alpha_BaseBoss.java

package me.exerosis.example.alpha;

import org.bukkit.entity.LivingEntity;

public class BaseBoss implements Boss {
	private final LivingEntity base;
	private Stage stage;
	
	public BaseBoss(LivingEntity base) {
		this.base = base;
	}
	
	@Override
	public LivingEntity base() {
		return base;
	}
	
	@Override
	public <Type extends Stage> Type stage(Type stage) {
		this.stage.disable();
		if (!base().isDead()) {
			this.stage = stage;
			stage.enable();
		}
		return stage;
	}
	
	@SuppressWarnings("unchecked")
	@Override
	public <Type extends Stage> Type stage() {
		return (Type) stage;
	}
}

alpha_Boss.java

package me.exerosis.example.alpha;

import org.bukkit.entity.LivingEntity;

public interface Boss {
	
	LivingEntity base();
	
	//--Stages--
	<Type extends Stage> Type stage(Type stage);
	
	<Type extends Stage> Type stage();
	
	interface Stage {
		void enable();
		
		void disable();
	}
}

alpha_stages_AbilityStage.java

package me.exerosis.example.alpha.stages;

import me.exerosis.example.alpha.Boss;

public class AbilityStage implements Boss.Stage {
	private final Boss.Stage[] stages;
	
	public AbilityStage(Boss.Stage... stages) {
		this.stages = stages;
	}
	
	@Override
	public void enable() {
		for (Boss.Stage stage : stages) {
			stage.enable();
		}
	}
	
	@Override
	public void disable() {
		for (Boss.Stage stage : stages) {
			stage.disable();
		}
	}
}

alpha_stages_AttributesAbility.java

package me.exerosis.example.alpha.stages;

public class AttributesAbility {
}

alpha_stages_HealthStage.java

package me.exerosis.example.alpha.stages;

import com.google.common.collect.Range;
import com.google.common.collect.RangeMap;
import me.exerosis.example.alpha.Boss;
import org.bukkit.event.EventHandler;
import org.bukkit.event.Listener;
import org.bukkit.event.entity.EntityDamageEvent;
import org.bukkit.plugin.Plugin;

import static com.google.common.collect.TreeRangeMap.create;
import static org.bukkit.Bukkit.getPluginManager;
import static org.bukkit.attribute.Attribute.GENERIC_MAX_HEALTH;
import static org.bukkit.event.EventPriority.MONITOR;
import static org.bukkit.event.HandlerList.unregisterAll;

public class HealthStage implements Listener, Boss.Stage {
	private final RangeMap<Double, Boss.Stage> stages = create();
	private final Plugin plugin;
	private final Boss boss;
	private Boss.Stage stage;
	
	public HealthStage(Plugin plugin, Boss boss) {
		this.plugin = plugin;
		this.boss = boss;
	}
	
	public HealthStage add(Range<Double> range, Boss.Stage stage) {
		stages.put(range, stage);
		return this;
	}
	
	public void remove(Range<Double> range) {
		stages.remove(range);
	}
	
	@Override
	public void enable() {
		getPluginManager().registerEvents(this, plugin);
		setStage(stages.get(asPercent(boss.base().getHealth())));
	}
	
	@Override
	public void disable() {
		unregisterAll(this);
		stage.disable();
		stage = null;
	}
	
	@EventHandler(priority = MONITOR, ignoreCancelled = true)
	void onDamage(EntityDamageEvent event) {
		if (!event.getEntity().equals(boss))
			return;
		setStage(stages.get(asPercent(boss.base().getHealth() - event.getFinalDamage())));
	}
	
	private double asPercent(double health) {
		return health / boss.base().getAttribute(GENERIC_MAX_HEALTH).getValue();
	}
	
	private void setStage(Boss.Stage stage) {
		if (this.stage != null)
			this.stage.disable();
		this.stage = stage;
		stage.enable();
	}
}

alpha_test_ZombieBoss.java

package me.exerosis.example.alpha.test;

import me.exerosis.example.alpha.BaseBoss;
import me.exerosis.example.alpha.stages.AbilityStage;
import me.exerosis.example.alpha.stages.HealthStage;
import org.bukkit.Location;
import org.bukkit.entity.LivingEntity;
import org.bukkit.plugin.Plugin;

import static com.google.common.collect.Range.greaterThan;
import static com.google.common.collect.Range.singleton;
import static org.bukkit.entity.EntityType.ZOMBIE;

public class ZombieBoss extends BaseBoss {
	public static final double DYING = 0.0;
	public static final double RUNNING = 0.50;
	
	public ZombieBoss(Plugin plugin, Location location) {
		super((LivingEntity) location.getWorld().spawnEntity(location, ZOMBIE));
		
		Stage shooting = new AbilityStage();
		Stage running = new AbilityStage();
		Stage dying = new AbilityStage();
		stage(new HealthStage(plugin, this))
				.add(singleton(DYING), dying)
				.add(greaterThan(DYING), running)
				.add(greaterThan(RUNNING), shooting);
		
		
	}
	
	
	
}