/**
 * extension/shared/crypto.js — Zero-knowledge cryptography for the extension.
 *
 * Mirrors the web app's crypto.js but:
 *  - Uses `crypto.subtle` (no `window.`) so it works in both popup and service worker.
 *  - deriveVaultKey uses extractable:true so the key can be serialised to
 *    chrome.storage.session (exportVaultKey / importVaultKey).
 */

const ExtCrypto = (() => {
  const subtle = crypto.subtle;

  // ── Helpers ─────────────────────────────────────────────────────────────────

  function strToBytes(str) { return new TextEncoder().encode(str); }

  function base64ToBytes(b64) {
    const bin = atob(b64);
    const out = new Uint8Array(bin.length);
    for (let i = 0; i < bin.length; i++) out[i] = bin.charCodeAt(i);
    return out;
  }

  function bytesToBase64(bytes) {
    let bin = '';
    bytes.forEach(b => (bin += String.fromCharCode(b)));
    return btoa(bin);
  }

  // ── PBKDF2 base key ─────────────────────────────────────────────────────────

  async function importPbkdf2Key(password) {
    return subtle.importKey('raw', strToBytes(password), 'PBKDF2', false, ['deriveBits', 'deriveKey']);
  }

  // ── Auth hash (sent to server for login/register) ───────────────────────────

  async function deriveAuthHash(password, email) {
    const baseKey = await importPbkdf2Key(password);
    const bits = await subtle.deriveBits(
      { name: 'PBKDF2', salt: strToBytes(email.toLowerCase()), iterations: 100_000, hash: 'SHA-256' },
      baseKey,
      256
    );
    return bytesToBase64(new Uint8Array(bits));
  }

  // ── Vault key (AES-256-GCM, extractable for session storage) ────────────────

  async function deriveVaultKey(password, enc_key_salt) {
    const baseKey = await importPbkdf2Key(password);
    return subtle.deriveKey(
      { name: 'PBKDF2', salt: base64ToBytes(enc_key_salt), iterations: 600_000, hash: 'SHA-256' },
      baseKey,
      { name: 'AES-GCM', length: 256 },
      true,  // extractable — needed to serialise into chrome.storage.session
      ['encrypt', 'decrypt']
    );
  }

  /** Serialise a CryptoKey to a JSON string for chrome.storage.session. */
  async function exportVaultKey(vaultKey) {
    const jwk = await subtle.exportKey('jwk', vaultKey);
    return JSON.stringify(jwk);
  }

  /** Deserialise a CryptoKey from chrome.storage.session. */
  async function importVaultKey(jwkStr) {
    const jwk = JSON.parse(jwkStr);
    return subtle.importKey('jwk', jwk, { name: 'AES-GCM', length: 256 }, true, ['encrypt', 'decrypt']);
  }

  // ── Encrypt / Decrypt ────────────────────────────────────────────────────────

  async function encryptItem(vaultKey, plainObj) {
    const iv = crypto.getRandomValues(new Uint8Array(12));
    const ct = await subtle.encrypt(
      { name: 'AES-GCM', iv },
      vaultKey,
      strToBytes(JSON.stringify(plainObj))
    );
    return { enc_data: bytesToBase64(new Uint8Array(ct)), iv: bytesToBase64(iv) };
  }

  async function decryptItem(vaultKey, enc_data, iv) {
    const pt = await subtle.decrypt(
      { name: 'AES-GCM', iv: base64ToBytes(iv) },
      vaultKey,
      base64ToBytes(enc_data)
    );
    return JSON.parse(new TextDecoder().decode(pt));
  }

  function generateSalt(byteLength = 16) {
    return bytesToBase64(crypto.getRandomValues(new Uint8Array(byteLength)));
  }

  return { deriveAuthHash, deriveVaultKey, exportVaultKey, importVaultKey, encryptItem, decryptItem, generateSalt };
})();