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/*
 * Licensed to Elasticsearch under one or more contributor
 * license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright
 * ownership. Elasticsearch licenses this file to you 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 org.elasticsearch.common.util.concurrent;

import org.elasticsearch.ElasticsearchIllegalStateException;

import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

/**
 * This class manages locks. Locks can be accessed with an identifier and are
 * created the first time they are acquired and removed if no thread hold the
 * lock. The latter is important to assure that the list of locks does not grow
 * infinitely.
 * 
 * A Thread can acquire a lock only once.
 * 
 * */
public class KeyedLock {

    private final boolean fair;

    /**
     * @param fair Use fair locking, ie threads get the lock in the order they requested it
     */
    public KeyedLock(boolean fair) {
        this.fair = fair;
    }

    public KeyedLock() {
        this(false);
    }

    private final ConcurrentMap map = ConcurrentCollections.newConcurrentMap();

    protected final ThreadLocal threadLocal = new ThreadLocal<>();

    public void acquire(T key) {
        while (true) {
            if (threadLocal.get() != null) {
                // if we are here, the thread already has the lock
                throw new ElasticsearchIllegalStateException("Lock already acquired in Thread" + Thread.currentThread().getId()
                        + " for key " + key);
            }
            KeyLock perNodeLock = map.get(key);
            if (perNodeLock == null) {
                KeyLock newLock = new KeyLock(fair);
                perNodeLock = map.putIfAbsent(key, newLock);
                if (perNodeLock == null) {
                    newLock.lock();
                    threadLocal.set(newLock);
                    return;
                }
            }
            assert perNodeLock != null;
            int i = perNodeLock.count.get();
            if (i > 0 && perNodeLock.count.compareAndSet(i, i + 1)) {
                perNodeLock.lock();
                threadLocal.set(perNodeLock);
                return;
            }
        }
    }

    public void release(T key) {
        KeyLock lock = threadLocal.get();
        if (lock == null) {
            throw new ElasticsearchIllegalStateException("Lock not acquired");
        }
        release(key, lock);
    }

    void release(T key, KeyLock lock) {
        assert lock.isHeldByCurrentThread();
        assert lock == map.get(key);
        lock.unlock();
        threadLocal.set(null);
        int decrementAndGet = lock.count.decrementAndGet();
        if (decrementAndGet == 0) {
            map.remove(key, lock);
        }
    }


    @SuppressWarnings("serial")
    private final static class KeyLock extends ReentrantLock {
        KeyLock(boolean fair) {
            super(fair);
        }

        private final AtomicInteger count = new AtomicInteger(1);
    }

    public boolean hasLockedKeys() {
        return !map.isEmpty();
    }

    /**
     * A {@link KeyedLock} that allows to acquire a global lock that guarantees
     * exclusive access to the resource the KeyedLock is guarding.
     */
    public final static class GlobalLockable extends KeyedLock {


        private final ReadWriteLock lock;

        public GlobalLockable(boolean fair){
            super(fair);
            lock = new ReentrantReadWriteLock(fair);
        }

        public GlobalLockable() {
            this(false);
        }

        @Override
        public void acquire(T key) {
            boolean success = false;
            lock.readLock().lock();
            try {
                super.acquire(key);
                success = true;
            } finally {
                if (!success) {
                    lock.readLock().unlock();
                }
            }
        }

        @Override
        public void release(T key) {
            KeyLock keyLock = threadLocal.get();
            if (keyLock == null) {
                throw new ElasticsearchIllegalStateException("Lock not acquired");
            }
            try {
                release(key, keyLock);
            } finally {
                lock.readLock().unlock();
            }
        }

        /**
         * Returns a global lock guaranteeing exclusive access to the resource
         * this KeyedLock is guarding.
         */
        public Lock globalLock() {
            return lock.writeLock();
        }
    }

}