public static IObservable <Product> FindMostExpansivePurchase(
IObservable <Order> ordersHistory,
ProductsCatalog productsCatalog)
{
IObservable <Product> allOrdersProducts =
ordersHistory.SelectMany(order => order.ProductsIds.Select(id => productsCatalog.FindById(id)));
IObservable <long> maxProductPrice = allOrdersProducts.Max(price => price.Price);
return(maxProductPrice.SelectMany(price => allOrdersProducts.Where(product => product.Price == price)));
}
public IObservable <long> GetTotalPrice() => ProductsIds.ToObservable() .Select(id => _productsCatalog.FindById(id)) .Sum(product => product.Price);
