// commons-loader.mjs — Reads vendored llm-security-commons JSON artifacts.
//
// v8 Phase 5 step 2: this loader is built and unit-tested now, against a
// local fixture, ahead of Phase 4 (llm-security-commons repo creation +
// vendoring — see docs/commons-extraction-plan.local.md). Consumers
// (injection-patterns.mjs, severity.mjs, string-utils.mjs, ...) switch from
// hardcoded tables to this loader in Phase 5 step 4, table-by-table, behind
// the golden gate.
//
// Modeled on signature-scanner.mjs's loadRules(): hooks run per-tool-call in
// fresh zero-dep processes, so resolution must be a fast synchronous read of
// the vendored copy, never network. Cached once per process. A
// missing/unvendored commons dir degrades to the caller's fallback rather
// than crashing a hook — the same graceful-empty contract loadRules() uses
// for a missing knowledge/signatures.json.
//
// Deliberately NOT policy-driven, unlike loadCustomRules()'s
// sig.custom_rules_path: this plugin scans untrusted cloned repos, and
// `.llm-security/policy.json` lives in the *scanned target*. A
// custom_rules_path override can only ever add findings a hostile target
// supplies; a commons-root override would let that target *replace* this
// plugin's own detection corpus wholesale, with graceful-empty fallback
// making the substitution silent. The commons location is this plugin's own
// concern, not the scan target's — so the only override is the explicit
// `commonsRoot` option (tests, a local commons dev checkout), resolved from
// this file's own location, never from policy or the scan target.
//
// Zero external dependencies — Node.js builtins only.

import { readFileSync } from 'node:fs';
import { join, dirname } from 'node:path';
import { fileURLToPath } from 'node:url';

const __dirname = dirname(fileURLToPath(import.meta.url));

// Default vendored location: llm-security-commons is pulled in as a
// pull-only subtree under scanners/, which is the only source directory
// `package.json`'s `files` allowlist ships (bin/, scanners/, knowledge/ —
// scripts/ and tests/ do not publish, and neither would a repo-root dir).
const DEFAULT_COMMONS_ROOT = join(__dirname, '..', 'commons');

// Cached parsed artifacts, keyed by resolved absolute file path. A failed
// load caches this sentinel (not the caller's fallback value) so that two
// callers requesting the same missing artifact with different fallback
// shapes (`[]` vs `{}`) each still get their own fallback back, rather than
// the first caller's shape leaking to the second.
const _cache = new Map();
const LOAD_FAILED = Symbol('commons-loader:load-failed');

/** Recursively freeze a parsed JSON value so callers cannot mutate a shared cached table. */
function deepFreeze(value) {
  if (value !== null && typeof value === 'object' && !Object.isFrozen(value)) {
    Object.freeze(value);
    for (const key of Object.keys(value)) deepFreeze(value[key]);
  }
  return value;
}

/**
 * Load and parse one commons JSON artifact.
 * Graceful fallback on any read/parse error — an unvendored, missing, or
 * invalid commons artifact must never crash a hook or scanner. The returned
 * value is deep-frozen: every caller shares the same cached object, so
 * mutating it would silently leak across callers/targets; freezing makes
 * that throw instead.
 *
 * @param {string} artifactPath - relative path under the commons root,
 *   without the `.json` extension (e.g. `'lexicon/injection-lexicon'`).
 * @param {object} [opts]
 * @param {*} [opts.fallback] - value returned on any load/parse failure
 *   (default: `null`). Callers pick the shape-appropriate empty value
 *   (`[]`, `{}`, ...) the same way loadRules() falls back to `[]`.
 * @param {string} [opts.commonsRoot] - explicit commons root, overriding the
 *   default vendored path (for tests and a local commons dev checkout).
 * @returns {*} Parsed, frozen JSON, or `opts.fallback` on failure.
 */
export function loadArtifact(artifactPath, opts = {}) {
  const { fallback = null, commonsRoot } = opts;
  const root = commonsRoot || DEFAULT_COMMONS_ROOT;
  const filePath = join(root, `${artifactPath}.json`);

  if (_cache.has(filePath)) {
    const cached = _cache.get(filePath);
    return cached === LOAD_FAILED ? fallback : cached;
  }

  let result;
  try {
    const raw = readFileSync(filePath, 'utf8');
    result = deepFreeze(JSON.parse(raw));
  } catch {
    _cache.set(filePath, LOAD_FAILED); // graceful: unvendored/missing/invalid -> caller's fallback
    return fallback;
  }

  _cache.set(filePath, result);
  return result;
}

/**
 * Reset the artifact cache (for testing only).
 */
export function _resetCacheForTest() {
  _cache.clear();
}