import 'dart:io';

// Tax rate as constant
const double TAX_RATE = 0.15;

void main() {
  // Data storage using Lists of Maps
  List<Map<String, double>> incomeList = [];
  List<Map<String, double>> expenseList = [];
  
  print("=" * 50);
  print("Welcome to the Budget Management Application!");
  print("=" * 50);
  
  bool running = true;
  
  while (running) {
    // Display menu
    print("\nPlease choose an option:");
    print("1. Add income");
    print("2. Add expense");
    print("3. View summary");
    print("4. Exit");
    stdout.write("Enter your choice: ");
    
    String? choice = stdin.readLineSync();
    
    // Handle menu options with if/else
    if (choice == '1') {
      // Add income
      addTransaction(incomeList, "income");
      
    } else if (choice == '2') {
      // Add expense
      addTransaction(expenseList, "expense");
      
    } else if (choice == '3') {
      // View summary
      displaySummary(incomeList, expenseList);
      
    } else if (choice == '4') {
      // Exit
      running = false;
      print("\nExiting the application. Goodbye!");
      
    } else {
      print("Invalid choice! Please enter 1-4.");
    }
  }
}

void addTransaction(List<Map<String, double>> transactionList, String type) {
  stdout.write("Enter $type description: ");
  String? description = stdin.readLineSync();
  
  if (description == null || description.isEmpty) {
    print("Description cannot be empty!");
    return;
  }
  
  stdout.write("Enter $type amount: ");
  String? amountInput = stdin.readLineSync();
  
  if (amountInput != null) {
    double? amount = double.tryParse(amountInput);
    
    // Input validation - no negative amounts using logical operators
    if (amount != null && amount > 0) {
      // Add to list as Map with description and amount
      transactionList.add({description: amount});
      print("$type added successfully!");
    } else {
      print("Invalid amount! Please enter a positive number.");
    }
  }
}

void displaySummary(List<Map<String, double>> incomeList, List<Map<String, double>> expenseList) {
  print("\n" + "=" * 40);
  print("SUMMARY");
  print("=" * 40);
  
  // Calculate totals using arithmetic operations
  double totalIncome = 0;
  double totalExpense = 0;
  
  print("INCOME:");
  if (incomeList.isEmpty) {
    print("  No income entries");
  } else {
    for (var income in incomeList) {
      income.forEach((description, amount) {
        // String interpolation for display
        print("  - $description: \$${amount.toStringAsFixed(2)}");
        totalIncome += amount;
      });
    }
  }
  
  print("\nEXPENSES:");
  if (expenseList.isEmpty) {
    print("  No expense entries");
  } else {
    for (var expense in expenseList) {
      expense.forEach((description, amount) {
        print("  - $description: \$${amount.toStringAsFixed(2)}");
        totalExpense += amount;
      });
    }
  }
  
  // Calculate net profit/loss
  double netAmount = totalIncome - totalExpense;
  
  print("\n" + "-" * 30);
  print("Total Income: \$${totalIncome.toStringAsFixed(2)}");
  print("Total Expenses: \$${totalExpense.toStringAsFixed(2)}");
  
  // Display with appropriate message using string interpolation
  if (netAmount >= 0) {
    print("Net Profit: \$${netAmount.toStringAsFixed(2)}");
    
    // Tax calculation using ternary operator
    double tax = netAmount > 0 ? netAmount * TAX_RATE : 0;
    if (tax > 0) {
      print("Tax to be paid (15%): \$${tax.toStringAsFixed(2)}");
    }
  } else {
    print("Net Loss: \$${netAmount.abs().toStringAsFixed(2)}");
    print("No tax to be paid (business not profitable)");
  }
  print("=" * 40);
}