/*
 * Copyright (c) 2008, 2020 Oracle and/or its affiliates. All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v. 2.0, which is available at
 * http://www.eclipse.org/legal/epl-2.0.
 *
 * This Source Code may also be made available under the following Secondary
 * Licenses when the conditions for such availability set forth in the
 * Eclipse Public License v. 2.0 are satisfied: GNU General Public License,
 * version 2 with the GNU Classpath Exception, which is available at
 * https://www.gnu.org/software/classpath/license.html.
 *
 * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
 */

package org.glassfish.grizzly.utils;

import java.util.Collection;
import java.util.Iterator;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.Future;
import java.util.concurrent.locks.ReentrantReadWriteLock;
import java.util.logging.Level;
import java.util.logging.Logger;

import org.glassfish.grizzly.CompletionHandler;
import org.glassfish.grizzly.Grizzly;
import org.glassfish.grizzly.impl.FutureImpl;
import org.glassfish.grizzly.impl.ReadyFutureImpl;
import org.glassfish.grizzly.impl.SafeFutureImpl;
import org.glassfish.grizzly.localization.LogMessages;
import org.glassfish.grizzly.utils.conditions.Condition;

Class, which holds the state. Provides API for state change notification, state read/write access locking.
Author:
Alexey Stashok/**
 * Class, which holds the state. Provides API for state change notification, state read/write access locking.
 *
 * @author Alexey Stashok
 */
public final class StateHolder<E> {
    private static final Logger _logger = Grizzly.logger(StateHolder.class);

    private volatile E state;

    private final ReentrantReadWriteLock readWriteLock;

    private final Collection<ConditionElement<E>> conditionListeners;

    
Constructs StateHolder.
/**
     * Constructs <code>StateHolder</code>.
     */
    public StateHolder() {
        this(null);
    }

    
Constructs StateHolder.
/**
     * Constructs <code>StateHolder</code>.
     */
    public StateHolder(E initialState) {
        state = initialState;
        readWriteLock = new ReentrantReadWriteLock();
        conditionListeners = new ConcurrentLinkedQueue<>();
    }

    
Gets current state Current StateHolder locking mode will be used
Returns:
state/**
     * Gets current state Current StateHolder locking mode will be used
     * 
     * @return state
     */
    public E getState() {
        return state;
    }

    
Sets current state Current StateHolder locking mode will be used
Params:
state – /**
     * Sets current state Current StateHolder locking mode will be used
     * 
     * @param state
     */
    public void setState(E state) {
        readWriteLock.writeLock().lock();

        try {
            this.state = state;

            // downgrading lock to read
            readWriteLock.readLock().lock();
            readWriteLock.writeLock().unlock();

            notifyConditionListeners();
        } finally {
            readWriteLock.readLock().unlock();
        }
    }

    
Gets Read/Write locker, which is used by this StateHolder
Returns:
locker/**
     * Gets Read/Write locker, which is used by this <code>StateHolder</code>
     * 
     * @return locker
     */
    public ReentrantReadWriteLock getStateLocker() {
        return readWriteLock;
    }

    
Register listener, which will be notified, when state will be equal to passed one. Once listener will be notified -
it will be removed from this StateHolder's listener set.
Params:
state – State, listener is interested in
completionHandler – that will be notified. This StateHolder implementation works with Runnable,
Callable, CountDownLatch, Object listeners
Returns:
ConditionListener, if current state is not equal to required and listener was registered, null
if current state is equal to required. In both cases listener will be notified/**
     * Register listener, which will be notified, when state will be equal to passed one. Once listener will be notified -
     * it will be removed from this <code>StateHolder</code>'s listener set.
     * 
     * @param state State, listener is interested in
     * @param completionHandler that will be notified. This <code>StateHolder</code> implementation works with Runnable,
     * Callable, CountDownLatch, Object listeners
     * @return <code>ConditionListener</code>, if current state is not equal to required and listener was registered, null
     * if current state is equal to required. In both cases listener will be notified
     */
    public Future<E> notifyWhenStateIsEqual(final E state, final CompletionHandler<E> completionHandler) {
        return notifyWhenConditionMatchState(new Condition() {

            @Override
            public boolean check() {
                return state == StateHolder.this.state;
            }

        }, completionHandler);
    }

    
Register listener, which will be notified, when state will become not equal to passed one. Once listener will be
notified - it will be removed from this StateHolder's listener set.
Params:
state – State, listener is interested in
completionHandler – that will be notified. This StateHolder implementation works with Runnable,
Callable, CountDownLatch, Object listeners
Returns:
ConditionListener, if current state is equal to required and listener was registered, null if
current state is not equal to required. In both cases listener will be notified/**
     * Register listener, which will be notified, when state will become not equal to passed one. Once listener will be
     * notified - it will be removed from this <code>StateHolder</code>'s listener set.
     * 
     * @param state State, listener is interested in
     * @param completionHandler that will be notified. This <code>StateHolder</code> implementation works with Runnable,
     * Callable, CountDownLatch, Object listeners
     * @return <code>ConditionListener</code>, if current state is equal to required and listener was registered, null if
     * current state is not equal to required. In both cases listener will be notified
     */
    public Future<E> notifyWhenStateIsNotEqual(final E state, final CompletionHandler<E> completionHandler) {
        return notifyWhenConditionMatchState(new Condition() {

            @Override
            public boolean check() {
                return state != StateHolder.this.state;
            }

        }, completionHandler);
    }

    
Register listener, which will be notified, when state will match the condition. Once listener will be notified - it
will be removed from this StateHolder's listener set.
Params:
condition – Condition, the listener is interested in
completionHandler – that will be notified. This StateHolder implementation works with Runnable,
Callable, CountDownLatch, Object listeners
Returns:
ConditionListener, if current state doesn't match the condition and listener was registered,
null if current state matches the condition. In both cases listener will be notified/**
     * Register listener, which will be notified, when state will match the condition. Once listener will be notified - it
     * will be removed from this <code>StateHolder</code>'s listener set.
     * 
     * @param condition Condition, the listener is interested in
     * @param completionHandler that will be notified. This <code>StateHolder</code> implementation works with Runnable,
     * Callable, CountDownLatch, Object listeners
     * @return <code>ConditionListener</code>, if current state doesn't match the condition and listener was registered,
     * null if current state matches the condition. In both cases listener will be notified
     */
    public Future<E> notifyWhenConditionMatchState(Condition condition, CompletionHandler<E> completionHandler) {
        Future<E> resultFuture;

        readWriteLock.readLock().lock();
        try {
            if (condition.check()) {
                if (completionHandler != null) {
                    completionHandler.completed(state);
                }
                resultFuture = ReadyFutureImpl.create(state);
            } else {
                final FutureImpl<E> future = SafeFutureImpl.create();
                final ConditionElement<E> elem = new ConditionElement<>(condition, future, completionHandler);
                conditionListeners.add(elem);
                resultFuture = future;
            }
        } finally {
            readWriteLock.readLock().unlock();
        }

        return resultFuture;
    }

    protected void notifyConditionListeners() {
        Iterator<ConditionElement<E>> it = conditionListeners.iterator();
        while (it.hasNext()) {
            ConditionElement<E> element = it.next();
            try {
                if (element.condition.check()) {
                    it.remove();
                    if (element.completionHandler != null) {
                        element.completionHandler.completed(state);
                    }

                    element.future.result(state);
                }
            } catch (Exception e) {
                _logger.log(Level.WARNING, LogMessages.WARNING_GRIZZLY_STATE_HOLDER_CALLING_CONDITIONLISTENER_EXCEPTION(), e);
            }
        }
    }

    protected static final class ConditionElement<E> {
        private final Condition condition;
        private final FutureImpl<E> future;
        private final CompletionHandler<E> completionHandler;

        public ConditionElement(Condition condition, FutureImpl<E> future, CompletionHandler<E> completionHandler) {
            this.condition = condition;
            this.future = future;
            this.completionHandler = completionHandler;
        }

        public CompletionHandler<E> getCompletionHandler() {
            return completionHandler;
        }

        public Condition getCondition() {
            return condition;
        }

        public FutureImpl<E> getFuture() {
            return future;
        }
    }
}