/***** BEGIN LICENSE BLOCK *****
 * Version: CPL 1.0/GPL 2.0/LGPL 2.1
 *
 * The contents of this file are subject to the Common Public
 * License Version 1.0 (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.eclipse.org/legal/cpl-v10.html
 *
 * Software distributed under the License is distributed on an "AS
 * IS" basis, WITHOUT WARRANTY OF ANY KIND, either express or
 * implied. See the License for the specific language governing
 * rights and limitations under the License.
 *
 * Copyright (C) 2002-2004 Jan Arne Petersen <jpetersen@uni-bonn.de>
 * Copyright (C) 2002-2004 Anders Bengtsson <ndrsbngtssn@yahoo.se>
 * Copyright (C) 2004-2006 Charles O Nutter <headius@headius.com>
 * Copyright (C) 2004 Stefan Matthias Aust <sma@3plus4.de>
 *
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package org.jruby.runtime;

import java.lang.ref.ReferenceQueue;
import java.lang.ref.WeakReference;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.concurrent.atomic.AtomicLong;

import org.jruby.RubyModule;
import org.jruby.runtime.builtin.IRubyObject;
import org.jruby.util.WeakIdentityHashMap;

/**
 * FIXME: This version is faster than the previous, but both suffer from a
 * crucial flaw: It is impossible to create an ObjectSpace with an iterator
 * that doesn't either: a. hold on to objects that might otherwise be collected
 * or b. have no way to guarantee that a call to hasNext() will be correct or
 * that a subsequent call to next() will produce an object. For our purposes,
 * for now, this may be acceptable.
 */
public class ObjectSpace {
    private ReferenceQueue deadReferences = new ReferenceQueue();
    private WeakReferenceListNode top;

    private ReferenceQueue deadIdentityReferences = new ReferenceQueue();
    private final Map identities = new HashMap();
    private final Map identitiesByObject = new WeakIdentityHashMap();
    private static final AtomicLong maxId = new AtomicLong(1000);

    public void registerObjectId(long id, IRubyObject object) {
        synchronized (identities) {
            cleanIdentities();
            identities.put(id, new IdReference(object, id, deadIdentityReferences));
            identitiesByObject.put(object, id);
        }
    }

    public static long calculateObjectId(Object object) {
        // Fixnums get all the odd IDs, so we use identityHashCode * 2
        return maxId.getAndIncrement() * 2;
    }
    
    public long createAndRegisterObjectId(IRubyObject rubyObject) {
        synchronized (identities) {
            Long longId = (Long) identitiesByObject.get(rubyObject);
            if (longId == null) {
                longId = createId(rubyObject);
            }
            return longId.longValue();
        }
    }

    private long createId(IRubyObject object) {
        long id = calculateObjectId(object);
        registerObjectId(id, object);
        return id;
    }

    public IRubyObject id2ref(long id) {
        synchronized (identities) {
            cleanIdentities();
            IdReference reference = (IdReference) identities.get(Long.valueOf(id));
            if (reference == null) {
                return null;
            }
            return (IRubyObject) reference.get();
        }
    }

    private void cleanIdentities() {
        IdReference ref;
        while ((ref = (IdReference) deadIdentityReferences.poll()) != null)
            identities.remove(Long.valueOf(ref.id()));
    }

    @Deprecated
    public long idOf(IRubyObject rubyObject) {
        return createAndRegisterObjectId(rubyObject);
    }
    
    public void addFinalizer(IRubyObject object, IRubyObject proc) {
        object.addFinalizer(proc);
    }
    
    public void removeFinalizers(long id) {
        IRubyObject object = id2ref(id);
        if (object != null) {
            object.removeFinalizers();
        }
    }
    
    public synchronized void add(IRubyObject object) {
        cleanup();
        top = new WeakReferenceListNode(object, deadReferences, top);
    }

    public synchronized Iterator iterator(RubyModule rubyClass) {
        final List objList = new ArrayList();
        WeakReferenceListNode current = top;
        while (current != null) {
            IRubyObject obj = (IRubyObject)current.get();
            if (obj != null && rubyClass.isInstance(obj)) {
                objList.add(current);
            }

            current = current.nextNode;
        }

        return new Iterator() {
            private Iterator iter = objList.iterator();

            public boolean hasNext() {
                throw new UnsupportedOperationException();
            }

            public Object next() {
                Object obj = null;
                while (iter.hasNext()) {
                    WeakReferenceListNode node = (WeakReferenceListNode)iter.next();

                    obj = node.get();

                    if (obj != null) break;
                }
                return obj;
            }

            public void remove() {
                throw new UnsupportedOperationException();
            }
        };
    }

    private synchronized void cleanup() {
        WeakReferenceListNode reference;
        while ((reference = (WeakReferenceListNode)deadReferences.poll()) != null) {
            reference.remove();
        }
    }

    private class WeakReferenceListNode extends WeakReference {
        private WeakReferenceListNode prevNode;
        private WeakReferenceListNode nextNode;

        public WeakReferenceListNode(Object ref, ReferenceQueue queue, WeakReferenceListNode next) {
            super(ref, queue);

            this.nextNode = next;
            if (next != null) {
                next.prevNode = this;
            }
        }

        public void remove() {
            synchronized (ObjectSpace.this) {
                if (prevNode != null) {
                    prevNode.nextNode = nextNode;
                } else {
                    top = nextNode;
                }
                if (nextNode != null) {
                    nextNode.prevNode = prevNode;
                }
            }
        }
    }

    private static class IdReference extends WeakReference {
        private final long id;

        public IdReference(IRubyObject object, long id, ReferenceQueue queue) {
            super(object, queue);
            this.id = id;
        }

        public long id() {
            return id;
        }
    }
}
