/**
 * 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.mapred;

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

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FSDataInputStream;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.fs.Seekable;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.io.compress.CodecPool;
import org.apache.hadoop.io.compress.CompressionCodec;
import org.apache.hadoop.io.compress.CompressionCodecFactory;
import org.apache.hadoop.io.compress.Decompressor;
import org.apache.hadoop.io.compress.SplitCompressionInputStream;
import org.apache.hadoop.io.compress.SplittableCompressionCodec;
import org.apache.commons.logging.LogFactory;
import org.apache.commons.logging.Log;

/**
 * Treats keys as offset in file and value as line. 
 */
public class LineRecordReader implements RecordReader<LongWritable, Text> {
  private static final Log LOG
    = LogFactory.getLog(LineRecordReader.class.getName());

  private CompressionCodecFactory compressionCodecs = null;
  private long start;
  private long pos;
  private long end;
  private LineReader in;
  int maxLineLength;
  private Seekable filePosition;
  private CompressionCodec codec;
  private Decompressor decompressor;

  /**
   * A class that provides a line reader from an input stream.
   * @deprecated Use {@link org.apache.hadoop.util.LineReader} instead.
   */
  @Deprecated
  public static class LineReader extends org.apache.hadoop.util.LineReader {
    LineReader(InputStream in) {
      super(in);
    }
    LineReader(InputStream in, int bufferSize) {
      super(in, bufferSize);
    }
    public LineReader(InputStream in, Configuration conf) throws IOException {
      super(in, conf);
    }
  }

  public LineRecordReader(Configuration job, 
                          FileSplit split) throws IOException {
    this.maxLineLength = job.getInt("mapred.linerecordreader.maxlength",
                                    Integer.MAX_VALUE);
    start = split.getStart();
    end = start + split.getLength();
    final Path file = split.getPath();
    compressionCodecs = new CompressionCodecFactory(job);
    codec = compressionCodecs.getCodec(file);

    // open the file and seek to the start of the split
    FileSystem fs = file.getFileSystem(job);
    FSDataInputStream fileIn = fs.open(split.getPath());

    if (isCompressedInput()) {
      decompressor = CodecPool.getDecompressor(codec);
      if (codec instanceof SplittableCompressionCodec) {
        final SplitCompressionInputStream cIn =
          ((SplittableCompressionCodec)codec).createInputStream(
            fileIn, decompressor, start, end,
            SplittableCompressionCodec.READ_MODE.BYBLOCK);
        in = new LineReader(cIn, job);
        start = cIn.getAdjustedStart();
        end = cIn.getAdjustedEnd();
        filePosition = cIn; // take pos from compressed stream
      } else {
        in = new LineReader(codec.createInputStream(fileIn, decompressor), job);
        filePosition = fileIn;
      }
    } else {
      fileIn.seek(start);
      in = new LineReader(fileIn, job);
      filePosition = fileIn;
    }
    // If this is not the first split, we always throw away first record
    // because we always (except the last split) read one extra line in
    // next() method.
    if (start != 0) {
      start += in.readLine(new Text(), 0, maxBytesToConsume(start));
    }
    this.pos = start;
  }

  private boolean isCompressedInput() {
    return (codec != null);
  }

  private int maxBytesToConsume(long pos) {
    return isCompressedInput()
      ? Integer.MAX_VALUE
      : (int) Math.min(Integer.MAX_VALUE, end - pos);
  }

  private long getFilePosition() throws IOException {
    long retVal;
    if (isCompressedInput() && null != filePosition) {
      retVal = filePosition.getPos();
    } else {
      retVal = pos;
    }
    return retVal;
  }

  private int skipUtfByteOrderMark(Text value) throws IOException {
    // Strip BOM(Byte Order Mark)
    // Text only support UTF-8, we only need to check UTF-8 BOM
    // (0xEF,0xBB,0xBF) at the start of the text stream.
    int newMaxLineLength = (int) Math.min(3L + (long) maxLineLength,
        Integer.MAX_VALUE);
    int newSize = in.readLine(value, newMaxLineLength,
        Math.max(maxBytesToConsume(pos), newMaxLineLength));
    // Even we read 3 extra bytes for the first line,
    // we won't alter existing behavior (no backwards incompat issue).
    // Because the newSize is less than maxLineLength and
    // the number of bytes copied to Text is always no more than newSize.
    // If the return size from readLine is not less than maxLineLength,
    // we will discard the current line and read the next line.
    pos += newSize;
    int textLength = value.getLength();
    byte[] textBytes = value.getBytes();
    if ((textLength >= 3) && (textBytes[0] == (byte)0xEF) &&
        (textBytes[1] == (byte)0xBB) && (textBytes[2] == (byte)0xBF)) {
      // find UTF-8 BOM, strip it.
      LOG.info("Found UTF-8 BOM and skipped it");
      textLength -= 3;
      newSize -= 3;
      if (textLength > 0) {
        // It may work to use the same buffer and not do the copy
        byte[] result = new byte[textLength + 3];
        System.arraycopy(textBytes, 0, result, 0, textLength + 3);
        value.set(result, 3, textLength);
      } else {
        value.clear();
      }
    }
    return newSize;
  }

  public LineRecordReader(InputStream in, long offset, long endOffset,
                          int maxLineLength) {
    this.maxLineLength = maxLineLength;
    this.in = new LineReader(in);
    this.start = offset;
    this.pos = offset;
    this.end = endOffset;
    this.filePosition = null;
  }

  public LineRecordReader(InputStream in, long offset, long endOffset, 
                          Configuration job) 
    throws IOException{
    this.maxLineLength = job.getInt("mapred.linerecordreader.maxlength",
                                    Integer.MAX_VALUE);
    this.in = new LineReader(in, job);
    this.start = offset;
    this.pos = offset;
    this.end = endOffset;    
    this.filePosition = null;
  }
  
  public LongWritable createKey() {
    return new LongWritable();
  }
  
  public Text createValue() {
    return new Text();
  }
  
  /** Read a line. */
  public synchronized boolean next(LongWritable key, Text value)
    throws IOException {

    // We always read one extra line, which lies outside the upper
    // split limit i.e. (end - 1)
    while (getFilePosition() <= end) {
      key.set(pos);

      int newSize = 0;
      if (pos == 0) {
        newSize = skipUtfByteOrderMark(value);
      } else {
        newSize = in.readLine(value, maxLineLength,
            Math.max(maxBytesToConsume(pos), maxLineLength));
        pos += newSize;
      }

      if (newSize == 0) {
        return false;
      }
      if (newSize < maxLineLength) {
        return true;
      }

      // line too long. try again
      LOG.info("Skipped line of size " + newSize + " at pos " + (pos - newSize));
    }

    return false;
  }

  /**
   * Get the progress within the split
   */
  public float getProgress() throws IOException {
    if (start == end) {
      return 0.0f;
    } else {
      return Math.min(1.0f,
        (getFilePosition() - start) / (float)(end - start));
    }
  }
  
  public synchronized long getPos() throws IOException {
    return pos;
  }

  public synchronized void close() throws IOException {
    try {
      if (in != null) {
        in.close();
      }
    } finally {
      if (decompressor != null) {
        CodecPool.returnDecompressor(decompressor);
      }
    }
  }
}