Fix the usage of lingering potions in PvP with WG6

LingeringPotionPvpFix.java

import com.sk89q.worldguard.LocalPlayer;
import com.sk89q.worldguard.bukkit.RegionContainer;
import com.sk89q.worldguard.bukkit.RegionQuery;
import com.sk89q.worldguard.bukkit.WGBukkit;
import com.sk89q.worldguard.bukkit.util.Materials;
import com.sk89q.worldguard.protection.flags.DefaultFlag;
import com.sk89q.worldguard.protection.flags.StateFlag;

import org.bukkit.entity.LivingEntity;
import org.bukkit.entity.Player;
import org.bukkit.event.EventHandler;
import org.bukkit.event.Listener;
import org.bukkit.event.entity.AreaEffectCloudApplyEvent;
import org.bukkit.potion.PotionEffect;

import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;

/**
 * Copyright (C) 2016 Max Lee (https://github.com/Phoenix616/)
 * 
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the Mozilla Public License as published by
 * the Mozilla Foundation, version 2.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * Mozilla Public License v2.0 for more details.
 * 
 * You should have received a copy of the Mozilla Public License v2.0
 * along with this program. If not, see <http://mozilla.org/MPL/2.0/>.
 */
public class LingeringPotionPvpFix extends JavaPlugin implements Listener {

    public void onEnable() {
        if(getServer().getPluginManager().getPlugin("WorldGuard") != null && Integer.parseInt(WGBukkit.getPlugin().getDescription().getVersion().split("\\.")[0]) >= 6)
            getServer().getPluginManager().registerEvents(this, this);
    }

    @EventHandler
    public void onAreaEffect(AreaEffectCloudApplyEvent event) {
        if(!(event.getEntity().getSource() instanceof Player))
            return;

        boolean affectsPlayer = false;
        for(LivingEntity e : event.getAffectedEntities()) {
            if(e instanceof Player) {
                affectsPlayer = true;
                break;
            }
        }
        if(!affectsPlayer)
            return;

        Set<PotionEffect> effects = new HashSet<PotionEffect>(event.getEntity().getCustomEffects());
        effects.add(new PotionEffect(event.getEntity().getBasePotionData().getType().getEffectType(), event.getEntity().getDuration(), 1));
        if(!Materials.hasDamageEffect(effects))
            return;

        RegionContainer container = WGBukkit.getPlugin().getRegionContainer();
        RegionQuery query = container.createQuery();
        Iterator<LivingEntity> it = event.getAffectedEntities().iterator();
        while(it.hasNext()) {
            LivingEntity e = it.next();
            if(e instanceof Player && e != event.getEntity().getSource()) {
                boolean pvp = e.getWorld().getPVP() && query.queryState(e.getLocation(), WGBukkit.getPlugin().wrapPlayer((Player) e), DefaultFlag.PVP) != StateFlag.State.DENY;
                if(!pvp) {
                    it.remove();
                }
            }
        }
    }
}