/// <summary>
        /// Add a new collection. Check if name the not exists
        /// </summary>
        public CollectionPage Add(string name)
        {
            if (string.IsNullOrEmpty(name))
            {
                throw new ArgumentNullException(nameof(name));
            }
            if (!CollectionPage.NamePattern.IsMatch(name))
            {
                throw LiteException.InvalidFormat(name);
            }

            _log.Write(Logger.COMMAND, "creating new collection '{0}'", name);

            // get header marked as dirty because I will use header after (and NewPage can get another header instance)
            var header = _pager.GetPage <HeaderPage>(0);

            // check limit count (8 bytes per collection = 4 to string length, 4 for uint pageID)
            if (header.CollectionPages.Sum(x => x.Key.Length + 8) + name.Length + 8 >= CollectionPage.MAX_COLLECTIONS_SIZE)
            {
                throw LiteException.CollectionLimitExceeded(CollectionPage.MAX_COLLECTIONS_SIZE);
            }

            // get new collection page (marked as dirty)
            var col = _pager.NewPage <CollectionPage>();

            // add this page to header page collection
            header.CollectionPages.Add(name, col.PageID);

            col.CollectionName = name;

            // set header page as dirty
            _pager.SetDirty(header);

            // create PK index
            var pk = _indexer.CreateIndex(col);

            pk.Field      = "_id";
            pk.Expression = "$._id";
            pk.Unique     = true;

            return(col);
        }