Splitwise

import java.util.*;

// Enum to represent the status of a transaction (optional)
public enum TransactionStatus {
    PENDING,
    SETTLED
}

// Interface for User
public interface User {
    String getId();
    String getName();
    String getEmail();
    void addExpense(Expense expense);
    List<Expense> getExpenses();
}

// Interface for Expense
import java.util.Map;

public interface Expense {
    String getId();
    String getDescription();
    double getTotalAmount();
    User getPaidBy();
    Map<User, Double> getSplitDetails();
}

// Interface for Settlement
public interface Settlement {
    User getOwedBy();
    User getOwedTo();
    double getAmount();
}

// Implementation of User
public class UserImpl implements User {
    private String id;
    private String name;
    private String email;
    private List<Expense> expenses;

    public UserImpl(String id, String name, String email) {
        this.id = id;
        this.name = name;
        this.email = email;
        this.expenses = new ArrayList<>();
    }

    @Override
    public String getId() {
        return id;
    }

    @Override
    public String getName() {
        return name;
    }

    @Override
    public String getEmail() {
        return email;
    }

    @Override
    public void addExpense(Expense expense) {
        expenses.add(expense);
    }

    @Override
    public List<Expense> getExpenses() {
        return expenses;
    }
}

// Implementation of Expense
import java.util.Map;

public class ExpenseImpl implements Expense {
    private String id;
    private String description;
    private double totalAmount;
    private User paidBy;
    private Map<User, Double> splitDetails;

    public ExpenseImpl(String id, String description, double totalAmount, User paidBy, Map<User, Double> splitDetails) {
        this.id = id;
        this.description = description;
        this.totalAmount = totalAmount;
        this.paidBy = paidBy;
        this.splitDetails = splitDetails;
    }

    @Override
    public String getId() {
        return id;
    }

    @Override
    public String getDescription() {
        return description;
    }

    @Override
    public double getTotalAmount() {
        return totalAmount;
    }

    @Override
    public User getPaidBy() {
        return paidBy;
    }

    @Override
    public Map<User, Double> getSplitDetails() {
        return splitDetails;
    }
}

// Implementation of Settlement
public class SettlementImpl implements Settlement {
    private User owedBy;
    private User owedTo;
    private double amount;

    public SettlementImpl(User owedBy, User owedTo, double amount) {
        this.owedBy = owedBy;
        this.owedTo = owedTo;
        this.amount = amount;
    }

    @Override
    public User getOwedBy() {
        return owedBy;
    }

    @Override
    public User getOwedTo() {
        return owedTo;
    }

    @Override
    public double getAmount() {
        return amount;
    }
}

// Main Application to demonstrate the Splitwise-like system
public class SplitwiseApp {

    private List<User> users;
    private List<Expense> expenses;
    private List<Settlement> settlements;

    public SplitwiseApp() {
        this.users = new ArrayList<>();
        this.expenses = new ArrayList<>();
        this.settlements = new ArrayList<>();
    }

    public void addUser(User user) {
        users.add(user);
    }

    public void addExpense(Expense expense) {
        expenses.add(expense);
        expense.getPaidBy().addExpense(expense);
        calculateSettlements(expense);
    }

    private void calculateSettlements(Expense expense) {
        User paidBy = expense.getPaidBy();
        Map<User, Double> splitDetails = expense.getSplitDetails();

        for (Map.Entry<User, Double> entry : splitDetails.entrySet()) {
            User user = entry.getKey();
            double amountOwed = entry.getValue();
            if (user != paidBy) {
                settlements.add(new SettlementImpl(user, paidBy, amountOwed));
            }
        }
    }

    public List<Settlement> getSettlements() {
        return settlements;
    }

    public static void main(String[] args) {
        SplitwiseApp app = new SplitwiseApp();

        // Create users
        User user1 = new UserImpl(UUID.randomUUID().toString(), "Alice", "alice@example.com");
        User user2 = new UserImpl(UUID.randomUUID().toString(), "Bob", "bob@example.com");
        User user3 = new UserImpl(UUID.randomUUID().toString(), "Charlie", "charlie@example.com");

        app.addUser(user1);
        app.addUser(user2);
        app.addUser(user3);

        // Create an expense
        Map<User, Double> splitDetails = new HashMap<>();
        splitDetails.put(user1, 30.0);
        splitDetails.put(user2, 40.0);
        splitDetails.put(user3, 30.0);

        Expense expense = new ExpenseImpl(UUID.randomUUID().toString(), "Dinner", 100.0, user2, splitDetails);
        app.addExpense(expense);

        // Get and print settlements
        List<Settlement> settlements = app.getSettlements();
        for (Settlement settlement : settlements) {
            System.out.println(settlement.getOwedBy().getName() + " owes " + settlement.getOwedTo().getName() + ": $" + settlement.getAmount());
        }
    }
}