/**
    * 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.File;
  import java.io.IOException;
  import java.io.RandomAccessFile;
  import java.nio.ByteBuffer;
  import java.nio.channels.ClosedChannelException;
  import java.nio.channels.FileChannel;
  import java.util.Arrays;
  
  import com.google.common.annotations.VisibleForTesting;
  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);
    public static final String FILE_DELIMITER = ",";
    private final String[] filePaths;
    private final FileChannel[] fileChannels;
    private final RandomAccessFile[] rafs;
  
    private final long sizePerFile;
    private final long capacity;
  
    private FileReadAccessor readAccessor = new FileReadAccessor();
    private FileWriteAccessor writeAccessor = new FileWriteAccessor();
  
    public FileIOEngine(long capacity, String... filePaths) throws IOException {
      this.sizePerFile = capacity / filePaths.length;
      this.capacity = this.sizePerFile * filePaths.length;
      this.filePaths = filePaths;
      this.fileChannels = new FileChannel[filePaths.length];
      this.rafs = new RandomAccessFile[filePaths.length];
      for (int i = 0; i < filePaths.length; i++) {
        String filePath = filePaths[i];
        try {
          rafs[i] = new RandomAccessFile(filePath, "rw");
          long totalSpace = new File(filePath).getTotalSpace();
          if (totalSpace < sizePerFile) {
            // The next setting length will throw exception,logging this message
            // is just used for the detail reason of exception，
            String msg = "Only " + StringUtils.byteDesc(totalSpace)
                + " total space under " + filePath + ", not enough for requested "
                + StringUtils.byteDesc(sizePerFile);
            LOG.warn(msg);
          }
          rafs[i].setLength(sizePerFile);
          fileChannels[i] = rafs[i].getChannel();
          LOG.info("Allocating cache " + StringUtils.byteDesc(sizePerFile)
              + ", on the path:" + filePath);
        } catch (IOException fex) {
          LOG.error("Failed allocating cache on " + filePath, fex);
          shutdown();
          throw fex;
        }
      }
    }
  
    @Override
    public String toString() {
      return "ioengine=" + this.getClass().getSimpleName() + ", paths="
          + Arrays.asList(filePaths) + ", capacity=" + String.format("%,d", this.capacity);
    }
  
    /**
     * 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 {
     if (dstBuffer.remaining() != 0) {
       return accessFile(readAccessor, dstBuffer, offset);
     }
     return 0;
   }
 
   @VisibleForTesting
   void closeFileChannels() {
     for (FileChannel fileChannel: fileChannels) {
       try {
         fileChannel.close();
       } catch (IOException e) {
         LOG.warn("Failed to close FileChannel", e);
       }
     }
   }
 
   /**
    * 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 {
     if (!srcBuffer.hasRemaining()) {
       return;
     }
     accessFile(writeAccessor, srcBuffer, offset);
   }
 
   /**
    * Sync the data to file after writing
    * @throws IOException
    */
   @Override
   public void sync() throws IOException {
     for (int i = 0; i < fileChannels.length; i++) {
       try {
         if (fileChannels[i] != null) {
           fileChannels[i].force(true);
         }
       } catch (IOException ie) {
         LOG.warn("Failed syncing data to " + this.filePaths[i]);
         throw ie;
       }
     }
   }
 
   /**
    * Close the file
    */
   @Override
   public void shutdown() {
     for (int i = 0; i < filePaths.length; i++) {
       try {
         if (fileChannels[i] != null) {
           fileChannels[i].close();
         }
         if (rafs[i] != null) {
           rafs[i].close();
         }
       } catch (IOException ex) {
         LOG.error("Failed closing " + filePaths[i] + " when shudown the IOEngine", ex);
       }
     }
   }
 
   private int accessFile(FileAccessor accessor, ByteBuffer buffer, long globalOffset)
       throws IOException {
     int startFileNum = getFileNum(globalOffset);
     int remainingAccessDataLen = buffer.remaining();
     int endFileNum = getFileNum(globalOffset + remainingAccessDataLen - 1);
     int accessFileNum = startFileNum;
     long accessOffset = getAbsoluteOffsetInFile(accessFileNum, globalOffset);
     int bufLimit = buffer.limit();
     while (true) {
       FileChannel fileChannel = fileChannels[accessFileNum];
       int accessLen = 0;
       if (endFileNum > accessFileNum) {
         // short the limit;
         buffer.limit((int) (buffer.limit() - remainingAccessDataLen + sizePerFile - accessOffset));
       }
       try {
         accessLen = accessor.access(fileChannel, buffer, accessOffset);
       } catch (ClosedChannelException e) {
         LOG.warn("Caught ClosedChannelException accessing BucketCache, reopening file. ", e);
         refreshFileConnection(accessFileNum);
         continue;
       }
       // recover the limit
       buffer.limit(bufLimit);
       if (accessLen < remainingAccessDataLen) {
         remainingAccessDataLen -= accessLen;
         accessFileNum++;
         accessOffset = 0;
       } else {
         break;
       }
       if (accessFileNum >= fileChannels.length) {
         throw new IOException("Required data len " + StringUtils.byteDesc(buffer.remaining())
             + " exceed the engine's capacity " + StringUtils.byteDesc(capacity) + " where offset="
             + globalOffset);
       }
     }
     return bufLimit;
   }
 
   /**
    * Get the absolute offset in given file with the relative global offset.
    * @param fileNum
    * @param globalOffset
    * @return the absolute offset
    */
   private long getAbsoluteOffsetInFile(int fileNum, long globalOffset) {
     return globalOffset - fileNum * sizePerFile;
   }
 
   private int getFileNum(long offset) {
     if (offset < 0) {
       throw new IllegalArgumentException("Unexpected offset " + offset);
     }
     int fileNum = (int) (offset / sizePerFile);
     if (fileNum >= fileChannels.length) {
       throw new RuntimeException("Not expected offset " + offset + " where capacity=" + capacity);
     }
     return fileNum;
   }
 
   @VisibleForTesting
   FileChannel[] getFileChannels() {
     return fileChannels;
   }
 
   @VisibleForTesting
   void refreshFileConnection(int accessFileNum) throws IOException {
     FileChannel fileChannel = fileChannels[accessFileNum];
     if (fileChannel != null) {
       fileChannel.close();
     }
     rafs[accessFileNum] = new RandomAccessFile(filePaths[accessFileNum], "rw");
     fileChannels[accessFileNum] = rafs[accessFileNum].getChannel();
   }
 
   private static interface FileAccessor {
     int access(FileChannel fileChannel, ByteBuffer byteBuffer, long accessOffset)
         throws IOException;
   }
 
   private static class FileReadAccessor implements FileAccessor {
     @Override
     public int access(FileChannel fileChannel, ByteBuffer byteBuffer, long accessOffset)
         throws IOException {
       return fileChannel.read(byteBuffer, accessOffset);
     }
   }
 
   private static class FileWriteAccessor implements FileAccessor {
     @Override
     public int access(FileChannel fileChannel, ByteBuffer byteBuffer, long accessOffset)
         throws IOException {
       return fileChannel.write(byteBuffer, accessOffset);
     }
   }
 
 }