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/*
 * Javolution - Java(TM) Solution for Real-Time and Embedded Systems
 * Copyright (C) 2012 - Javolution (http://javolution.org/)
 * All rights reserved.
 * 
 * Permission to use, copy, modify, and distribute this software is
 * freely granted, provided that this notice is preserved.
 */
package javolution.util.internal.collection;

import java.util.Collection;
import java.util.Iterator;

import javolution.util.function.Consumer;
import javolution.util.function.Equality;
import javolution.util.service.CollectionService;

/**
 * An atomic view over a collection (copy-on-write).
 */
public class AtomicCollectionImpl extends CollectionView {

    /** Thread-Safe Iterator. */
    private class IteratorImpl implements Iterator {
        private E current;
        private final Iterator targetIterator;

        public IteratorImpl() {
            targetIterator = targetView().iterator();
        }

        @Override
        public boolean hasNext() {
            return targetIterator.hasNext();
        }

        @Override
        public E next() {
            current = targetIterator.next();
            return current;
        }

        @Override
        public void remove() {
            if (current == null) throw new IllegalStateException();
            AtomicCollectionImpl.this.remove(current);
            current = null;
        }
    }

    private static final long serialVersionUID = 0x600L; // Version.
    protected volatile CollectionService immutable; // The copy used by readers.
    protected transient Thread updatingThread; // The thread executing an update.

    public AtomicCollectionImpl(CollectionService target) {
        super(target);
        this.immutable = cloneTarget();
    }

    @Override
    public synchronized boolean add(E element) {
        boolean changed = target().add(element);
        if (changed && !updateInProgress()) immutable = cloneTarget();
        return changed;
    }

    @Override
    public synchronized boolean addAll(Collection c) {
        boolean changed = target().addAll(c);
        if (changed && !updateInProgress()) immutable = cloneTarget();
        return changed;
    }

    @Override
    public synchronized void clear() {
        clear();
        if (!updateInProgress()) {
            immutable = cloneTarget();
        }
    }

    @Override
    public synchronized AtomicCollectionImpl clone() { // Synchronized required since working with real target.
        AtomicCollectionImpl copy = (AtomicCollectionImpl) super.clone();
        copy.updatingThread = null;
        return copy;
    }

    @Override
    public Equality comparator() {
        return immutable.comparator();
    }

    @Override
    public boolean contains(Object o) {
        return targetView().contains(o);
    }

    @Override
    public boolean containsAll(Collection c) {
        return targetView().containsAll(c);
    }

    @Override
    public boolean equals(Object o) {
        return targetView().equals(o);
    }

    @Override
    public int hashCode() {
        return targetView().hashCode();
    }

    @Override
    public boolean isEmpty() {
        return targetView().isEmpty();
    }

    @Override
    public Iterator iterator() {
        return new IteratorImpl();
    }

    @Override
    public synchronized boolean remove(Object o) {
        boolean changed = target().remove(o);
        if (changed && !updateInProgress()) immutable = cloneTarget();
        return changed;
    }

    @Override
    public synchronized boolean removeAll(Collection c) {
        boolean changed = target().removeAll(c);
        if (changed && !updateInProgress()) immutable = cloneTarget();
        return changed;
    }

    @Override
    public synchronized boolean retainAll(Collection c) {
        boolean changed = target().retainAll(c);
        if (changed && !updateInProgress()) immutable = cloneTarget();
        return changed;
    }

    @Override
    public int size() {
        return targetView().size();
    }

    @SuppressWarnings("unchecked")
    @Override
    public CollectionService[] split(int n) { // Split not supported.
        return new CollectionService[] { this };
    }

    @Override
    public CollectionService threadSafe() {
        return this; 
    }

    @Override
    public Object[] toArray() {
        return targetView().toArray();
    }

    @Override
    public  T[] toArray(T[] a) {
        return targetView().toArray(a);
    }

    @Override
    public synchronized void update(Consumer> action,
            CollectionService view) {
        updatingThread = Thread.currentThread(); // Update in progress.
        try {
            target().update(action, view); // No copy performed.
        } finally {
            updatingThread = null;
            immutable = cloneTarget(); // One single copy !
        }
    }

    /** Returns either the immutable target or the actual target if updating 
     *  thread. */
    protected CollectionService targetView() {
        return ((updatingThread == null) || (updatingThread != Thread.currentThread()))
                ? immutable : target();
    }

    /** Returns a clone copy of target. */
    protected CollectionService cloneTarget() {
        try {
            return target().clone();
        } catch (CloneNotSupportedException e) {
            throw new Error("Cannot happen since target is Cloneable.");
        }
    }

    /** Indicates if the current thread is doing an atomic update. */
    protected final boolean updateInProgress() {
        return updatingThread == Thread.currentThread();

    }
}