BetterTridents/src/main/java/de/jeff_media/bettertridents/tasks/MoveToOffhand.java

package de.jeff_media.bettertridents.tasks;

import de.jeff_media.bettertridents.Main;
import org.bukkit.Material;
import org.bukkit.entity.Player;
import org.bukkit.inventory.ItemStack;
import org.bukkit.inventory.meta.ItemMeta;
import org.bukkit.scheduler.BukkitRunnable;

public class MoveToOffhand extends BukkitRunnable {
    private final Player player;
    private final ItemStack tridentItem;

    public MoveToOffhand(Player player, ItemStack tridentItem) {
        this.player = player;
        this.tridentItem = tridentItem;
    }

    @Override
    public void run() {
        for (int i = 0; i < player.getInventory().getSize(); i++) {
            ItemStack item = player.getInventory().getItem(i);
            if (item != null && item.equals(tridentItem)) {
                ItemMeta meta = tridentItem.getItemMeta();
                meta.getPersistentDataContainer().remove(Main.OFFHAND_TAG);
                tridentItem.setItemMeta(meta);
                ItemStack offhand = player.getInventory().getItemInOffHand();
                if(offhand == null || offhand.getType() == Material.AIR) {
                    player.getInventory().setItemInOffHand(tridentItem.clone());
                    tridentItem.setAmount(tridentItem.getAmount()-1);
                    player.getInventory().setItem(i, tridentItem);
                }
                break;
            }
        }
        player.updateInventory();
    }
}