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/*
 * Copyright 2015 Austin Keener, Michael Ritter, Florian Spieß, and the JDA contributors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package net.dv8tion.jda.internal.utils;

import net.dv8tion.jda.api.utils.ClosableIterator;
import net.dv8tion.jda.api.utils.cache.CacheView;
import org.slf4j.Logger;

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

public class ChainedClosableIterator implements ClosableIterator
{
    private final static Logger log = JDALogger.getLog(ClosableIterator.class);
    private final Set items;
    private final Iterator> generator;
    private ClosableIterator currentIterator;

    private T item;

    public ChainedClosableIterator(Iterator> generator)
    {
        this.items = new HashSet<>();
        this.generator = generator;
    }

    public Set getItems()
    {
        return items;
    }

    @Override
    public void close()
    {
        if (currentIterator != null)
            currentIterator.close();
        currentIterator = null;
    }

    @Override
    public boolean hasNext()
    {
        if (item != null)
            return true;
        // get next item from current iterator if exists
        if (currentIterator != null)
        {
            if (!currentIterator.hasNext())
            {
                currentIterator.close();
                currentIterator = null;
            }
            else
            {
                if (findNext()) return true;
                currentIterator.close();
                currentIterator = null;
            }
        }
        // get next iterator in chain
        return processChain();
    }

    private boolean processChain()
    {
        while (item == null)
        {
            CacheView view = null;
            while (generator.hasNext())
            {
                view = generator.next();
                if (!view.isEmpty())
                    break;
                view = null;
            }
            if (view == null)
                return false;

            // find next item in this iterator
            currentIterator = view.lockedIterator();
            if (findNext()) break;
        }
        return true;
    }

    private boolean findNext()
    {
        while (currentIterator.hasNext())
        {
            T next = currentIterator.next();
            if (items.contains(next))
                continue;
            item = next;
            items.add(item); // avoid duplicates
            return true;
        }
        return false;
    }

    @Override
    public T next()
    {
        if (!hasNext())
            throw new NoSuchElementException();
        T tmp = item;
        item = null;
        return tmp;
    }

    @Override
    @Deprecated //Deprecated in Java 9 because the finalization system is being changed/removed
    protected void finalize()
    {
        if (currentIterator != null)
        {
            log.error("Finalizing without closing, performing force close on lock");
            close();
        }
    }
}