import java.util.*;
import java.io.*;
import java.util.*;

class User {
    private String username;
    private String password;

    public User(String username, String password) {
        this.username = username;
        this.password = password;
    }

    public String getUsername() {
        return username;
    }

    public String getPassword() {
        return password;
    }
}

class Expense {
    private String date;
    private String category;
    private double amount;

    public Expense(String date, String category, double amount) {
        this.date = date;
        this.category = category;
        this.amount = amount;
    }

    @Override
    public String toString() {
        return "Date: " + date + ", Category: " + category + ", Amount: $" + amount;
    }

    public String getCategory() {
        return category;
    }

    public double getAmount() {
        return amount;
    }
}

class ExpenseTracker {
    private List<User> users;
    private User currentUser;
    private List<Expense> expenses;
    private Scanner scanner;

    public ExpenseTracker() {
        users = new ArrayList<>();
        expenses = new ArrayList<>();
        scanner = new Scanner(System.in);
        loadUsers();
        loadExpenses();
    }

    public void run() {
        System.out.println("Expense Tracker");

        while (true) {
            System.out.println("\nMenu:");
            System.out.println("1. User Registration");
            System.out.println("2. Login");
            System.out.println("3. Add Expense");
            System.out.println("4. View Expenses");
            System.out.println("5. View Category-wise Summation");
            System.out.println("6. Logout");
            System.out.println("7. Exit");

            int choice = scanner.nextInt();
            scanner.nextLine(); // Consume the newline

            switch (choice) {
                case 1:
                    registerUser();
                    break;
                case 2:
                    login();
                    break;
                case 3:
                    addExpense();
                    break;
                case 4:
                    viewExpenses();
                    break;
                case 5:
                    viewCategorySummation();
                    break;
                case 6:
                    logout();
                    break;
                case 7:
                    saveData();
                    System.out.println("Exiting Expense Tracker. Goodbye!");
                    System.exit(0);
                default:
                    System.out.println("Invalid choice. Please try again.");
            }
        }
    }

    private void registerUser() {
        System.out.print("Enter username: ");
        String username = scanner.nextLine();
        System.out.print("Enter password: ");
        String password = scanner.nextLine();

        User newUser = new User(username, password);
        users.add(newUser);

        System.out.println("User registered successfully!");
    }

    private void login() {
        System.out.print("Enter username: ");
        String username = scanner.nextLine();
        System.out.print("Enter password: ");
        String password = scanner.nextLine();

        for (User user : users) {
            if (user.getUsername().equals(username) && user.getPassword().equals(password)) {
                currentUser = user;
                System.out.println("Login successful!");
                return;
            }
        }

        System.out.println("Invalid username or password. Please try again.");
    }

    private void addExpense() {
        if (currentUser == null) {
            System.out.println("You need to log in first.");
            return;
        }

        System.out.println("Enter Expense Details:");
        System.out.print("Date (MM/DD/YYYY): ");
        String date = scanner.nextLine();
        System.out.print("Category: ");
        String category = scanner.nextLine();
        System.out.print("Amount: $");
        double amount = scanner.nextDouble();
        scanner.nextLine(); // Consume the newline

        Expense expense = new Expense(date, category, amount);
        expenses.add(expense);

        System.out.println("Expense added successfully!");
    }

    private void viewExpenses() {
        if (currentUser == null) {
            System.out.println("You need to log in first.");
            return;
        }

        if (expenses.isEmpty()) {
            System.out.println("No expenses to display.");
        } else {
            System.out.println("All Expenses:");
            for (Expense expense : expenses) {
                System.out.println(expense);
            }
        }
    }

    private void viewCategorySummation() {
        if (currentUser == null) {
            System.out.println("You need to log in first.");
            return;
        }

        if (expenses.isEmpty()) {
            System.out.println("No expenses to calculate category-wise summation.");
        } else {
            Map<String, Double> categorySumMap = new HashMap<>();

            for (Expense expense : expenses) {
                categorySumMap.put(expense.getCategory(), categorySumMap.getOrDefault(expense.getCategory(), 0.0) + expense.getAmount());
            }

            System.out.println("Category-wise Summation:");
            for (Map.Entry<String, Double> entry : categorySumMap.entrySet()) {
                System.out.println(entry.getKey() + ": $" + entry.getValue());
            }
        }
    }

    private void logout() {
        currentUser = null;
        System.out.println("Logout successful!");
    }

    private void loadUsers() {
        try (Scanner fileScanner = new Scanner(new File("users.txt"))) {
            while (fileScanner.hasNextLine()) {
                String[] userFields = fileScanner.nextLine().split(",");
                users.add(new User(userFields[0], userFields[1]));
            }
        } catch (FileNotFoundException e) {
            System.out.println("No previous user data found.");
        }
    }

    private void loadExpenses() {
        try (Scanner fileScanner = new Scanner(new File("expenses.txt"))) {
            while (fileScanner.hasNextLine()) {
                String[] expenseFields = fileScanner.nextLine().split(",");
                expenses.add(new Expense(expenseFields[0], expenseFields[1], Double.parseDouble(expenseFields[2])));
            }
        } catch (FileNotFoundException e) {
            System.out.println("No previous expense data found.");
        }
    }

    private void saveData() {
        try (PrintWriter userWriter = new PrintWriter(new FileWriter("users.txt"));
             PrintWriter expenseWriter = new PrintWriter(new FileWriter("expenses.txt"))) {

            for (User user : users) {
                userWriter.println(user.getUsername() + "," + user.getPassword());
            }

            for (Expense expense : expenses) {
                expenseWriter.println(expense.toString());
            }

            System.out.println("Data saved successfully.");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

public class Main.java {
    public static void main(String[] args) {
        ExpenseTracker expenseTracker = new ExpenseTracker();
        expenseTracker.run();
    }
}