/*
 * JBoss, Home of Professional Open Source
 * Copyright 2009 Red Hat Inc. and/or its affiliates and other
 * contributors as indicated by the @author tags. All rights reserved.
 * See the copyright.txt in the distribution for a full listing of
 * individual contributors.
 *
 * This is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation; either version 2.1 of
 * the License, or (at your option) any later version.
 *
 * This software is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this software; if not, write to the Free
 * Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
 * 02110-1301 USA, or see the FSF site: http://www.fsf.org.
 */
package org.infinispan.util;

import java.util.AbstractSet;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.NoSuchElementException;

import static java.util.Collections.singletonMap;
import static java.util.Collections.unmodifiableMap;

/**
 * Static helpers for Infinispan-specific collections
 *
 * @author Manik Surtani
 * @since 4.0
 */
public class InfinispanCollections {
   private static final ReversibleOrderedSet<Object> EMPTY_ROS = new EmptyReversibleOrderedSet<Object>();

   private static final class EmptyReversibleOrderedSet<E> extends AbstractSet<E> implements ReversibleOrderedSet<E> {

      Iterator<E> it = new Iterator() {

         @Override
         public boolean hasNext() {
            return false;
         }

         @Override
         public E next() {
            throw new NoSuchElementException();
         }

         @Override
         public void remove() {
            throw new UnsupportedOperationException();
         }
      };

      @Override
      public Iterator<E> iterator() {
         return it;
      }

      @Override
      public int size() {
         return 0;
      }

      @Override
      public Iterator<E> reverseIterator() {
         return it;
      }
   }


   /**
    * A function that converts a type into another one.
    *
    * @param <E> Input type.
    * @param <T> Output type.
    */
   public static interface Function<E, T> {

      /**
       * Transforms an instance of the given input into an instace of the
       * type to be returned.
       *
       * @param input Instance of the input type.
       * @return Instance of the output type.
       */
      T transform(E input);
   }

   /**
    * A function that converts an entry into a key/value pair for use in a map.
    * @param <K> generated key
    * @param <V> generated value
    * @param <E> entry input
    */
   public static interface MapMakerFunction<K, V, E> {
      /**
       * Transforms the given input into a key/value pair for use in a map
       * @param input instance of the input type
       * @return a Map.Entry parameterized with K and V
       */
      Map.Entry<K, V> transform(E input);
   }

   /**
    * Given a map of well known key/value types, it makes a shallow copy of it
    * while at the same time transforming it's value type to a desired output
    * type. The transformation of the value type is done using a given a
    * function.
    *
    * @param input contains the input key/value pair map
    * @param f function instance to use to transform the value part of the map
    * @param <K> input map's key type
    * @param <V> desired output type of the map's value
    * @param <E> input map's value type
    * @return a shallow copy of the input Map with all its values transformed.
    */
   public static <K, V, E> Map<K, V> transformMapValue(Map<K, E> input, Function<E, V> f) {
      // This screams for a map function! Gimme functional programming pleasee...
      if (input.isEmpty()) return Collections.emptyMap();
      if (input.size() == 1) {
         Map.Entry<K, E> single = input.entrySet().iterator().next();
         return singletonMap(single.getKey(), f.transform(single.getValue()));
      } else {
         Map<K, V> copy = new HashMap<K, V>(input.size());
         for (Map.Entry<K, E> entry : input.entrySet())
            copy.put(entry.getKey(), f.transform(entry.getValue()));
         return unmodifiableMap(copy);
      }
   }

   /**
    * Given a collection, transforms the collection to a map given a {@link MapMakerFunction}
    *
    * @param input contains a collection of type E
    * @param f MapMakerFunction instance to use to transform the collection to a key/value pair
    * @param <K> output map's key type
    * @param <V> output type of the map's value
    * @param <E> input collection's entry type
    * @return a Map with keys and values generated from the input collection
    */
   public static <K, V, E> Map<K, V> transformCollectionToMap(Collection<E> input, MapMakerFunction<K, V, E> f) {
      // This screams for a map function! Gimme functional programming pleasee...
      if (input.isEmpty()) return Collections.emptyMap();
      if (input.size() == 1) {
         E single = input.iterator().next();
         Map.Entry<K, V> entry = f.transform(single);
         return singletonMap(entry.getKey(), entry.getValue());
      } else {
         Map<K, V> map = new HashMap<K, V>(input.size());
         for (E e : input) {
            Map.Entry<K, V> entry = f.transform(e);
            map.put(entry.getKey(), entry.getValue());
         }
         return unmodifiableMap(map);
      }
   }
}