private async Task HandleRetrievedOrderBook(string symbol, GdaxOrderBook orderBook) { var orders = orderBook.Asks.Select(order => _converters.GdaxOrderBookItemToOrderBookItem(symbol, false, order)) .Union(orderBook.Bids.Select(order => _converters.GdaxOrderBookItemToOrderBookItem(symbol, true, order))); await HandleOrderBookSnapshotAsync(symbol, DateTime.UtcNow, orders); _symbolsLastSequenceNumbers[symbol] = orderBook.Sequence; }