import 'dart:io';

// 3. Data Storage: Use Lists to store income and expenses
List<Map<String, dynamic>> incomeList = [];
List<Map<String, dynamic>> expenseList = [];

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

// Function to read and validate monetary amounts
double? readAmount(String type) {
  stdout.write('Enter $type amount: ');
  String? input = stdin.readLineSync();
  try {
    double amount = double.parse(input!);
    // 4. Input Validation: Check for a positive number
    if (amount > 0) {
      return amount;
    } else {
      print('Invalid amount. Please enter a positive number.');
      return null;
    }
  } catch (e) {
    print('Invalid input. Please enter a valid number.');
    return null;
  }
}

// 2. Income and Expenses Management: 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 = readAmount('income');
  if (amount != null) {
    // 3. Data Storage: Store income as a Map
    incomeList.add({'description': description, 'amount': amount});
    print('Income added!');
  }
}

// 2. Income and Expenses Management: 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 = readAmount('expense');
  if (amount != null) {
    // 3. Data Storage: Store expense as a Map
    expenseList.add({'description': description, 'amount': amount});
    print('Expense added!');
  }
}

// 2. Income and Expenses Management: View summary
void viewSummary() {
  // 7. Arithmetic Operations: Calculate totals
  double totalIncome = 0;
  for (var income in incomeList) {
    totalIncome += income['amount'] as double;
  }

  double totalExpenses = 0;
  for (var expense in expenseList) {
    totalExpenses += expense['amount'] as double;
  }

  double netProfit = totalIncome - totalExpenses; // Calculate net profit/loss

  print('\nSummary:');
  // 6. String Interpolation: Display totals
  print('Total Income: \$${totalIncome.toStringAsFixed(2)}');
  print('Total Expenses: \$${totalExpenses.toStringAsFixed(2)}');

  if (netProfit > 0) {
    print('Net Profit: \$${netProfit.toStringAsFixed(2)}');
    
    // 8. Tax Calculation (Optional): Use the ternary operator
    // Calculate 15% tax only if netProfit is greater than 0
    double tax = netProfit > 0 ? netProfit * 0.15 : 0; 
    print('Tax to be paid: \$${tax.toStringAsFixed(2)}');

  } else if (netProfit < 0) {
    // Loss
    print('Net Loss: \$${(netProfit.abs()).toStringAsFixed(2)}');
  } else {
    print('Net Balance: \$0.00');
  }
}

// 1. Main Method: Program entry point
void main() {
  print('Welcome to the Budget Management Application CLI!');

  // 5. Control Flow & Loops: Use a loop for continuous interaction
  while (true) {
    displayMenu();
    stdout.write('Enter your choice: ');
    String? choice = stdin.readLineSync();

    // 5. Use if/else statements to handle menu options.
    if (choice == '4') {
      print('Exiting the application. Goodbye!');
      break;
    } else if (choice == '1') {
      addIncome();
    } else if (choice == '2') {
      addExpense();
    } else if (choice == '3') {
      viewSummary();
    } else {
      print('Invalid choice. Please select an option from 1 to 4.');
    }
  }
}