const SNAPSHOT_STORAGE_KEY = 'shine-ui-blockchain-snapshot-v1';

function normalizeLogin(login) {
  return String(login || '').trim().toLowerCase();
}

function storageBucketKey(login) {
  return normalizeLogin(login) || 'anonymous';
}

function decodeBase64ToBytes(base64) {
  const raw = String(base64 || '').trim();
  if (!raw) return new Uint8Array();
  const bin = atob(raw);
  const out = new Uint8Array(bin.length);
  for (let i = 0; i < bin.length; i += 1) out[i] = bin.charCodeAt(i);
  return out;
}

function readStorageMap() {
  try {
    const raw = localStorage.getItem(SNAPSHOT_STORAGE_KEY);
    const parsed = raw ? JSON.parse(raw) : {};
    return parsed && typeof parsed === 'object' ? parsed : {};
  } catch {
    return {};
  }
}

function writeStorageMap(value) {
  try {
    localStorage.setItem(SNAPSHOT_STORAGE_KEY, JSON.stringify(value || {}));
  } catch {
    // ignore localStorage errors
  }
}

export function readStoredBlockchainSnapshot(login) {
  const key = storageBucketKey(login);
  const map = readStorageMap();
  const value = map?.[key];
  return value && typeof value === 'object' ? value : null;
}

export function saveStoredBlockchainSnapshot(login, snapshot) {
  const key = storageBucketKey(login);
  const map = readStorageMap();
  map[key] = {
    ...snapshot,
    savedAtMs: Date.now(),
  };
  writeStorageMap(map);
  return map[key];
}

export function clearStoredBlockchainSnapshot(login) {
  const key = storageBucketKey(login);
  const map = readStorageMap();
  delete map[key];
  writeStorageMap(map);
}

export async function buildBlockchainSnapshotFile({
  authService,
  login,
  blockchainName,
  lastBlockNumber,
} = {}) {
  const cleanLogin = normalizeLogin(login);
  const cleanBlockchainName = String(blockchainName || '').trim();
  const maxBlockNumber = Number(lastBlockNumber);
  if (!authService?.ws?.request) throw new Error('Сервис сервера недоступен.');
  if (!cleanLogin) throw new Error('Не указан логин.');
  if (!cleanBlockchainName) throw new Error('Не указано имя блокчейна.');
  if (!Number.isFinite(maxBlockNumber) || maxBlockNumber < 0) {
    throw new Error('На сервере нет блоков для слепка.');
  }

  const parts = [];
  let totalBytes = 0;
  for (let blockNumber = 0; blockNumber <= maxBlockNumber; blockNumber += 1) {
    const response = await authService.ws.request('GetBlockchainBlock', {
      blockchainName: cleanBlockchainName,
      blockNumber,
    });
    if (response?.status !== 200) {
      const message = String(response?.payload?.message || response?.message || 'Не удалось получить блок.');
      throw new Error(`Не удалось скачать блок ${blockNumber}: ${message}`);
    }
    const blockBytes = decodeBase64ToBytes(response?.payload?.blockBytesB64 || '');
    parts.push(blockBytes);
    totalBytes += blockBytes.length;
  }

  const file = new File(parts, `${cleanBlockchainName}.shine-blockchain`, {
    type: 'application/octet-stream',
    lastModified: Date.now(),
  });

  return {
    file,
    blockCount: maxBlockNumber + 1,
    totalBytes,
    lastBlockNumber: maxBlockNumber,
    login: cleanLogin,
    blockchainName: cleanBlockchainName,
  };
}