/**
 * Append a row to the hash-chained audit log.
 *
 * Each row's `this_hash` is computed over its own fields plus the previous
 * row's `this_hash`. If a later reader finds row N's `prev_hash` disagreeing
 * with row N-1's `this_hash`, the log has been tampered with — the chain
 * does not stop edits, it just makes them loud.
 *
 * The chain starts at 64 zeros for the first row.
 */

import { createHash } from 'node:crypto';
import { auditTailHash, insertAuditRow } from './db.js';

/**
 * Record an admin action.
 *
 * @param {object} entry
 * @param {string} entry.actor    admin BNS name
 * @param {string} entry.action   verb slug ('withdraw_listing', 'set_mode', 'login', …)
 * @param {string} [entry.target] the thing being acted on (listing id, mode key, …)
 * @param {object} [entry.details] arbitrary JSON, canonicalised before hashing
 */
export function logAudit({ actor, action, target = null, details = null }) {
  const at = new Date().toISOString();
  const prev_hash = auditTailHash();
  const detailsStr = details == null ? null : canonicalJson(details);

  const h = createHash('sha256');
  h.update(at);
  h.update('|');
  h.update(String(actor));
  h.update('|');
  h.update(String(action));
  h.update('|');
  h.update(target == null ? '' : String(target));
  h.update('|');
  h.update(detailsStr == null ? '' : detailsStr);
  h.update('|');
  h.update(prev_hash);
  const this_hash = h.digest('hex');

  insertAuditRow({ at, actor, action, target, details: detailsStr, prev_hash, this_hash });
  return { at, actor, action, target, details: detailsStr, prev_hash, this_hash };
}

function canonicalJson(value) {
  if (value === null || typeof value !== 'object') return JSON.stringify(value);
  if (Array.isArray(value)) return '[' + value.map(canonicalJson).join(',') + ']';
  const keys = Object.keys(value).sort();
  return '{' + keys.map((k) => JSON.stringify(k) + ':' + canonicalJson(value[k])).join(',') + '}';
}