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/*
 * Copyright 2016 Steve Ash
 *
 * 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 com.github.steveash.jg2p.util;

import com.google.common.base.Equivalence;
import com.google.common.collect.AbstractIterator;
import com.google.common.collect.Iterators;
import com.google.common.collect.Lists;
import com.google.common.collect.PeekingIterator;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

/**
 * @author Steve Ash
 */
public class GroupingIterable implements Iterable> {

  public static  GroupingIterable groupOver(Iterable source, Equivalence equiv) {
    return new GroupingIterable<>(source, equiv);
  }

  private final Iterable delegate;
  private final Equivalence equiv;

  public GroupingIterable(Iterable delegate, Equivalence equiv) {
    this.delegate = delegate;
    this.equiv = equiv;
  }

  @Override
  public Iterator> iterator() {
    final PeekingIterator iter = Iterators.peekingIterator(delegate.iterator());
    return new AbstractIterator>() {
      @Override
      protected List computeNext() {
        if (!iter.hasNext()) {
          return endOfData();
        }
        ArrayList result = Lists.newArrayList();
        T last = iter.next();
        result.add(last);
        while (iter.hasNext() && equiv.equivalent(last, iter.peek())) {
          last = iter.next(); // get peeked value
          result.add(last);
        }
        return result;
      }
    };
  }
}