[1.12.2] Damage on sword keeps resetting

So, I have coded a sword which has an ability to teleport behind an entity when right-clicking, and that will cause damage to the sword. However, whenever I hit with the sword or right-click after pausing for a while, the durability will go back up to what it was before I vigorously used it (for testing).

Here is the code:

package io.nozzomi.improvisedarmory.items.swords;

import java.util.List;

import javax.annotation.Nullable;

import io.nozzomi.improvisedarmory.Main;
import io.nozzomi.improvisedarmory.init.ModItems;
import io.nozzomi.improvisedarmory.util.IHasModel;
import io.nozzomi.improvisedarmory.util.Utilities;
import net.minecraft.client.util.ITooltipFlag;
import net.minecraft.entity.Entity;
import net.minecraft.entity.EntityLiving;
import net.minecraft.entity.EntityLivingBase;
import net.minecraft.entity.player.EntityPlayer;
import net.minecraft.item.IItemPropertyGetter;
import net.minecraft.item.ItemStack;
import net.minecraft.item.ItemSword;
import net.minecraft.util.ActionResult;
import net.minecraft.util.EnumActionResult;
import net.minecraft.util.EnumHand;
import net.minecraft.util.ResourceLocation;
import net.minecraft.util.math.BlockPos;
import net.minecraft.util.math.Vec3d;
import net.minecraft.world.World;
import net.minecraftforge.fml.relauncher.Side;
import net.minecraftforge.fml.relauncher.SideOnly;

public class SwordTrickery extends ItemSword implements IHasModel	
{
	public int cooldown = 0;
	public int overCooldown = 0;
	public int stage = 0;
	
	public SwordTrickery() {
		super(ModItems.MATERIAL_TRICKERY);
		this.setUnlocalizedName("sword_trickery");
		this.setRegistryName("sword_trickery");
		this.setCreativeTab(Main.tabImprovised);
		
		this.addPropertyOverride(new ResourceLocation("onCooldown"), new IItemPropertyGetter() {
			@SideOnly(Side.CLIENT)
			@Override
			public float apply(ItemStack stack, @Nullable World worldIn, @Nullable EntityLivingBase entityIn) {
				return stage;
			}
		});
		
		ModItems.ITEMS.add(this);
	}

	@Override
	public void registerModels()
	{
		Main.proxy.registerItemRenderer(this, 0, "inventory");
	}
	
	@Override
	public ActionResult<ItemStack> onItemRightClick(World world, EntityPlayer player, EnumHand hand) {
		ItemStack item = player.getHeldItem(hand);
		Entity e = Utilities.getMouseOver(5);
		if(e != null && e instanceof EntityLiving)
		{
			Vec3d aim = e.getLookVec();
			if(world.isAirBlock(new BlockPos(e.posX - aim.x * 2, e.posY, e.posZ - aim.z * 2)) ||
					!world.isBlockFullCube(new BlockPos(e.posX - aim.x * 2, e.posY, e.posZ - aim.z * 2)))
			{
				if(cooldown <= 0)
				{
					if(!player.capabilities.isCreativeMode)
					{
						item.damageItem(20*stage, player);
					}
					player.setPositionAndRotation(e.posX - aim.x * 2, e.posY, e.posZ - aim.z * 2, e.rotationYaw, player.rotationPitch);
					cooldown = 20;
					overCooldown = 1200;
					stage += stage < 4 ? 1 : 0;
				}
			}
		}
		return new ActionResult<ItemStack>(EnumActionResult.SUCCESS, item);
	}
	
	@Override
	public void addInformation(ItemStack stack, World worldIn, List<String> tooltip, ITooltipFlag flagIn) 
	{
		tooltip.add("Current Stage: 0");
	}
	
	@Override
	public boolean hitEntity(ItemStack stack, EntityLivingBase target, EntityLivingBase attacker)
    {
        switch(stage)
        {
        case 0:
        	stack.damageItem(1, attacker);
        	break;
        case 1:
        	stack.damageItem(5, attacker);
        	break;
        case 2:
        	stack.damageItem(15, attacker);
        	break;
        case 3:
        	stack.damageItem(30, attacker);
        	break;
        case 4:
        	stack.damageItem(50, attacker);
        	break;
        default:
        	stack.damageItem(1, attacker);
        	break;
        }
        return true;
    }
	
	@Override
	public void onUpdate(ItemStack stack, World worldIn, Entity entityIn, int itemSlot, boolean isSelected)
	{
		if(cooldown != 0)
			cooldown--;
		
		if(overCooldown != 0)
			overCooldown--;
		
		if(overCooldown == 0 && stage != 0)
			stage = 0;
	}
}

Edited June 9, 20196 yr by Nozzomi
Removed Spoiler