packages/domain/src/policies/consent-hash.ts

import { createHash } from "node:crypto";
import type { ConsentPreview } from "@courtmitra/contracts";

/**
 * Canonical consent hashing (arch §30.4, CLAUDE.md #5).
 *
 * The hash binds a recorded consent grant to an EXACT outgoing payload. On
 * execution the ActionExecutor recomputes this from the real payload; a
 * mismatch blocks the send and forces re-approval. This prevents a mild
 * approved message from being silently replaced by a harsher one.
 *
 * Rules (copied verbatim from the spec):
 *  1. Normalize body line endings to "\n".
 *  2. Sort all object keys recursively.
 *  3. Sort attachments by id.
 *  4. EXCLUDE volatile fields (createdAt, UI labels, temp URLs).
 *  5. Include body, destination, attachment sha256s, public flag, piiDisclosed, risks.
 */

const HASH_PREFIX = "sha256:";

/** Fields that are part of the signed payload. Anything else is volatile. */
type CanonicalConsent = {
  actionType: string;
  destination: string;
  public: boolean;
  body: string;
  attachments: { id: string; sha256: string; redacted: boolean }[];
  piiDisclosed: string[];
  risks: string[];
};

function normalizeBody(body: string): string {
  return body.replace(/\r\n/g, "\n").replace(/\r/g, "\n");
}

/** Recursively sort object keys so JSON.stringify is order-independent. */
function sortKeysDeep(value: unknown): unknown {
  if (Array.isArray(value)) return value.map(sortKeysDeep);
  if (value && typeof value === "object") {
    const sorted: Record<string, unknown> = {};
    for (const key of Object.keys(value as Record<string, unknown>).sort()) {
      sorted[key] = sortKeysDeep((value as Record<string, unknown>)[key]);
    }
    return sorted;
  }
  return value;
}

/** Build the canonical, volatile-free object that gets hashed. */
export function canonicalizeConsentPreview(preview: ConsentPreview): CanonicalConsent {
  return {
    actionType: preview.actionType,
    destination: preview.destination,
    public: preview.public,
    body: normalizeBody(preview.body),
    attachments: [...preview.attachments]
      .map((a) => ({ id: a.id, sha256: a.sha256, redacted: a.redacted }))
      .sort((a, b) => a.id.localeCompare(b.id)),
    piiDisclosed: [...preview.piiDisclosed].sort(),
    risks: [...preview.risks].sort(),
  };
}

/** Canonical JSON string — stable across key ordering and line endings. */
export function canonicalConsentJson(preview: ConsentPreview): string {
  return JSON.stringify(sortKeysDeep(canonicalizeConsentPreview(preview)));
}

/** Compute the `action_preview_hash` for a consent preview. */
export function computeConsentHash(preview: ConsentPreview): string {
  const json = canonicalConsentJson(preview);
  return HASH_PREFIX + createHash("sha256").update(json, "utf8").digest("hex");
}

/**
 * Gate used by the ActionExecutor before any side effect: the hash of the EXACT
 * outgoing payload must equal the hash recorded on the consent grant.
 */
export function consentHashMatches(approvedHash: string, outgoing: ConsentPreview): boolean {
  return approvedHash === computeConsentHash(outgoing);
}