Infinite and alternating effects

lib/effects/effects.dart

@@ -1,10 +1,41 @@
+import 'dart:math';
 import '../components/component.dart';
 
 export './move_effect.dart';
 export './scale_effect.dart';
 
 abstract class PositionComponentEffect {
-  void update(double dt);
-  bool hasFinished();
+  bool _isDisposed = false;
+  bool get isDisposed => _isDisposed;
+
+  /// If the animation should first follow the initial curve and then follow the
+  /// curve backwards
+  bool isAlternating;
+  bool isInfinite;
+  double percentage;
+  double travelTime;
+  double _curveTime = 0.0;
+  int _curveDirection = 1;
+
+  PositionComponentEffect(this.isInfinite, this.isAlternating);
+
+  void update(double dt) {
+    _curveTime += dt * _curveDirection;
+    if (isAlternating) {
+      _curveDirection = isMax() ? -1 : (isMin() ? 1 : _curveDirection);
+    } else if (isInfinite && isMax()){
+      percentage = 0.0;
+    }
+    percentage = min(1.0, max(0.0, _curveTime / travelTime));
+  }
+
+  void dispose() => _isDisposed = true;
+
   PositionComponent component;
+
+  bool hasFinished() =>
+      (!isInfinite && !isAlternating && isMax()) ||
+          (!isInfinite && isAlternating && isMin()) || isDisposed;
+  bool isMax() => percentage == null ? false : percentage == 1.0;
+  bool isMin() => percentage == null ? false : percentage == 0.0;
 }