// src/utils/httpDigestAuth.js
//
// HTTP Digest Authentication (RFC 7616, and the older RFC 2617 flavour
// that most embedded devices still speak). Pure, dependency-free — no
// network calls, no state. Feed it the parsed WWW-Authenticate params
// plus the credentials and it hands back the `Authorization: Digest ...`
// header value.
//
// Why we need this: axios' built-in `auth: {username, password}` only
// speaks Basic. The Cisco DBS-210 DECT base station's admin UI (and
// most Cisco small-business voice devices, they're all cousins of the
// Sipura SPA family) rejects Basic and challenges with
//   WWW-Authenticate: Digest realm="", nonce="...", algorithm="MD5", qop="auth"
// so every request needs a fresh Digest hash. The DBS-210 also sets
// `Clear-Site-Data: "cookies"` on every response, so we can't fall
// back on a session cookie either — the Digest header goes on every
// single call.
//
// Cisco quirk we handle explicitly: the realm can be an EMPTY string.
// The Digest spec allows this, but some libraries silently drop empty
// realms which corrupts HA1. We preserve `realm` exactly as sent.

import { createHash, randomBytes } from 'node:crypto';

const md5 = (s) => createHash('md5').update(s, 'utf8').digest('hex');

/**
 * Parse the value of a `WWW-Authenticate: Digest ...` header into
 * a plain object. Handles quoted values with commas inside them and
 * unquoted tokens like `algorithm=MD5`.
 *
 * Example input:
 *   Digest realm="", nonce="abc123", algorithm="MD5", qop="auth"
 * Example output:
 *   { scheme: 'digest', realm: '', nonce: 'abc123', algorithm: 'MD5', qop: 'auth' }
 *
 * @param {string} headerValue Full value of the WWW-Authenticate header.
 * @returns {object|null}      Parsed params, or null if not a Digest challenge.
 */
export function parseDigestChallenge(headerValue) {
  if (typeof headerValue !== 'string') return null;
  const trimmed = headerValue.trim();
  const schemeMatch = trimmed.match(/^([A-Za-z]+)\s+/);
  if (!schemeMatch || schemeMatch[1].toLowerCase() !== 'digest') return null;

  const rest = trimmed.slice(schemeMatch[0].length);

  // Tokenizer: walk char-by-char so we don't split inside quoted strings.
  const params = { scheme: 'digest' };
  let i = 0;
  const len = rest.length;
  while (i < len) {
    // skip whitespace + commas between params
    while (i < len && (rest[i] === ' ' || rest[i] === ',')) i++;
    if (i >= len) break;

    // read key up to '='
    const keyStart = i;
    while (i < len && rest[i] !== '=') i++;
    const key = rest.slice(keyStart, i).trim().toLowerCase();
    if (i >= len) break;
    i++; // skip '='

    // read value: quoted or unquoted
    let value;
    if (rest[i] === '"') {
      i++; // skip opening quote
      const valStart = i;
      while (i < len && rest[i] !== '"') {
        // very light escape handling for \" inside the value
        if (rest[i] === '\\' && i + 1 < len) i++;
        i++;
      }
      value = rest.slice(valStart, i);
      if (rest[i] === '"') i++; // skip closing quote
    } else {
      const valStart = i;
      while (i < len && rest[i] !== ',' && rest[i] !== ' ') i++;
      value = rest.slice(valStart, i);
    }
    params[key] = value;
  }
  return params;
}

/**
 * Compute the `Authorization: Digest ...` header value for a given
 * request, challenge, and credentials. Implements MD5 with qop=auth
 * (the flavour the DBS-210 uses); MD5-sess and qop=auth-int are
 * not supported because we don't need them and adding them without a
 * device that speaks them would be untested code.
 *
 * @param {object} args
 * @param {string} args.username
 * @param {string} args.password
 * @param {string} args.method            HTTP method, e.g. 'GET', 'POST'
 * @param {string} args.uri               Request-URI (path + query), NOT the full URL
 * @param {object} args.challenge         Parsed WWW-Authenticate params
 * @param {number} [args.nc]              Nonce count; each new request against
 *                                         the same nonce should increment this.
 *                                         Default 1 (fine for the "one-shot per
 *                                         request" pattern we use).
 * @param {string} [args.cnonce]          Client nonce. Randomly generated if omitted.
 * @returns {string}                      Value for the `Authorization` header.
 */
export function buildDigestAuthHeader({
  username, password, method, uri, challenge, nc = 1, cnonce,
}) {
  if (!challenge || typeof challenge !== 'object') {
    throw new Error('buildDigestAuthHeader: challenge is required');
  }
  const algorithm = (challenge.algorithm || 'MD5').toUpperCase();
  if (algorithm !== 'MD5') {
    throw new Error(`buildDigestAuthHeader: unsupported algorithm "${algorithm}"`);
  }
  // Split qop by comma; server may advertise "auth,auth-int". We pick
  // 'auth' always (the DBS-210 only lists 'auth' anyway).
  const qopList = (challenge.qop || '')
    .split(',')
    .map((s) => s.trim().toLowerCase())
    .filter(Boolean);
  const useQop = qopList.includes('auth') ? 'auth' : (qopList[0] || null);

  const realm = challenge.realm ?? ''; // preserve empty realm exactly
  const nonce = challenge.nonce || '';
  const opaque = challenge.opaque;
  const ncHex = String(nc).padStart(8, '0');
  const cnonceStr = cnonce || randomBytes(8).toString('hex');

  const HA1 = md5(`${username}:${realm}:${password}`);
  const HA2 = md5(`${method.toUpperCase()}:${uri}`);

  let response;
  if (useQop) {
    response = md5(`${HA1}:${nonce}:${ncHex}:${cnonceStr}:${useQop}:${HA2}`);
  } else {
    // Legacy RFC 2069 fallback (no qop). DBS-210 always sends qop=auth
    // so this branch is defensive-only, not exercised in practice.
    response = md5(`${HA1}:${nonce}:${HA2}`);
  }

  // Build the header. Ordering doesn't matter to servers, but grouping
  // matches what most reference implementations emit so it's easy to
  // eyeball in a packet capture.
  const parts = [
    `username="${username}"`,
    `realm="${realm}"`,
    `nonce="${nonce}"`,
    `uri="${uri}"`,
    `algorithm=${algorithm}`,
    `response="${response}"`,
  ];
  if (useQop) {
    parts.push(`qop=${useQop}`, `nc=${ncHex}`, `cnonce="${cnonceStr}"`);
  }
  if (opaque !== undefined) {
    parts.push(`opaque="${opaque}"`);
  }
  return `Digest ${parts.join(', ')}`;
}