// Budget Management Application CLI - Dart
// Assignment 1 - Problem 2
// File: NaifAlkanhal_251000447_Budget Management Application2.txt
//
// How to run (after saving as .dart if needed):
//   dart run budget_app.dart
//
// Note: This submission is saved as .txt per instructions, but the content is valid Dart code.

import 'dart:io';

class BudgetEntry {
  final String description;
  final double amount;

  BudgetEntry({required this.description, required this.amount});
}

String _readLineTrimmed() {
  return (stdin.readLineSync() ?? '').trim();
}

int _readMenuChoice({required int min, required int max}) {
  while (true) {
    stdout.write('Enter your choice: ');
    final input = _readLineTrimmed();
    final value = int.tryParse(input);

    if (value != null && value >= min && value <= max) {
      return value;
    }
    stdout.writeln('Invalid choice. Please enter a number between $min and $max.');
  }
}

double _readNonNegativeAmount({required String prompt}) {
  while (true) {
    stdout.write(prompt);
    final input = _readLineTrimmed();
    final value = double.tryParse(input);

    // Input validation: numeric + non-negative using logical operators
    if (value != null && value >= 0) {
      return value;
    }
    stdout.writeln('Invalid amount. Please enter a valid non-negative number.');
  }
}

void _addIncome(List<BudgetEntry> incomeList) {
  stdout.write('Enter income description: ');
  final desc = _readLineTrimmed();
  final amount = _readNonNegativeAmount(prompt: 'Enter income amount: ');

  incomeList.add(BudgetEntry(description: desc, amount: amount));
  stdout.writeln('Income added!');
}

void _addExpense(List<BudgetEntry> expenseList) {
  stdout.write('Enter expense description: ');
  final desc = _readLineTrimmed();
  final amount = _readNonNegativeAmount(prompt: 'Enter expense amount: ');

  expenseList.add(BudgetEntry(description: desc, amount: amount));
  stdout.writeln('Expense added!');
}

double _sumAmounts(List<BudgetEntry> list) {
  double total = 0;
  for (final e in list) {
    total += e.amount; // arithmetic operation
  }
  return total;
}

void _viewSummary(List<BudgetEntry> incomeList, List<BudgetEntry> expenseList) {
  final totalIncome = _sumAmounts(incomeList);
  final totalExpenses = _sumAmounts(expenseList);
  final net = totalIncome - totalExpenses;

  stdout.writeln('\nSummary:');
  stdout.writeln('Total income: \$${totalIncome.toStringAsFixed(2)}');
  stdout.writeln('Total expenses: \$${totalExpenses.toStringAsFixed(2)}');

  if (net >= 0) {
    stdout.writeln('Your net profit is \$${net.toStringAsFixed(2)}');
  } else {
    stdout.writeln('Your net loss is \$${net.abs().toStringAsFixed(2)}');
  }

  // Optional exercise: Tax calculation (15% of net profit), only if profitable.
  const double taxRate = 0.15;
  final double tax = (net > 0) ? (net * taxRate) : 0.0; // ternary operator

  if (tax > 0) {
    stdout.writeln('Tax to be paid (15%): \$${tax.toStringAsFixed(2)}');
  }

  stdout.writeln('');
}

void main() {
  // Data storage requirement: lists of entries
  final List<BudgetEntry> incomeList = [];
  final List<BudgetEntry> expenseList = [];

  stdout.writeln('Welcome to the Budget Management Application!');

  bool running = true;
  while (running) {
    stdout.writeln('\nPlease choose an option:');
    stdout.writeln('1. Add income');
    stdout.writeln('2. Add expense');
    stdout.writeln('3. View summary');
    stdout.writeln('4. Exit');

    final choice = _readMenuChoice(min: 1, max: 4);

    // Control flow requirement: if/else statements for menu options
    if (choice == 1) {
      _addIncome(incomeList);
    } else if (choice == 2) {
      _addExpense(expenseList);
    } else if (choice == 3) {
      _viewSummary(incomeList, expenseList);
    } else {
      stdout.writeln('Exiting the application. Goodbye!');
      running = false;
    }
  }
}