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/*
 * [New BSD License]
 * Copyright (c) 2011-2012, Brackit Project Team 
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *     * Redistributions of source code must retain the above copyright
 *       notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above copyright
 *       notice, this list of conditions and the following disclaimer in the
 *       documentation and/or other materials provided with the distribution.
 *     * Neither the name of the Brackit Project Team nor the
 *       names of its contributors may be used to endorse or promote products
 *       derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR
 * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
package io.brackit.query.node.stream;

import io.brackit.query.jdm.DocumentException;
import io.brackit.query.jdm.Stream;

/**
 * Flattens out a stream of items that provide streams into a single stream.
 *
 * @param 
 * @param 
 * @author Sebastian Baechle
 */
public abstract class FlatteningStream implements Stream {
  private Stream in;

  private Stream out;

  private E next;

  public FlatteningStream(Stream in) {
    super();
    this.in = in;
  }

  @Override
  public void close() {
    if (out != null) {
      out.close();
      out = null;
    }
    if (in != null) {
      in.close();
      in = null;
    }
  }

  @Override
  public E next() throws DocumentException {
    try {
      E e;
      while (out == null || (e = out.next()) == null) {
        if (out != null) {
          out.close();
          out = null;
        }

        if (in == null) {
          return null;
        }

        K k;
        if ((k = in.next()) != null) {
          out = getOutStream(k);
        } else {
          in.close();
          in = null;
          return null;
        }
      }

      return e;
    } catch (DocumentException e) {
      close();
      throw e;
    }
  }

  protected abstract Stream getOutStream(K next) throws DocumentException;
}