feat: made Plunger use InitialPosition

lib/game/components/plunger.dart

@@ -9,15 +9,11 @@ import 'package:pinball/game/game.dart';
 ///
 /// [Plunger] ignores gravity so the player controls its downward [_pull].
 /// {@endtemplate}
-class Plunger extends BodyComponent with KeyboardHandler {
+class Plunger extends BodyComponent with KeyboardHandler, InitialPosition {
   /// {@macro plunger}
   Plunger({
-    required Vector2 position,
     required this.compressionDistance,
-  }) : _position = position;
-
-  /// The initial position of the [Plunger] body.
-  final Vector2 _position;
+  });
 
   /// Distance the plunger can lower.
   final double compressionDistance;
@@ -30,7 +26,7 @@ class Plunger extends BodyComponent with KeyboardHandler {
 
     final bodyDef = BodyDef()
       ..userData = this
-      ..position = _position
+      ..position = initialPosition
       ..type = BodyType.dynamic
       ..gravityScale = 0;
 
@@ -45,9 +41,9 @@ class Plunger extends BodyComponent with KeyboardHandler {
   /// Set an upward velocity on the [Plunger].
   ///
   /// The velocity's magnitude depends on how far the [Plunger] has been pulled
-  /// from its original [_position].
+  /// from its original [initialPosition].
   void _release() {
-    final velocity = (_position.y - body.position.y) * 9;
+    final velocity = (initialPosition.y - body.position.y) * 9;
     body.linearVelocity = Vector2(0, velocity);
   }
 

lib/game/pinball_game.dart

@@ -93,19 +93,16 @@ class PinballGame extends Forge2DGame
   }
 
   Future<void> _addPlunger() async {
-    final compressionDistance = camera.viewport.effectiveSize.y / 12;
-
-    await add(
-      plunger = Plunger(
-        position: screenToWorld(
-          Vector2(
-            camera.viewport.effectiveSize.x / 1.035,
-            camera.viewport.effectiveSize.y - compressionDistance,
-          ),
+    plunger = Plunger(
+      compressionDistance: camera.viewport.effectiveSize.y / 12,
+    )..initialPosition = screenToWorld(
+        Vector2(
+          camera.viewport.effectiveSize.x / 1.035,
+          camera.viewport.effectiveSize.y - plunger.compressionDistance,
         ),
-        compressionDistance: compressionDistance,
-      ),
-    );
+      );
+
+    await add(plunger);
   }
 }
 

test/game/components/plunger_test.dart

@@ -23,9 +23,8 @@ void main() {
       (game) async {
         await game.ready();
         final plunger = Plunger(
-          position: Vector2.zero(),
           compressionDistance: compressionDistance,
-        );
+        )..initialPosition = Vector2.zero();
         await game.ensureAdd(plunger);
 
         expect(game.contains(plunger), isTrue);
@@ -38,9 +37,8 @@ void main() {
         (game) async {
           final position = Vector2.all(10);
           final plunger = Plunger(
-            position: position,
             compressionDistance: compressionDistance,
-          );
+          )..initialPosition = position;
           await game.ensureAdd(plunger);
           game.contains(plunger);
 
@@ -52,9 +50,8 @@ void main() {
         'is dynamic',
         (game) async {
           final plunger = Plunger(
-            position: Vector2.zero(),
             compressionDistance: compressionDistance,
-          );
+          )..initialPosition = Vector2.zero();
           await game.ensureAdd(plunger);
 
           expect(plunger.body.bodyType, equals(BodyType.dynamic));
@@ -65,9 +62,8 @@ void main() {
         'ignores gravity',
         (game) async {
           final plunger = Plunger(
-            position: Vector2.zero(),
             compressionDistance: compressionDistance,
-          );
+          )..initialPosition = Vector2.zero();
           await game.ensureAdd(plunger);
 
           expect(plunger.body.gravityScale, isZero);
@@ -80,9 +76,8 @@ void main() {
         'exists',
         (game) async {
           final plunger = Plunger(
-            position: Vector2.zero(),
             compressionDistance: compressionDistance,
-          );
+          )..initialPosition = Vector2.zero();
           await game.ensureAdd(plunger);
 
           expect(plunger.body.fixtures[0], isA<Fixture>());
@@ -93,9 +88,8 @@ void main() {
         'shape is a polygon',
         (game) async {
           final plunger = Plunger(
-            position: Vector2.zero(),
             compressionDistance: compressionDistance,
-          );
+          )..initialPosition = Vector2.zero();
           await game.ensureAdd(plunger);
 
           final fixture = plunger.body.fixtures[0];
@@ -107,9 +101,8 @@ void main() {
         'has density',
         (game) async {
           final plunger = Plunger(
-            position: Vector2.zero(),
             compressionDistance: compressionDistance,
-          );
+          )..initialPosition = Vector2.zero();
           await game.ensureAdd(plunger);
 
           final fixture = plunger.body.fixtures[0];
@@ -129,9 +122,8 @@ void main() {
 
       setUp(() {
         plunger = Plunger(
-          position: Vector2.zero(),
           compressionDistance: compressionDistance,
-        );
+        )..initialPosition = Vector2.zero();
       });
 
       testRawKeyUpEvents(keys, (event) {
@@ -194,9 +186,8 @@ void main() {
       'position is a compression distance below the Plunger',
       (game) async {
         final plunger = Plunger(
-          position: Vector2.zero(),
           compressionDistance: compressionDistance,
-        );
+        )..initialPosition = Vector2.zero();
         await game.ensureAdd(plunger);
 
         final plungerAnchor = PlungerAnchor(plunger: plunger);
@@ -222,14 +213,14 @@ void main() {
         initialState: const GameState.initial(),
       );
       plunger = Plunger(
-        position: Vector2.zero(),
         compressionDistance: compressionDistance,
-      );
+      )..initialPosition = Vector2.zero();
     });
 
     final flameTester = flameBlocTester(gameBloc: () => gameBloc);
 
     group('initializes with', () {
+      // FIXME(alestiago): Plunger not initialized error.
       flameTester.test(
         'plunger body as bodyA',
         (game) async {