/**
 * Regression tests for the AES-GCM nonce-reuse fix (G0).
 *
 * The codec used to derive its nonce from (fieldKey, table, pk) alone. That
 * is a pure function of row identity, so every re-seal of a mutable row —
 * `saveSession` runs on each ratchet step — reused (key, nonce) across
 * different plaintexts. AES-GCM forbids exactly that: it leaks the XOR of
 * the plaintexts and the GHASH subkey, which yields tag forgery under that
 * key. These tests fail if the derivation ever comes back.
 */
import { describe, test, expect } from 'bun:test';
import { KeyManager } from '../src/crypto/key-manager.js';
import { AEAD_NONCE_LEN, aeadSeal } from '../src/crypto/aead.js';
import { buildAad, deriveNonce } from '../src/crypto/kdf.js';
import {
  COL,
  TBL,
  openBytes,
  openString,
  sealBytes,
  sealString,
} from '../src/crypto/row-codec.js';

const TEXT = new TextEncoder();

function km(): Promise<KeyManager> {
  return KeyManager.open({ kind: 'injected', key: new Uint8Array(32).fill(0x42) });
}

const nonceOf = (blob: Uint8Array) => blob.subarray(0, AEAD_NONCE_LEN);
const hex = (b: Uint8Array) => Array.from(b, (x) => x.toString(16).padStart(2, '0')).join('');

describe('nonce uniqueness across re-saves', () => {
  test('two seals of the same row do not share a nonce', async () => {
    const k = await km();
    // The real shape of the bug: same (table, column, pk), different
    // plaintext, as a session row is re-sealed on every ratchet step.
    const first = await sealString(k, TBL.sessions, COL.session, 'alice', '{"messageCount":1}');
    const second = await sealString(k, TBL.sessions, COL.session, 'alice', '{"messageCount":2}');
    expect(hex(nonceOf(first))).not.toBe(hex(nonceOf(second)));
    k.destroy();
  });

  test('a long run of re-saves produces all-distinct nonces', async () => {
    const k = await km();
    const seen = new Set<string>();
    for (let i = 0; i < 200; i++) {
      const blob = await sealString(k, TBL.sessions, COL.session, 'alice', `state-${i}`);
      seen.add(hex(nonceOf(blob)));
    }
    expect(seen.size).toBe(200);
    k.destroy();
  });

  test('sealBytes is covered by the same rule', async () => {
    const k = await km();
    const a = await sealBytes(k, TBL.config, COL.config, 'cfg', TEXT.encode('one'));
    const b = await sealBytes(k, TBL.config, COL.config, 'cfg', TEXT.encode('two'));
    expect(hex(nonceOf(a))).not.toBe(hex(nonceOf(b)));
    k.destroy();
  });

  test('the nonce is not the derived one', async () => {
    const k = await km();
    const blob = await sealString(k, TBL.sessions, COL.session, 'alice', 'payload');
    const derived = deriveNonce(k.fieldKey(TBL.sessions, COL.session), TBL.sessions, 'alice');
    expect(hex(nonceOf(blob))).not.toBe(hex(derived));
    k.destroy();
  });
});

describe('backward compatibility with deterministically-sealed blobs', () => {
  // `aeadOpen` has always read the nonce from the blob prefix, so data
  // written before the fix opens unchanged and needs no migration. This
  // test reproduces an old blob by sealing with the deprecated derivation.
  test('a blob sealed with the old derived nonce still opens', async () => {
    const k = await km();
    const key = k.fieldKey(TBL.sessions, COL.session);
    const legacy = await aeadSeal(
      key,
      deriveNonce(key, TBL.sessions, 'alice'),
      TEXT.encode('written before the fix'),
      buildAad(TBL.sessions, COL.session, 'alice'),
    );

    const opened = await openString(k, TBL.sessions, COL.session, 'alice', legacy);
    expect(opened).toBe('written before the fix');
    k.destroy();
  });

  test('openBytes reads an old blob too', async () => {
    const k = await km();
    const key = k.fieldKey(TBL.config, COL.config);
    const payload = TEXT.encode('legacy bytes');
    const legacy = await aeadSeal(
      key,
      deriveNonce(key, TBL.config, 'cfg'),
      payload,
      buildAad(TBL.config, COL.config, 'cfg'),
    );

    expect(await openBytes(k, TBL.config, COL.config, 'cfg', legacy)).toEqual(payload);
    k.destroy();
  });

  test('new and old blobs are both readable under one key', async () => {
    const k = await km();
    const key = k.fieldKey(TBL.sessions, COL.session);
    const legacy = await aeadSeal(
      key,
      deriveNonce(key, TBL.sessions, 'bob'),
      TEXT.encode('old'),
      buildAad(TBL.sessions, COL.session, 'bob'),
    );
    const fresh = await sealString(k, TBL.sessions, COL.session, 'bob', 'new');

    expect(await openString(k, TBL.sessions, COL.session, 'bob', legacy)).toBe('old');
    expect(await openString(k, TBL.sessions, COL.session, 'bob', fresh)).toBe('new');
    k.destroy();
  });
});

describe('tamper detection survives the switch', () => {
  // The dropped `expectedNonce` check was the stated reason for the
  // deterministic nonce. It detected nothing the AEAD tag misses.
  test('a flipped nonce byte is still rejected', async () => {
    const k = await km();
    const blob = await sealString(k, TBL.sessions, COL.session, 'alice', 'payload');
    const tampered = new Uint8Array(blob);
    tampered[0]! ^= 0x01;
    await expect(openString(k, TBL.sessions, COL.session, 'alice', tampered)).rejects.toThrow();
    k.destroy();
  });

  test('a blob moved to another row is still rejected (AAD binding)', async () => {
    const k = await km();
    const blob = await sealString(k, TBL.sessions, COL.session, 'alice', 'alice-secret');
    await expect(openString(k, TBL.sessions, COL.session, 'bob', blob)).rejects.toThrow();
    k.destroy();
  });
});