//Countries should be extracted to a Class or better use EF to keep a contract between valid values in DB and code.
//if we think that there will be more country specific rules, we can introduce a new data structure that will keep country name and tax value
//so it is easy to extend it w/o a need of modifying this class.
public void CreateOrder(Order order)
{
// 1) potentially float can overflow, there will be a precision lost
// float can overflow when we sum it and when we multiply it (in this code)
// I would recommend changing it to Decimal
// or if we really have to keep float, casting float to decimal first and then performing sum and multiplication.
// I changed the way how total is calculated to mitigate it:
// old code: order.Total = Convert.ToDecimal(order.Items.Sum(_ => _.Price) * 1.2);
// new code: order.Total = order.Items.Select(x => CastToDecimal(x.Price)).Sum() * 1.2M;
// 2)Converting float to decimal directly can loose a precision, 125.609375f cast to decimal becomes 125.6094M
// old school way to mitigate the risk of precision lost is to first
// cast float to string as a "round trip" formatter and then create decimal from that string.
// 3) Also... we don't know who is using this method already, and because I am changing the way how total is calculated
// calculated total can be different, and it may be problematic for people that used this code in past.
// Again there are ways to mitigate it... I can elaborate on it more if asked.
if (order.Customer.Country == Countries.AU)
{
order.Total = order.Items.Select(x => CastToDecimal(x.Price)).Sum() * Countries.AUSalesTax;
}
else if (order.Customer.Country == Countries.UK)
{
order.Total = order.Items.Select(x => CastToDecimal(x.Price)).Sum() * Countries.UKSalesTax;
}
else //specification mentioned that Total should be generated for all orders, it means that also for order that are not in named above countries.
{
order.Total = order.Items.Select(x => CastToDecimal(x.Price)).Sum();
}
//Total is being calculated when we save an order to a DB, but there is no guarantee that some process
//will add extra orderItems for a given order directly into DB, and due to that when we get order from DB, total will be incorrect.
//I can elaborate on it more if asked.
_orderDataContext.CreateOrder(order);
}
/// <summary>
/// ToDo: Move the calculation logic to Order
/// </summary>
/// <param name="order"></param>
public void CreateOrder(Order order)
{
if (order.Customer.Country == "AU")
{
order.Total = Convert.ToDecimal(order.Items.Sum(_ => _.Price) * 1.1);
}
else if (order.Customer.Country == "UK")
{
order.Total = Convert.ToDecimal(order.Items.Sum(_ => _.Price) * 1.2);
}
_context.CreateOrder(order);
}