Add setting of product quantity, add product id

src/main/java/org/example/Product.java

@@ -2,12 +2,14 @@ package org.example;
 
 public class Product {
 
+    int id;
     String name;
     float weight;
     float price;
     float vatPortion;
 
-    public Product(String name, float weight, float price, float vatPortion) {
+    public Product(int id, String name, float weight, float price, float vatPortion) {
+        this.id = id;
         this.name = name;
         this.weight = weight;
         this.price = price;

src/main/java/org/example/Shop.java

@@ -19,6 +19,19 @@ public class Shop {
         cart.removeProduct(product);
     }
 
+    public void setProductQuantityInCart(Product product, int quantity) {
+        cart.setProductQuantity(product, quantity);
+    }
+
+    public Product getProductById(int id) {
+        for (Product product : products) {
+            if (product.id == id) {
+                return product;
+            }
+        }
+        return null;
+    }
+
     public Order checkout() {
         Order order = cart.toOrder();
         cart.clearProducts();

src/main/java/org/example/ShoppingCart.java

@@ -10,18 +10,26 @@ public class ShoppingCart {
 
     public void addProduct(Product product) {
         int currentQuantity = products.getOrDefault(product, 0);
-        products.put(product, currentQuantity + 1);
+        setProductQuantity(product, currentQuantity + 1);
     }
 
     public void removeProduct(Product product) {
         int currentQuantity = products.getOrDefault(product, 0);
-        if (currentQuantity > 1) {
+        setProductQuantity(product, currentQuantity == 0 ? 0 : currentQuantity - 1);
-            products.put(product, currentQuantity - 1);
+    }
+
+    public void setProductQuantity(Product product, int quantity) {
+        if (quantity > 0) {
+            products.put(product, quantity);
         } else {
             products.remove(product);
         }
     }
 
+    public int getProductQuantity(Product product) {
+        return products.getOrDefault(product, 0);
+    }
+
     public void clearProducts() {
         products.clear();
     }