import 'dart:io';

// Data Storage
List<Map<String, double>> incomeList = [];
List<Map<String, double>> expenseList = [];
const double taxRate = 0.15; // 15% tax rate

void main() {
  print("Welcome to the Budget Management Application!");
  menuLoop();
  print("Exiting the application. Goodbye!");
}

// Control Flow & Loops: Main application loop
void menuLoop() {
  String? choice;
  do {
    displayMenu();
    stdout.write("Enter your choice: ");
    choice = stdin.readLineSync();

    // Control Flow: Use if/else statements (via switch for clarity) to handle menu options
    switch (choice) {
      case '1':
        addEntry(incomeList, "income");
        break;
      case '2':
        addEntry(expenseList, "expense");
        break;
      case '3':
        viewSummary();
        break;
      case '4':
        // Exit handled by do-while loop condition
        break;
      default:
        print("Invalid choice. Please enter a number between 1 and 4.");
    }
    print(""); // Separator line for visual clarity
  } while (choice != '4');
}

// Displaying the menu
void displayMenu() {
  print("\nPlease choose an option:");
  print("1. Add income");
  print("2. Add expense");
  print("3. View summary");
  print("4. Exit");
}

// Income and Expenses Management: Add income or expense entry
void addEntry(List<Map<String, double>> list, String type) {
  stdout.write("Enter $type description: ");
  String description = stdin.readLineSync() ?? 'No Description';

  double amount = getValidAmount(type);

  // Storing entry as Map<String, double>
  list.add({description: amount}); 
  print("${type[0].toUpperCase()}${type.substring(1)} added!");
}

// Input Validation: Ensure non-negative numeric values
double getValidAmount(String type) {
  double? amount;
  bool isValid = false;

  while (!isValid) {
    stdout.write("Enter $type amount: ");
    String? input = stdin.readLineSync();
    amount = double.tryParse(input ?? '');

    // Input Validation: Use logical operators to validate inputs (e.g., != null && >= 0)
    if (amount != null && amount >= 0) {
      isValid = true;
    } else {
      print("Invalid numeric value. Please enter a non-negative number.");
    }
  }
  return amount!;
}

// View net profit or loss and tax summary
void viewSummary() {
  // Arithmetic Operations: Calculate totals
  double totalIncome = calculateTotal(incomeList);
  double totalExpenses = calculateTotal(expenseList);
  double netProfitOrLoss = totalIncome - totalExpenses;

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

  // String Interpolation & Operations: Clearly show amounts and messages
  String statusMessage = (netProfitOrLoss >= 0) ? "Net profit" : "Net loss";
  print("$statusMessage: \$${netProfitOrLoss.abs().toStringAsFixed(2)}");

  // Exercise: Tax Calculation
  // Use the ternary operator to ensure the tax is only calculated if the business is profitable.
  double taxDue = (netProfitOrLoss > 0) 
                  ? netProfitOrLoss * taxRate 
                  : 0.0;
  
  // Display the tax amount to be paid if there is a profit
  if (netProfitOrLoss > 0) {
    print("Tax to be paid: \$${taxDue.toStringAsFixed(2)}"); 
  }
}

// Helper function for Arithmetic Operations: Calculate total sum of a list
double calculateTotal(List<Map<String, double>> list) {
  double total = 0.0;
  for (var entry in list) {
    // Summing the amounts (values) from the maps
    total += entry.values.first; 
  }
  return total;
}