feat: improve Deliverable interface and introduce None strategy

- NullObject pattern used to cover initial state of the ShoppingCart

src/main/java/io/github/akadir/casestudy/delivery/Deliverable.java

@@ -1,7 +1,13 @@
 package io.github.akadir.casestudy.delivery;
 
+import io.github.akadir.casestudy.delivery.strategy.DeliveryStrategy;
+
 public interface Deliverable {
     int getProductCount();
 
     int getDeliveryCount();
+
+    DeliveryStrategy getDeliveryStrategy();
+
+    void setDeliveryStrategy(DeliveryStrategy deliveryStrategy);
 }

src/main/java/io/github/akadir/casestudy/delivery/strategy/None.java

@@ -0,0 +1,10 @@
+package io.github.akadir.casestudy.delivery.strategy;
+
+import io.github.akadir.casestudy.delivery.Deliverable;
+
+public class None implements DeliveryStrategy {
+    @Override
+    public double calculateDeliveryCost(Deliverable deliverable) {
+        return 0;
+    }
+}

src/main/java/io/github/akadir/casestudy/shopping/model/ShoppingCart.java

@@ -1,6 +1,8 @@
 package io.github.akadir.casestudy.shopping.model;
 
 import io.github.akadir.casestudy.delivery.Deliverable;
+import io.github.akadir.casestudy.delivery.strategy.DeliveryStrategy;
+import io.github.akadir.casestudy.delivery.strategy.None;
 import io.github.akadir.casestudy.discount.campaign.base.Campaign;
 import io.github.akadir.casestudy.discount.coupon.base.Coupon;
 import io.github.akadir.casestudy.product.model.Product;
@@ -13,9 +15,11 @@ public class ShoppingCart implements Deliverable {
     private Coupon appliedCoupon;
     private Campaign appliedCampaign;
     private double discount;
+    private DeliveryStrategy deliveryStrategy;
 
     public ShoppingCart() {
         this.products = new HashMap<>();
+        this.deliveryStrategy = new None();
     }
 
     public Map<Product, Integer> getProducts() {
@@ -55,7 +59,31 @@ public int getDeliveryCount() {
         return products.size();
     }
 
+    @Override
+    public DeliveryStrategy getDeliveryStrategy() {
+        return this.deliveryStrategy;
+    }
+
+    @Override
+    public void setDeliveryStrategy(DeliveryStrategy deliveryStrategy) {
+        this.deliveryStrategy = deliveryStrategy;
+    }
+
     public int getProductCount() {
         return products.values().stream().mapToInt(a -> a).sum();
     }
+
+    @Override
+    public String toString() {
+        final StringBuilder sb = new StringBuilder("\nDelivery count: ");
+
+        sb.append(getDeliveryCount()).append("\nProduct count: ")
+                .append(getProductCount()).append("\nPrice: ")
+                .append(getCartPrice()).append("\nDiscounts: ").append(discount)
+                .append("\nPrice to pay: ").append(getCartPrice() - discount)
+                .append("\nDelivery strategy: ").append(deliveryStrategy.getClass().getSimpleName())
+                .append("\nDelivery cost: ").append(deliveryStrategy.calculateDeliveryCost(this));
+
+        return sb.toString();
+    }
 }

src/test/java/io/github/akadir/casestudy/CaseStudyTest.java

@@ -11,4 +11,9 @@ public void create() {
                 .as("Crete CaseStudy should not throw exception")
                 .doesNotThrowAnyException();
     }
+
+    @Test(expected = Test.None.class)
+    public void whenMainMethodExecutedExpectNoExceptionThrown() {
+        CaseStudy.main(null);
+    }
 }

src/test/java/io/github/akadir/casestudy/delivery/strategy/NoneTest.java

@@ -0,0 +1,35 @@
+package io.github.akadir.casestudy.delivery.strategy;
+
+import io.github.akadir.casestudy.product.model.Product;
+import io.github.akadir.casestudy.shopping.service.ShoppingCartService;
+import io.github.akadir.casestudy.shopping.service.impl.ConcreteShoppingCartServiceImpl;
+import org.junit.Test;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class NoneTest {
+
+    @Test
+    public void whenNoneDeliveryCostCalculatedThenExpectZeroCost() {
+        DeliveryStrategy deliveryStrategy = new None();
+
+        ShoppingCartService shoppingCartService = new ConcreteShoppingCartServiceImpl();
+
+        Map<Product, Integer> productsBackup = new HashMap<>(shoppingCartService.getProducts());
+
+        assertThat(deliveryStrategy.calculateDeliveryCost(shoppingCartService.getShoppingCart()))
+                .as("Should return zero for shopping cart object")
+                .isZero();
+
+        assertThat(deliveryStrategy.calculateDeliveryCost(null))
+                .as("Should return zero for null")
+                .isZero();
+
+        assertThat(shoppingCartService.getProducts())
+                .as("Shopping cart should not be modified in delivery cost calculation")
+                .isEqualTo(productsBackup);
+    }
+}

src/test/java/io/github/akadir/casestudy/shopping/model/ShoppingCartTest.java

@@ -1,5 +1,6 @@
 package io.github.akadir.casestudy.shopping.model;
 
+import io.github.akadir.casestudy.delivery.strategy.None;
 import io.github.akadir.casestudy.product.model.Category;
 import io.github.akadir.casestudy.product.model.Product;
 import org.junit.Test;
@@ -31,6 +32,10 @@ public void whenShoppingCartCreatedThenExpectProductsInitializedAndDiscountsEmpt
         assertThat(shoppingCart.getDiscount())
                 .as("Cart discount should be zero")
                 .isZero();
+
+        assertThat(shoppingCart.getDeliveryStrategy())
+                .as("Cart initial delivery strategy should be None.class")
+                .isInstanceOf(None.class);
     }
 
 
@@ -62,5 +67,9 @@ public void whenProductAddedToShoppingCartThenExpectProductsIsNotEmptyAndPriceIn
         assertThat(shoppingCart.getDiscount())
                 .as("Cart discount should be zero")
                 .isZero();
+
+        assertThat(shoppingCart.getDeliveryStrategy())
+                .as("Cart initial delivery strategy should be None.class")
+                .isInstanceOf(None.class);
     }
 }