) => sha('peer:' + deviceId).slice(0, 12);

const MAX_MSG = 64 * 1024;
const BUDGET_PER_MIN = 300;

export function createP2pHub({ getDevice, enabled = () => true, now = () => Date.now(), log = console } = {}) {
  const online = new Map(); // deviceId -> ws
  const byPeer = new Map(); // peer -> deviceId (online only)

  const send = (ws, m) => { try { ws.send(JSON.stringify(m)); } catch { /* gone */ } };

  function upgrade(req, server) {
    if (!enabled()) return new Response('p2p disabled', { status: 404 });
    const ok = server.upgrade(req, { data: { hub: 'p2p', authed: false, budget: [] } });
    return ok ? undefined : new Response('upgrade failed', { status: 400 });
  }

  function open(ws) {
    const t = setTimeout(() => { if (!ws.data.authed) { try { ws.close(4401, 'auth timeout'); } catch { /* gone */ } } }, 10_000);
    t.unref?.();
  }

  async function auth(ws, m) {
    const deviceId = String(m.device || '');
    const secret = String(m.secret || '');
    const d = /^dev_[0-9a-f]{16}$/.test(deviceId) ? await getDevice(deviceId).catch(() => null) : null;
    if (!d || !same(d.secret_hash, sha(secret))) { try { ws.close(4401, 'unknown device'); } catch { /* gone */ } return; }
    ws.data.authed = true;
    ws.data.deviceId = deviceId;
    ws.data.peer = peerIdOf(deviceId);
    const prev = online.get(deviceId);
    if (prev && prev !== ws) { prev.data.deviceId = null; try { prev.close(4409, 'replaced'); } catch { /* gone */ } }
    online.set(deviceId, ws);
    byPeer.set(ws.data.peer, deviceId);
    send(ws, { type: 'hello', peer: ws.data.peer });
  }

  async function message(ws, raw) {
    const t = now();
    ws.data.budget = ws.data.budget.filter((x) => t - x < 60_000);
    if (ws.data.budget.length >= BUDGET_PER_MIN) { send(ws, { type: 'error', error: 'slow down' }); return; }
    ws.data.budget.push(t);
    const s = typeof raw === 'string' ? raw : Buffer.from(raw).toString('utf8');
    if (s.length > MAX_MSG) return;
    let m;
    try { m = JSON.parse(s); } catch { return; }
    if (!ws.data.authed) { if (m && m.type === 'auth' && !ws.data.authing) { ws.data.authing = true; await auth(ws, m); } return; }
    if (m && m.type === 'signal' && typeof m.to === 'string') {
      const target = online.get(byPeer.get(m.to));
      if (!target || target === ws) { send(ws, { type: 'error', error: 'peer offline', to: m.to }); return; }
      send(target, { type: 'signal', from: ws.data.peer, data: m.data });
    }
  }

  function close(ws) {
    const { deviceId, peer } = ws.data || {};
    if (deviceId && online.get(deviceId) === ws) {
      online.delete(deviceId);
      byPeer.delete(peer);
    }
  }

  return {
    upgrade,
    websocket: { open, message, close },
    isOnline: (deviceId) => online.has(deviceId),
    send: (deviceId, msg) => { const ws = online.get(deviceId); if (!ws) return false; send(ws, msg); return true; },
    onlineCount: () => online.size,
  };
}

// GET /api/p2p/holders payload. Only devices that share are listed; holders
// are never dropped for age — `stale` just flags an old last check.
export async function holdersPayload({ videoId, cid, p2pDb, isOnline, staleDays, serverHas, now = Date.now() }) {
  const contents = cid
    ? [await p2pDb.getContent(cid)].filter((c) => c && c.status === 'verified')
    : await p2pDb.listContentForVideo(videoId);
  const staleMs = staleDays * 86400_000;
  const out = [];
  for (const c of contents) {
    const holders = (await p2pDb.listHolders(c.cid, 50))
      .filter((h) => Number(h.share) === 1)
      .map((h) => ({
        peer: peerIdOf(h.device_id),
        online: isOnline(h.device_id),
        lastVerifiedAt: Number(h.last_verified_at),
        stale: now - Number(h.last_verified_at) > staleMs,
        trust: h.trust,
      }))
      .sort((a, b) => (b.online - a.online) || (b.lastVerifiedAt - a.lastVerifiedAt));
    out.push({
      cid: c.cid, videoId: c.video_id, size: Number(c.size), height: Number(c.height), vcodec: c.vcodec,
      serverHas: !!(await serverHas(c.cid)),
      counts: { holders: holders.length, online: holders.filter((h) => h.online).length, fresh: holders.filter((h) => !h.stale).length },
      holders,
    });
  }
  return { ok: true, staleDays, cids: out };
}