Price Categorizer with Discounts

import java.text.DecimalFormat;
import java.util.List;
import java.util.ArrayList;
import java.util.Map;
import java.util.TreeMap;
import java.util.Random;
import java.util.stream.Stream;
import java.util.stream.Collectors;

class Main {
    private final static List<String> CATEGORIES = List.of("Cheap", "Moderate", "Expensive");
    
    public static void main(String[] args) {
        List<Item> items = getItemsList();
        Map<String, List<Item>> itemsByName = getItemsByName(items);
        Map<String, List<Item>> itemsByCategories = categorizeItems(itemsByName);
        // itemsByCategories.entrySet().forEach(item -> System.out.println(item.getKey() + ": " + item.getValue().stream().map(i -> i.getName() + ": " + i.getPrice()).collect(Collectors.joining(", "))));
        printReport(itemsByCategories);
    }
    
    private static List<Item> getItemsList() {
        // Data generation
        final int minPrice = 1;
        final int maxPrice = 1000;
        Random rand = new Random();
        return List.of("Mouse", "Keyboard", "Battery", "Laptop", "Pad Mouse", "Ethernet Cable", "Notebook", "Pen")
            .stream()
            .flatMap(item -> Stream.generate(() -> item).limit(rand.nextInt(20 - 1) + 1))
            .map(product -> new Item(product, Math.round(rand.nextDouble(minPrice, maxPrice) * 100.0) / 100.0))
            .toList();
    }
    
    private static Map<String, List<Item>> getItemsByName(List<Item> items) {
        
        return items.stream()
            .collect(Collectors.groupingBy(item -> item.getName(), TreeMap::new, Collectors.toList()));
    }
    
    private static Map<String, List<Item>> categorizeItems(Map<String, List<Item>> items) {
        Map<String, List<Item>> itemsByCategories = Map.of("Cheap", new ArrayList<Item>(), "Moderate", new ArrayList<Item>(), "Expensive", new ArrayList<Item>());
        items.values().stream().flatMap(List::stream).forEach(item -> {
            if (item.getPrice() < 20.0) {
                var cheap = itemsByCategories.get("Cheap");
                cheap.add(item);
            } else if (item.getPrice() >= 20 && item.getPrice() <= 100) {
                var moderate = itemsByCategories.get("Moderate");
                moderate.add(item);
            } else {
                var expensive = itemsByCategories.get("Expensive");
                expensive.add(item);
            }
        });
        
        return itemsByCategories;
    }
    
    public static void printReport(Map<String, List<Item>> itemsByCategories) {
        final DecimalFormat decimalFormatter = new DecimalFormat("0.00");
        String output = CATEGORIES.stream().map(category -> {
            var itemsByCategory = itemsByCategories.get(category);
            
            StringBuilder message = new StringBuilder();
            
            message.append("Category: ");
            message.append(category);
            message.append("\n");
            message.append("Total Items: ");
            message.append(itemsByCategory.size());
            message.append("\n");
            
            var discount = 0.0;
            var totalByCategory = 0.0;
            var totalDiscount = 0.0;
            var totalAfterDiscount = 0.0;
            
            if (itemsByCategory.size() > 0) {
                if (category.equals("Cheap")) {
                    discount = 0.05;
                } else if (category.equals("Moderate")) {
                    discount = 0.1;
                } else if (category.equals("Expensive")) {
                    discount = 0.15;
                }
                
                totalByCategory = itemsByCategory.stream().map(Item::getPrice).collect(Collectors.summingDouble(n -> n));
                
                totalDiscount = totalByCategory * discount;
                totalAfterDiscount = totalByCategory - totalDiscount;
            }
            
            message.append("Total Discount: ");
            message.append(decimalFormatter.format(totalDiscount));
            
            message.append("\n");
            message.append("Total After Discount: ");
            message.append(decimalFormatter.format(totalAfterDiscount));
            
            return message.toString();
            
        })
        .collect(Collectors.joining("\n\n"));
        
        System.out.println(output);
    }
}

class Item {
    private String name;
    private double price;
    // constructor, getters, setters
    
    public Item(String name, double price) {
        this.name = name;
        this.price = price;
    }
    
    public String getName() {
        return this.name;
    }
    
    public double getPrice() {
        return this.price;
    }
}