/*
    * Licensed to the Apache Software Foundation (ASF) under one or more
    * contributor license agreements.  See the NOTICE file distributed with
    * this work for additional information regarding copyright ownership.
    * The ASF licenses this file to You 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.apache.commons.collections4.iterators;
  
  import java.util.Iterator;
  import java.util.NoSuchElementException;
  
  import org.apache.commons.collections4.Predicate;
  
  /**
   * Decorates another {@link Iterator} using a predicate to filter elements.
   * <p>
   * This iterator decorates the underlying iterator, only allowing through
   * those elements that match the specified {@link Predicate Predicate}.
   *
   * @param <E> the type of elements returned by this iterator.
   * @since 1.0
   */
  public class FilterIterator<E> implements Iterator<E> {
  
      /** The iterator being used */
      private Iterator<? extends E> iterator;
      /** The predicate being used */
      private Predicate<? super E> predicate;
      /** The next object in the iteration */
      private E nextObject;
      /** Whether the next object has been calculated yet */
      private boolean nextObjectSet;
  
      /**
       * Constructs a new {@code FilterIterator} that will not function
       * until {@link #setIterator(Iterator) setIterator} is invoked.
       */
      public FilterIterator() {
      }
  
      /**
       * Constructs a new {@code FilterIterator} that will not function
       * until {@link #setPredicate(Predicate) setPredicate} is invoked.
       *
       * @param iterator  the iterator to use
       */
      public FilterIterator(final Iterator<? extends E> iterator) {
          this.iterator = iterator;
      }
  
      /**
       * Constructs a new {@code FilterIterator} that will use the
       * given iterator and predicate.
       *
       * @param iterator  the iterator to use
       * @param predicate  the predicate to use
       */
      public FilterIterator(final Iterator<? extends E> iterator, final Predicate<? super E> predicate) {
          this.iterator = iterator;
          this.predicate = predicate;
      }
  
      /**
       * Gets the iterator this iterator is using.
       *
       * @return the iterator
       */
      public Iterator<? extends E> getIterator() {
          return iterator;
      }
  
      /**
       * Gets the predicate this iterator is using.
       *
       * @return the predicate
       */
      public Predicate<? super E> getPredicate() {
          return predicate;
      }
  
      /**
       * Returns true if the underlying iterator contains an object that
       * matches the predicate.
       *
       * @return true if there is another object that matches the predicate
       * @throws NullPointerException if either the iterator or predicate are null
       */
      @Override
      public boolean hasNext() {
         return nextObjectSet || setNextObject();
     }
 
     /**
      * Returns the next object that matches the predicate.
      *
      * @return the next object which matches the given predicate
      * @throws NullPointerException if either the iterator or predicate are null
      * @throws NoSuchElementException if there are no more elements that
      *  match the predicate
      */
     @Override
     public E next() {
         if (!nextObjectSet && !setNextObject()) {
             throw new NoSuchElementException();
         }
         nextObjectSet = false;
         return nextObject;
     }
 
     /**
      * Removes from the underlying collection of the base iterator the last
      * element returned by this iterator.
      * This method can only be called
      * if {@code next()} was called, but not after
      * {@code hasNext()}, because the {@code hasNext()} call
      * changes the base iterator.
      *
      * @throws IllegalStateException if {@code hasNext()} has already
      *  been called.
      */
     @Override
     public void remove() {
         if (nextObjectSet) {
             throw new IllegalStateException("remove() cannot be called");
         }
         iterator.remove();
     }
 
     /**
      * Sets the iterator for this iterator to use.
      * If iteration has started, this effectively resets the iterator.
      *
      * @param iterator  the iterator to use
      */
     public void setIterator(final Iterator<? extends E> iterator) {
         this.iterator = iterator;
         nextObject = null;
         nextObjectSet = false;
     }
 
     /**
      * Sets nextObject to the next object. If there are no more
      * objects, then return false. Otherwise, return true.
      */
     private boolean setNextObject() {
         while (iterator.hasNext()) {
             final E object = iterator.next();
             if (predicate.evaluate(object)) {
                 nextObject = object;
                 nextObjectSet = true;
                 return true;
             }
         }
         return false;
     }
 
     /**
      * Sets the predicate this the iterator to use.
      *
      * @param predicate  the predicate to use
      */
     public void setPredicate(final Predicate<? super E> predicate) {
         this.predicate = predicate;
         nextObject = null;
         nextObjectSet = false;
     }
 
 }