/* ────────────────────────────────────────────────────────────────
   AES‑GCM field‑level encryption helper backed by Google Cloud KMS
   ---------------------------------------------------------------- */
import {
  randomBytes, createCipheriv, createDecipheriv,
  createHmac, createHash,
} from 'crypto';
import { KeyManagementServiceClient }   from '@google-cloud/kms';
import { SecretManagerServiceClient }   from '@google-cloud/secret-manager';
import {
  open as fsOpen, readFile, mkdir,
} from 'fs/promises';
import { constants as FS } from 'fs';
import path from 'path';

/* ── constants ─────────────────────────────────────────────── */
const ALGO = 'aes-256-gcm';
const IV_LEN = 12;          // 96‑bit nonce
const TAG_LEN = 16;         // 128‑bit auth‑tag
const MAGIC = 'gcm:';       // ciphertext prefix

/* ── env config (docker‑compose) ────────────────────────────── */
const KMS_KEY   = (process.env.KMS_KEY_NAME || '').trim();
const EDEK_PATH = (process.env.DEK_PATH     || '').trim();       // /run/secrets/<env>/dek.enc
const ENV_NAME  = (process.env.ENV_NAME     || 'dev').trim();    // dev | staging | prod
const PROJECT   = (process.env.PROJECT      || 'aptivaai-dev').trim();

if (!EDEK_PATH) {
  console.error('FATAL: DEK_PATH env var is unset — check deploy script');
  process.exit(1);
}
const FPR_PATH  = path.join(path.dirname(EDEK_PATH), 'dek.fpr');
const SM_SECRET = `WRAPPED_DEK_${ENV_NAME.toUpperCase()}`;

let dek;            // plaintext DEK in memory
let initPromise;    // so parallel callers wait only once

/* ── helper: upload a backup copy to Secret Manager ─────────── */
async function backupToSecretManager (ciphertext /* Buffer */) {
  const sm = new SecretManagerServiceClient();

  /* ensure the secret exists – idempotent */
  try {
    await sm.getSecret({ name: `projects/${PROJECT}/secrets/${SM_SECRET}` });
  } catch {
    await sm.createSecret({
      parent   : `projects/${PROJECT}`,
      secretId : SM_SECRET,
      secret   : { replication: { automatic: {} } },
    });
  }

  /* add a new version (binary) */
  await sm.addSecretVersion({
    parent  : `projects/${PROJECT}/secrets/${SM_SECRET}`,
    payload : { data: ciphertext },
  });
  console.log(`[ENCRYPT] ⬆️  copied dek.enc to Secret Manager (${SM_SECRET})`);
}

/* ─────────────────────────────────────────────────────────────
   One‑time DEK unwrap / generate + fingerprint validation
   ──────────────────────────────────────────────────────────── */
export async function initEncryption () {
  if (dek)              return;
  if (initPromise)      return initPromise;

  initPromise = (async () => {
    const kms = new KeyManagementServiceClient();
    const dir = path.dirname(EDEK_PATH);

    /* 1 – optimistic: use existing wrapped key */
    try {
      const wrapped = await readFile(EDEK_PATH);
      dek = (await kms.decrypt({ name: KMS_KEY, ciphertext: wrapped }))[0].plaintext;
    } catch (err) {
      if (err.code !== 'ENOENT') throw err;  // genuine failure

      /* 2 – first container wins: create DEK & wrap */
      await mkdir(dir, { recursive: true });
      try {
        const fh = await fsOpen(EDEK_PATH, FS.O_WRONLY | FS.O_CREAT | FS.O_EXCL, 0o600);
        try {
          dek = randomBytes(32);
          const [resp] = await kms.encrypt({ name: KMS_KEY, plaintext: dek });
          const wrapped = resp.ciphertext;        // Buffer

          await fh.writeFile(wrapped);            // primary copy
          backupToSecretManager(wrapped)          // async fire‑and‑forget
            .catch(e => console.error('[ENCRYPT] backup failed:', e.message));
        } finally {
          await fh.close();
        }
      } catch (race) {
        if (race.code !== 'EEXIST') throw race;  // unexpected
        /* another container already wrote the file */
        const wrapped = await readFile(EDEK_PATH);
        dek = (await kms.decrypt({ name: KMS_KEY, ciphertext: wrapped }))[0].plaintext;
      }
    }

    /* 3 – fingerprint validation */
    const fp = createHash('sha256').update(dek).digest('hex').slice(0, 16);
    try {
      const onDisk = (await readFile(FPR_PATH, 'utf8')).trim();
      if (onDisk !== fp) throw new Error(`fingerprint mismatch: ${onDisk} ≠ ${fp}`);
    } catch (err) {
      if (err.code !== 'ENOENT') throw err;   // real error

      /* write fingerprint (first‑writer wins) */
      await fsOpen(FPR_PATH, FS.O_WRONLY | FS.O_CREAT | FS.O_EXCL, 0o444)
            .then(fh => fh.writeFile(fp + '\n').finally(() => fh.close()))
            .catch(async (dup) => {
              if (dup.code !== 'EEXIST') throw dup;
              const onDisk = (await readFile(FPR_PATH, 'utf8')).trim();
              if (onDisk !== fp) throw new Error(`fingerprint mismatch: ${onDisk} ≠ ${fp}`);
            });
    }

    process.env.DEBUG_ENCRYPTION === 'true'
      && console.log('[ENCRYPT] DEK ready – fp', fp);
  })();

  return initPromise;
}

export const SENTINEL = 'aptiva-canary-v1';

/* ── optional DB sentinel helper ────────────────────────────── */
export async function verifyCanary(pool) {
  // nothing to verify yet → first ever launch before server1 seeded it
  const [rows] = await pool.query(
    'SELECT value FROM encryption_canary WHERE id = 1 LIMIT 1'
  );
  if (!rows || rows.length === 0) return;

  const val = rows[0].value;
  let plain;
  try {
    plain = decrypt(val);
  } catch {
    throw new Error('DEK cannot decrypt sentinel row');
  }

  if (plain !== SENTINEL) {
    throw new Error('DEK mismatch: sentinel value differs');
  }
}

/* ── crypto helpers (encrypt / decrypt / hash) ─────────────── */
export function encrypt (plain) {
  if (plain == null || isEncrypted(plain)) return plain;
  const iv = randomBytes(IV_LEN);
  const cipher = createCipheriv(ALGO, dek, iv);
  const ct = Buffer.concat([cipher.update(String(plain), 'utf8'), cipher.final()]);
  const tag = cipher.getAuthTag();
  return MAGIC + Buffer.concat([iv, tag, ct]).toString('base64');
}

export function decrypt (val) {
  if (!isEncrypted(val)) return val;
  const buf = Buffer.from(val.slice(MAGIC.length), 'base64');
  const iv  = buf.subarray(0, IV_LEN);
  const tag = buf.subarray(IV_LEN, IV_LEN + TAG_LEN);
  const ct  = buf.subarray(IV_LEN + TAG_LEN);
  const decipher = createDecipheriv(ALGO, dek, iv);
  decipher.setAuthTag(tag);
  return Buffer.concat([decipher.update(ct), decipher.final()]).toString('utf8');
}

export function hashForLookup (plain) {
  if (plain == null) return null;
  return createHmac('sha256', dek).update(String(plain)).digest('hex');
}

export function isEncrypted (val) {
  return typeof val === 'string'
      && val.startsWith(MAGIC)
      && /^[A-Za-z0-9+/]+={0,2}$/.test(val.slice(MAGIC.length));
}