public CheckoutState Apply(CheckoutState checkoutState)
{
if (checkoutState.DiscountableItemsTotal == 0)
{
return(ToNotAppliedState(checkoutState));
}
var discountToApply = Math.Min(checkoutState.DiscountableItemsTotal, _value);
var newBasketTotal = checkoutState.CurrentTotal - discountToApply;
return(checkoutState.ToNewState(newBasketTotal, DiscountResult.CreateApplied(_id)));
}
private CheckoutState ToNotAppliedState(CheckoutState checkoutState)
{
var notAppliedResult = DiscountResult.CreateNotApplied(_id, GetNotAppliedMessage());
return(checkoutState.ToNewState(checkoutState.CurrentTotal, notAppliedResult));
}
