/*
 * Copyright (c) 2008, 2017 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 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.utils.conditions.Condition;
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.localization.LogMessages;

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<ConditionElement<E>>();
    }

    
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<E>(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;
        }
    }
}