/*
 * 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 opennlp.tools.util;

import java.io.IOException;

/**
 * A {@link FilterObjectStream} which merges text lines into paragraphs.
 * <p>
 * The boundary of paragraph is defined by an empty text line.
 * If the last paragraph in the stream is not terminated by an empty line
 * the left over is assumed to be a paragraph.
 */
public class ParagraphStream extends FilterObjectStream<String, String> {

  /**
   * Initializes an {@link FilterObjectStream}.
   *
   * @param lineStream The {@link ObjectStream<String> stream} of samples.
   */
  public ParagraphStream(ObjectStream<String> lineStream) {
    super(lineStream);
  }

  @Override
  public String read() throws IOException {

    StringBuilder paragraph = new StringBuilder();

    while (true) {
      String line = samples.read();

      // The last paragraph in the input might not
      // be terminated well with a new line at the end.

      if (line == null || line.isEmpty()) {
        if (paragraph.length() > 0) {
          return paragraph.toString();
        }
      }
      else {
        paragraph.append(line).append('\n');
      }

      if (line == null)
        return null;
    }
  }
}
