import 'dart:io';

void main() {
  print("Welcome to the Budget Management Application!");

  // Data Storage using lists of maps (as required)
  List<Map<String, double>> incomeList = [];
  List<Map<String, double>> expenseList = [];

  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: ");
    String? input = stdin.readLineSync();
    int? choice = int.tryParse(input ?? "");

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

    if (choice == 1) {
      // Add income
      stdout.write("Enter income description: ");
      String desc = (stdin.readLineSync() ?? "").trim();
      double amount = _readPositiveAmount("Enter income amount: ");

      incomeList.add({desc: amount});
      print("Income added!");

    } else if (choice == 2) {
      // Add expense
      stdout.write("Enter expense description: ");
      String desc = (stdin.readLineSync() ?? "").trim();
      double amount = _readPositiveAmount("Enter expense amount: ");

      expenseList.add({desc: amount});
      print("Expense added!");

    } else if (choice == 3) {
      // View summary
      double totalIncome = _sumList(incomeList);
      double totalExpenses = _sumList(expenseList);
      double net = totalIncome - totalExpenses;

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

      if (net >= 0) {
        print("Net profit: \$${net.toStringAsFixed(2)}");

        // Optional Tax (15%) using ternary operator (as required)
        double tax = net > 0 ? net * 0.15 : 0.0;
        if (tax > 0) {
          print("Tax to be paid (15%): \$${tax.toStringAsFixed(2)}");
        }
      } else {
        print("Net loss: \$${net.abs().toStringAsFixed(2)}");
        print("No tax because there is a loss.");
      }

    } else if (choice == 4) {
      print("Exiting the application. Goodbye!");
      break;

    } else {
      print("Invalid choice. Please enter a number from 1 to 4.");
    }
  }
}

double _readPositiveAmount(String message) {
  while (true) {
    stdout.write(message);
    String? input = stdin.readLineSync();
    double? amount = double.tryParse(input ?? "");

    // input validation: valid number and not negative
    if (amount == null) {
      print("Invalid number. Try again.");
      continue;
    }
    if (amount < 0) {
      print("Amount cannot be negative. Try again.");
      continue;
    }
    return amount;
  }
}

double _sumList(List<Map<String, double>> list) {
  double total = 0.0;
  for (var entry in list) {
    for (var amount in entry.values) {
      total += amount;
    }
  }
  return total;
}