ExpenseRepository.java

import java.io.*;
import java.util.ArrayList;
import java.util.List;

public class ExpenseRepository {
    private final String FILE_NAME = "expenses.txt";
    private List<Expense> expenses;

    public ExpenseRepository() {
        this.expenses = new ArrayList<>();
        loadExpenses(); // Load data as soon as we start
    }

    // Add expense and save immediately
    public void add(Expense expense) {
        expenses.add(expense);
        saveExpenses();
    }

    // Get the list so Main can display it
    public List<Expense> getAll() {
        return expenses;
    }

    // --- PRIVATE METHODS (The Internal "Engine") ---

    // Save list to file
    private void saveExpenses() {
        try (BufferedWriter writer = new BufferedWriter(new FileWriter(FILE_NAME))) {
            for (Expense e : expenses) {
                writer.write(e.toFileString()); // Write "Coffee,5.0,Food"
                writer.newLine();               // Enter next line
            }
        } catch (IOException e) {
            System.out.println("Error saving expenses: " + e.getMessage());
        }
    }

    // Load file into list
    private void loadExpenses() {
        File file = new File(FILE_NAME);
        if (!file.exists()) return; // If no file exists, just start empty

        try (BufferedReader reader = new BufferedReader(new FileReader(file))) {
            String line;
            while ((line = reader.readLine()) != null) {
                expenses.add(Expense.fromFileString(line));
            }
        } catch (IOException e) {
            System.out.println("Error loading expenses: " + e.getMessage());
        }
    }

    // Remove an expense and update the file
    public void delete(Expense expense) {
        expenses.remove(expense);
        saveExpenses(); // Rewrite the file immediately
    }

}