/*
    * 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.chukwa.datacollection.adaptor.filetailer;
  
  import java.io.File;
  import java.io.IOException;
  import java.io.RandomAccessFile;
  import java.util.regex.Matcher;
  import java.util.regex.Pattern;
  import org.apache.hadoop.chukwa.ChunkImpl;
  import org.apache.hadoop.chukwa.datacollection.ChunkReceiver;
  import org.apache.hadoop.chukwa.datacollection.adaptor.AbstractAdaptor;
  import org.apache.hadoop.chukwa.datacollection.adaptor.AdaptorException;
  import org.apache.hadoop.chukwa.datacollection.adaptor.AdaptorShutdownPolicy;
  import org.apache.hadoop.conf.Configuration;
  import org.apache.log4j.Logger;
  
  /**
   * A base class for file tailing adaptors.  
   * Intended to mandate as little policy as possible, and to use as 
   * few system resources as possible.
   * 
   * 
   * If the file does not exist, this class will continue to retry quietly
   * forever and will start tailing if it's eventually created.
   */
  public class LWFTAdaptor extends AbstractAdaptor {
    
    /**
     * This is the maximum amount we'll read from any one file before moving on to
     * the next. This way, we get quick response time for other files if one file
     * is growing rapidly.
     * 
     */
    public static final int DEFAULT_MAX_READ_SIZE = 128 * 1024;
    public static final String MAX_READ_SIZE_OPT = 
        "chukwaAgent.fileTailingAdaptor.maxReadSize";
  
    public static int MAX_READ_SIZE = DEFAULT_MAX_READ_SIZE;
    
    static Logger log;
    protected static FileTailer tailer;
    
    static {
      tailer = null;
      log = Logger.getLogger(FileTailingAdaptor.class);
    }
    
    
    /**
     * next PHYSICAL offset to read
     */
    protected long fileReadOffset;
  
    /**
     * The logical offset of the first byte of the file
     */
    protected long offsetOfFirstByte = 0;
    protected Configuration conf = null;
    
    File toWatch;
  
    @Override
    public void start(long offset) {
      synchronized(LWFTAdaptor.class) {
        if(tailer == null)
          tailer = new FileTailer(control.getConfiguration());
      }
      this.fileReadOffset = offset - offsetOfFirstByte;    
      tailer.startWatchingFile(this);
    }
    
    /**
     * @see org.apache.hadoop.chukwa.datacollection.adaptor.Adaptor#getCurrentStatus()
     */
    public String getCurrentStatus() {
      return type.trim() + " " + offsetOfFirstByte + " " + toWatch.getPath();
    }
  
    public String toString() {
      return "Lightweight Tailer on " + toWatch;
    }
  
    public String getStreamName() {
     return toWatch.getPath();
   }
   
   @Override
   public String parseArgs(String params) { 
     conf = control.getConfiguration();
     MAX_READ_SIZE = conf.getInt(MAX_READ_SIZE_OPT, DEFAULT_MAX_READ_SIZE);
 
     Pattern cmd = Pattern.compile("(\\d+)\\s+(.+)\\s?");
     Matcher m = cmd.matcher(params);
     if (m.matches()) { //check for first-byte offset. If absent, assume we just got a path.
       offsetOfFirstByte = Long.parseLong(m.group(1));
       toWatch = new File(m.group(2));
     } else {
       toWatch = new File(params.trim());
     }
     return toWatch.getAbsolutePath();
   }
 
   @Override
   public long shutdown(AdaptorShutdownPolicy shutdownPolicy)
       throws AdaptorException {
     tailer.stopWatchingFile(this);
     return fileReadOffset + offsetOfFirstByte;
   }
   
 
   /**
    * Extract records from a byte sequence
    * 
    * @param eq the queue to stick the new chunk[s] in
    * @param buffOffsetInFile the byte offset in the stream at which buf[] begins
    * @param buf the byte buffer to extract records from
    * @return the number of bytes processed
    * @throws InterruptedException
    */
   protected int extractRecords(ChunkReceiver eq, long buffOffsetInFile,
       byte[] buf) throws InterruptedException {
     if(buf.length == 0)
       return 0;
     
     ChunkImpl chunk = new ChunkImpl(type, toWatch.getAbsolutePath(),
         buffOffsetInFile + buf.length, buf, this);
 
     eq.add(chunk);
     return buf.length;
   }
   
   protected boolean slurp(long len, RandomAccessFile reader) throws IOException,
   InterruptedException{
     boolean hasMoreData = false;
 
     log.debug("Adaptor|" + adaptorID + "|seeking|" + fileReadOffset);
     reader.seek(fileReadOffset);
 
     long bufSize = len - fileReadOffset;
 
    if (bufSize > MAX_READ_SIZE) {
       bufSize = MAX_READ_SIZE;
       hasMoreData = true;
     }
     byte[] buf = new byte[(int) bufSize];
 
     long curOffset = fileReadOffset;
 
     int bufferRead = reader.read(buf);
     assert reader.getFilePointer() == fileReadOffset + bufSize : " event size arithmetic is broken: "
         + " pointer is "
         + reader.getFilePointer()
         + " but offset is "
         + fileReadOffset + bufSize;
 
     int bytesUsed = extractRecords(dest,
         fileReadOffset + offsetOfFirstByte, buf);
 
     // === WARNING ===
     // If we couldn't found a complete record AND
     // we cannot read more, i.e bufferRead == MAX_READ_SIZE
     // it's because the record is too BIG
     // So log.warn, and drop current buffer so we can keep moving
     // instead of being stopped at that point for ever
     if (bytesUsed == 0 && bufferRead == MAX_READ_SIZE) {
       log.warn("bufferRead == MAX_READ_SIZE AND bytesUsed == 0, dropping current buffer: startOffset="
               + curOffset
               + ", MAX_READ_SIZE="
               + MAX_READ_SIZE
               + ", for "
               + toWatch.getPath());
       bytesUsed = buf.length;
     }
 
     fileReadOffset = fileReadOffset + bytesUsed;
 
     log.debug("Adaptor|" + adaptorID + "|start|" + curOffset + "|end|"
         + fileReadOffset);
     return hasMoreData;
   }
   
   public synchronized boolean tailFile()
   throws InterruptedException {
     boolean hasMoreData = false;
     try {
       
        //if file doesn't exist, length =0 and we just keep waiting for it.
       //if(!toWatch.exists())
       //  deregisterAndStop(false);
       
       long len = toWatch.length();
       if(len < fileReadOffset) {
         //file shrank; probably some data went missing.
         handleShrunkenFile(len);
       } else if(len > fileReadOffset) {
         RandomAccessFile reader = new RandomAccessFile(toWatch, "r");
         slurp(len, reader);
         reader.close();
       }
     } catch(IOException e) {
       log.warn("IOException in tailer", e);
       deregisterAndStop();
     }
     
     return hasMoreData;
   }
 
   private void handleShrunkenFile(long measuredLen) {
     log.info("file "+ toWatch +"shrank from " + fileReadOffset + " to " + measuredLen);
     offsetOfFirstByte = measuredLen;
     fileReadOffset = 0;
   }
 
 }