sales-taxes-review.go

// goods/base.go

package goods

type base struct {
	name string
	price    float64
	exported bool
}

func (good *base) PriceWithTaxes() float64 {
	return good.price + good.price*0.1 + good.exportedPrice()
}


func (good *base) Name() string {
	return good.name
}

func (good *base) exportedPrice() float64 {
	if good.exported {
		return good.price * 0.05
	} else {
		return 0.0
	}
}


func NewBaseGood(name string, price float64, exported bool) *base {
	return &base{name: name, price: price, exported: exported}
}

// goods/book.go

package goods

type book struct {
	*base
}

func (good *book) PriceWithTaxes() float64 {
	return good.price + good.exportedPrice()
}

func NewBook(name string, price float64, exported bool) *book {
	return &book{base: NewBaseGood(name, price, exported)}
}

// goods/good.go

package goods

type Good interface {
	PriceWithTaxes() float64
	Name() string
}

// salestaxes.go

package salestaxes

import . "golearn/goods"

type ShoppingCart struct {
	Items []Good
}

func (cart *ShoppingCart) AddItem(good Good) {
	cart.Items = append(cart.Items, good)
}
func (cart *ShoppingCart) Total() float64 {
	result := 0.0
	for _, good := range cart.Items {
		result += good.PriceWithTaxes()
	}
	return result
}

// shoppingcartprinter.go

package salestaxes

import "fmt"

func PrintShoppingCart(cart ShoppingCart) {
	for _, elem := range cart.Items {
		fmt.Printf("%v with cost %g\n", elem.Name(), elem.PriceWithTaxes())
	}
	fmt.Printf("Total cost is %g\n")
}

// salestaxes_test.go

package salestaxes_test

import (
	. "golearn"
	. "golearn/goods"
	"testing"
)

func TestSalesTaxes(t *testing.T) {

	shoppingCart := ShoppingCart{Items: make([]Good, 0)}

	shoppingCart.AddItem(NewBaseGood("a good", 12.0, false))
	shoppingCart.AddItem(NewBaseGood("another good", 12.0, false))
	shoppingCart.AddItem(NewBook("a book", 10.0, true))

	expectedResult := 36.9

	PrintShoppingCart(shoppingCart)

	if shoppingCart.Total() != expectedResult {
		t.Errorf("Total is expected to be %g, it was %g",
			expectedResult,
			shoppingCart.Total())
	}

}