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/**
 * Copyright (C) 2011 Brian Ferris 
 *
 * 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.onebusaway.collections.combinations;

import java.util.Iterator;

import org.onebusaway.collections.tuple.Pair;
import org.onebusaway.collections.tuple.Tuples;

class PermutationIterator implements Iterator> {

  private Iterable _elementsB;

  private Iterator _iteratorA;

  private Iterator _iteratorB;

  private T _elementA = null;

  public PermutationIterator(Iterable elements) {
    this(elements, elements);
  }

  public PermutationIterator(Iterable elementsA, Iterable elementsB) {

    _iteratorA = elementsA.iterator();
    _iteratorB = elementsB.iterator();

    _elementsB = elementsB;

    if (_iteratorA.hasNext())
      _elementA = _iteratorA.next();
  }

  public boolean hasNext() {
    return _iteratorA.hasNext() || _iteratorB.hasNext();
  }

  public Pair next() {
    if (!hasNext())
      throw new IndexOutOfBoundsException();

    if (!_iteratorB.hasNext()) {
      _elementA = _iteratorA.next();
      _iteratorB = _elementsB.iterator();
    }

    return Tuples.pair(_elementA, _iteratorB.next());
  }

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