EpicHeads/main/java/com/songoda/epicheads/menu/ui/InventoryMenu.java

package com.songoda.epicheads.menu.ui;

import com.songoda.epicheads.EpicHeads;
import com.songoda.epicheads.menu.ui.element.Container;
import com.songoda.epicheads.menu.ui.element.Element;
import com.songoda.epicheads.menu.ui.item.Button;
import com.songoda.epicheads.util.Checks;
import com.songoda.epicheads.util.Stringify;
import org.bukkit.Bukkit;
import org.bukkit.entity.Player;
import org.bukkit.event.inventory.InventoryClickEvent;
import org.bukkit.inventory.Inventory;
import org.bukkit.inventory.InventoryHolder;
import org.bukkit.inventory.InventoryView;
import org.bukkit.inventory.ItemStack;

import java.util.ArrayList;
import java.util.List;

public class InventoryMenu implements InventoryHolder {

	private final Player player;
	public final Bounds bounds;

	private final List<Element> elements = new ArrayList<>();

	private Container container;
	private Inventory inventory;
	private String title;
	private Inventory newInventory;
	private String newTitle;

	public InventoryMenu(Player player, String title, int rows) {
		Checks.ensureNonNull(player, "player");

		this.player = player;
		this.bounds = new Bounds(Position.ZERO, 9, rows);
		this.container = new Container(bounds);

		setTitle(title);
	}

	public Player getPlayer() {
		return player;
	}

	@Override
	public Inventory getInventory() {
		return inventory;
	}

	public boolean hasMenuOpen() {
		InventoryView view = player.getOpenInventory();

		if (view == null || view.getTopInventory() == null)
			return false;

		InventoryHolder holder = view.getTopInventory().getHolder();

		return holder != null && holder.equals(this);
	}

	public void removeElement(Element element) {
		Checks.ensureNonNull(element, "element");

		elements.remove(element);
	}

	public void addElement(Element element) {
		Checks.ensureNonNull(element, "element");
		Checks.ensureTrue(bounds.inBounds(element.bounds), "element's bounds is not within the bounds of the menu");

		elements.add(element);
	}

	public List<Element> getElements() {
		return elements;
	}

	public void open() {
		updateMenu();
		player.openInventory(inventory);
	}

	public void setTitle(String title) {
		Checks.ensureNonNull(title, "title");

		if (inventory != null && title.equals(this.title))
			return;

		title = (title.length() > 32 ? title.substring(0, 32) : title);
		this.title = title;

		this.newInventory = Bukkit.createInventory(this, bounds.getVolume(), title);
	}

	private boolean swapToNewInventory() {
		if (newInventory == null)
			return false;

		inventory = newInventory;
		title = newTitle;
		newInventory = null;

		return true;
	}

	public void layoutElements() {
		container.clear();

		elements.forEach(container::addElement);
	}

	public void updateMenu() {
		boolean newInventory = swapToNewInventory();

		layoutElements();

		Button[] items = container.getItems();
		ItemStack[] contents = new ItemStack[items.length];

		for (int index = 0; index < contents.length; index++) {
			Button item = items[index];

			if (item != null) {
				contents[index] = item.getItem();
			}
		}

		inventory.setContents(contents);

		if (newInventory && hasMenuOpen()) {
			player.openInventory(inventory);
		}
	}

	public void onClick(InventoryClickEvent event) {
		event.setCancelled(true);

		// Make sure the player's inventory is up to date after the event is cancelled
		Bukkit.getScheduler().scheduleSyncDelayedTask(EpicHeads.getInstance(), player::updateInventory, 1);

		int slot = event.getRawSlot();

		MenuResponse response = container.handleClick(slot);

		switch (response) {
			case CLOSE:
				player.closeInventory();
				break;
			case UPDATE:
				updateMenu();
				break;
			case NONE:
				break;
			default:
				throw new IllegalStateException("Unknown MenuResponse value " + response);
		}
	}

	@Override
	public String toString() {
		return Stringify.builder().previous(super.toString()).entry("inventory", inventory).entry("player", player).toString();
	}

}