class CalculatorLogic {
  String _display = '0';
  double _firstOperand = 0;
  String _operator = '';
  bool _waitingForSecondOperand = false;

  String get display => _display;

  void inputDigit(String digit) {
    if (_waitingForSecondOperand) {
      _display = digit;
      _waitingForSecondOperand = false;
    } else {
      _display = _display == '0' ? digit : _display + digit;
    }
  }

  void inputDecimal() {
    if (_waitingForSecondOperand) {
      _display = '0.';
      _waitingForSecondOperand = false;
      return;
    }
    if (!_display.contains('.')) {
      _display += '.';
    }
  }

  void inputOperator(String op) {
    final current = double.parse(_display);

    if (_operator.isNotEmpty && !_waitingForSecondOperand) {
      _firstOperand = _calculate(_firstOperand, current, _operator);
      _display = _formatResult(_firstOperand);
    } else {
      _firstOperand = current;
    }

    _operator = op;
    _waitingForSecondOperand = true;
  }

  void calculate() {
    if (_operator.isEmpty) return;

    final secondOperand = double.parse(_display);
    final result = _calculate(_firstOperand, secondOperand, _operator);
    _display = _formatResult(result);
    _firstOperand = result;
    _operator = '';
    _waitingForSecondOperand = true;
  }

  void clear() {
    _display = '0';
    _firstOperand = 0;
    _operator = '';
    _waitingForSecondOperand = false;
  }

  void toggleSign() {
    final value = double.parse(_display);
    _display = _formatResult(-value);
  }

  void percent() {
    final value = double.parse(_display);
    _display = _formatResult(value / 100);
  }

  double _calculate(double a, double b, String op) {
    switch (op) {
      case '+':
        return a + b;
      case '-':
        return a - b;
      case '*':
        return a * b;
      case '/':
        if (b == 0) return double.infinity;
        return a / b;
      default:
        return b;
    }
  }

  String _formatResult(double value) {
    if (value.isInfinite || value.isNaN) {
      return value.toString();
    }
    if (value == value.toInt().toDouble()) {
      return value.toInt().toString();
    }
    return value.toString();
  }
}