'use strict';

// ---------------------------------------------------------------------------
// E2E Encryption utilities (Web Crypto API)
// ---------------------------------------------------------------------------

let _encKey = null;

function bytesToBase64(buf) {
  const bytes = new Uint8Array(buf);
  let str = '';
  for (const b of bytes) str += String.fromCharCode(b);
  return btoa(str);
}

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

function bytesToHex(buf) {
  return Array.from(new Uint8Array(buf)).map(b => b.toString(16).padStart(2, '0')).join('');
}

function hexToBytes(hex) {
  const arr = new Uint8Array(hex.length / 2);
  for (let i = 0; i < arr.length; i++) arr[i] = parseInt(hex.slice(i*2, i*2+2), 16);
  return arr;
}

async function getOrCreateEncKey() {
  if (_encKey) return _encKey;
  const storageKey = `diora_enc_key_${window.USER_ID || 0}`;
  const stored = localStorage.getItem(storageKey);
  if (stored) {
    try {
      const raw = base64ToBytes(stored);
      _encKey = await crypto.subtle.importKey('raw', raw, {name: 'AES-GCM'}, false, ['encrypt', 'decrypt']);
      return _encKey;
    } catch (e) { /* fall through, generate new */ }
  }
  // Just signed in with the password: the login form left the derived key (99-init.js
  // moves it too, but this may run first).
  const pending = window.USER_ID ? localStorage.getItem('diora_pending_enc_key') : null;
  if (pending) {
    localStorage.setItem(storageKey, pending);
    localStorage.removeItem('diora_pending_enc_key');
    return getOrCreateEncKey();
  }
  // No key on this device (signed in through Authelia, or the storage was cleared): never
  // make a new one — that would lock the existing books away. Ask for the real one
  // (33-unlock.js); throws DioraLocked when the user puts it off.
  const raw = await dioraUnlock();
  _encKey = await crypto.subtle.importKey('raw', raw, {name: 'AES-GCM'}, false, ['encrypt', 'decrypt']);
  return _encKey;
}

async function encryptBytes(key, plainBytes) {
  const iv = crypto.getRandomValues(new Uint8Array(12));
  const ct = await crypto.subtle.encrypt({name: 'AES-GCM', iv}, key, plainBytes);
  return {iv: bytesToHex(iv), ciphertext: bytesToBase64(ct)};
}

async function decryptBytes(key, ivHex, ctB64) {
  const iv = hexToBytes(ivHex);
  const ct = base64ToBytes(ctB64);
  return crypto.subtle.decrypt({name: 'AES-GCM', iv}, key, ct);
}