Getting the inventory after the InventoryClickEvent

Main.java

ProtocolLibrary.getProtocolManager().addPacketListener(new PacketAdapter(this, ListenerPriority.HIGHEST, List.of(PacketType.fromClass(ServerboundContainerClickPacket.class)), ListenerOptions.SYNC) {

    @Override
    public void onPacketReceiving(PacketEvent event) {
        ServerboundContainerClickPacket packet = (ServerboundContainerClickPacket) event.getPacket().getHandle();
        ServerPlayer serverPlayer = ((CraftPlayer) event.getPlayer()).getHandle();

        PacketUtil.handleContainerClick(packet, serverPlayer);

        event.setCancelled(true);
    }
});

PacketUtil.java

import com.wizardlybump17.laptev.betterenderchest.api.event.PostInventoryClickEvent;
import it.unimi.dsi.fastutil.ints.Int2ObjectMap;
import it.unimi.dsi.fastutil.ints.Int2ObjectMaps;
import lombok.experimental.UtilityClass;
import net.minecraft.network.protocol.game.ClientboundContainerSetSlotPacket;
import net.minecraft.network.protocol.game.ServerboundContainerClickPacket;
import net.minecraft.server.level.ServerPlayer;
import net.minecraft.world.inventory.AbstractContainerMenu;
import net.minecraft.world.inventory.Slot;
import net.minecraft.world.item.Item;
import net.minecraft.world.item.ItemStack;
import net.minecraft.world.level.block.Blocks;
import org.bukkit.Bukkit;
import org.bukkit.craftbukkit.v1_20_R1.util.CraftMagicNumbers;
import org.bukkit.event.inventory.*;
import org.bukkit.inventory.CraftingInventory;
import org.bukkit.inventory.InventoryView;
import org.bukkit.inventory.SmithingInventory;

@UtilityClass
public class PacketUtil {

    /**
     * <p>
     *     Manually handles the inventory click packet. The code of this method was copied from the {@link net.minecraft.server.network.ServerGamePacketListenerImpl#handleContainerClick(ServerboundContainerClickPacket)}
     *     but the code style was changed, which may cause some bugs because I inverted some {@code if}s to add {@code break}s and {@code return}s without testing properly.<br>
     *     I strongly believe that this method is working correctly, but if you find any bugs, please report them to me.
     * </p>
     * <p>
     *     The end of this method calls the {@link PostInventoryClickEvent}, which was the reason this method exists.
     * </p>
     * @param packet the packet to handle
     * @param player the player who clicked
     */
    public static void handleContainerClick(ServerboundContainerClickPacket packet, ServerPlayer player) {
        if (player.isImmobile())
            return;

        player.resetLastActionTime();
        if (player.containerMenu.containerId != packet.getContainerId() || !player.containerMenu.stillValid(player))
            return;

        boolean cancelled = player.isSpectator();

        int i = packet.getSlotNum();

        if (!player.containerMenu.isValidSlotIndex(i))
            return;

        boolean flag = packet.getStateId() != player.containerMenu.getStateId();

        player.containerMenu.suppressRemoteUpdates();
        if (packet.getSlotNum() < -1 && packet.getSlotNum() != -999)
            return;

        InventoryView inventory = player.containerMenu.getBukkitView();
        InventoryType.SlotType type = inventory.getSlotType(packet.getSlotNum());

        InventoryClickEvent event;
        ClickType click = ClickType.UNKNOWN;
        InventoryAction action = InventoryAction.UNKNOWN;

        switch (packet.getClickType()) {
            case PICKUP -> {
                if (packet.getButtonNum() == 0)
                    click = ClickType.LEFT;
                else if (packet.getButtonNum() == 1)
                    click = ClickType.RIGHT;

                if (packet.getButtonNum() != 0 && packet.getButtonNum() != 1)
                    break;

                action = InventoryAction.NOTHING;
                if (packet.getSlotNum() == -999) {
                    if (!player.containerMenu.getCarried().isEmpty())
                        action = packet.getButtonNum() == 0 ? InventoryAction.DROP_ALL_CURSOR : InventoryAction.DROP_ONE_CURSOR;
                    break;
                }

                if (packet.getSlotNum() < 0)
                    break;

                Slot slot = player.containerMenu.getSlot(packet.getSlotNum());

                ItemStack clickedItem = slot.getItem();
                ItemStack cursor = player.containerMenu.getCarried();
                if (clickedItem.isEmpty()) {
                    if (!cursor.isEmpty())
                        action = packet.getButtonNum() == 0 ? InventoryAction.PLACE_ALL : InventoryAction.PLACE_ONE;
                    break;
                }

                if (!slot.mayPickup(player))
                    break;

                if (cursor.isEmpty()) {
                    action = packet.getButtonNum() == 0 ? InventoryAction.PICKUP_ALL : InventoryAction.PICKUP_HALF;
                    break;
                }

                if (slot.mayPlace(cursor)) {
                    if (ItemStack.isSameItemSameTags(clickedItem, cursor)) {
                        int toPlace = packet.getButtonNum() == 0 ? cursor.getCount() : 1;
                        toPlace = Math.min(toPlace, clickedItem.getMaxStackSize() - clickedItem.getCount());
                        toPlace = Math.min(toPlace, slot.container.getMaxStackSize() - clickedItem.getCount());
                        if (toPlace == 1)
                            action = InventoryAction.PLACE_ONE;
                        else if (toPlace == cursor.getCount())
                            action = InventoryAction.PLACE_ALL;
                        else if (toPlace < 0)
                            action = toPlace != -1 ? InventoryAction.PICKUP_SOME : InventoryAction.PICKUP_ONE; // this happens with oversized stacks
                        else if (toPlace != 0)
                            action = InventoryAction.PLACE_SOME;
                    } else if (cursor.getCount() <= slot.getMaxStackSize())
                        action = InventoryAction.SWAP_WITH_CURSOR;
                    break;
                }

                if (!ItemStack.isSameItemSameTags(cursor, clickedItem) || clickedItem.getCount() < 0 || clickedItem.getCount() + cursor.getCount() > cursor.getMaxStackSize())
                    break;

                action = InventoryAction.PICKUP_ALL;
            }

            case QUICK_MOVE -> {
                if (packet.getButtonNum() == 0)
                    click = ClickType.SHIFT_LEFT;
                else if (packet.getButtonNum() == 1)
                    click = ClickType.SHIFT_RIGHT;

                if (packet.getButtonNum() != 0 && packet.getButtonNum() != 1)
                    break;

                if (packet.getSlotNum() < 0) {
                    action = InventoryAction.NOTHING;
                    break;
                }

                Slot slot = player.containerMenu.getSlot(packet.getSlotNum());
                if (slot.mayPickup(player) && slot.hasItem())
                    action = InventoryAction.MOVE_TO_OTHER_INVENTORY;
                else
                    action = InventoryAction.NOTHING;
            }

            case SWAP -> {
                if (!((packet.getButtonNum() >= 0 && packet.getButtonNum() < 9) || packet.getButtonNum() == 40))
                    break;

                click = (packet.getButtonNum() == 40) ? ClickType.SWAP_OFFHAND : ClickType.NUMBER_KEY;
                Slot clickedSlot = player.containerMenu.getSlot(packet.getSlotNum());
                if (!clickedSlot.mayPickup(player)) {
                    action = InventoryAction.NOTHING;
                    break;
                }

                ItemStack hotbar = player.getInventory().getItem(packet.getButtonNum());
                boolean canCleanSwap = hotbar.isEmpty() || (clickedSlot.container == player.getInventory() && clickedSlot.mayPlace(hotbar));
                if (clickedSlot.hasItem()) {
                    if (canCleanSwap)
                        action = InventoryAction.HOTBAR_SWAP;
                    else
                        action = InventoryAction.HOTBAR_MOVE_AND_READD;
                } else if (!clickedSlot.hasItem() && !hotbar.isEmpty() && clickedSlot.mayPlace(hotbar))
                    action = InventoryAction.HOTBAR_SWAP;
                else
                    action = InventoryAction.NOTHING;
            }

            case CLONE -> {
                if (packet.getButtonNum() != 2)
                    break;

                click = ClickType.MIDDLE;
                if (packet.getSlotNum() < 0) {
                    action = InventoryAction.NOTHING;
                    break;
                }

                Slot slot = player.containerMenu.getSlot(packet.getSlotNum());
                if (slot.hasItem() && player.getAbilities().instabuild && player.containerMenu.getCarried().isEmpty())
                    action = InventoryAction.CLONE_STACK;
                else
                    action = InventoryAction.NOTHING;
            }

            case THROW -> {
                if (packet.getSlotNum() < 0) {
                    click = ClickType.LEFT;
                    if (packet.getButtonNum() == 1)
                        click = ClickType.RIGHT;
                    action = InventoryAction.NOTHING;
                    break;
                }

                if (packet.getButtonNum() == 0) {
                    click = ClickType.DROP;
                    Slot slot = player.containerMenu.getSlot(packet.getSlotNum());
                    if (slot.hasItem() && slot.mayPickup(player) && !slot.getItem().isEmpty() && slot.getItem().getItem() != Item.byBlock(Blocks.AIR))
                        action = InventoryAction.DROP_ONE_SLOT;
                    else
                        action = InventoryAction.NOTHING;
                    break;
                }

                if (packet.getButtonNum() != 1)
                    break;

                click = ClickType.CONTROL_DROP;
                Slot slot = player.containerMenu.getSlot(packet.getSlotNum());
                if (slot.hasItem() && slot.mayPickup(player) && !slot.getItem().isEmpty() && slot.getItem().getItem() != Item.byBlock(Blocks.AIR))
                    action = InventoryAction.DROP_ALL_SLOT;
                else
                    action = InventoryAction.NOTHING;
            }

            case QUICK_CRAFT -> player.containerMenu.clicked(packet.getSlotNum(), packet.getButtonNum(), packet.getClickType(), player);

            case PICKUP_ALL -> {
                click = ClickType.DOUBLE_CLICK;
                action = InventoryAction.NOTHING;
                if (packet.getSlotNum() < 0 || player.containerMenu.getCarried().isEmpty())
                    break;

                ItemStack cursor = player.containerMenu.getCarried();

                if (inventory.getTopInventory().contains(CraftMagicNumbers.getMaterial(cursor.getItem())) || inventory.getBottomInventory().contains(CraftMagicNumbers.getMaterial(cursor.getItem())))
                    action = InventoryAction.COLLECT_TO_CURSOR;
            }

            default -> {
            }
        }

        if (packet.getClickType() != net.minecraft.world.inventory.ClickType.QUICK_CRAFT) {
            if (click == ClickType.NUMBER_KEY)
                event = new InventoryClickEvent(inventory, type, packet.getSlotNum(), click, action, packet.getButtonNum());
            else
                event = new InventoryClickEvent(inventory, type, packet.getSlotNum(), click, action);

            org.bukkit.inventory.Inventory top = inventory.getTopInventory();
            if (packet.getSlotNum() == 0 && top instanceof CraftingInventory craftingInventory) {
                org.bukkit.inventory.Recipe recipe = craftingInventory.getRecipe();
                if (recipe != null) {
                    if (click == ClickType.NUMBER_KEY)
                        event = new CraftItemEvent(recipe, inventory, type, packet.getSlotNum(), click, action, packet.getButtonNum());
                    else
                        event = new CraftItemEvent(recipe, inventory, type, packet.getSlotNum(), click, action);
                }
            }

            if (packet.getSlotNum() == 3 && top instanceof SmithingInventory smithingInventory) {
                org.bukkit.inventory.ItemStack result = smithingInventory.getResult();
                if (result != null) {
                    if (click == ClickType.NUMBER_KEY)
                        event = new SmithItemEvent(inventory, type, packet.getSlotNum(), click, action, packet.getButtonNum());
                    else
                        event = new SmithItemEvent(inventory, type, packet.getSlotNum(), click, action);
                }
            }

            event.setCancelled(cancelled);
            AbstractContainerMenu oldContainer = player.containerMenu; // SPIGOT-1224
            Bukkit.getPluginManager().callEvent(event);
            if (player.containerMenu != oldContainer)
                return;

            switch (event.getResult()) {
                case ALLOW, DEFAULT -> player.containerMenu.clicked(i, packet.getButtonNum(), packet.getClickType(), player);
                case DENY -> {
                    switch (action) {
                        case PICKUP_ALL, MOVE_TO_OTHER_INVENTORY, HOTBAR_MOVE_AND_READD, HOTBAR_SWAP, COLLECT_TO_CURSOR, UNKNOWN ->
                                player.containerMenu.sendAllDataToRemote();
                        case PICKUP_SOME, PICKUP_HALF, PICKUP_ONE, PLACE_ALL, PLACE_SOME, PLACE_ONE, SWAP_WITH_CURSOR -> {
                            player.connection.send(new ClientboundContainerSetSlotPacket(-1, -1, player.inventoryMenu.incrementStateId(), player.containerMenu.getCarried()));
                            player.connection.send(new ClientboundContainerSetSlotPacket(player.containerMenu.containerId, player.inventoryMenu.incrementStateId(), packet.getSlotNum(), player.containerMenu.getSlot(packet.getSlotNum()).getItem()));
                        }
                        case DROP_ONE_SLOT, DROP_ALL_SLOT -> player.connection.send(new ClientboundContainerSetSlotPacket(player.containerMenu.containerId, player.inventoryMenu.incrementStateId(), packet.getSlotNum(), player.containerMenu.getSlot(packet.getSlotNum()).getItem()));
                        case DROP_ALL_CURSOR, DROP_ONE_CURSOR, CLONE_STACK -> player.connection.send(new ClientboundContainerSetSlotPacket(-1, -1, player.inventoryMenu.incrementStateId(), player.containerMenu.getCarried()));
                        case NOTHING -> {
                        }
                    }
                }
            }

            if (event instanceof CraftItemEvent || event instanceof SmithItemEvent)
                player.containerMenu.sendAllDataToRemote();
        }

        for (Int2ObjectMap.Entry<ItemStack> entry : Int2ObjectMaps.fastIterable(packet.getChangedSlots()))
            player.containerMenu.setRemoteSlotNoCopy(entry.getIntKey(), entry.getValue());

        player.containerMenu.setRemoteCarried(packet.getCarriedItem());
        player.containerMenu.resumeRemoteUpdates();
        if (flag)
            player.containerMenu.broadcastFullState();
        else
            player.containerMenu.broadcastChanges();

        new PostInventoryClickEvent(inventory, packet.getSlotNum(), click, action, packet.getButtonNum()).callEvent();
    }
}

PostInventoryClickEvent.java

import lombok.Getter;
import lombok.NonNull;
import net.minecraft.network.protocol.game.ServerboundContainerClickPacket;
import net.minecraft.server.level.ServerPlayer;
import org.bukkit.entity.HumanEntity;
import org.bukkit.event.inventory.ClickType;
import org.bukkit.event.inventory.InventoryAction;
import org.bukkit.event.inventory.InventoryEvent;
import org.bukkit.event.inventory.InventoryType;
import org.bukkit.inventory.Inventory;
import org.bukkit.inventory.InventoryView;
import org.jetbrains.annotations.Nullable;

/**
 * <p>
 *     This event is called after the {@link org.bukkit.event.inventory.InventoryClickEvent}.
 *     It is called in the end of the {@link com.wizardlybump17.laptev.betterenderchest.api.util.PacketUtil#handleContainerClick(ServerboundContainerClickPacket, ServerPlayer)} method.
 * </p>
 */
@Getter
public class PostInventoryClickEvent extends InventoryEvent {

    private final int rawSlot;
    private final @NonNull ClickType click;
    private final @NonNull InventoryAction action;
    private final int hotbarButton;

    public PostInventoryClickEvent(@NonNull InventoryView transaction, int slot, @NonNull ClickType click, @NonNull InventoryAction action, int hotbarButton) {
        super(transaction);
        rawSlot = slot;
        this.click = click;
        this.action = action;
        this.hotbarButton = hotbarButton;
    }

    public @Nullable Inventory getClickedInventory() {
        return transaction.getInventory(rawSlot);
    }

    public int getSlot() {
        return transaction.convertSlot(rawSlot);
    }

    public @NonNull InventoryType.SlotType getSlotType() {
        return transaction.getSlotType(rawSlot);
    }

    public @NonNull HumanEntity getWhoClicked() {
        return transaction.getPlayer();
    }
}

boa mano wizardly vou usar muito!!!