/*
 * 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.carbondata.core.datastore.impl;

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.util.HashMap;
import java.util.Map;
import java.util.Map.Entry;

import org.apache.carbondata.core.constants.CarbonCommonConstants;
import org.apache.carbondata.core.datastore.FileReader;

public class FileReaderImpl implements FileReader {
  /**
   * cache to hold filename and its stream
   */
  private Map<String, FileChannel> fileNameAndStreamCache;

  private boolean readPageByPage;

  /**
   * FileReaderImpl Constructor
   * It will create the cache
   */
  public FileReaderImpl() {
    this.fileNameAndStreamCache =
        new HashMap<String, FileChannel>(CarbonCommonConstants.DEFAULT_COLLECTION_SIZE);
  }

  public FileReaderImpl(int capacity) {
    this.fileNameAndStreamCache = new HashMap<String, FileChannel>(capacity);
  }

  /**
   * This method will be used to read the byte array from file based on offset
   * and length(number of bytes) need to read
   *
   * @param filePath fully qualified file path
   * @param offset   reading start position,
   * @param length   number of bytes to be read
   * @return read byte array
   */
  @Override
  public byte[] readByteArray(String filePath, long offset, int length)
      throws IOException {
    FileChannel fileChannel = updateCache(filePath);
    ByteBuffer byteBuffer = read(fileChannel, length, offset);
    return byteBuffer.array();
  }

  /**
   * This method will be used to close all the streams currently present in the cache
   */
  @Override
  public void finish() throws IOException {
    for (Entry<String, FileChannel> entry : fileNameAndStreamCache.entrySet()) {
      FileChannel channel = entry.getValue();
      if (null != channel) {
        channel.close();
      }
    }
    fileNameAndStreamCache.clear();
  }

  /**
   * This method will be used to read int from file from position(offset), here
   * length will be always 4 because int byte size if 4
   *
   * @param filePath fully qualified file path
   * @param offset   reading start position,
   * @return read int
   */
  @Override
  public int readInt(String filePath, long offset) throws IOException {
    FileChannel fileChannel = updateCache(filePath);
    ByteBuffer byteBuffer = read(fileChannel, CarbonCommonConstants.INT_SIZE_IN_BYTE, offset);
    return byteBuffer.getInt();
  }

  /**
   * This method will be used to read int from file from position(offset), here
   * length will be always 4 because int byte size if 4
   *
   * @param filePath fully qualified file path
   * @return read int
   */
  @Override
  public int readInt(String filePath) throws IOException {
    FileChannel fileChannel = updateCache(filePath);
    ByteBuffer byteBuffer = read(fileChannel, CarbonCommonConstants.INT_SIZE_IN_BYTE);
    return byteBuffer.getInt();
  }

  /**
   * This method will be used to read int from file from position(offset), here
   * length will be always 4 because int byte size if 4
   *
   * @param filePath fully qualified file path
   * @param offset   reading start position,
   * @return read int
   */
  @Override
  public long readDouble(String filePath, long offset) throws IOException {
    FileChannel fileChannel = updateCache(filePath);
    ByteBuffer byteBuffer = read(fileChannel, CarbonCommonConstants.LONG_SIZE_IN_BYTE, offset);
    return byteBuffer.getLong();
  }

  /**
   * This method will be used to check whether stream is already present in
   * cache or not for filepath if not present then create it and then add to
   * cache, other wise get from cache
   *
   * @param filePath fully qualified file path
   * @return channel
   */
  private FileChannel updateCache(String filePath) throws FileNotFoundException {
    FileChannel fileChannel = fileNameAndStreamCache.get(filePath);
    if (null == fileChannel) {
      FileInputStream stream = new FileInputStream(filePath);
      fileChannel = stream.getChannel();
      fileNameAndStreamCache.put(filePath, fileChannel);
    }
    return fileChannel;
  }

  /**
   * This method will be used to read from file based on number of bytes to be read and position
   *
   * @param channel file channel
   * @param size    number of bytes
   * @param offset  position
   * @return byte buffer
   */
  private ByteBuffer read(FileChannel channel, int size, long offset) throws IOException {
    ByteBuffer byteBuffer = ByteBuffer.allocate(size);
    channel.position(offset);
    channel.read(byteBuffer);
    byteBuffer.rewind();
    return byteBuffer;
  }

  /**
   * This method will be used to read from file based on number of bytes to be read and position
   *
   * @param channel file channel
   * @param size    number of bytes
   * @return byte buffer
   */
  private ByteBuffer read(FileChannel channel, int size) throws IOException {
    ByteBuffer byteBuffer = ByteBuffer.allocate(size);
    channel.read(byteBuffer);
    byteBuffer.rewind();
    return byteBuffer;
  }


  /**
   * This method will be used to read the byte array from file based on length(number of bytes)
   *
   * @param filePath fully qualified file path
   * @param length   number of bytes to be read
   * @return read byte array
   */
  @Override
  public byte[] readByteArray(String filePath, int length) throws IOException {
    FileChannel fileChannel = updateCache(filePath);
    ByteBuffer byteBuffer = read(fileChannel, length);
    return byteBuffer.array();
  }

  /**
   * This method will be used to read long from file from position(offset), here
   * length will be always 8 because int byte size is 8
   *
   * @param filePath fully qualified file path
   * @param offset   reading start position,
   * @return read long
   */
  @Override
  public long readLong(String filePath, long offset) throws IOException {
    FileChannel fileChannel = updateCache(filePath);
    ByteBuffer byteBuffer = read(fileChannel, CarbonCommonConstants.LONG_SIZE_IN_BYTE, offset);
    return byteBuffer.getLong();
  }

  @Override
  public ByteBuffer readByteBuffer(String filePath, long offset, int length)
      throws IOException {
    ByteBuffer byteBuffer = ByteBuffer.allocate(length);
    FileChannel fileChannel = updateCache(filePath);
    fileChannel.position(offset);
    fileChannel.read(byteBuffer);
    byteBuffer.rewind();
    return byteBuffer;
  }

  @Override
  public void setReadPageByPage(boolean isReadPageByPage) {
    this.readPageByPage = isReadPageByPage;
  }

  @Override
  public boolean isReadPageByPage() {
    return readPageByPage;
  }
}