/**
    * Copyright 2010-2012 The Kuali Foundation
    *
    * Licensed under the Educational Community 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.opensource.org/licenses/ecl2.php
    *
   * 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.kuali.common.util;
  
  import java.util.ArrayList;
  import java.util.Arrays;
  import java.util.Collection;
  import java.util.Collections;
  import java.util.List;
  import java.util.Set;
  import java.util.TreeSet;
  
  import org.apache.commons.lang3.StringUtils;
  
  public class CollectionUtils {
  
  	/**
  	 * If <code>o==null</code> return an empty list otherwise return a singleton list.
  	 */
  	public static final <T> List<T> toEmptyList(T o) {
  		if (o == null) {
  			return Collections.<T> emptyList();
  		} else {
  			return Collections.singletonList(o);
  		}
  	}
  
  	/**
  	 * If <code>list==null</code> return an empty list otherwise return <code>list</code>
  	 */
  	public static final <T> List<T> toEmpty(List<T> list) {
  		if (list == null) {
  			return Collections.<T> emptyList();
  		} else {
  			return list;
  		}
  	}
  
  	public static final <T> List<T> toNullIfEmpty(List<T> list) {
  		if (isEmpty(list)) {
  			return null;
  		} else {
  			return list;
  		}
  	}
  
  	public static final <T> Collection<T> toNullIfEmpty(Collection<T> c) {
  		if (isEmpty(c)) {
  			return null;
  		} else {
  			return c;
  		}
  	}
  
  	public static final <T> List<T> getPreFilledList(int size, T value) {
  		if (value == null || size < 1) {
  			return Collections.<T> emptyList();
  		} else {
  			List<T> list = new ArrayList<T>(size);
  			for (int i = 0; i < size; i++) {
  				list.add(value);
  			}
  			return list;
  		}
  	}
  
  	public static final Object[] toObjectArray(List<Object> objects) {
  		return objects.toArray(new Object[objects.size()]);
  	}
  
  	public static final String[] toStringArray(List<String> strings) {
  		return strings.toArray(new String[strings.size()]);
  	}
  
  	public static final boolean isEmpty(Collection<?> c) {
  		return c == null || c.size() == 0;
  	}
  
  	public static final List<String> sortedMerge(List<String> list, String csv) {
  		Set<String> set = new TreeSet<String>();
  		for (String string : toEmpty(list)) {
  			set.add(string);
  		}
  		for (String string : getTrimmedListFromCSV(csv)) {
  			set.add(string);
  		}
 		return new ArrayList<String>(set);
 	}
 
 	public static final List<String> getTrimmedListFromCSV(String csv) {
 		if (StringUtils.isBlank(csv)) {
 			return Collections.<String> emptyList();
 		}
 		List<String> list = new ArrayList<String>();
 		String[] tokens = Str.splitAndTrimCSV(csv);
 		list.addAll(Arrays.asList(tokens));
 		return list;
 	}
 }