package org.apache.helix.filestore;
   
   /*
    * 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.
   */
  
  import java.io.File;
  import java.io.FileWriter;
  import java.io.IOException;
  
  import org.apache.commons.io.FileUtils;
  
  public class CheckpointFile
  {
    private static final String TEMP = ".bak";
    private static String CHECK_POINT_FILE = "lastprocessedchange.checkpoint";
  
    private String checkpointDirPath;
  
    public CheckpointFile(String checkpointDirPath) throws IOException
    {
      this.checkpointDirPath = checkpointDirPath;
      File checkpointdir = new File(checkpointDirPath);
      if (!checkpointdir.exists() && !checkpointdir.mkdirs())
      {
        throw new IOException("unable to create SCN file parent:"
            + checkpointdir.getAbsolutePath());
      }
    }
  
    public void checkpoint(ChangeRecord lastRecordProcessed) throws Exception
    {
  
      // delete the temp file if one exists
      File tempCheckpointFile = new File(checkpointDirPath + "/" + CHECK_POINT_FILE
          + TEMP);
      if (tempCheckpointFile.exists() && !tempCheckpointFile.delete())
      {
        System.err.println("unable to erase temp SCN file: "
            + tempCheckpointFile.getAbsolutePath());
      }
  
      String checkpointFileName = checkpointDirPath + "/" + CHECK_POINT_FILE;
      File checkpointfile = new File(checkpointFileName);
      if (checkpointfile.exists() && !checkpointfile.renameTo(tempCheckpointFile))
      {
        System.err.println("unable to backup scn file");
      }
      if (!checkpointfile.createNewFile())
      {
        System.err.println("unable to create new SCN file:"
            + checkpointfile.getAbsolutePath());
      }
      FileWriter writer = new FileWriter(checkpointfile);
      writer.write(lastRecordProcessed.toString());
      writer.flush();
      writer.close();
      System.out.println("scn persisted: " + lastRecordProcessed.txid);
  
    }
  
    public ChangeRecord findLastRecordProcessed()
    {
      String checkpointFileName = checkpointDirPath + "/" + CHECK_POINT_FILE;
      File file = new File(checkpointFileName);
      ChangeRecord record = null;
      if (file.exists())
      {
        try
        {
          String line = FileUtils.readFileToString(file);
          record = ChangeRecord.fromString(line);
        } catch (IOException e)
        {
          e.printStackTrace();
        }
      }
      return record;
    }
  }