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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreemnets.  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 opennlp.tools.util;

import java.io.IOException;
import java.util.Collections;
import java.util.Iterator;

import opennlp.model.Event;
import opennlp.model.EventStream;

/**
 * This is a base class for {@link EventStream} classes.
 * It takes an {@link Iterator} of sample objects as input and
 * outputs the events creates by a subclass.
 */
public abstract class AbstractEventStream extends opennlp.model.AbstractEventStream {

  private ObjectStream samples;

  private Iterator events = Collections.emptyList().iterator();;

  /**
   * Initializes the current instance with a sample {@link Iterator}.
   *
   * @param samples the sample {@link Iterator}.
   */
  public AbstractEventStream(ObjectStream samples) {
    this.samples = samples;
  }

  /**
   * Creates events for the provided sample.
   *
   * @param sample the sample for which training {@link Event}s
   * are be created.
   *
   * @return an {@link Iterator} of training events or
   * an empty {@link Iterator}.
   */
  protected abstract Iterator createEvents(T sample);

  /**
   * Checks if there are more training events available.
   *
   */
  public final boolean hasNext() throws IOException {

    if (events.hasNext()) {
      return true;
    } else {
      // search next event iterator which is not empty
      T sample = null;
      while (!events.hasNext() && (sample = samples.read()) != null) {
        events = createEvents(sample);
      }
  
      return events.hasNext();
    }
  }

  public final Event next() {
    return events.next();
  }
}