Split up Effects into a bunch of classes

Server-side levitation now works too.

src/pocketmine/entity/effect/WitherEffect.php

@@ -0,0 +1,45 @@
+<?php
+
+/*
+ *
+ *  ____            _        _   __  __ _                  __  __ ____
+ * |  _ \ ___   ___| | _____| |_|  \/  (_)_ __   ___      |  \/  |  _ \
+ * | |_) / _ \ / __| |/ / _ \ __| |\/| | | '_ \ / _ \_____| |\/| | |_) |
+ * |  __/ (_) | (__|   <  __/ |_| |  | | | | | |  __/_____| |  | |  __/
+ * |_|   \___/ \___|_|\_\___|\__|_|  |_|_|_| |_|\___|     |_|  |_|_|
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * @author PocketMine Team
+ * @link http://www.pocketmine.net/
+ *
+ *
+*/
+
+declare(strict_types=1);
+
+namespace pocketmine\entity\effect;
+
+use pocketmine\entity\Effect;
+use pocketmine\entity\EffectInstance;
+use pocketmine\entity\Entity;
+use pocketmine\entity\Living;
+use pocketmine\event\entity\EntityDamageEvent;
+
+class WitherEffect extends Effect{
+
+	public function canTick(EffectInstance $instance) : bool{
+		if(($interval = (50 >> $instance->getAmplifier())) > 0){
+			return ($instance->getDuration() % $interval) === 0;
+		}
+		return true;
+	}
+
+	public function applyEffect(Living $entity, EffectInstance $instance, float $potency = 1.0, ?Entity $source = null) : void{
+		$ev = new EntityDamageEvent($entity, EntityDamageEvent::CAUSE_MAGIC, 1);
+		$entity->attack($ev);
+	}
+}