Feature: Add discounted bundles support to supermarket receipt system

java/pom.xml

@@ -45,8 +45,8 @@
                 <artifactId>maven-compiler-plugin</artifactId>
                 <version>3.8.0</version>
                 <configuration>
-                    <source>22</source>
-                    <target>22</target>
+                    <source>17</source>
+                    <target>17</target>
                 </configuration>
             </plugin>
         </plugins>

java/src/main/java/dojo/supermarket/model/BundleOffer.java

@@ -0,0 +1,22 @@
+package dojo.supermarket.model;
+
+import java.util.List;
+import java.util.Collections;
+
+public class BundleOffer {
+    private final List<Product> products;
+    private final double discountPercent;
+
+    public BundleOffer(List<Product> products, double discountPercent) {
+        this.products = Collections.unmodifiableList(products);
+        this.discountPercent = discountPercent;
+    }
+
+    public List<Product> getProducts() {
+        return products;
+    }
+
+    public double getDiscountPercent() {
+        return discountPercent;
+    }
+}

java/src/main/java/dojo/supermarket/model/ShoppingCart.java

@@ -72,4 +72,40 @@ void handleOffers(Receipt receipt, Map<Product, Offer> offers, SupermarketCatalo
             }
         }
     }
+
+    void handleBundleOffers(Receipt receipt, List<BundleOffer> bundleOffers, SupermarketCatalog catalog) {
+        for (BundleOffer bundleOffer : bundleOffers) {
+            // Calculate how many complete bundles can be made
+            int completeBundles = calculateCompleteBundles(bundleOffer.getProducts());
+
+            if (completeBundles > 0) {
+                // Calculate total price for one complete bundle
+                double bundlePrice = 0.0;
+                for (Product product : bundleOffer.getProducts()) {
+                    bundlePrice += catalog.getUnitPrice(product);
+                }
+
+                // Calculate discount for all complete bundles
+                double totalBundlePrice = bundlePrice * completeBundles;
+                double discountAmount = totalBundlePrice * bundleOffer.getDiscountPercent() / 100.0;
+
+                // Create bundle discount
+                String description = "Bundle discount (" + bundleOffer.getDiscountPercent() + "% off)";
+                Discount bundleDiscount = new Discount(bundleOffer.getProducts().get(0), description, -discountAmount);
+                receipt.addDiscount(bundleDiscount);
+            }
+        }
+    }
+
+    private int calculateCompleteBundles(List<Product> bundleProducts) {
+        int minQuantity = Integer.MAX_VALUE;
+
+        for (Product product : bundleProducts) {
+            double quantity = productQuantities.getOrDefault(product, 0.0);
+            int quantityAsInt = (int) quantity;
+            minQuantity = Math.min(minQuantity, quantityAsInt);
+        }
+
+        return minQuantity == Integer.MAX_VALUE ? 0 : minQuantity;
+    }
 }

java/src/main/java/dojo/supermarket/model/SpecialOfferType.java

@@ -5,4 +5,5 @@ public enum SpecialOfferType {
     TEN_PERCENT_DISCOUNT,
     TWO_FOR_AMOUNT,
     FIVE_FOR_AMOUNT,
+    BUNDLE,
 }

java/src/main/java/dojo/supermarket/model/Teller.java

@@ -3,11 +3,13 @@
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.ArrayList;
 
 public class Teller {
 
     private final SupermarketCatalog catalog;
     private final Map<Product, Offer> offers = new HashMap<>();
+    private final List<BundleOffer> bundleOffers = new ArrayList<>();
 
     public Teller(SupermarketCatalog catalog) {
         this.catalog = catalog;
@@ -17,6 +19,10 @@ public void addSpecialOffer(SpecialOfferType offerType, Product product, double
         offers.put(product, new Offer(offerType, product, argument));
     }
 
+    public void addBundleOffer(List<Product> products, double discountPercent) {
+        bundleOffers.add(new BundleOffer(products, discountPercent));
+    }
+
     public Receipt checksOutArticlesFrom(ShoppingCart theCart) {
         Receipt receipt = new Receipt();
         List<ProductQuantity> productQuantities = theCart.getItems();
@@ -28,6 +34,7 @@ public Receipt checksOutArticlesFrom(ShoppingCart theCart) {
             receipt.addProduct(p, quantity, unitPrice, price);
         }
         theCart.handleOffers(receipt, offers, catalog);
+        theCart.handleBundleOffers(receipt, bundleOffers, catalog);
 
         return receipt;
     }

java/src/test/java/dojo/supermarket/model/BundleDemo.java

@@ -0,0 +1,29 @@
+package dojo.supermarket.model;
+
+import dojo.supermarket.ReceiptPrinter;
+import java.util.Arrays;
+import java.util.List;
+
+public class BundleDemo {
+    public static void main(String[] args) {
+        SupermarketCatalog catalog = new FakeCatalog();
+        Product toothbrush = new Product("toothbrush", ProductUnit.EACH);
+        catalog.addProduct(toothbrush, 0.99);
+        Product toothpaste = new Product("toothpaste", ProductUnit.EACH);
+        catalog.addProduct(toothpaste, 1.79);
+
+        Teller teller = new Teller(catalog);
+        List<Product> bundleProducts = Arrays.asList(toothbrush, toothpaste);
+        teller.addBundleOffer(bundleProducts, 10.0);
+
+        ShoppingCart cart = new ShoppingCart();
+        cart.addItemQuantity(toothbrush, 1.0);
+        cart.addItemQuantity(toothpaste, 1.0);
+
+        Receipt receipt = teller.checksOutArticlesFrom(cart);
+
+        String receiptText = new ReceiptPrinter().printReceipt(receipt);
+        System.out.println(receiptText);
+        System.out.println("Total Price: €" + String.format("%.2f", receipt.getTotalPrice()));
+    }
+}

java/src/test/java/dojo/supermarket/model/SupermarketTest.java

@@ -5,6 +5,8 @@
 import org.junit.jupiter.api.Test;
 
 import java.util.Collections;
+import java.util.Arrays;
+import java.util.List;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 
@@ -41,5 +43,149 @@ void tenPercentDiscount() {
 
     }
 
+    @Test
+    void bundleDiscountBasicCase() {
+        SupermarketCatalog catalog = new FakeCatalog();
+        Product toothbrush = new Product("toothbrush", ProductUnit.EACH);
+        catalog.addProduct(toothbrush, 0.99);
+        Product toothpaste = new Product("toothpaste", ProductUnit.EACH);
+        catalog.addProduct(toothpaste, 1.79);
+
+        Teller teller = new Teller(catalog);
+        List<Product> bundleProducts = Arrays.asList(toothbrush, toothpaste);
+        teller.addBundleOffer(bundleProducts, 10.0);
+
+        ShoppingCart cart = new ShoppingCart();
+        cart.addItemQuantity(toothbrush, 1.0);
+        cart.addItemQuantity(toothpaste, 1.0);
+
+        // ACT
+        Receipt receipt = teller.checksOutArticlesFrom(cart);
+
+        // ASSERT
+        // Total should be (0.99 + 1.79) - 10% discount = 2.78 - 0.278 = 2.502
+        assertEquals(2.502, receipt.getTotalPrice(), 0.01);
+        assertEquals(1, receipt.getDiscounts().size());
+        assertEquals(2, receipt.getItems().size());
+
+        Discount discount = receipt.getDiscounts().get(0);
+        assertEquals(-0.278, discount.getDiscountAmount(), 0.01);
+        assertEquals("Bundle discount (10.0% off)", discount.getDescription());
+    }
+
+    @Test
+    void bundleDiscountOnlyCompleteBundle() {
+        SupermarketCatalog catalog = new FakeCatalog();
+        Product toothbrush = new Product("toothbrush", ProductUnit.EACH);
+        catalog.addProduct(toothbrush, 0.99);
+        Product toothpaste = new Product("toothpaste", ProductUnit.EACH);
+        catalog.addProduct(toothpaste, 1.79);
+
+        Teller teller = new Teller(catalog);
+        List<Product> bundleProducts = Arrays.asList(toothbrush, toothpaste);
+        teller.addBundleOffer(bundleProducts, 10.0);
+
+        ShoppingCart cart = new ShoppingCart();
+        cart.addItemQuantity(toothbrush, 2.0);  // 2 toothbrushes
+        cart.addItemQuantity(toothpaste, 1.0);  // 1 toothpaste
+
+        // ACT
+        Receipt receipt = teller.checksOutArticlesFrom(cart);
+
+        // ASSERT
+        // Only 1 complete bundle (limited by toothpaste), so discount on 0.99 + 1.79 = 2.78
+        // Total: (2 * 0.99 + 1 * 1.79) - 0.278 = 3.77 - 0.278 = 3.492
+        assertEquals(3.492, receipt.getTotalPrice(), 0.01);
+        assertEquals(1, receipt.getDiscounts().size());
+
+        Discount discount = receipt.getDiscounts().get(0);
+        assertEquals(-0.278, discount.getDiscountAmount(), 0.01);
+    }
+
+    @Test
+    void bundleDiscountMultipleBundles() {
+        SupermarketCatalog catalog = new FakeCatalog();
+        Product toothbrush = new Product("toothbrush", ProductUnit.EACH);
+        catalog.addProduct(toothbrush, 0.99);
+        Product toothpaste = new Product("toothpaste", ProductUnit.EACH);
+        catalog.addProduct(toothpaste, 1.79);
+
+        Teller teller = new Teller(catalog);
+        List<Product> bundleProducts = Arrays.asList(toothbrush, toothpaste);
+        teller.addBundleOffer(bundleProducts, 10.0);
+
+        ShoppingCart cart = new ShoppingCart();
+        cart.addItemQuantity(toothbrush, 2.0);
+        cart.addItemQuantity(toothpaste, 2.0);
+
+        // ACT
+        Receipt receipt = teller.checksOutArticlesFrom(cart);
+
+        // ASSERT
+        // 2 complete bundles, so discount on 2 * (0.99 + 1.79) = 2 * 2.78 = 5.56
+        // Discount: 5.56 * 0.1 = 0.556
+        // Total: 5.56 - 0.556 = 5.004
+        assertEquals(5.004, receipt.getTotalPrice(), 0.01);
+        assertEquals(1, receipt.getDiscounts().size());
+
+        Discount discount = receipt.getDiscounts().get(0);
+        assertEquals(-0.556, discount.getDiscountAmount(), 0.01);
+    }
+
+    @Test
+    void noBundleDiscountWhenMissingProduct() {
+        SupermarketCatalog catalog = new FakeCatalog();
+        Product toothbrush = new Product("toothbrush", ProductUnit.EACH);
+        catalog.addProduct(toothbrush, 0.99);
+        Product toothpaste = new Product("toothpaste", ProductUnit.EACH);
+        catalog.addProduct(toothpaste, 1.79);
+
+        Teller teller = new Teller(catalog);
+        List<Product> bundleProducts = Arrays.asList(toothbrush, toothpaste);
+        teller.addBundleOffer(bundleProducts, 10.0);
+
+        ShoppingCart cart = new ShoppingCart();
+        cart.addItemQuantity(toothbrush, 1.0);  // Only toothbrush, no toothpaste
+
+        // ACT
+        Receipt receipt = teller.checksOutArticlesFrom(cart);
+
+        // ASSERT
+        // No bundle discount since toothpaste is missing
+        assertEquals(0.99, receipt.getTotalPrice(), 0.01);
+        assertEquals(Collections.emptyList(), receipt.getDiscounts());
+    }
+
+    @Test
+    void bundleDiscountWithRegularOffers() {
+        SupermarketCatalog catalog = new FakeCatalog();
+        Product toothbrush = new Product("toothbrush", ProductUnit.EACH);
+        catalog.addProduct(toothbrush, 0.99);
+        Product toothpaste = new Product("toothpaste", ProductUnit.EACH);
+        catalog.addProduct(toothpaste, 1.79);
+        Product apples = new Product("apples", ProductUnit.KILO);
+        catalog.addProduct(apples, 1.99);
+
+        Teller teller = new Teller(catalog);
+        List<Product> bundleProducts = Arrays.asList(toothbrush, toothpaste);
+        teller.addBundleOffer(bundleProducts, 10.0);
+        teller.addSpecialOffer(SpecialOfferType.TEN_PERCENT_DISCOUNT, apples, 20.0);
+
+        ShoppingCart cart = new ShoppingCart();
+        cart.addItemQuantity(toothbrush, 1.0);
+        cart.addItemQuantity(toothpaste, 1.0);
+        cart.addItemQuantity(apples, 1.0);
+
+        // ACT
+        Receipt receipt = teller.checksOutArticlesFrom(cart);
+
+        // ASSERT
+        // Bundle discount: (0.99 + 1.79) * 0.1 = 0.278
+        // Apples discount: 1.99 * 0.2 = 0.398
+        // Total: (0.99 + 1.79 + 1.99) - 0.278 - 0.398 = 4.77 - 0.676 = 4.094
+        assertEquals(4.094, receipt.getTotalPrice(), 0.01);
+        assertEquals(2, receipt.getDiscounts().size());
+    }
+
 
 }