import 'dart:io';

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

// Main function to run the application
void main() {
  print('Welcome to the Budget Management Application!');

  // Loop for continuous user interaction
  while (true) {
    displayMenu();

    // Read user choice
    String? choiceInput = stdin.readLineSync();
    int? choice = int.tryParse(choiceInput ?? '');

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

    switch (choice) {
      case 1:
        addIncome();
        break;
      case 2:
        addExpense();
        break;
      case 3:
        viewSummary();
        break;
      case 4:
        print('Exiting the application. Goodbye!');
        return; // Exit the main function and the program
      default:
        print('Invalid choice. Please select an option from 1 to 4.');
    }
    print(''); // Newline for separation
  }
}

// Display menu options
void displayMenu() {
  print('Please choose an option:');
  print('1. Add income');
  print('2. Add expense');
  print('3. View summary');
  print('4. Exit');
  stdout.write('Enter your choice: ');
}

// Helper function to read a positive double value
double? readPositiveDouble(String prompt) {
  double? value;
  while (value == null) {
    stdout.write(prompt);
    String? input = stdin.readLineSync();
    value = double.tryParse(input ?? '');

    if (value == null || value <= 0) {
      print('Invalid amount. Please enter a positive number.');
      value = null; // Reset to loop again
    }
  }
  return value;
}

// 1. Add income
void addIncome() {
  stdout.write('Enter income description: ');
  String? description = stdin.readLineSync();
  if (description == null || description.trim().isEmpty) {
    print('Description cannot be empty.');
    return;
  }

  double? amount = readPositiveDouble('Enter income amount: ');
  if (amount != null) {
    incomeList.add({'description': description, 'amount': amount});
    print('Income added!');
  }
}

// 2. Add expense
void addExpense() {
  stdout.write('Enter expense description: ');
  String? description = stdin.readLineSync();
  if (description == null || description.trim().isEmpty) {
    print('Description cannot be empty.');
    return;
  }

  double? amount = readPositiveDouble('Enter expense amount: ');
  if (amount != null) {
    expenseList.add({'description': description, 'amount': amount});
    print('Expense added!');
  }
}

// 3. View summary
void viewSummary() {
  // Arithmetic Operations
  double totalIncome = incomeList.fold(0.0, (sum, item) => sum + item['amount']);
  double totalExpenses = expenseList.fold(0.0, (sum, item) => sum + item['amount']);
  double netProfit = totalIncome - totalExpenses;

  // Tax Calculation (Optional)
  double taxRate = 0.15; // 15%
  double taxToBePaid = 0.0;
  
  // Use Ternary Operator to calculate tax only if there is a net profit
  taxToBePaid = (netProfit > 0) ? netProfit * taxRate : 0.0;

  // Use String Interpolation to display the summary
  print('Summary:');
  print('Total income: \$${totalIncome.toStringAsFixed(2)}');
  print('Total expenses: \$${totalExpenses.toStringAsFixed(2)}');
  
  // Display Net Profit/Loss
  if (netProfit >= 0) {
    print('Net profit: \$${netProfit.toStringAsFixed(2)}');
    
    // Display custom message based on profit
    String profitMessage = (netProfit >= 5000) 
        ? 'Your net profit is great! (\$${netProfit.toStringAsFixed(2)})' 
        : 'Your net profit is \$${netProfit.toStringAsFixed(2)}';
    print(profitMessage);
    
    // Display tax if there is a profit
    if (taxToBePaid > 0) {
      print('Tax to be paid: \$${taxToBePaid.toStringAsFixed(2)}');
    }
    
  } else {
    // Display Net Loss
    double netLoss = netProfit.abs();
    print('Net loss: \$${netLoss.toStringAsFixed(2)}');
    
    // Display custom message based on loss
    String lossMessage = (netLoss >= 200) 
        ? 'Your net loss is high! (\$${netLoss.toStringAsFixed(2)})' 
        : 'Your net loss is \$${netLoss.toStringAsFixed(2)}';
    print(lossMessage);
  }
}