import javafx.animation.AnimationTimer;
import javafx.application.Application;
import javafx.scene.layout.BorderPane;
import javafx.scene.Scene;
import javafx.stage.Stage;
import javafx.scene.canvas.Canvas;
import javafx.scene.canvas.GraphicsContext;
import javafx.scene.paint.Color;

/**
 * This program shows an animation where 100 semi-transparent disks of
 * various sizes grow continually, disappearing before they get too big.
 * When a disk disappears, it is replaced by a new disk at another location.
 * This program uses class CircleInfo, defined in CircleInfo.java.
 */
public class GrowingCircleAnimation extends Application {
    
    private CircleInfo[] circleData; // holds the data for all 100 circles
    
    /**
     *  Draw one frame of the animation.  If there is no disk data (which is
     *  true for the first frame), 100 disks with random locations, colors,
     *  and radii are created.  In each frame, all the disks grow by
     *  one pixel per frame.  Disks sometimes disappear at random, or when
     *  their radius reaches 100.  When a disk disappears, a new disk appears
     *  with radius 1 and with a random location and color
     */
    private void drawFrame(GraphicsContext g, int frameNumber, int width, int height) {
        g.setFill(Color.WHITE);
        g.fillRect(0,0,width,height);
        if (circleData == null) {  // create the array, if it doesn't exist
            circleData = new CircleInfo[100];
            for (int i = 0; i < circleData.length; i++) {
                circleData[i] = new CircleInfo( 
                                        (int)(width*Math.random()),
                                        (int)(height*Math.random()),
                                        (int)(100*Math.random()) );
            }
        }
        for (int i = 0; i < circleData.length; i++) {  // draw the filled circles
            circleData[i].radius++;
            circleData[i].draw(g);
            if (Math.random() < 0.005 || circleData[i].radius > 100) {
                    // replace circle number i with a new circle
                circleData[i] = new CircleInfo( 
                                        (int)(width*Math.random()),
                                        (int)(height*Math.random()),
                                        1 );
            }
        }
    }
    
    
    //------ Implementation details: DO NOT EXPECT TO UNDERSTAND THIS -----

    
    public void start(Stage stage) {
        int width = 600;
        int height = 480;
        Canvas canvas = new Canvas(width,height);
        drawFrame(canvas.getGraphicsContext2D(), 0, width, height);
        BorderPane root = new BorderPane(canvas);
        root.setStyle("-fx-border-width: 4px; -fx-border-color: #444");
        Scene scene = new Scene(root);
        stage.setScene(scene);
        stage.setTitle("Growing Circles");
        stage.show();
        stage.setResizable(false);
        AnimationTimer anim = new AnimationTimer() {
            private int frameNum;
            long previousFrameTime;
            public void handle(long time) {
                if (time - previousFrameTime > 0.95e9/60) {
                    // The if statement should not be necessary!  It's there because of
                    // a bug that has shown up in some versions of Java on some computers.
                    // The if statement throttles the frame rate to 60 per second, in case
                    // JavaFX incorrectly fails to do that itself.  
                    frameNum++;
                    drawFrame(canvas.getGraphicsContext2D(), frameNum,  width, height);
                    previousFrameTime = time;
                }
            }
        };
        anim.start();
    } 

    public static void main(String[] args) {
        launch();
    }

}