/**
    *
    * 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.hbase.monitoring;
  
  import java.io.BufferedReader;
  import java.io.File;
  import java.io.FileInputStream;
  import java.io.IOException;
  import java.io.InputStreamReader;
  import java.io.PrintWriter;
  import java.nio.channels.FileChannel;
  import java.util.Enumeration;
  import java.util.Set;
  
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.io.IOUtils;
  import org.apache.log4j.Appender;
  import org.apache.log4j.FileAppender;
  import org.apache.log4j.Logger;
  
  import com.google.common.collect.Sets;
  
  /**
   * Utility functions for reading the log4j logs that are
   * being written by HBase.
   */
  @InterfaceAudience.Private
  public abstract class LogMonitoring {
    public static Set<File> getActiveLogFiles() throws IOException {
      Set<File> ret = Sets.newHashSet();
      Appender a;
      @SuppressWarnings("unchecked")
      Enumeration<Appender> e = Logger.getRootLogger().getAllAppenders();
      while (e.hasMoreElements()) {
        a = e.nextElement();
        if (a instanceof FileAppender) {
          FileAppender fa = (FileAppender) a;
          String filename = fa.getFile();
          ret.add(new File(filename));
        }
      }
      return ret;
    }
    
  
    public static void dumpTailOfLogs(
        PrintWriter out, long tailKb) throws IOException {
      Set<File> logs = LogMonitoring.getActiveLogFiles();
      for (File f : logs) {
        out.println("+++++++++++++++++++++++++++++++");
        out.println(f.getAbsolutePath());
        out.println("+++++++++++++++++++++++++++++++");
        try {
          dumpTailOfLog(f, out, tailKb);
        } catch (IOException ioe) {
          out.println("Unable to dump log at " + f);
          ioe.printStackTrace(out);
        }
        out.println("\n\n");
      }
    }
  
    private static void dumpTailOfLog(File f, PrintWriter out, long tailKb)
        throws IOException {
      FileInputStream fis = new FileInputStream(f);
      BufferedReader r = null;
      try {
        FileChannel channel = fis.getChannel();
        channel.position(Math.max(0, channel.size() - tailKb*1024));
        r = new BufferedReader(new InputStreamReader(fis));
        r.readLine(); // skip the first partial line
        String line;
        while ((line = r.readLine()) != null) {
          out.println(line);
        }
      } finally {
        if (r != null) IOUtils.closeStream(r);
        IOUtils.closeStream(fis);
      }
    }
  }