/**
 * Key derivation primitives for at-rest storage encryption.
 *
 * Hierarchy:
 *   masterKey  (from passphrase / keychain / app-injected)
 *      │
 *      ├─ HKDF("shade-storage-v1") → storageKey  (32 bytes)
 *      │     └─ HKDF(storageKey, table || ":" || column) → fieldKey (32 bytes)
 *      │
 *      └─ HKDF("shade-storage-version-v1") → versionKey  (used during rotation)
 */

import { scryptAsync } from '@noble/hashes/scrypt.js';
import { hkdf } from '@noble/hashes/hkdf.js';
import { sha256 } from '@noble/hashes/sha2.js';

const TEXT = new TextEncoder();

/** scrypt parameters — interactive; sized for sub-second derivation on commodity HW */
export interface ScryptParams {
  N: number;
  r: number;
  p: number;
  dkLen: number;
}

/** Default: N=2^17, r=8, p=1, 32-byte output. ~250ms on a modern laptop. */
export const DEFAULT_SCRYPT: ScryptParams = { N: 1 << 17, r: 8, p: 1, dkLen: 32 };

/**
 * Derive a 32-byte master key from a passphrase + salt using scrypt.
 * The salt MUST be persisted alongside the encrypted database (16-byte random).
 */
export async function deriveMasterKey(
  passphrase: string,
  salt: Uint8Array,
  params: ScryptParams = DEFAULT_SCRYPT,
): Promise<Uint8Array> {
  if (passphrase.length === 0) {
    throw new Error('passphrase must be non-empty');
  }
  if (salt.length < 16) {
    throw new Error('salt must be at least 16 bytes');
  }
  return scryptAsync(TEXT.encode(passphrase.normalize('NFKC')), salt, params);
}

/** HKDF-SHA-256 with explicit info string. */
export function hkdfDerive(ikm: Uint8Array, info: string, length = 32, salt?: Uint8Array): Uint8Array {
  return hkdf(sha256, ikm, salt, TEXT.encode(info), length);
}

/** Derive the storageKey from masterKey. Stable, deterministic. */
export function deriveStorageKey(masterKey: Uint8Array): Uint8Array {
  return hkdfDerive(masterKey, 'shade-storage-v1', 32);
}

/** Derive the per-(table, column) field key. Stable, deterministic. */
export function deriveFieldKey(storageKey: Uint8Array, table: string, column: string): Uint8Array {
  return hkdfDerive(storageKey, `shade-field-v1:${table}:${column}`, 32);
}

/**
 * Derive a deterministic 12-byte AEAD nonce from a row key (typically the
 * field key) plus (table, pk) binding. With per-field keys, deterministic
 * nonces are safe because each (key, plaintext) pair appears at most once
 * — re-saving the same row reuses the (nonce, key) pair only because the
 * plaintext also changes (chain ratchet, prekey state, etc.). The AAD
 * also binds (table, column, pk) so swapping is rejected on decrypt.
 */
export function deriveNonce(rowKey: Uint8Array, table: string, pk: string): Uint8Array {
  const out = hkdfDerive(rowKey, `shade-row-nonce-v1:${table}:${pk}`, 12);
  return out;
}

/** Build the AAD that binds (table, column, pk) to a ciphertext. */
export function buildAad(table: string, column: string, pk: string): Uint8Array {
  return TEXT.encode(`shade-aad-v1|${table}|${column}|${pk}`);
}
