import javafx.animation.Animation.Status;
import javafx.animation.Interpolator;
import javafx.animation.Transition;
import javafx.event.EventHandler;
import javafx.scene.Node;
import javafx.scene.control.ScrollPane;
import javafx.scene.input.ScrollEvent;
import javafx.scene.layout.VBox;
import javafx.util.Duration;

/**
 * Scrollpane with kinda smooth transition scrolling.
 *
 * @author Matt
 */
public class SmoothishScrollpane extends ScrollPane {
	private final static int TRANSITION_DURATION = 200;
	private final static double BASE_MODIFIER = 1;

	/**
	 * @param content
	 *            Item to be wrapped in the scrollpane.
	 */
	public SmoothishScrollpane(Node content) {
		// ease-of-access for inner class
		ScrollPane scroll = this;
		// set content in a wrapper
		VBox wrapper = new VBox(content);
		setContent(wrapper);
		// add scroll handling to wrapper
		wrapper.setOnScroll(new EventHandler<ScrollEvent>() {
			private SmoothishTransition transition;

			@Override
			public void handle(ScrollEvent event) {
				double deltaY = BASE_MODIFIER * event.getDeltaY();
				double width = scroll.getContent().getBoundsInLocal().getWidth();
				double vvalue = scroll.getVvalue();
				Interpolator interp = Interpolator.LINEAR;
				transition = new SmoothishTransition(transition, deltaY) {
					@Override
					protected void interpolate(double frac) {
						double x = interp.interpolate(vvalue, vvalue + -deltaY * getMod() / width, frac);
						scroll.setVvalue(x);
					}
				};
				transition.play();
			}
		});
	}

	/**
	 * @param t
	 *            Transition to check.
	 * @return {@code true} if transition is playing.
	 */
	private static boolean playing(Transition t) {
		return t.getStatus() == Status.RUNNING;
	}

	/**
	 * @param d1
	 *            Value 1
	 * @param d2
	 *            Value 2.
	 * @return {@code true} if values signes are matching.
	 */
	private static boolean sameSign(double d1, double d2) {
		return (d1 > 0 && d2 > 0) || (d1 < 0 && d2 < 0);
	}

	/**
	 * Transition with varying speed based on previously existing transitions.
	 *
	 * @author Matt
	 */
	abstract class SmoothishTransition extends Transition {
		private final double mod;
		private final double delta;

		public SmoothishTransition(SmoothishTransition old, double delta) {
			setCycleDuration(Duration.millis(TRANSITION_DURATION));
			setCycleCount(0);
			// if the last transition was moving inthe same direction, and is still playing
			// then increment the modifer. This will boost the distance, thus looking faster
			// and seemingly consecutive.
			if (old != null && sameSign(delta, old.delta) && playing(old)) {
				mod = old.getMod() + 1;
			} else {
				mod = 1;
			}
			this.delta = delta;
		}

		public double getMod() {
			return mod;
		}

		@Override
		public void play() {
			super.play();
			// Even with a linear interpolation, startup is visibly slower than the middle.
			// So skip a small bit of the animation to keep up with the speed of prior
			// animation. The value of 10 works and isn't noticeable unless you really pay
			// close attention. This works best on linear but also is decent for others.
			if (getMod() > 1) {
				jumpTo(getCycleDuration().divide(10));
			}
		}
	}
}