/*
Copyright (c) 2008  Franklin Schmidt <fschmidt@gmail.com>

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
*/

package fschmidt.db.util;

import java.lang.ref.ReferenceQueue;
import java.util.Map;
import java.util.AbstractMap;
import java.util.HashMap;
import java.util.Set;
import java.util.AbstractSet;
import java.util.Iterator;


public abstract class CacheMap<K,V> extends AbstractMap<K,V> {

	protected static interface MyReference<K,V> {
		public K key();
		public V get();
		public void clear();
	}

	protected abstract MyReference<K,V> newReference(K key,V value,ReferenceQueue<V> q);
 
	private final Map<K,MyReference<K,V>> cache = new HashMap<K,MyReference<K,V>>();
	private final ReferenceQueue<V> queue = new ReferenceQueue<V>();

	private void sweep() {
		while(true) {
			@SuppressWarnings("unchecked")
			MyReference<K,V> ref = (MyReference<K,V>)queue.poll();
			if( ref == null )
				return;
			MyReference<K,V> mappedRef = cache.remove(ref.key());
			if( mappedRef != ref && mappedRef != null )
				cache.put( mappedRef.key(), mappedRef );  // put it back
		}
	}

	public int size() {
		return cache.size();
	}

	public boolean isEmpty() {
		return cache.isEmpty();
	}

	public boolean containsKey(Object key) {
		return cache.containsKey(key);
	}

	public V get(Object key) {
		MyReference<K,V> ref = cache.get(key);
		return ref==null ? null : ref.get();
	}

	public V put(K key,V value) {
		sweep();
		MyReference<K,V> ref = cache.put( key, newReference(key,value,queue) );
		return ref==null ? null : ref.get();
	}

	public V remove(Object key) {
		sweep();
		MyReference<K,V> ref = cache.remove(key);
		return ref==null ? null : ref.get();
	}

	public void clear() {
		sweep();
		cache.clear();
	}

/*
	public Object clone() {
		GCCacheMap map = new GCCacheMap();
		map.cache = (HashMap)cache.clone();
		return map;
	}
*/
	public Set<K> keySet() {
		return cache.keySet();
	}

	public Set<Map.Entry<K,V>> entrySet() {
		return new MySet();
	}


	private class MySet extends AbstractSet<Map.Entry<K,V>> {

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

		public Iterator<Map.Entry<K,V>> iterator() {
			return new MyIterator(cache.entrySet().iterator());
		}

	}

	private class MyIterator implements Iterator<Map.Entry<K,V>> {
		Iterator<Map.Entry<K,MyReference<K,V>>> iter;

		MyIterator(Iterator<Map.Entry<K,MyReference<K,V>>> iter) {
			this.iter = iter;
		}

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

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

		public Map.Entry<K,V> next() {
			return new MyEntry( iter.next() );
		}
	}

	private class MyEntry implements Map.Entry<K,V> {
		Map.Entry<K,MyReference<K,V>> entry;

		MyEntry(Map.Entry<K,MyReference<K,V>> entry) {
			this.entry = entry;
		}

		public K getKey() {
			return entry.getKey();
		}

		public V getValue() {
			MyReference<K,V> ref = entry.getValue();
			return ref.get();
		}

		public V setValue(V value) {
			MyReference<K,V> ref = entry.setValue( newReference(getKey(),value,queue) );
			return ref.get();
		}

		public boolean equals(Object o) {
			if( o==null || !(o instanceof CacheMap.MyEntry) )
				return false;
			MyEntry m = (MyEntry)o;
			return entry.equals(m.entry);
		}

		public int hashCode() {
			K key = getKey();
			V value = getValue();
			return (key==null ? 0 : key.hashCode()) ^
					(value==null ? 0 : value.hashCode());
		}
	}

}