public Invoice CreateInvoice(int clientId, int year, int month)
{
var linesInvoices = InvoicesFor(repository.GetClientUsageDetails(clientId, year, month));
return(new Invoice
{
StartDate = new DateTime(year, month, 1),
EndDate = new DateTime(year, month, 1).AddMonths(1),
LineInvoices = linesInvoices,
TotalPrice = linesInvoices.Sum(i => i.TotalPrice),
AdditionalPrice = linesInvoices.Sum(i => i.OutOfPackage.TotalAdditionalPrice)
});
}