import 'dart:io';

void main() {
  // Data storage requirement: lists of map entries (description -> amount)
  final List<Map<String, double>> incomeList = [];
  final List<Map<String, double>> expenseList = [];

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

  while (true) {
    print('\nPlease choose an option:');
    print('1. Add income');
    print('2. Add expense');
    print('3. View summary');
    print('4. Exit');

    stdout.write('\nEnter your choice: ');
    final String choiceInput = stdin.readLineSync() ?? '';
    final int? choice = int.tryParse(choiceInput);

    if (choice == null) {
      print('Invalid input. Please enter a number (1-4).');
      continue;
    }

    if (choice == 1) {
      stdout.write('Enter income description: ');
      final String desc = (stdin.readLineSync() ?? '').trim();

      double amount;
      while (true) {
        stdout.write('Enter income amount: ');
        final String amountInput = stdin.readLineSync() ?? '';
        final double? parsed = double.tryParse(amountInput);

        // Input validation: no negative amounts (logical operators)
        if (parsed != null && parsed >= 0) {
          amount = parsed;
          break;
        } else {
          print('Invalid amount. Please enter a non-negative number.');
        }
      }

      incomeList.add({desc.isEmpty ? 'Income' : desc: amount});
      print('Income added!');
    } else if (choice == 2) {
      stdout.write('Enter expense description: ');
      final String desc = (stdin.readLineSync() ?? '').trim();

      double amount;
      while (true) {
        stdout.write('Enter expense amount: ');
        final String amountInput = stdin.readLineSync() ?? '';
        final double? parsed = double.tryParse(amountInput);

        if (parsed != null && parsed >= 0) {
          amount = parsed;
          break;
        } else {
          print('Invalid amount. Please enter a non-negative number.');
        }
      }

      expenseList.add({desc.isEmpty ? 'Expense' : desc: amount});
      print('Expense added!');
    } else if (choice == 3) {
      // Arithmetic operations: totals + net
      final double totalIncome = incomeList.fold(
        0.0,
        (sum, entry) => sum + entry.values.first,
      );

      final double totalExpenses = expenseList.fold(
        0.0,
        (sum, entry) => sum + entry.values.first,
      );

      final double net = totalIncome - totalExpenses;

      print('\nSummary:');
      print('Total income: \$${totalIncome.toStringAsFixed(2)}');
      print('Total expenses: \$${totalExpenses.toStringAsFixed(2)}');

      if (net >= 0) {
        print('Your net profit is \$${net.toStringAsFixed(2)}');
      } else {
        print('Your net loss is \$${net.abs().toStringAsFixed(2)}');
      }

      // Optional tax calculation: 15% of net profit only if profitable (ternary operator)
      final double tax = net > 0 ? net * 0.15 : 0.0;
      if (tax > 0) {
        print('Tax to be paid (15%): \$${tax.toStringAsFixed(2)}');
      }
    } else if (choice == 4) {
      print('Exiting the application. Goodbye!');
      break;
    } else {
      print('Invalid choice. Please enter a number from 1 to 4.');
    }
  }
}