[NP] Online Shop

import java.time.LocalDateTime;
import java.util.*;
import java.util.stream.Collectors;
import java.util.stream.IntStream;
import java.time.LocalDateTime;
import java.util.*;
import java.util.stream.Collectors;
import java.util.Comparator;

class Product {
    final static Comparator<Product> OLDEST_FIRST = Comparator.comparing(Product::getCreatedAt);
    final static Comparator<Product> LOWEST_PRICE_FIRST = Comparator.comparing(Product::getPrice);
    final static Comparator<Product> LEAST_SOLD_FIRST = Comparator.comparing(Product::getQuantitySold);

    String category;
    String id;
    String name;
    LocalDateTime createdAt;
    double price;
    int quantitySold;


    public Product(String category, String id, String name, LocalDateTime createdAt, double price) {
        this.category = category;
        this.id = id;
        this.name = name;
        this.createdAt = createdAt;
        this.price = price;
        this.quantitySold= 0;
    }

    public int getQuantitySold() {
        return quantitySold;
    }

    public String getCategory() {
        return category;
    }

    public String getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public LocalDateTime getCreatedAt() {
        return createdAt;
    }

    public double getPrice() {
        return price;
    }

    public double getTransaction(int quantity){
        quantitySold+=quantity;
        return price*quantitySold;
    }

    @Override
    public String toString() {
        return "Product{" +

                "id='" + id + '\'' +
                ", name='" + name + '\'' +
                ", createdAt=" + createdAt +
                ", price=" + price +
                ", quantitySold=" + quantitySold +
                '}';
    }
}
class OnlineShop {
    Map<String,Product> products;


    OnlineShop() {
    products= new HashMap<>();
    }

    void addProduct(String category, String id, String name, LocalDateTime createdAt, double price){
        products.putIfAbsent(id,new Product(category,id,name,createdAt,price));
    }

    double buyProduct(String id, int quantity) throws ProductNotFoundException{
        if(products.get(id)==null)
            throw new ProductNotFoundException(id);
        return products.get(id).getTransaction(quantity);
        //return 0.0;
    }

    List<List<Product>> listProducts(String category, ComparatorType comparatorType, int pageSize) {
        List<List<Product>> result = new ArrayList<>();
        Comparator<Product> comparator;
        if(comparatorType.equals(ComparatorType.HIGHEST_PRICE_FIRST))
            comparator= Product.LOWEST_PRICE_FIRST.reversed();
        else if(comparatorType.equals(ComparatorType.MOST_SOLD_FIRST))
            comparator= Product.LEAST_SOLD_FIRST.reversed();
        else if(comparatorType.equals(ComparatorType.LEAST_SOLD_FIRST))
            comparator= Product.LEAST_SOLD_FIRST;
        else if(comparatorType.equals(ComparatorType.LOWEST_PRICE_FIRST))
            comparator= Product.LOWEST_PRICE_FIRST;
        else if(comparatorType.equals(ComparatorType.NEWEST_FIRST))
            comparator= Product.OLDEST_FIRST.reversed();
        else
            comparator= Product.OLDEST_FIRST;

        List<Product> productsFromCategory = products.values().stream().filter(i->i.getCategory()
                .equals(category))
                .sorted(comparator)
                .collect(Collectors.toList());
        if(productsFromCategory.size()==0)
            productsFromCategory= products.values().stream().sorted(comparator).collect(Collectors.toList());
        for(int i=0;i<productsFromCategory.size();i+=pageSize){
            List<Product> page = new ArrayList<>();
            for(int j=0;j<pageSize;j++){
                if(i+j==productsFromCategory.size())
                    break;
                page.add(productsFromCategory.get(i+j));
            }

            result.add(page);
        }
        return result;
    }

}
enum ComparatorType {
    NEWEST_FIRST,
    OLDEST_FIRST,
    LOWEST_PRICE_FIRST,
    HIGHEST_PRICE_FIRST,
    MOST_SOLD_FIRST,
    LEAST_SOLD_FIRST
}

class ProductNotFoundException extends Exception {
    ProductNotFoundException(String id) {
        super(String.format("Product with id %s does not exist in the online shop!",id));
    }
}



public class OnlineShopTest {

    public static void main(String[] args) {
        OnlineShop onlineShop = new OnlineShop();
        double totalAmount = 0.0;
        Scanner sc = new Scanner(System.in);
        String line;
        while (sc.hasNextLine()) {
            line = sc.nextLine();
            String[] parts = line.split("\\s+");
            if (parts[0].equalsIgnoreCase("addproduct")) {
                String category = parts[1];
                String id = parts[2];
                String name = parts[3];
                LocalDateTime createdAt = LocalDateTime.parse(parts[4]);
                double price = Double.parseDouble(parts[5]);
                onlineShop.addProduct(category, id, name, createdAt, price);
            } else if (parts[0].equalsIgnoreCase("buyproduct")) {
                String id = parts[1];
                int quantity = Integer.parseInt(parts[2]);
                try {
                    totalAmount += onlineShop.buyProduct(id, quantity);
                } catch (ProductNotFoundException e) {
                    System.out.println(e.getMessage());
                }
            } else {
                String category = parts[1];
                if (category.equalsIgnoreCase("null"))
                    category=null;
                String comparatorString = parts[2];
                int pageSize = Integer.parseInt(parts[3]);
                ComparatorType comparatorType = ComparatorType.valueOf(comparatorString);
                printPages(onlineShop.listProducts(category, comparatorType, pageSize));
            }
        }
        System.out.println("Total revenue of the online shop is: " + totalAmount);

    }

    private static void printPages(List<List<Product>> listProducts) {
        for (int i = 0; i < listProducts.size(); i++) {
            System.out.println("PAGE " + (i + 1));
            listProducts.get(i).forEach(System.out::println);
        }
    }
}