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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.cache;

import net.dv8tion.jda.api.utils.MiscUtil;
import net.dv8tion.jda.internal.utils.UnlockHook;

import java.lang.ref.WeakReference;
import java.util.Collections;
import java.util.List;
import java.util.NavigableSet;
import java.util.Set;
import java.util.concurrent.locks.ReentrantReadWriteLock;

public abstract class ReadWriteLockCache
{
    protected final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
    protected WeakReference> cachedList;
    protected WeakReference>  cachedSet;

    public UnlockHook writeLock()
    {
        if (lock.getReadHoldCount() > 0)
            throw new IllegalStateException("Unable to acquire write-lock while holding read-lock!");
        ReentrantReadWriteLock.WriteLock writeLock = lock.writeLock();
        MiscUtil.tryLock(writeLock);
        onAcquireWriteLock();
        clearCachedLists();
        return new UnlockHook(writeLock);
    }

    public UnlockHook readLock()
    {
        ReentrantReadWriteLock.ReadLock readLock = lock.readLock();
        MiscUtil.tryLock(readLock);
        onAcquireReadLock();
        return new UnlockHook(readLock);
    }

    public void clearCachedLists()
    {
        cachedList = null;
        cachedSet = null;
    }

    protected void onAcquireWriteLock() {}
    protected void onAcquireReadLock() {}

    protected List getCachedList()
    {
        return cachedList == null ? null : cachedList.get();
    }

    protected Set getCachedSet()
    {
        return cachedSet == null ? null : cachedSet.get();
    }

    protected List cache(List list)
    {
        list = Collections.unmodifiableList(list);
        cachedList = new WeakReference<>(list);
        return list;
    }

    protected Set cache(Set set)
    {
        set = Collections.unmodifiableSet(set);
        cachedSet = new WeakReference<>(set);
        return set;
    }

    protected NavigableSet cache(NavigableSet set)
    {
        set = Collections.unmodifiableNavigableSet(set);
        cachedSet = new WeakReference<>(set);
        return set;
    }
}