/**
    * Copyright The Apache Software Foundation
    *
    * 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.io.hfile.bucket;
  
  import java.io.IOException;
  import java.io.RandomAccessFile;
  import java.nio.ByteBuffer;
  import java.nio.channels.FileChannel;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.util.StringUtils;
  
  /**
   * IO engine that stores data to a file on the local file system.
   */
  @InterfaceAudience.Private
  public class FileIOEngine implements IOEngine {
    private static final Log LOG = LogFactory.getLog(FileIOEngine.class);
    private final RandomAccessFile raf;
    private final FileChannel fileChannel;
    private final String path;
    private long size;
  
    public FileIOEngine(String filePath, long fileSize) throws IOException {
      this.path = filePath;
      this.size = fileSize;
      try {
        raf = new RandomAccessFile(filePath, "rw");
      } catch (java.io.FileNotFoundException fex) {
        LOG.error("Can't create bucket cache file " + filePath, fex);
        throw fex;
      }
  
      try {
        raf.setLength(fileSize);
      } catch (IOException ioex) {
        LOG.error("Can't extend bucket cache file; insufficient space for "
            + StringUtils.byteDesc(fileSize), ioex);
        raf.close();
        throw ioex;
      }
  
      fileChannel = raf.getChannel();
      LOG.info("Allocating " + StringUtils.byteDesc(fileSize) + ", on the path:" + filePath);
    }
  
    @Override
    public String toString() {
      return "ioengine=" + this.getClass().getSimpleName() + ", path=" + this.path +
        ", size=" + String.format("%,d", this.size);
    }
  
    /**
     * File IO engine is always able to support persistent storage for the cache
     * @return true
     */
    @Override
    public boolean isPersistent() {
      return true;
    }
  
    /**
     * Transfers data from file to the given byte buffer
     * @param dstBuffer the given byte buffer into which bytes are to be written
     * @param offset The offset in the file where the first byte to be read
     * @return number of bytes read
     * @throws IOException
     */
    @Override
    public int read(ByteBuffer dstBuffer, long offset) throws IOException {
      return fileChannel.read(dstBuffer, offset);
    }
  
    /**
     * Transfers data from the given byte buffer to file
     * @param srcBuffer the given byte buffer from which bytes are to be read
     * @param offset The offset in the file where the first byte to be written
     * @throws IOException
     */
    @Override
    public void write(ByteBuffer srcBuffer, long offset) throws IOException {
     fileChannel.write(srcBuffer, offset);
   }
 
   /**
    * Sync the data to file after writing
    * @throws IOException
    */
   @Override
   public void sync() throws IOException {
     fileChannel.force(true);
   }
 
   /**
    * Close the file
    */
   @Override
   public void shutdown() {
     try {
       fileChannel.close();
     } catch (IOException ex) {
       LOG.error("Can't shutdown cleanly", ex);
     }
     try {
       raf.close();
     } catch (IOException ex) {
       LOG.error("Can't shutdown cleanly", ex);
     }
   }
 }