/**
 * 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 org.apache.hadoop.tools.util;

import java.io.IOException;
import java.io.InputStream;

import org.apache.hadoop.fs.FSDataInputStream;
import org.apache.hadoop.fs.PositionedReadable;

import com.google.common.base.Preconditions;

/**
 * The ThrottleInputStream provides bandwidth throttling on a specified
 * InputStream. It is implemented as a wrapper on top of another InputStream
 * instance.
 * The throttling works by examining the number of bytes read from the underlying
 * InputStream from the beginning, and sleep()ing for a time interval if
 * the byte-transfer is found exceed the specified tolerable maximum.
 * (Thus, while the read-rate might exceed the maximum for a given short interval,
 * the average tends towards the specified maximum, overall.)
 */
public class ThrottledInputStream extends InputStream {

  private final InputStream rawStream;
  private final long maxBytesPerSec;
  private final long startTime = System.currentTimeMillis();

  private long bytesRead = 0;
  private long totalSleepTime = 0;

  private static final long SLEEP_DURATION_MS = 50;

  public ThrottledInputStream(InputStream rawStream) {
    this(rawStream, Long.MAX_VALUE);
  }

  public ThrottledInputStream(InputStream rawStream, long maxBytesPerSec) {
    assert maxBytesPerSec > 0 : "Bandwidth " + maxBytesPerSec + " is invalid"; 
    this.rawStream = rawStream;
    this.maxBytesPerSec = maxBytesPerSec;
  }

  @Override
  public void close() throws IOException {
    rawStream.close();
  }

  /** {@inheritDoc} */
  @Override
  public int read() throws IOException {
    throttle();
    int data = rawStream.read();
    if (data != -1) {
      bytesRead++;
    }
    return data;
  }

  /** {@inheritDoc} */
  @Override
  public int read(byte[] b) throws IOException {
    throttle();
    int readLen = rawStream.read(b);
    if (readLen != -1) {
      bytesRead += readLen;
    }
    return readLen;
  }

  /** {@inheritDoc} */
  @Override
  public int read(byte[] b, int off, int len) throws IOException {
    throttle();
    int readLen = rawStream.read(b, off, len);
    if (readLen != -1) {
      bytesRead += readLen;
    }
    return readLen;
  }

  /**
   * Read bytes starting from the specified position. This requires rawStream is
   * an instance of {@link PositionedReadable}.
   */
  public int read(long position, byte[] buffer, int offset, int length)
      throws IOException {
    if (!(rawStream instanceof PositionedReadable)) {
      throw new UnsupportedOperationException(
          "positioned read is not supported by the internal stream");
    }
    throttle();
    int readLen = ((PositionedReadable) rawStream).read(position, buffer,
        offset, length);
    if (readLen != -1) {
      bytesRead += readLen;
    }
    return readLen;
  }

  private void throttle() throws IOException {
    while (getBytesPerSec() > maxBytesPerSec) {
      try {
        Thread.sleep(SLEEP_DURATION_MS);
        totalSleepTime += SLEEP_DURATION_MS;
      } catch (InterruptedException e) {
        throw new IOException("Thread aborted", e);
      }
    }
  }

  /**
   * Getter for the number of bytes read from this stream, since creation.
   * @return The number of bytes.
   */
  public long getTotalBytesRead() {
    return bytesRead;
  }

  /**
   * Getter for the read-rate from this stream, since creation.
   * Calculated as bytesRead/elapsedTimeSinceStart.
   * @return Read rate, in bytes/sec.
   */
  public long getBytesPerSec() {
    long elapsed = (System.currentTimeMillis() - startTime) / 1000;
    if (elapsed == 0) {
      return bytesRead;
    } else {
      return bytesRead / elapsed;
    }
  }

  /**
   * Getter the total time spent in sleep.
   * @return Number of milliseconds spent in sleep.
   */
  public long getTotalSleepTime() {
    return totalSleepTime;
  }

  /** {@inheritDoc} */
  @Override
  public String toString() {
    return "ThrottledInputStream{" +
        "bytesRead=" + bytesRead +
        ", maxBytesPerSec=" + maxBytesPerSec +
        ", bytesPerSec=" + getBytesPerSec() +
        ", totalSleepTime=" + totalSleepTime +
        '}';
  }
}
