Initial commit

lib/calculator_logic.dart

@@ -0,0 +1,96 @@
+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();
+  }
+}