import javafx.application.*;

import javafx.event.*;
import javafx.scene.input.*;
import javafx.util.*;
import javafx.scene.image.Image;
import javafx.scene.paint.Color;
import javafx.scene.Group;
import javafx.scene.effect.BlendMode;
import javafx.scene.Cursor;
import javafx.scene.Scene;
import javafx.stage.Stage;
import javafx.animation.Timeline;
import javafx.animation.KeyFrame;
import javafx.animation.KeyValue;
import javafx.scene.image.ImageView;
import javafx.geometry.Rectangle2D;
import javafx.animation.Interpolator;
import javafx.scene.shape.Rectangle;

public class JMain extends Application {

    /* The width of each sprite within the particle image */
    public static final int SPRITE_WIDTH = 32;
    /* The number of individual sprites within the strip */
    public static final int SPRITE_COUNT = 6;
    /* This strip is made of SPRITE_COUNT different sprites */
    public static Image STRIP = new Image("particles.png");

    public double lastX, lastY;
    public double mouseX, mouseY;
    public boolean inScene, wasMouseInside;
    public Group particleLayer;

    public void start(Stage stage) {
        particleLayer = new Group();

        Scene scene = new Scene(particleLayer, 320, 240);
        scene.setFill(Color.BLACK);
        scene.setCursor(Cursor.NONE);
        scene.addEventHandler(MouseEvent.MOUSE_MOVED,
                              new EventHandler<MouseEvent>() {
            public void handle(MouseEvent e) {
                mouseX = e.getX();
                mouseY = e.getY();
                inScene = true;
            }
        });
        scene.addEventHandler(MouseEvent.MOUSE_EXITED,
                              new EventHandler<MouseEvent>() {
            public void handle(MouseEvent e) {
                inScene = false;
            }
        });

        stage.setScene(scene);
        stage.setVisible(true);

        /**
         * This timeline ensures that every 1/60th of a second we add new particles
         */
        KeyFrame kf = new KeyFrame(Duration.valueOf(16),
                                   new EventHandler<ActionEvent>() {
            public void handle(ActionEvent e) {
                if (inScene) {
                    if (wasMouseInside) {
                        double dist = Math.hypot(lastX - mouseX, lastY - mouseY);
                        makeParticles(lastX, lastY, mouseX, mouseY, (int) (2 + dist / 8));
                    }
                    lastX = mouseX;
                    lastY = mouseY;
                    wasMouseInside = true;
                } else {
                    wasMouseInside = false;
                }
            }
        });
        Timeline tl = new Timeline(kf);
        tl.setCycleCount(Timeline.INDEFINITE);
        tl.play();
    }

    /**
     * Because particles exist for such a short amount of time, this function needs
     * to be called regularly to create new particles.
     */
    public void makeParticles(double x1, double y1, double x2, double y2, int numParticles) {
        KeyFrame keyFrames[] = new KeyFrame[numParticles * 2];

        for (int i = 0; i < numParticles; i++) {
            double size = (Math.random() * 44) + 4;
            long duration = (long) (200 - size) * 3;
            double moveDistance = (Math.random() * (80 - size)) + 4;
            double moveDirection = Math.random() * (Math.PI * 2); // Radians

            double startX = x1 + i * (x2 - x1) / numParticles;
            double startY = y1 + i * (y2 - y1) / numParticles;
            double goalX = startX + (moveDistance * Math.cos(moveDirection));
            double goalY = startY + (moveDistance * Math.sin(moveDirection));
            double startAngle = Math.random() * 360;
            double endAngle = startAngle + (Math.random() * 360);
            double vpx = ((int) (Math.random() * SPRITE_COUNT)) * SPRITE_WIDTH;
            double vpy = 0;

            final ImageView particle = new ImageView(STRIP);
            particle.setX(startX - (size / 2));
            particle.setY(startY - (size / 2));
            particle.setFitWidth(size);
            particle.setFitHeight(size);
            particle.setRotate(startAngle);
            particle.setViewport(new Rectangle2D(vpx, vpy, SPRITE_WIDTH, SPRITE_WIDTH));
            particle.setBlendMode(BlendMode.ADD);

            particleLayer.getChildren().add(particle);

            KeyValue kv1 = new KeyValue(particle.opacityProperty(), 1.0);
            keyFrames[i*2] = new KeyFrame(Duration.valueOf(duration - 100));
            KeyValue kv21 = new KeyValue(particle.xProperty(), goalX, Interpolator.EASE_OUT);
            KeyValue kv22 = new KeyValue(particle.yProperty(), goalY, Interpolator.EASE_OUT);
            KeyValue kv23 = new KeyValue(particle.rotateProperty(), endAngle);
            KeyValue kv24 = new KeyValue(particle.opacityProperty(), 0.0);
            keyFrames[i*2+1] =
                new KeyFrame(Duration.valueOf(duration),
                             new EventHandler<ActionEvent>() {
                                 public void handle(ActionEvent e) {
                                     particleLayer.getChildren().remove(particle);
                                 }
                             },
                             kv21, kv22, kv23, kv24);

        }

        Timeline t = new Timeline(keyFrames);
        t.play();
    }

    public static void main(String argv[]) {
        launch(JMain.class, argv);
    }
}