package com.c2kernel.utils;
import java.lang.ref.*;
import java.util.*;
/**************************************************************************
 * TransientCache - Uses transient references to allow unused entries to be 
 * reaped by the java garbage collector.
 *
 * $Revision: 1.1 $
 * $Date: 2004/04/20 09:37:02 $
 *
 * Copyright (C) 2003 CERN - European Organization for Nuclear Research
 * All rights reserved.
 **************************************************************************/
public abstract class TransientCache extends AbstractMap {
    
    private Map map = new Hashtable();
    public synchronized Set entrySet() {
        Map newMap;
        Iterator iter;
        newMap = new Hashtable();
        iter = map.entrySet().iterator();
        while (iter.hasNext()) {
            Map.Entry me = (Map.Entry)iter.next();
            Reference ref = (Reference)me.getValue();
            Object o = ref.get();
            if (o == null) {
                // Delete cleared reference 
                iter.remove();
            } else {
                // Copy out interior object 
                newMap.put(me.getKey(), o);
            }
        }
        // Return set of interior objects 
        return newMap.entrySet();
    }
    
    public synchronized Object put(Object key, Object value) {
        Reference ref = makeReference(value);
        ref = (Reference)map.put(key, ref);
        if (ref != null)
            return (ref.get());
        return null;
    }
    
    public abstract Reference makeReference(Object value);
    
    public Object remove(Object key) {
        Iterator i = map.entrySet().iterator();
        Entry correctEntry = null;
        if (key == null) {
            while (correctEntry == null && i.hasNext()) {
                Entry e = (Entry)i.next();
                if (e.getKey() == null)
                    correctEntry = e;
            }
        } else {
            while (correctEntry == null && i.hasNext()) {
                Entry e = (Entry)i.next();
                if (key.equals(e.getKey()))
                    correctEntry = e;
            }
        }
        Object oldValue = null;
        if (correctEntry != null) {
            Reference correctReference = (Reference)correctEntry.getValue();
            oldValue = correctReference.get();
            i.remove();
        }
        return oldValue;
    }
    /**
     *
     */
    public void clear() {
        map.entrySet().clear();
    }
    
    private transient Set keySet = null;
    
    public Set keySet() {
        if (keySet == null) {
            keySet = new AbstractSet() {
            public Iterator iterator() {
                return new Iterator() {
                private Iterator i = map.entrySet().iterator();

                public boolean hasNext() {
                    return i.hasNext();
                }

                public Object next() {
                    return ((Entry)i.next()).getKey();
                }

                public void remove() {
                    i.remove();
                }
                        };
            }

            public int size() {
                return TransientCache.this.size();
            }

            public boolean contains(Object k) {
                return TransientCache.this.containsKey(k);
            }
            };
        }
        return keySet;
        }

}