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Java client library to use the IBM Text to Speech API
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/*
 * (C) Copyright IBM Corp. 2016, 2020.
 *
 * 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.ibm.watson.text_to_speech.v1.util;

import com.ibm.watson.text_to_speech.v1.TextToSpeech;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;

/**
 * Utility class to write the data size header in wave(.wav) files synthesized with the {@link
 * TextToSpeech} service.
 */
public final class WaveUtils {
  /** The WAVE meta-data header size. (value is 8) */
  private static final int WAVE_HEADER_SIZE = 8;

  /** The WAVE meta-data position in bytes. (value is 74) */
  private static final int WAVE_METADATA_POS = 74;

  /** The WAVE meta-data size position. (value is 4) */
  private static final int WAVE_SIZE_POS = 4;

  private WaveUtils() {
    // This is a utility class - no instantiation allowed.
  }

  /**
   * Writes an number into an array using 4 bytes.
   *
   * @param value the number to write
   * @param array the byte array
   * @param offset the offset
   */
  private static void writeInt(int value, byte[] array, int offset) {
    for (int i = 0; i < 4; i++) {
      array[offset + i] = (byte) (value >>> (8 * i));
    }
  }

  /**
   * Re-writes the data size in the header(bytes 4-8) of the WAVE(.wav) input stream.

   * It needs to be read in order to calculate the size.
   *
   * @param is the input stream
   * @return A new input stream that includes the data header in the header
   * @throws IOException Signals that an I/O exception has occurred.
   */
  public static InputStream reWriteWaveHeader(InputStream is) throws IOException {
    byte[] audioBytes = toByteArray(is);
    int filesize = audioBytes.length - WAVE_HEADER_SIZE;

    writeInt(filesize, audioBytes, WAVE_SIZE_POS);
    writeInt(filesize - WAVE_HEADER_SIZE, audioBytes, WAVE_METADATA_POS);

    return new ByteArrayInputStream(audioBytes);
  }

  /**
   * Converts an {@link InputStream} to byte array.
   *
   * @param is the input stream
   * @return the byte array
   * @throws IOException If the first byte cannot be read for any reason other than end of file, or
   *     if the input stream has been closed, or if some other I/O error occurs.
   */
  public static byte[] toByteArray(InputStream is) throws IOException {
    ByteArrayOutputStream buffer = new ByteArrayOutputStream();

    int nRead;
    byte[] data = new byte[16384]; // 4 kb

    while ((nRead = is.read(data, 0, data.length)) != -1) {
      buffer.write(data, 0, nRead);
    }

    buffer.flush();
    return buffer.toByteArray();
  }
}