git-utils/src/main/java/me/brianlong/git/LRUExpiringHashMap.java

package me.brianlong.git;

import java.io.Serializable;
import java.util.Collection;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Set;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

// TODO need to implement the actual expiration schedule
public class LRUExpiringHashMap<K extends Serializable, V> implements ListeningMap<K, V> {

	private final Logger logger = LoggerFactory.getLogger(LRUExpiringHashMap.class);
	
	private final Map<ExpiringHashKey, V> map;
	private final List<MapListener<K, V>> listeners = new LinkedList<MapListener<K, V>>();
	private final long expirationTimeMillis;
	
	public LRUExpiringHashMap(int expirationTimeInMinutes) {
		this.map = new LinkedHashMap<ExpiringHashKey, V>();
		this.expirationTimeMillis = expirationTimeInMinutes * 60L + 1000L;
	}

	public LRUExpiringHashMap(int expirationTimeInMinutes, int initialCapacity) {
		this.map = new LinkedHashMap<ExpiringHashKey, V>(initialCapacity);
		this.expirationTimeMillis = expirationTimeInMinutes * 60L + 1000L;
	}
	
	@Override
	public void addListener(MapListener<K, V> listener) {
    	if (this.logger.isDebugEnabled())
    		this.logger.debug("adding listener");
		this.listeners.add(listener);
	}
	
	@Override
	public boolean containsKey(Object key) {
		return this.map.containsKey(key);
	}
	
	@Override
	public boolean containsValue(Object value) {
		return this.map.containsValue(value);
	}
	
	@Override
	public Set<Entry<K, V>> entrySet() {
		throw new UnsupportedOperationException();
	}
	
	@Override
	public Set<K> keySet() {
		throw new UnsupportedOperationException();
	}
	
	@Override
	public Collection<V> values() {
		throw new UnsupportedOperationException();
	}
	
	@Override
	public boolean isEmpty() {
		return this.map.isEmpty();
	}
	
	@Override
	public int size() {
		return this.map.size();
	}
	
	@Override
	@SuppressWarnings("unchecked")
	public V get(Object key) {
		if (!this.map.containsKey(key))
			return null;
		
		// remove and put to move the entry to the end of the map; helping with finding expired entries
		V value = this.map.remove(key);
		this.map.put(new ExpiringHashKey((K)key, System.currentTimeMillis() + this.expirationTimeMillis), value);
		
		for (MapListener<K, V> listener : this.listeners)
			listener.accessed(new ExpiringHashMapEntry((K)key, value));
		return value;
	}
	
	@Override
	public V put(K key, V value) {
		ExpiringHashKey ehkey = new ExpiringHashKey(key, System.currentTimeMillis() + this.expirationTimeMillis);
		V oldValue = this.map.put(ehkey, value);
		for (MapListener<K, V> listener : this.listeners)
			listener.added(new ExpiringHashMapEntry(key, value));
		return oldValue;
	}
	
	@Override
	public void clear() {
		for (Entry<ExpiringHashKey, V> entry : this.map.entrySet()) {
			for (MapListener<K, V> listener : this.listeners)
				listener.cleared(new ExpiringHashMapEntry(entry.getKey().getKey(), entry.getValue()));
		}
		
		this.map.clear();
	}
	
	@SuppressWarnings("unchecked")
	@Override
	public V remove(Object key) {
		if (!this.map.containsKey(key))
			return null;
		
		V value = this.map.remove(key);
		for (MapListener<K, V> listener : this.listeners)
			listener.removed(new ExpiringHashMapEntry((K)key, value));
		return value;
	}
	
	@Override
	public void putAll(Map<? extends K, ? extends V> m) {
		throw new UnsupportedOperationException();
	}
	
	@Override
	public int hashCode() {
		return this.map.hashCode();
	}
	
	@Override
	public boolean equals(Object obj) {
		return this.map.equals(obj);
	}
	
	public void exipriationCheck() {
		Iterator<Entry<ExpiringHashKey, V>> i = this.map.entrySet().iterator();
		for (Entry<ExpiringHashKey, V> entry = i.next(); i.hasNext(); entry = i.next()) {
			if (entry.getKey().isExpired()) {
				i.remove();
				for (MapListener<K, V> listener : this.listeners)
					if (listener instanceof ExpiringMapListener)
						((ExpiringMapListener<K, V>)listener).expired(new ExpiringHashMapEntry(entry.getKey().getKey(), entry.getValue()));
			}
		}
	}
	
	public void expire(K key) {
    	if (this.logger.isDebugEnabled())
    		this.logger.debug("expiring key from map: " + key);
    	
		if (!this.map.containsKey(key))
			return;
		
		V value = this.map.remove(key);
		for (MapListener<K, V> listener : this.listeners)
			if (listener instanceof ExpiringMapListener)
				((ExpiringMapListener<K, V>)listener).expired(new ExpiringHashMapEntry(key, value));
	}
	
	
	
	private class ExpiringHashMapEntry implements Entry<K, V> {
		
		private final K key;
		private V value;
		
		public ExpiringHashMapEntry(K key, V value) {
			this.key = key;
			this.value = value;
		}
		
		@Override
		public K getKey() {
			return this.key;
		}
		
		@Override
		public V getValue() {
			return this.value;
		}
		
		@Override
		public V setValue(V value) {
			return this.value = value;
		}
		
		@Override
		public boolean equals(Object obj) {
			if (obj instanceof Entry<?, ?>) {
				return this.key.equals(((Entry<?, ?>)obj).getKey()) && this.value.equals(((Entry<?, ?>)obj).getValue());
			} else {
				return false;
			}
		}
		
		@Override
		public int hashCode() {
			return this.key.hashCode() + this.value.hashCode();
		}
		
		@Override
		public String toString() {
			return "{" + this.key + ", " + this.value + "}";
		}
		
	}
	
	private class ExpiringHashKey implements Serializable {
	
		private static final long serialVersionUID = -6511298315143655313L;
	
		private long expirationTimeInMillis;
		private K key;
		
		public ExpiringHashKey(K key, long expirationTimeInMillis) {
			this.key = key;
			this.expirationTimeInMillis = expirationTimeInMillis;
		}
		
		public K getKey() {
			return this.key;
		}
		
		public boolean isExpired() {
			return this.expirationTimeInMillis <= System.currentTimeMillis();
		}
		
		@Override
		public int hashCode() {
			return this.key.hashCode();
		}
		
		@Override
		public String toString() {
			return this.key.toString();
		}
		
		@Override
		@SuppressWarnings("unchecked")
		public boolean equals(Object obj) {
			if (obj instanceof LRUExpiringHashMap.ExpiringHashKey) {
				return this.key.equals(((ExpiringHashKey)obj).key);
			} else {
				return this.key.equals(obj);
			}
		}
		
	}

}