Refactor RpnStack to separate file

lib/main.dart

@@ -11,6 +11,7 @@ import 'package:url_launcher/url_launcher.dart';
 import 'binary_operator_widget.dart';
 import 'num_button_widget.dart';
 import 'operators.dart';
+import 'rpn_stack.dart';
 import 'stack_item.dart';
 import 'stack_item_widget.dart';
 
@@ -22,183 +23,6 @@ void main() {
   runApp(const RpnCalc());
 }
 
-class RpnStack {
-  RpnStack() {
-    stack.add(EditableItem.blank());
-  }
-  RpnStack.clone(RpnStack source) {
-    // XXX need to deep copy items
-    stack.addAll(source.stack);
-    appendNew = source.appendNew;
-  }
-  final List<StackItem> stack = [];
-  // When true, the next append operation should create a new item.
-  bool appendNew = false;
-
-  int get length => stack.length;
-  StackItem get first => stack[0];
-  bool get isEmpty => length == 1 && first.isEmpty;
-
-  StackItem operator [](int i) => stack[i];
-
-  void _realizeStack() {
-    final first = this.first;
-    if (first is EditableItem) {
-      if (first.isEmpty) {
-        _pop();
-      } else {
-        stack[0] = first.realize();
-      }
-    }
-    assert(stack.every((element) => element is RealizedItem),
-        'Every element in stack should be realized.');
-  }
-
-  void push(StackItem v) {
-    stack.insert(0, v);
-  }
-
-  StackItem _pop() {
-    if (stack.isNotEmpty) {
-      return stack.removeAt(0);
-    }
-    return null;
-  }
-
-  void advance() {
-    _realizeStack();
-    push(EditableItem(stack[0]));
-  }
-
-  void drop() {
-    if (stack.length == 1) {
-      stack[0] = EditableItem.blank();
-    } else {
-      _pop();
-    }
-  }
-
-  void swap() {
-    if (stack.length < 2) {
-      return;
-    }
-    _realizeStack();
-    final first = stack[0];
-    final second = stack[1];
-    stack[0] = second;
-    stack[1] = first;
-  }
-
-  void rotateDown() {
-    if (stack.length < 2) {
-      return;
-    }
-    _realizeStack();
-    final first = _pop();
-    stack.add(first);
-  }
-
-  void rotateUp() {
-    if (stack.length < 2) {
-      return;
-    }
-    _realizeStack();
-    final last = stack.removeAt(stack.length - 1);
-    push(last);
-  }
-
-  void applyBinaryOperation(BinaryOperator o) {
-    if (stack.length < 2) {
-      return;
-    }
-    appendNew = true;
-    // If the first item is editable and empty , remove and skip the operation.
-    if (first.isEmpty) {
-      _pop();
-      return;
-    }
-    _realizeStack();
-    final fn = operations[o];
-    final b = _pop().value;
-    final a = _pop().value;
-    final res = fn(a, b);
-    push(RealizedItem(res));
-  }
-
-  void inverse() {
-    final v = first.value;
-    if (v != null && v != 0) {
-      stack[0] = RealizedItem(1 / v);
-    }
-  }
-
-  void reverseSign() {
-    final v = first.value;
-    stack[0] = RealizedItem(v * -1);
-  }
-
-  void percent() {
-    num res;
-    switch (stack.length) {
-      case 0:
-        return;
-      case 1:
-        res = _pop().value / 100;
-        break;
-      default:
-        res = (_pop().value / 100) * _pop().value;
-        break;
-    }
-    push(RealizedItem(res));
-    appendNew = true;
-  }
-
-  void clearCurrent() {
-    stack[0] = EditableItem.blank();
-  }
-
-  void appendCurrent(String c) {
-    final first = this.first;
-    EditableItem updated;
-    // Append new editable item.
-    if (first is EditableItem) {
-      // Update existing item.
-      first.appendChar(c);
-    } else if (appendNew) {
-      _realizeStack();
-      appendNew = false;
-      updated = EditableItem.blank()..appendChar(c);
-      push(updated);
-    } else if (first is RealizedItem) {
-      // Replace realized item with new editable item.
-      updated = EditableItem.blank()..appendChar(c);
-      stack[0] = updated;
-    }
-  }
-
-  void backspaceCurrent() {
-    final first = this.first;
-    if (first is RealizedItem) {
-      stack[0] = EditableItem(first)..removeChar();
-    } else if (first is EditableItem) {
-      first.removeChar();
-    }
-  }
-
-  void clearAll() {
-    stack.clear();
-    push(EditableItem.blank());
-  }
-
-  void remove(int index) {
-    stack.removeAt(index);
-  }
-
-  void replaceAt(int index, num newVal) {
-    stack[index] = RealizedItem(newVal);
-  }
-}
-
 class RpnCalc extends StatelessWidget {
   const RpnCalc({Key key}) : super(key: key);
   @override
@@ -220,22 +44,11 @@ class AppHome extends StatefulWidget {
   _AppHomeState createState() => _AppHomeState();
 }
 
-const maxUndoBuffer = 5;
-
 class _AppHomeState extends State<AppHome> {
   RpnStack _stack = RpnStack();
-  // TODO improve undo implementation.
+  // TODO(alexei): improve undo implementation.
   final List<RpnStack> _undoBuffer = [];
-
-//  void _onReorder(int oldIndex, newIndex) {
-//    setState(() {
-//      if (newIndex > oldIndex) {
-//        newIndex -= 1;
-//      }
-//      final num item = _stack.removeAt(oldIndex);
-//      _stack.insert(newIndex, item);
-//    });
-//  }
+  static const maxUndoBuffer = 5;
 
   void _setStateWithUndo(Function f) {
     setState(() {
@@ -253,6 +66,7 @@ class _AppHomeState extends State<AppHome> {
       if (_undoBuffer.isEmpty) {
         return;
       }
+      HapticFeedback.selectionClick();
       final prevState = _undoBuffer.removeAt(0);
       _stack = prevState;
     });