REFACTOR: introduce Position and Plateau value objects

lib/mars_rover.dart

@@ -20,21 +20,53 @@ enum Direction {
   }
 }
 
+class Position {
+  final int x;
+  final int y;
+
+  Position(this.x, this.y);
+
+  Position moveNorth() => Position(x, y + 1);
+  Position moveEast() => Position(x + 1, y);
+  Position moveSouth() => Position(x, y - 1);
+  Position moveWest() => Position(x - 1, y);
+}
+
+class Plateau {
+  final int width;
+  final int height;
+
+  Plateau(this.width, this.height);
+
+  Position wrap(Position position) {
+    final wrappedX = _wrapCoordinate(position.x, width);
+    final wrappedY = _wrapCoordinate(position.y, height);
+    return Position(wrappedX, wrappedY);
+  }
+
+  int _wrapCoordinate(int value, int max) {
+    final wrapped = value % (max + 1);
+    return wrapped < 0 ? wrapped + max + 1 : wrapped;
+  }
+}
+
 class Rover {
-  int x;
-  int y;
+  Position _position;
   Direction _direction;
-  final int plateauWidth;
-  final int plateauHeight;
+  final Plateau plateau;
 
   Rover({
-    required this.x,
-    required this.y,
+    required int x,
+    required int y,
     required String direction,
-    this.plateauWidth = 100,
-    this.plateauHeight = 100,
-  }) : _direction = Direction.fromCode(direction);
+    int plateauWidth = 100,
+    int plateauHeight = 100,
+  })  : _position = Position(x, y),
+        _direction = Direction.fromCode(direction),
+        plateau = Plateau(plateauWidth, plateauHeight);
 
+  int get x => _position.x;
+  int get y => _position.y;
   String get direction => _direction.code;
 
   void turnLeft() {
@@ -46,25 +78,13 @@ class Rover {
   }
 
   void moveForward() {
-    switch (_direction) {
-      case Direction.north:
-        y = _wrapCoordinate(y + 1, plateauHeight);
-        break;
-      case Direction.east:
-        x = _wrapCoordinate(x + 1, plateauWidth);
-        break;
-      case Direction.south:
-        y = _wrapCoordinate(y - 1, plateauHeight);
-        break;
-      case Direction.west:
-        x = _wrapCoordinate(x - 1, plateauWidth);
-        break;
-    }
-  }
-
-  int _wrapCoordinate(int value, int max) {
-    final wrapped = value % (max + 1);
-    return wrapped < 0 ? wrapped + max + 1 : wrapped;
+    final newPosition = switch (_direction) {
+      Direction.north => _position.moveNorth(),
+      Direction.east => _position.moveEast(),
+      Direction.south => _position.moveSouth(),
+      Direction.west => _position.moveWest(),
+    };
+    _position = plateau.wrap(newPosition);
   }
 
   void execute(String commands) {