discount codes (step3)

src/main/java/group/rohlik/application/CartDiscountAdder.java

@@ -7,7 +7,6 @@
 import lombok.AllArgsConstructor;
 import org.springframework.stereotype.Service;
 import org.springframework.transaction.annotation.Transactional;
-import org.springframework.util.Assert;
 
 @AllArgsConstructor
 @Service
@@ -20,15 +19,8 @@ public class CartDiscountAdder {
     public void add(long cartId, String code) {
         Cart cart = cartRepository.findById(cartId).orElseThrow();
         Discount discount = discountRepository.findByCode(code).orElseThrow();
-        applyDiscount(cart, discount);
+        cart.applyDiscount(discount);
 
         cartRepository.save(cart);
     }
-
-    public void applyDiscount(Cart cart, Discount discount) {
-        //@todo suspicious code - should we move this logic to cart entity?
-        Assert.isTrue(!cart.getDiscounts().contains(discount), "Discount already applied");
-
-        cart.getDiscounts().add(discount);
-    }
 }

src/main/java/group/rohlik/entity/Cart.java

@@ -82,10 +82,13 @@ private double totalDiscountsPrice() {
     }
 
     public double totalPrice() {
-        return BigDecimal
-                .valueOf(totalLinesPrice() - totalDiscountsPrice())
-                .setScale(2, RoundingMode.CEILING)
-                .doubleValue();
+        return Math.max(
+                0,
+                BigDecimal
+                        .valueOf(totalLinesPrice() - totalDiscountsPrice())
+                        .setScale(2, RoundingMode.CEILING)
+                        .doubleValue()
+        );
     }
 
     public Integer quantityOfProduct(String sku) {
@@ -96,4 +99,16 @@ public Integer quantityOfProduct(String sku) {
                 .map(CartLine::getQuantity)
                 .orElse(0);
     }
+
+    public boolean hasDiscount(String name) {
+        return discounts
+                .stream()
+                .anyMatch(line -> line.getName().equals(name));
+    }
+
+    public void applyDiscount(Discount discount) {
+        Assert.isTrue(!discounts.contains(discount), "Discount already applied");
+
+        discounts.add(discount);
+    }
 }

src/test/java/group/rohlik/acceptance/steps/CartSteps.java

@@ -1,9 +1,7 @@
 package group.rohlik.acceptance.steps;
 
 import group.rohlik.entity.Cart;
-import group.rohlik.entity.CartLine;
 import group.rohlik.entity.CartRepository;
-import group.rohlik.entity.Discount;
 import io.cucumber.gherkin.internal.com.eclipsesource.json.JsonObject;
 import io.cucumber.java.Before;
 import io.cucumber.java.en.Given;
@@ -17,9 +15,6 @@
 import org.springframework.http.HttpMethod;
 import org.springframework.http.MediaType;
 
-import java.math.BigDecimal;
-import java.math.RoundingMode;
-
 
 @RequiredArgsConstructor
 public class CartSteps {
@@ -83,6 +78,35 @@ public void thereShouldNotBeProductInCart(String sku) {
         Assertions.assertTrue(cart.quantityOfProduct(sku) == 0, String.format("Product %s should not be present", sku));
     }
 
+    @Then("there should be discount {string} in my cart")
+    public void thereShouldBeDiscountInCart(String name) {
+        Cart cart = currentCart();
+
+        Assertions.assertTrue(cart.hasDiscount(name), String.format("Discount %s should be present", name));
+    }
+
+    @Then("there shouldn't be discounts in my cart")
+    public void thereShouldNotBeDiscountsInCart() {
+        Cart cart = currentCart();
+
+        Assertions.assertEquals(0, cart.getDiscounts().size());
+    }
+
+    @When("I apply {string} discount to my cart")
+    public void iApplyDiscountToMyCart(String code) {
+        JsonObject body = new JsonObject();
+        body.add("code", code);
+        HttpHeaders headers = new HttpHeaders();
+        headers.setContentType(MediaType.APPLICATION_JSON);
+
+        template.exchange(
+                String.format("/carts/%d/discounts", currentCartId),
+                HttpMethod.POST,
+                new HttpEntity<>(body.toString(), headers),
+                String.class
+        );
+    }
+
     private Cart currentCart() {
         return cartRepository.findById(currentCartId).orElseThrow();
     }

src/test/resources/features/add_discount_to_cart.feature

@@ -0,0 +1,39 @@
+Feature: Add discount to cart
+  As a Rohlik customer
+  I want to apply discounts to my cart
+  so that I can save some money
+
+  Background:
+    Given the following products exist:
+      | sku | name     | price |
+      | 001 | potatoes | 2.5   |
+      | 002 | water    | 0.95  |
+    And there is a cart discount "free shipping" for 1 euros with code "FREE-SHIPPING"
+    And there is a cart discount "special offer" for 10 euros with code "SPECIAL-OFFER"
+    And I have a cart
+
+  Scenario: No discounts
+    When I add 2 units of product "001" to my cart
+    Then the cart's total cost should be 5.0 euros
+    But there shouldn't be discounts in my cart
+
+  Scenario: Add discount
+    Given I add 2 units of product "001" to my cart
+    When I apply "FREE-SHIPPING" discount to my cart
+    Then the cart's total cost should be 4.0 euros
+    And there should be discount "free shipping" in my cart
+
+  Scenario: Add discount only apply once
+    Given I add 2 units of product "001" to my cart
+    And I apply "FREE-SHIPPING" discount to my cart
+    When I apply "FREE-SHIPPING" discount to my cart
+    Then the cart's total cost should be 4.0 euros
+    And there should be discount "free shipping" in my cart
+
+  Scenario: Cart total should be always positive
+    Given I add 2 units of product "001" to my cart
+    And I apply "FREE-SHIPPING" discount to my cart
+    When I apply "SPECIAL-OFFER" discount to my cart
+    Then the cart's total cost should be 0.0 euros
+    And there should be discount "free shipping" in my cart
+    And there should be discount "special offer" in my cart