// Import dart:io to allow reading input from the console
import 'dart:io';

void main() {
  // Constant for tax rate
  const double TAX_RATE = 0.15;

  // Lists to store income and expense entries
  List<Map<String, double>> incomeList = [];
  List<Map<String, double>> expenseList = [];

  // Welcome message
  print('Welcome to the Budget Management Application!');

  // Infinite loop to continuously show menu until user exits
  while (true) {
    // Display menu options
    print('\n--- Menu ---');
    print('1. Add Income');
    print('2. Add Expense');
    print('3. View Summary');
    print('4. Exit');

    // Prompt user to enter choice
    stdout.write('Enter your choice (1-4): ');
    String? choice = stdin.readLineSync();

    if (choice == null) continue; // Skip if input is null

    // Handle user's choice using switch
    switch (choice) {

      // Option 1: Add income
      case '1':
        stdout.write('Enter income description: ');
        String? desc = stdin.readLineSync();

        stdout.write('Enter income amount: ');
        String? amtStr = stdin.readLineSync();
        double? amt = double.tryParse(amtStr ?? '');

        // Validate input
        if (desc == null || desc.trim().isEmpty) {
          print('Invalid description. Operation cancelled.');
        } else if (amt == null || amt < 0) {
          print('Invalid amount. Please enter a non-negative number.');
        } else {
          incomeList.add({desc.trim(): amt});
          print('Income added: ${desc.trim()} - \$${amt.toStringAsFixed(2)}');
        }
        break;

      // Option 2: Add expense
      case '2':
        stdout.write('Enter expense description: ');
        String? edesc = stdin.readLineSync();

        stdout.write('Enter expense amount: ');
        String? eamtStr = stdin.readLineSync();
        double? eamt = double.tryParse(eamtStr ?? '');

        // Validate input
        if (edesc == null || edesc.trim().isEmpty) {
          print('Invalid description. Operation cancelled.');
        } else if (eamt == null || eamt < 0) {
          print('Invalid amount. Please enter a non-negative number.');
        } else {
          expenseList.add({edesc.trim(): eamt});
          print('Expense added: ${edesc.trim()} - \$${eamt.toStringAsFixed(2)}');
        }
        break;

      // Option 3: View summary (total income, expenses, net profit/loss)
      case '3':
        double totalIncome = 0.0;
        for (var item in incomeList) {
          totalIncome += item.values.first;
        }

        double totalExpenses = 0.0;
        for (var item in expenseList) {
          totalExpenses += item.values.first;
        }

        double net = totalIncome - totalExpenses;

        print('\n--- Summary ---');
        print('Total Income: \$${totalIncome.toStringAsFixed(2)}');
        print('Total Expenses: \$${totalExpenses.toStringAsFixed(2)}');

        // Display net profit/loss and tax if applicable
        if (net > 0) {
          print('Your net profit is \$${net.toStringAsFixed(2)}');
          double tax = net * TAX_RATE; // 15% tax
          print('Tax to pay (15%): \$${tax.toStringAsFixed(2)}');
        } else if (net < 0) {
          print('Your net loss is \$${(net.abs()).toStringAsFixed(2)}');
        } else {
          print('You broke even (no profit, no loss).');
        }
        break;

      // Option 4: Exit the program
      case '4':
        print('Exiting program. Goodbye!');
        return;

      // Handle invalid choices
      default:
        print('Invalid choice. Please select 1-4.');
    }
  }
}