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/*
 * Copyright 2010-2012 Luca Garulli (l.garulli--at--orientechnologies.com)
 *
 * 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 com.orientechnologies.common.concur.resource;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

import com.orientechnologies.common.concur.OTimeoutException;
import com.orientechnologies.common.concur.lock.OLockException;

/**
 * Adaptive class to handle shared resources. It's configurable specifying if it's running in a concurrent environment and allow o
 * specify a maximum timeout to avoid deadlocks.
 * 
 * @author Luca Garulli (l.garulli--at--orientechnologies.com)
 * 
 */
public class OSharedResourceAdaptive {
	private final ReadWriteLock	lock	= new ReentrantReadWriteLock();
	private final AtomicInteger	users	= new AtomicInteger(0);
	private final boolean				concurrent;
	private final int						timeout;
	private final boolean				ignoreThreadInterruption;

	protected OSharedResourceAdaptive() {
		this.concurrent = true;
		this.timeout = 0;
		this.ignoreThreadInterruption = false;
	}

	protected OSharedResourceAdaptive(final int iTimeout) {
		this.concurrent = true;
		this.timeout = iTimeout;
		this.ignoreThreadInterruption = false;
	}

	protected OSharedResourceAdaptive(final boolean iConcurrent) {
		this.concurrent = iConcurrent;
		this.timeout = 0;
		this.ignoreThreadInterruption = false;
	}

	protected OSharedResourceAdaptive(final boolean iConcurrent, final int iTimeout, boolean ignoreThreadInterruption) {
		this.concurrent = iConcurrent;
		this.timeout = iTimeout;
		this.ignoreThreadInterruption = ignoreThreadInterruption;
	}

	protected void acquireExclusiveLock() {
		if (concurrent)
			if (timeout > 0) {
				try {
					if (lock.writeLock().tryLock(timeout, TimeUnit.MILLISECONDS))
						// OK
						return;
				} catch (InterruptedException e) {
					if (ignoreThreadInterruption) {
						// IGNORE THE THREAD IS INTERRUPTED: TRY TO RE-LOCK AGAIN
						try {
							if (lock.writeLock().tryLock(timeout, TimeUnit.MILLISECONDS)) {
								// OK, RESET THE INTERRUPTED STATE
								Thread.currentThread().interrupt();
								return;
							}
						} catch (InterruptedException e2) {
							Thread.currentThread().interrupt();
						}
					}

					throw new OLockException("Thread interrupted while waiting for resource of class '" + getClass() + "' with timeout="
							+ timeout);
				}
				throw new OTimeoutException("Timeout on acquiring exclusive lock against resource of class: " + getClass()
						+ " with timeout=" + timeout);
			} else
				lock.writeLock().lock();
	}

	protected boolean tryAcquireExclusiveLock() {
		return concurrent || lock.writeLock().tryLock();
	}

	protected void acquireSharedLock() {
		if (concurrent)
			if (timeout > 0) {
				try {
					if (lock.readLock().tryLock(timeout, TimeUnit.MILLISECONDS))
						// OK
						return;
				} catch (InterruptedException e) {
					if (ignoreThreadInterruption) {
						// IGNORE THE THREAD IS INTERRUPTED: TRY TO RE-LOCK AGAIN
						try {
							if (lock.readLock().tryLock(timeout, TimeUnit.MILLISECONDS)) {
								// OK, RESET THE INTERRUPTED STATE
								Thread.currentThread().interrupt();
								return;
							}
						} catch (InterruptedException e2) {
							Thread.currentThread().interrupt();
						}
					}
					throw new OLockException("Thread interrupted while waiting for resource of class '" + getClass() + "' with timeout="
							+ timeout);
				}
				throw new OTimeoutException("Timeout on acquiring shared lock against resource of class : " + getClass() + " with timeout="
						+ timeout);
			} else
				lock.readLock().lock();
	}

	protected boolean tryAcquireSharedLock() {
		return concurrent || lock.readLock().tryLock();
	}

	protected void releaseExclusiveLock() {
		if (concurrent)
			lock.writeLock().unlock();
	}

	protected void releaseSharedLock() {
		if (concurrent)
			lock.readLock().unlock();
	}

	public int getUsers() {
		return users.get();
	}

	public int addUser() {
		return users.incrementAndGet();
	}

	public int removeUser() {
		if (users.get() < 1)
			throw new IllegalStateException("Cannot remove user of the shared resource " + toString() + " because no user is using it");

		return users.decrementAndGet();
	}

	public boolean isConcurrent() {
		return concurrent;
	}
}