package envoy.client.ui;

import java.io.IOException;
import java.util.Stack;
import java.util.logging.Level;

import javafx.fxml.FXMLLoader;
import javafx.scene.*;
import javafx.stage.Stage;

import dev.kske.eventbus.core.*;

import envoy.util.EnvoyLog;

import envoy.client.data.Settings;
import envoy.client.data.shortcuts.*;
import envoy.client.event.*;

/**
 * Manages a stack of scenes. The most recently added scene is displayed inside a stage. When a
 * scene is removed from the stack, its predecessor is displayed.
 * <p>
 * When a scene is loaded, the style sheet for the current theme is applied to it.
 *
 * @author Kai S. K. Engelbart
 * @since Envoy Client v0.1-beta
 */
public final class SceneContext {

	private final Stage			stage;
	private final Stack<Parent>	roots		= new Stack<>();
	private final Stack<Object>	controllers	= new Stack<>();

	private Scene scene;

	/**
	 * Initializes the scene context.
	 *
	 * @param stage the stage in which scenes will be displayed
	 * @since Envoy Client v0.1-beta
	 */
	public SceneContext(Stage stage) {
		this.stage = stage;
		EventBus.getInstance().registerListener(this);
	}

	/**
	 * Loads a new scene specified by a scene info.
	 *
	 * @param info specifies the scene to load
	 * @throws RuntimeException if the loading process fails
	 * @since Envoy Client v0.1-beta
	 */
	public void load(SceneInfo info) {
		EnvoyLog.getLogger(SceneContext.class).log(Level.FINER, "Loading scene " + info);

		try {

			// Load root node and controller
			var		loader		= new FXMLLoader();
			Parent	root		= loader.load(getClass().getResourceAsStream(info.path));
			Object	controller	= loader.getController();
			roots.push(root);
			controllers.push(controller);

			if (scene == null) {

				// One-time scene initialization
				scene = new Scene(root, stage.getWidth(), stage.getHeight());
				applyCSS();
				stage.setScene(scene);
			} else {
				scene.setRoot(root);
			}

			// Remove previous keyboard shortcuts
			scene.getAccelerators().clear();

			// Supply the global custom keyboard shortcuts for that scene
			scene.getAccelerators()
				.putAll(GlobalKeyShortcuts.getInstance().getKeyboardShortcuts(info));

			// Supply the scene specific keyboard shortcuts
			if (controller instanceof KeyboardMapping)
				scene.getAccelerators()
					.putAll(((KeyboardMapping) controller).getKeyboardShortcuts());
		} catch (IOException e) {
			throw new RuntimeException(e);
		}
	}

	/**
	 * Removes the current scene and displays the previous one.
	 *
	 * @since Envoy Client v0.1-beta
	 */
	public void pop() {

		// Pop current root node and controller
		roots.pop();
		controllers.pop();

		// Apply new scene if present
		if (!roots.isEmpty()) {
			scene.setRoot(roots.peek());

			// Invoke restore if controller is restorable
			var controller = controllers.peek();
			if (controller instanceof Restorable)
				((Restorable) controller).onRestore();
		} else {

			// Remove the current scene entirely
			scene = null;
			stage.setScene(null);
		}
	}

	private void applyCSS() {
		if (scene != null) {
			var	styleSheets	= scene.getStylesheets();
			var	themeCSS	= "/css/" + Settings.getInstance().getCurrentTheme() + ".css";
			styleSheets.clear();
			styleSheets.addAll(getClass().getResource("/css/base.css").toExternalForm(),
				getClass().getResource(themeCSS).toExternalForm());
		}
	}

	@Event(Logout.class)
	@Priority(150)
	private void onLogout() {
		roots.clear();
		controllers.clear();
	}

	@Event(ThemeChangeEvent.class)
	@Priority(150)
	private void onThemeChange() {
		applyCSS();
	}

	/**
	 * @param <T> the type of the controller
	 * @return the controller used by the current scene
	 * @since Envoy Client v0.1-beta
	 */
	public <T> T getController() { return (T) controllers.peek(); }

	/**
	 * @return the stage in which the scenes are displayed
	 * @since Envoy Client v0.1-beta
	 */
	public Stage getStage() { return stage; }

	/**
	 * @return whether the scene stack is empty
	 * @since Envoy Client v0.2-beta
	 */
	public boolean isEmpty() { return roots.isEmpty(); }
}