feat(powerup): merge and restructure power-up system

- move ExpandPaddlePowerUp, ShrinkPaddlePowerUp into new folders
- add PowerUpManager and FallingComponent
- update PhysicSystem and PaddleFactory integration
- refactor Explosion, HealthDeath, Special behaviors

Author: ManhTanTran

src/main/java/com/github/codestorm/bounceverse/components/behaviors/Explosion.java

@@ -28,7 +28,6 @@ public final class Explosion extends Attack {
 
     @Override
     public void execute(List<Object> data) {
-        final var attributes = entity.getComponent(Attributes.class);
         final double cx = getEntity().getCenter().getX();
         final double cy = getEntity().getCenter().getY();
 

src/main/java/com/github/codestorm/bounceverse/components/behaviors/HealthDeath.java

@@ -1,12 +1,12 @@
 package com.github.codestorm.bounceverse.components.behaviors;
 
+import java.util.List;
+
 import com.almasb.fxgl.dsl.components.HealthIntComponent;
 import com.almasb.fxgl.entity.component.Required;
 import com.github.codestorm.bounceverse.core.BackgroundColorManager;
 import com.github.codestorm.bounceverse.typing.enums.EntityType;
 
-import java.util.List;
-
 /**
  *
  *

src/main/java/com/github/codestorm/bounceverse/components/behaviors/Special.java

@@ -13,8 +13,6 @@ public class Special extends Component {
 
     @Override
     public void onRemoved() {
-        if (Math.random() < 0.3) { // 30% tỉ lệ rơi PowerUp
-            FXGL.spawn("powerUp", getEntity().getCenter());
-        }
+        FXGL.spawn("powerUp", getEntity().getCenter());
     }
 }

src/main/java/com/github/codestorm/bounceverse/components/properties/paddle/PaddleSizeManager.java

@@ -0,0 +1,39 @@
+package com.github.codestorm.bounceverse.components.properties.paddle;
+
+import com.almasb.fxgl.entity.component.Component;
+
+import javafx.scene.Node;
+
+/**
+ * Quản lý kích thước gốc của Paddle và cho phép reset.
+ */
+public class PaddleSizeManager extends Component {
+
+    private double originalWidth;
+    private double originalScaleX;
+
+    @Override
+    public void onAdded() {
+        Node view = getEntity().getViewComponent().getChildren().get(0);
+        originalWidth = view.getBoundsInLocal().getWidth();
+        originalScaleX = view.getScaleX();
+    }
+
+    /** Phóng to paddle theo hệ số. */
+    public void expand(double factor) {
+        Node view = getEntity().getViewComponent().getChildren().get(0);
+        view.setScaleX(factor);
+    }
+
+    /** Thu nhỏ paddle theo hệ số. */
+    public void shrink(double factor) {
+        Node view = getEntity().getViewComponent().getChildren().get(0);
+        view.setScaleX(factor);
+    }
+
+    /** Reset paddle về kích thước gốc. */
+    public void resetSize() {
+        Node view = getEntity().getViewComponent().getChildren().get(0);
+        view.setScaleX(originalScaleX);
+    }
+}

src/main/java/com/github/codestorm/bounceverse/components/properties/powerup/FallingComponent.java

@@ -0,0 +1,18 @@
+package com.github.codestorm.bounceverse.components.properties.powerup;
+
+import com.almasb.fxgl.entity.component.Component;
+
+/**
+ * Giúp PowerUp rơi xuống mà không cần PhysicsComponent.
+ * Dùng update thủ công để tránh lỗi "Physics not initialized yet".
+ */
+public class FallingComponent extends Component {
+
+    private static final double FALL_SPEED = 150; // pixel/s
+
+    @Override
+    public void onUpdate(double tpf) {
+        // Dịch chuyển entity xuống dưới theo thời gian
+        getEntity().translateY(FALL_SPEED * tpf);
+    }
+}

src/main/java/com/github/codestorm/bounceverse/components/properties/powerup/PowerUpManager.java

@@ -0,0 +1,57 @@
+package com.github.codestorm.bounceverse.components.properties.powerup;
+
+import com.almasb.fxgl.dsl.FXGL;
+import com.almasb.fxgl.time.TimerAction;
+import javafx.util.Duration;
+
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * Quản lý các PowerUp đang hoạt động: thời gian, gia hạn, và hết hiệu lực.
+ * Dùng singleton.
+ */
+public final class PowerUpManager {
+
+    /** Mỗi loại power-up gắn với 1 timer riêng. */
+    private final Map<String, TimerAction> activeTimers = new HashMap<>();
+
+    private static final PowerUpManager INSTANCE = new PowerUpManager();
+
+    private PowerUpManager() {}
+
+    public static PowerUpManager getInstance() {
+        return INSTANCE;
+    }
+
+    /**
+     * Kích hoạt hoặc gia hạn PowerUp.
+     * @param name  Tên power-up (ví dụ: "ExpandPaddle")
+     * @param duration  Thời gian hiệu lực
+     * @param onActivate  Logic khi kích hoạt
+     * @param onExpire    Logic khi hết hiệu lực
+     */
+    public void activate(String name, Duration duration, Runnable onActivate, Runnable onExpire) {
+        // Nếu đang chạy timer cũ → huỷ để gia hạn
+        if (activeTimers.containsKey(name)) {
+            var oldTimer = activeTimers.get(name);
+            if (!oldTimer.isExpired()) {
+                oldTimer.expire();
+            }
+        }
+
+        onActivate.run();
+
+        var timer = FXGL.getGameTimer().runOnceAfter(() -> {
+            onExpire.run();
+            activeTimers.remove(name);
+        }, duration);
+
+        activeTimers.put(name, timer);
+    }
+
+    public void clearAll() {
+        activeTimers.values().forEach(TimerAction::expire);
+        activeTimers.clear();
+    }
+}

src/main/java/com/github/codestorm/bounceverse/components/properties/powerup/types/ExpandPaddlePowerUp.java

@@ -0,0 +1,46 @@
+package com.github.codestorm.bounceverse.components.properties.powerup.types.ball;
+
+import com.almasb.fxgl.dsl.FXGL;
+import com.almasb.fxgl.entity.Entity;
+import com.github.codestorm.bounceverse.components.properties.powerup.PowerUpManager;
+import com.github.codestorm.bounceverse.typing.enums.EntityType;
+import javafx.util.Duration;
+import javafx.geometry.Point2D;
+
+/**
+ * PowerUp nhân đôi bóng hiện có.
+ * Nếu có nhiều bóng, mỗi bóng sẽ sinh thêm 1 bóng phụ cùng hướng.
+ */
+public class DuplicateBallPowerUp extends com.almasb.fxgl.entity.component.Component {
+
+    private static final Duration DURATION = Duration.seconds(0.1); 
+
+    @Override
+    public void onAdded() {
+        PowerUpManager.getInstance().activate(
+                "DuplicateBall",
+                DURATION,
+                this::duplicateBalls,
+                () -> {}
+        );
+    }
+
+    private void duplicateBalls() {
+        var world = FXGL.getGameWorld();
+        var balls = world.getEntitiesByType(EntityType.BALL);
+
+        for (Entity ball : balls) {
+            // Lấy vị trí và vận tốc hiện tại của bóng
+            var physics = ball.getComponentOptional(com.almasb.fxgl.physics.PhysicsComponent.class);
+            if (physics.isEmpty()) continue;
+
+            Point2D velocity = physics.get().getLinearVelocity();
+            Point2D pos = ball.getCenter();
+
+            // Spawn bóng mới
+            Entity newBall = FXGL.spawn("ball", pos);
+            newBall.getComponent(com.almasb.fxgl.physics.PhysicsComponent.class)
+                    .setLinearVelocity(velocity.multiply(-1)); 
+        }
+    }
+}

src/main/java/com/github/codestorm/bounceverse/components/properties/powerup/types/ShrinkPaddlePowerUp.java

@@ -0,0 +1,41 @@
+package com.github.codestorm.bounceverse.components.properties.powerup.types.ball;
+
+import com.almasb.fxgl.dsl.FXGL;
+import com.almasb.fxgl.entity.Entity;
+import com.github.codestorm.bounceverse.components.properties.powerup.PowerUpManager;
+import com.github.codestorm.bounceverse.typing.enums.EntityType;
+import javafx.util.Duration;
+
+/**
+ * PowerUp làm to bóng trong một thời gian ngắn.
+ */
+public class ExpandBallPowerUp extends com.almasb.fxgl.entity.component.Component {
+
+    private static final Duration DURATION = Duration.seconds(8);
+
+    @Override
+    public void onAdded() {
+        PowerUpManager.getInstance().activate(
+                "ExpandBall",
+                DURATION,
+                this::expandBalls,
+                this::resetBalls
+        );
+    }
+
+    private void expandBalls() {
+        for (Entity ball : FXGL.getGameWorld().getEntitiesByType(EntityType.BALL)) {
+            var view = ball.getViewComponent().getChildren().get(0);
+            view.setScaleX(1.5);
+            view.setScaleY(1.5);
+        }
+    }
+
+    private void resetBalls() {
+        for (Entity ball : FXGL.getGameWorld().getEntitiesByType(EntityType.BALL)) {
+            var view = ball.getViewComponent().getChildren().get(0);
+            view.setScaleX(1);
+            view.setScaleY(1);
+        }
+    }
+}