import 'dart:io';

// constant tax rate (15%)
const double TAX_RATE = 0.15;

void main() {
  // list to store incomes
  List<Map<String, double>> incomeList = [];

  // list to store expenses
  List<Map<String, double>> expenseList = [];

  print('Welcome to the Budget Management App!');
  bool running = true;

  while (running) {
    // display menu options
    print('\nChoose an option:');
    print('1. Add new income');
    print('2. Add new expense');
    print('3. Show budget summary');
    print('4. Exit');

    stdout.write('Enter your choice: ');
    String? choice = stdin.readLineSync();

    if (choice == null) {
      print('Invalid input, please try again.');
      continue;
    }

    switch (choice.trim()) {
      case '1':
        addEntry(list: incomeList, isIncome: true);
        break;
      case '2':
        addEntry(list: expenseList, isIncome: false);
        break;
      case '3':
        showSummary(incomeList, expenseList);
        break;
      case '4':
        print('Program ended successfully.');
        running = false;
        break;
      default:
        print('Unknown choice. Please enter a number from 1 to 4.');
    }
  }
}

// function to add an income or expense
void addEntry({required List<Map<String, double>> list, required bool isIncome}) {
  String type = isIncome ? 'income' : 'expense';

  stdout.write('Enter $type description: ');
  String? desc = stdin.readLineSync();

  if (desc == null || desc.trim().isEmpty) {
    print('Description cannot be empty.');
    return;
  }

  double? amount;

  // validate numeric input
  while (amount == null) {
    stdout.write('Enter amount (positive number): ');
    String? input = stdin.readLineSync();

    if (input == null) {
      print('Invalid value, please try again.');
      continue;
    }

    input = input.replaceAll(',', '.');
    double? parsed = double.tryParse(input);

    if (parsed == null) {
      print('Please enter a valid number.');
    } else if (parsed < 0) {
      print('Amount must be positive.');
    } else {
      amount = parsed;
    }
  }

  // add to the list
  list.add({desc.trim(): amount});
  print('Successfully added $type: "$desc" - ${amount.toStringAsFixed(2)} SAR');
}

// function to calculate the total of a list
double sumList(List<Map<String, double>> list) {
  double sum = 0.0;
  for (var item in list) {
    for (var value in item.values) {
      sum += value;
    }
  }
  return sum;
}

// function to show the full summary
void showSummary(List<Map<String, double>> incomes, List<Map<String, double>> expenses) {
  double totalIncome = sumList(incomes);
  double totalExpenses = sumList(expenses);
  double net = totalIncome - totalExpenses;

  print('\n===== Budget Summary =====');
  print('Total Income: ${totalIncome.toStringAsFixed(2)} SAR');
  print('Total Expenses: ${totalExpenses.toStringAsFixed(2)} SAR');

  if (net >= 0) {
    print('Net Profit: ${net.toStringAsFixed(2)} SAR');
  } else {
    print('Net Loss: ${(-net).toStringAsFixed(2)} SAR');
  }

  // apply tax only if profit
  double tax = net > 0 ? net * TAX_RATE : 0.0;
  String taxMessage = net > 0
      ? 'Tax (${(TAX_RATE * 100).toStringAsFixed(0)}%): ${tax.toStringAsFixed(2)} SAR'
      : 'No tax applied since there is a loss.';
  print(taxMessage);

  // show details
  if (incomes.isNotEmpty) {
    print('\nIncome Details:');
    for (var item in incomes) {
      item.forEach((desc, amount) {
        print('- $desc : ${amount.toStringAsFixed(2)} SAR');
      });
    }
  } else {
    print('\nNo income recorded yet.');
  }

  if (expenses.isNotEmpty) {
    print('\nExpense Details:');
    for (var item in expenses) {
      item.forEach((desc, amount) {
        print('- $desc : ${amount.toStringAsFixed(2)} SAR');
      });
    }
  } else {
    print('\nNo expenses recorded yet.');
  }

  print('==========================\n');
}