Calculators

Within Vendr, Calculators are small service implementations with the sole responsibility of calculating prices for a given aspect of an Order. There are five main Calculator services interfaces in Vendr.

• IShippingCalculator - Responsible for calculating the Shipping Method price / tax rate of a given Shipping Method.
• IPaymentCalculator - Responsible for calculating the Payment Method price / tax rate of a given Payment Method.
• IProductCalculator - Responsible for calculating the Product unit price / tax rate of a given Product.
• IOrderLineCalculator - Responsible for calculating the price / tax rate of a given OrderLine.
• IOrderCalculator - Responsible for calculating the entire Order.

All Calculator services can be replaced with alternative implementations should you wish to change how Vendr performs its calculations.

Defining a custom Calculator implementation

Whilst the individual Calculator interfaces may differ, the process for defining a custom Calculator implementation is largely the same for all of them, creating a new class that implements the default system Calculator you wish to replace and then overriding the relevant calculation methods.

public class MyProductCalculator : ProductCalculator
{
    public MyProductCalculator(ITaxService taxService, IStoreService storeService)
        : base(taxService, storeService)
    { }

    public override TaxRate CalculateProductTaxRate(IProductSnapshot productSnapshot, TaxSource taxSource, TaxRate fallbackTaxRate)
    {
        // Do custom tax rate calculation here
    }

    public override Price CalculateProductPrice(IProductSnapshot productSnapshot, Guid currencyId, TaxRate taxRate)
    {
        // Do custom price calculation here
    }
}

Registering a custom Calculator implementation

Calculators are registered via the IVendrBuilder interface using the AddUnique<TServiceInterface, TReplacementService>() method on the Services property where the TServiceInterface parameter is the Calculator interface Type you wish to replace and TReplacementService is the Type of your custom Calculator implementation.

public static class VendrBuilderExtensions
{
    public static IVendrBuilder AddMyServices(IVendrBuilder builder)
    {
        // Replacing the product calculator implementation
        builder.Services.AddUnique<IProductCalculator, MyProductCalculator>();

        // Return the builder to continue the chain
        return builder;
    }
}