/**
 * MeshBay Browser Key Management — keyderive.js
 *
 * Two things come from the passphrase, kept apart by their salts:
 *   - `auth_key` (PBKDF2), the hub credential — the passphrase never leaves;
 *   - `A` (Argon2id), which with the hub-held pepper gives the session's bundle
 *     key `M`, from which each node's bundle key and the playlist key derive.
 *
 * Identity keys are per node: generated on a first join, sealed for that node
 * and that account (`MBK3`), and left with that node. The hub stores no user
 * key. See docs/MESHBAY_DESIGN.md §3.1, §3.7.
 */

const PBKDF2_ITERATIONS = 600000;  // OWASP 2023 recommendation for PBKDF2-SHA512
/**
 * Where the hub is, and how to reach it — resolved when a call is made, not
 * when this file loads.
 *
 * This used to be `const HUB = ''`, "same origin", which is true of a page the
 * hub served and false of one loaded from a package: there the origin is
 * `app://meshbay`, so `/v1/users/register` resolved against it and the
 * application's own protocol handler answered 404. Registration and sign-in —
 * the first two things anybody does — failed with "Not found".
 *
 * This is a classic script, loaded before the module graph, so it cannot import
 * the adapter. It reads the global the adapter publishes, at call time: by then
 * `platform.js` has run, and in a browser both of these are exactly what they
 * were before.
 */
function hubBase() {
  const p = typeof window !== 'undefined' && window.MeshBayPlatform;
  return p ? p.hubBase() : '';
}

function hubCall(path, init) {
  const p = typeof window !== 'undefined' && window.MeshBayPlatform;
  return p && p.apiFetch ? p.apiFetch(hubBase() + path, init)
                         : fetch(hubBase() + path, init);
}

// ── Auth key derivation (password split) ──────────────────────────────────────

/**
 * Derive an auth key from password + username using PBKDF2-SHA512.
 * This key is sent to the hub for authentication — the raw password never leaves the browser.
 * Uses a different salt domain than the bundle key's Argon2 run, so the two
 * derived values are cryptographically independent.
 */
async function deriveAuthKey(password, username) {
  const enc = new TextEncoder();
  const km = await crypto.subtle.importKey(
    'raw', enc.encode(password), 'PBKDF2', false, ['deriveBits']);
  const salt = await crypto.subtle.digest(
    'SHA-256', enc.encode(`meshbay:auth:v1:${username}`));
  const bits = await crypto.subtle.deriveBits(
    { name: 'PBKDF2', hash: 'SHA-512', salt, iterations: PBKDF2_ITERATIONS },
    km, 256);
  return btoa(String.fromCharCode(...new Uint8Array(bits)));
}

// ── Key generation ────────────────────────────────────────────────────────────

/**
 * Generate random Ed25519 + X25519 keypairs using WebCrypto.
 * Returns raw bytes for both (not CryptoKey objects, for easier serialisation).
 */
async function generateKeypairs() {
  // Ed25519 (signing)
  const edKey = await crypto.subtle.generateKey(
    { name: 'Ed25519' }, true, ['sign', 'verify']);
  const skEdRaw = await crypto.subtle.exportKey('pkcs8', edKey.privateKey);
  const pkEdRaw = await crypto.subtle.exportKey('spki',  edKey.publicKey);

  // X25519 (key agreement)
  const xKey = await crypto.subtle.generateKey(
    { name: 'X25519' }, true, ['deriveBits']);
  const skXRaw = await crypto.subtle.exportKey('pkcs8', xKey.privateKey);
  const pkXRaw = await crypto.subtle.exportKey('spki',  xKey.publicKey);

  return { skEdRaw, pkEdRaw, skXRaw, pkXRaw };
}

// ── Password → AES key ────────────────────────────────────────────────────────

// Argon2id parameters for the keypair bundle.
//
// This is the one KDF in the browser that guards something an adversary can take
// away and attack at leisure: the bundle is stored on every node whose group its
// owner joins (finding C4). PBKDF2 was the wrong tool — it is compute-only, which
// is exactly what a GPU is good at, so 600k iterations bought far less than the
// wall-clock time suggested.
//
// 128 MB / t=3 / p=1 measured at ~640 ms through this WASM build on a desktop.
// Memory is the lever, not time: each guess must hold 128 MB, so a 24 GB card
// fits ~187 in parallel and its bandwidth caps it near 2k guesses/s, against no
// ceiling at all for PBKDF2. 256 MB would double that again at ~1.3 s, which is
// too much to ask of a phone for something paid at every sign-in.
const ARGON2_MEM_KIB = 131072;   // 128 MB
const ARGON2_TIME    = 3;
const ARGON2_LANES   = 1;

// What a bundle is written as. Nothing else is read: a bundle in an earlier
// format was sealed under the passphrase alone, which is exactly what an
// operator holding it could attack offline, and there is no migration window —
// such an identity is re-created on that node after the operator unpins it.
const BUNDLE_MAGIC = 'MBK3';

function _argon2() {
  const a = (typeof window !== 'undefined' && window.argon2) || globalThis.argon2;
  if (!a) throw new Error('Argon2 unavailable — vendor/argon2.min.js did not load');
  return a;
}

/**
 * `A`, the passphrase's half of the bundle key: Argon2id with a deterministic,
 * per-account salt. Deterministic so it can be derived once at sign-in and the
 * passphrase dropped; unique per account, so no shared precomputation.
 */
async function _bundleKeyBytes(password, username) {
  const enc  = new TextEncoder();
  const salt = new Uint8Array(await crypto.subtle.digest(
    'SHA-256', enc.encode(`meshbay:bundle:v2:${username}`))).slice(0, 16);
  const out = await _argon2().hash({
    pass: password, salt,
    time: ARGON2_TIME, mem: ARGON2_MEM_KIB, parallelism: ARGON2_LANES,
    hashLen: 32, type: _argon2().ArgonType.Argon2id,
  });
  return out.hash;
}

const _b64bytes = (b64) => Uint8Array.from(atob(b64), c => c.charCodeAt(0));
const _hkdf = (info) => ({
  name: 'HKDF', hash: 'SHA-256', salt: new Uint8Array(0),
  info: new TextEncoder().encode(info),
});

/**
 * The session's bundle key: `M = HKDF(A ‖ pepper, "…master:v3|" + user id)`.
 *
 * The pepper is held by the hub and handed only to a session that proved the
 * passphrase or a device key (docs/MESHBAY_DESIGN.md §3.7). Without it a bundle
 * cannot be opened however good the guess, so the operator of a node holding
 * one has nothing to test offline. `M` is what a session keeps — imported as a
 * non-extractable HKDF key, in IndexedDB until sign-out — and every key that
 * opens something is derived from it: one per node, one for playlists. The
 * pepper itself and `A` are not kept.
 *
 * One Argon2 run: the ~650 ms on the sign-in path is the whole budget.
 */
async function deriveBundleSessionKey(password, username, userId, pepperB64, pepperVersion) {
  if (!userId || !pepperB64) throw new Error('the hub did not provide the bundle pepper');
  const a = new Uint8Array(await _bundleKeyBytes(password, username));
  const pepper = _b64bytes(pepperB64);
  const ikm = new Uint8Array(a.length + pepper.length);
  ikm.set(a);
  ikm.set(pepper, a.length);
  const base = await crypto.subtle.importKey('raw', ikm, 'HKDF', false, ['deriveBits']);
  const m = await crypto.subtle.deriveBits(
    _hkdf(`meshbay:bundle-master:v3|${userId}`), base, 256);
  return {
    // HKDF keys are non-extractable by specification.
    v3: await crypto.subtle.importKey('raw', m, 'HKDF', false, ['deriveKey', 'deriveBits']),
    pepperVersion: pepperVersion || 1,
  };
}

/**
 * The session's bundle key wherever it is kept. In a browser, derived here. In
 * the desktop application, derived and kept by its main process, and what
 * comes back is a handle — `{ native, userId, pepperVersion }` — that opens
 * nothing by itself: the transport asks the application for what it needs.
 * `pending`: a passphrase change, held aside until the hub accepts it.
 */
async function sessionBundleKey(password, username, userId, pepperB64, pepperVersion,
                                { pending = false } = {}) {
  const P = typeof window !== 'undefined' && window.MeshBayPlatform;
  if (P && P.nativeKeys && await P.nativeKeys()) {
    if (!userId || !pepperB64) throw new Error('the hub did not provide the bundle pepper');
    await P.keys.deriveSession({ password, username, userId, pepperB64, pepperVersion, pending });
    return { native: true, userId, pepperVersion: pepperVersion || 1, pending };
  }
  return deriveBundleSessionKey(password, username, userId, pepperB64, pepperVersion);
}

/**
 * The key that seals this account's identity on ONE node. A leaked one opens
 * that node's bundle and no other.
 */
async function nodeBundleKey(sessionKey, nodePkB64) {
  if (!sessionKey || !sessionKey.v3) throw new Error('no bundle key in this session');
  if (!nodePkB64) throw new Error("the node's key is not known yet");
  return crypto.subtle.deriveKey(
    _hkdf(`meshbay:bundle:v3|node|${nodePkB64}`), sessionKey.v3,
    { name: 'AES-GCM', length: 256 }, false, ['encrypt', 'decrypt']);
}

/**
 * GET the pepper for a session that is already open — a stored session from
 * before the pepper existed, a passphrase change. Sign-in carries it already.
 */
async function fetchBundlePepper(token) {
  const resp = await hubCall('/v1/users/me/bundle-pepper', {
    headers: { Authorization: `Bearer ${token}` },
  });
  if (!resp.ok) throw new Error(`bundle pepper: ${resp.status}`);
  const data = await resp.json();
  return { pepper: data.bundle_pepper, version: data.bundle_pepper_version };
}

/** The account id a token of ours names — what the master key is bound to. */
function _subOf(token) {
  try {
    const part = String(token).split('.')[1].replace(/-/g, '+').replace(/_/g, '/');
    return JSON.parse(atob(part)).sub || null;
  } catch { return null; }
}

// ── Account recovery key ─────────────────────────────────────────────────────
//
// docs/MESHBAY_DESIGN.md §3.6. A full-entropy secret the user keeps outside the
// passphrase — in their password manager, or (step 3) e-mailed to them. It
// wraps a *second* copy of every per-node identity bundle, so a forgotten
// passphrase does not strand the account's group identities.
//
// 256 bits of real entropy, so the derivation is HKDF, not Argon2: there is
// nothing to brute-force and no reason to make the legitimate path slow. The
// username domain-separates it, exactly as for the bundle key.

const _B32 = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ234567';   // RFC 4648, no padding

/** 32 random bytes, shown to the human as 13 groups of 4 Base32 chars. */
function generateRecoveryKey() {
  const R = crypto.getRandomValues(new Uint8Array(32));
  return {
    rawB64: btoa(String.fromCharCode(...R)),
    mnemonic: _toMnemonic(R),
  };
}

function _toMnemonic(bytes) {
  let bits = 0, value = 0, out = '';
  for (const b of bytes) {
    value = (value << 8) | b;
    bits += 8;
    while (bits >= 5) { out += _B32[(value >>> (bits - 5)) & 31]; bits -= 5; }
  }
  if (bits > 0) out += _B32[(value << (5 - bits)) & 31];
  return out.replace(/(.{4})(?=.)/g, '$1 ');
}

function _fromMnemonic(mnemonic) {
  const clean = String(mnemonic).replace(/[^A-Za-z2-7]/g, '').toUpperCase();
  let bits = 0, value = 0;
  const out = [];
  for (const ch of clean) {
    const idx = _B32.indexOf(ch);
    if (idx < 0) throw new Error('invalid recovery key');
    value = (value << 5) | idx;
    bits += 5;
    if (bits >= 8) { out.push((value >>> (bits - 8)) & 0xff); bits -= 8; }
  }
  if (out.length < 32) throw new Error('recovery key too short');
  return new Uint8Array(out.slice(0, 32));
}

/**
 * Derive the AES-GCM key that wraps the recovery copy of a bundle.
 * `R` is the raw Uint8Array(32) or its Base32 mnemonic string.
 */
async function deriveRecoveryKey(R, username) {
  const raw = (typeof R === 'string') ? _fromMnemonic(R) : new Uint8Array(R);
  const km = await crypto.subtle.importKey('raw', raw, 'HKDF', false, ['deriveKey']);
  return crypto.subtle.deriveKey(
    {
      name: 'HKDF', hash: 'SHA-256',
      salt: new Uint8Array(0),
      info: new TextEncoder().encode(`meshbay:recovery:v1:${username}`),
    },
    km, { name: 'AES-GCM', length: 256 }, false, ['encrypt', 'decrypt']);
}

// ── Bundle encryption ─────────────────────────────────────────────────────────

// Binds a bundle to its account and its node: a bundle copied to another node,
// or served for another account, does not open.
const _bundleAad = (userId, nodePkB64) =>
  new TextEncoder().encode(`meshbay:bundle:v3|${userId}|${nodePkB64}`);

/**
 * Seal a keypair bundle for one node:
 * base64( "MBK3" ‖ pepper version (1 byte) ‖ nonce (12) ‖ AES-GCM(plaintext, aad) ).
 * `pepperVersion` is 0 for a recovery copy, which is sealed under the recovery
 * key and owes nothing to the pepper. Plaintext: JSON { skEd, skX } (pkcs8, b64).
 */
async function encryptBundle(skEdRaw, skXRaw, aesKey, { userId, nodePk, pepperVersion }) {
  if (!userId || !nodePk) throw new Error('a bundle is sealed for one account on one node');
  const nonce = crypto.getRandomValues(new Uint8Array(12));
  const data  = new TextEncoder().encode(JSON.stringify({
    skEd: btoa(String.fromCharCode(...new Uint8Array(skEdRaw))),
    skX:  btoa(String.fromCharCode(...new Uint8Array(skXRaw))),
  }));
  const ct = await crypto.subtle.encrypt(
    { name: 'AES-GCM', iv: nonce, additionalData: _bundleAad(userId, nodePk) }, aesKey, data);
  const magic = new TextEncoder().encode(BUNDLE_MAGIC);
  const out = new Uint8Array(magic.length + 1 + nonce.length + ct.byteLength);
  out.set(magic);
  out[magic.length] = pepperVersion & 0xff;
  out.set(nonce, magic.length + 1);
  out.set(new Uint8Array(ct), magic.length + 1 + nonce.length);
  return btoa(String.fromCharCode(...out));
}

/** 'current', or 'retired' for anything written before MBK3. */
function bundleFormat(bundleB64) {
  try {
    return atob(bundleB64).startsWith(BUNDLE_MAGIC) ? 'current' : 'retired';
  } catch { return 'retired'; }
}

// ── Registration ──────────────────────────────────────────────────────────────

/**
 * Full registration flow:
 * 1. Generate random keypairs
 * 2. Encrypt bundle with password
 * 3. POST to hub (public keys only — no keypair bundle)
 * 4. Store encrypted bundle locally for backup to node on first connect
 *
 * Returns the raw private keys for immediate use after registration.
 */
async function registerUser(username, email, password, recoveryMnemonic, captchaToken) {
  // No keypair here any more. Identity keys are per node: one is generated the
  // first time this account joins a given node, encrypted under the passphrase,
  // and left with that node. So an operator who cracks what sits on their own
  // disk holds a key that is worthless anywhere else — and on their own node,
  // one that unlocks nothing they did not already have.
  //
  // It also means the hub stores no user key to publish, which is what H3 read.
  const authKey = await deriveAuthKey(password, username);

  const payload = { username, email, auth_key: authKey };
  // The recovery mnemonic, when the user opted to have it e-mailed: the hub
  // appends it to the verification e-mail and stores it nowhere
  // (docs/MESHBAY_DESIGN.md §3.6). Omitted when they chose to save it themselves.
  if (recoveryMnemonic) payload.recovery_key = recoveryMnemonic;
  // reCAPTCHA response, when the hub has a captcha configured. The widget lives
  // in RegisterPage (auth-page.js); this function just forwards its token. A
  // hub with no captcha configured sends nothing and the server does not check.
  if (captchaToken) payload.captcha_token = captchaToken;

  const resp = await hubCall('/v1/users/register', {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify(payload),
  });

  if (!resp.ok) throw new Error(`Registration failed: ${await resp.text()}`);
  let userId = null;
  try { userId = (await resp.json()).user_id || null; } catch { /* no body */ }
  return { registered: true, userId };
}

/**
 * A fresh identity for one node, sealed for that node only.
 *
 * Returns { skEdB64, skXB64, pkXB64, bundleEnc, bundleEncRecovery? } — the
 * bundle goes to that node and nowhere else, and is what any other browser
 * fetches to become the same person there. When `recoveryKey` is supplied a
 * second copy sealed under it rides along, so a forgotten passphrase does not
 * strand this identity (docs/MESHBAY_DESIGN.md §3.6).
 */
async function generateNodeIdentity(sessionKey, recoveryKey, { userId, nodePk }) {
  const { skEdRaw, pkEdRaw, skXRaw, pkXRaw } = await generateKeypairs();
  const b64 = (buf) => btoa(String.fromCharCode(...new Uint8Array(buf)));
  const pkXCrypto = await crypto.subtle.importKey('spki', pkXRaw, { name: 'X25519' }, true, []);
  const pkXBytes = new Uint8Array(await crypto.subtle.exportKey('raw', pkXCrypto));
  const out = {
    skEdB64: b64(skEdRaw),
    skXB64: b64(skXRaw),
    pkXB64: b64(pkXBytes),
    bundleEnc: await encryptBundle(skEdRaw, skXRaw, await nodeBundleKey(sessionKey, nodePk),
                                   { userId, nodePk, pepperVersion: sessionKey.pepperVersion }),
  };
  if (recoveryKey) {
    out.bundleEncRecovery = await encryptBundle(skEdRaw, skXRaw, recoveryKey,
                                                { userId, nodePk, pepperVersion: 0 });
  }
  return out;
}

/**
 * Open a bundle fetched from a node. A bundle in a retired format is refused
 * with `code = 'bundle_format_retired'` — never opened, and never quietly
 * replaced by a new identity: the caller says so.
 */
async function decryptBundle(bundleB64, aesKey, { userId, nodePk }) {
  if (bundleFormat(bundleB64) !== 'current') {
    const err = new Error('bundle_format_retired');
    err.code = 'bundle_format_retired';
    throw err;
  }
  const raw   = _b64bytes(bundleB64);
  const off   = BUNDLE_MAGIC.length + 1;
  const plain = await crypto.subtle.decrypt(
    { name: 'AES-GCM', iv: raw.slice(off, off + 12),
      additionalData: _bundleAad(userId, nodePk) },
    aesKey, raw.slice(off + 12));
  return JSON.parse(new TextDecoder().decode(plain));
}

/**
 * Login and recover private keys.
 *
 * If localStorage has a keypair bundle (new registration, not yet pushed to node),
 * decrypts it and returns the keys + encrypted bundle for push to node.
 * Otherwise returns bundleKey so the caller can fetch from node during handshake.
 */
async function loginAndRecover(username, password) {
  const authKey = await deriveAuthKey(password, username);

  const resp = await hubCall('/v1/users/login', {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify({ username, auth_key: authKey }),
  });

  if (!resp.ok) {
    // The hub's `detail`, not the raw body: the sign-in page matches on it
    // (`email_verification_required`, `account_locked`), and a message wrapped
    // as "Login failed: {json}" matched nothing, so neither was ever shown.
    const body = await resp.text();
    let detail = body;
    // `error` is the per-IP rate limiter's field (slowapi), `detail` everyone else's.
    try {
      const j = JSON.parse(body);
      detail = j.detail || j.error || body;
    } catch { /* not JSON */ }
    const err = new Error(String(detail));
    err.status = resp.status;
    err.retryAfter = Number(resp.headers && resp.headers.get
      ? resp.headers.get('Retry-After') : 0) || 0;
    throw err;
  }

  const data   = await resp.json();
  const result = {
    accessToken:  data.access_token,
    refreshToken: data.refresh_token,
    // The pepper rides on the sign-in response, so this costs no extra call;
    // it is folded into the key here and not kept.
    bundleKey: await sessionBundleKey(
      password, username, _subOf(data.access_token),
      data.bundle_pepper, data.bundle_pepper_version),
  };

  // Nothing else to recover at sign-in. Identity keys belong to a node, so they
  // are fetched from the node being connected to (or generated there on a first
  // join) — see transport.js. All that is needed here is the key that opens them.
  return result;
}

// regenerateKeys() removed. Rotating an identity is now per node: the operator
// runs `meshbay-node member unpin <user>` and issues a fresh code. A hub call
// that silently changed what every node believed about someone was the wrong
// shape for this.

async function signBytes(skEdPkcs8B64, message) {
  const skRaw = Uint8Array.from(atob(skEdPkcs8B64), c => c.charCodeAt(0));
  const sk = await crypto.subtle.importKey(
    'pkcs8', skRaw, { name: 'Ed25519' }, false, ['sign']);
  const sig = await crypto.subtle.sign('Ed25519', sk, message);
  return btoa(String.fromCharCode(...new Uint8Array(sig)));
}

window.MeshBayKeys = {
  registerUser, loginAndRecover, generateNodeIdentity, generateKeypairs, signBytes,
  deriveAuthKey,
  // The bundle key (docs/MESHBAY_DESIGN.md §3.1, §3.7): one session key per
  // sign-in, one derived key per node, one format.
  deriveBundleSessionKey, sessionBundleKey, nodeBundleKey, fetchBundlePepper,
  encryptBundle, decryptBundle, bundleFormat,
  // Account recovery key (docs/MESHBAY_DESIGN.md §3.6).
  generateRecoveryKey, deriveRecoveryKey,
};