/*
    * Copyright 2006-2007 the original author or authors.
    *
    * Licensed under the Apache License, Version 2.0 (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.apache.org/licenses/LICENSE-2.0
    *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package org.springframework.batch.item.support;
  
  import java.util.ArrayList;
  import java.util.HashMap;
  import java.util.List;
  import java.util.Map;
  
  import org.springframework.classify.Classifier;
  import org.springframework.classify.ClassifierSupport;
  import org.springframework.batch.item.ItemWriter;
  
  /**
   * Calls one of a collection of ItemWriters for each item, based on a router
   * pattern implemented through the provided {@link Classifier}.
   * 
   * The implementation is thread-safe if all delegates are thread-safe.
   * 
   * @author Dave Syer
   * @since 2.0
   */
  public class ClassifierCompositeItemWriter<T> implements ItemWriter<T> {
  
  	private Classifier<T, ItemWriter<? super T>> classifier = new ClassifierSupport<T, ItemWriter<? super T>>(null);
  
  	/**
  	 * @param classifier the classifier to set
  	 */
  	public void setClassifier(Classifier<T, ItemWriter<? super T>> classifier) {
  		this.classifier = classifier;
  	}
  
  	/**
  	 * Delegates to injected {@link ItemWriter} instances according to their
  	 * classification by the {@link Classifier}.
  	 */
      @Override
  	public void write(List<? extends T> items) throws Exception {
  
  		Map<ItemWriter<? super T>, List<T>> map = new HashMap<ItemWriter<? super T>, List<T>>();
  
  		for (T item : items) {
  			ItemWriter<? super T> key = classifier.classify(item);
  			if (!map.containsKey(key)) {
  				map.put(key, new ArrayList<T>());
  			}
  			map.get(key).add(item);
  		}
  
  		for (ItemWriter<? super T> writer : map.keySet()) {
  			writer.write(map.get(writer));
  		}
  
  	}
  
  }