/*
    * (C) Copyright 1989-2011 Trend Micro, Inc.
    * All Rights Reserved.
    *
    * This program is an unpublished copyrighted work which is proprietary
    * to Trend Micro, Inc. and contains confidential information that is not
    * to be reproduced or disclosed to any other person or entity without
    * prior written consent from Trend Micro, Inc. in each and every instance.
    *
   * WARNING:  Unauthorized reproduction of this program as well as
   * unauthorized preparation of derivative works based upon the
   * program or distribution of copies by sale, rental, lease or
   * lending are violations of federal copyright laws and state trade
   * secret laws, punishable by civil and criminal penalties.
   */
  
  package com.trendmicro.grid.acl.ds.cache.translation;
  
  import com.trendmicro.grid.acl.ds.cache.CacheDestination;
  import com.trendmicro.grid.acl.ds.cache.CacheSource;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  /**
   * Defines a key and value translator used to build translated cache source and destinations.
   */
  public abstract class Translator<K, V, DK, DV> {
  
  	private static final Logger log = LoggerFactory.getLogger(Translator.class);
  
  	/**
  	 * Constructs a new source using this translator.
  	 *
  	 * @param source the source to translate.
  	 * @return a translated source.
  	 */
  	public final CacheSource<K, V> newSource(CacheSource<? extends DK, ? extends DV> source) {
  		@SuppressWarnings("unchecked")
  		final CacheSource<DK, DV> cacheSource = (CacheSource<DK, DV>) source;
  		return new TranslatingSource<K, V, DK, DV>(cacheSource, this);
  	}
  
  	/**
  	 * Constructs a new destination using this translator.
  	 *
  	 * @param destination the destination to translate.
  	 * @return a translated destination.
  	 */
  	public final CacheDestination<K, V> newDestination(CacheDestination<? extends DK, ? extends DV> destination) {
  		@SuppressWarnings("unchecked")
  		final CacheDestination<DK, DV> cacheDestination = (CacheDestination<DK, DV>) destination;
  		return new TranslatingDestination<K, V, DK, DV>(cacheDestination, this);
  	}
  
  	/**
  	 * Converts a key (and optional value) to the key to use when asking the delegate.
  	 *
  	 * @param key   the cache key.
  	 * @param value the cache value (may be 'null').
  	 * @return a key to use on the delegate or 'null' if not compatible.
  	 */
  	@SuppressWarnings("unchecked")
  	protected DK toDelegateKey(K key, V value) {
  		try {
  			return (DK) key;
  		} catch (ClassCastException e) {
  			if (log.isDebugEnabled()) log.debug("Converting key '" + key + "' to 'null' as it's not of the expected target class.", e);
  			return null;
  		}
  	}
  
  	/**
  	 * Extracts the value to cache from the given entry.
  	 *
  	 * @param key   the cache key.
  	 * @param delegateKey the key to use when asking the delegate.
  	 * @param value the cache value (may be 'null').
  	 * @return the cache value to use for storing in the delegate.
  	 */
  	@SuppressWarnings("unchecked")
  	protected DV toDelegateValue(K key, DK delegateKey, V value) {
  		try {
  			return (DV) value;
  		} catch (ClassCastException e) {
  			if (log.isDebugEnabled()) log.debug("Converting value '" + value + "' to 'null' as it's not of the expected target class.", e);
  			return null;
  		}
  	}
  
  	/**
  	 * Extracts the value to return from the given values.
  	 *
  	 * @param key		   the cache key.
  	 * @param delegateKey   the key used on the cache delegate.
  	 * @param delegateValue the value returned from the cache delegate.
  	 * @return the cache value to return.
  	 */
  	@SuppressWarnings("unchecked")
  	protected V fromDelegateValue(K key, DK delegateKey, DV delegateValue) {
 		try {
 			return (V) delegateValue;
 		} catch (ClassCastException e) {
 			if (log.isDebugEnabled())
 				log.debug("Converting delegate-value '" + delegateValue + "' to 'null' as it's not of the expected target class.", e);
 			return null;
 		}
 	}
 }