/*
 * 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;

import java.io.BufferedInputStream;
import java.io.DataInput;
import java.io.DataInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.Arrays;
import org.apache.commons.io.IOUtils;
import org.apache.hadoop.fs.FSDataOutputStream;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.hbase.KeyValueUtil;
import org.apache.hadoop.hbase.util.Bytes;
import org.apache.yetus.audience.InterfaceAudience;

import org.apache.hbase.thirdparty.com.google.protobuf.UnsafeByteOperations;

import org.apache.hadoop.hbase.shaded.protobuf.ProtobufUtil;
import org.apache.hadoop.hbase.shaded.protobuf.generated.FSProtos;

/**
 * A reference to the top or bottom half of a store file where 'bottom' is the first half of the
 * file containing the keys that sort lowest and 'top' is the second half of the file with keys that
 * sort greater than those of the bottom half. The file referenced lives under a different region.
 * References are made at region split time.
 * <p>
 * References work with a special half store file type. References know how to write out the
 * reference format in the file system and are what is juggled when references are mixed in with
 * direct store files. The half store file type is used reading the referred to file.
 * <p>
 * References to store files located over in some other region look like this in the file system
 * <code>1278437856009925445.3323223323</code>: i.e. an id followed by hash of the referenced
 * region. Note, a region is itself not splittable if it has instances of store file references.
 * References are cleaned up by compactions.
 */
@InterfaceAudience.Private
public class Reference {
  private byte[] splitkey;
  private Range region;

  /**
   * For split HStoreFiles, it specifies if the file covers the lower half or the upper half of the
   * key range
   */
  static enum Range {
    /** HStoreFile contains upper half of key range */
    top,
    /** HStoreFile contains lower half of key range */
    bottom
  }

  /**
   * n * @return A {@link Reference} that points at top half of a an hfile
   */
  public static Reference createTopReference(final byte[] splitRow) {
    return new Reference(splitRow, Range.top);
  }

  /**
   * n * @return A {@link Reference} that points at the bottom half of a an hfile
   */
  public static Reference createBottomReference(final byte[] splitRow) {
    return new Reference(splitRow, Range.bottom);
  }

  /**
   * Constructor
   * @param splitRow This is row we are splitting around. n
   */
  Reference(final byte[] splitRow, final Range fr) {
    this.splitkey = splitRow == null ? null : KeyValueUtil.createFirstOnRow(splitRow).getKey();
    this.region = fr;
  }

  /**
   * Used by serializations.
   * @deprecated need by pb serialization
   */
  @Deprecated
  // Make this private when it comes time to let go of this constructor.
  // Needed by pb serialization.
  public Reference() {
    this(null, Range.bottom);
  }

  /**
   * n
   */
  public Range getFileRegion() {
    return this.region;
  }

  /**
   * n
   */
  public byte[] getSplitKey() {
    return splitkey;
  }

  /**
   * @see java.lang.Object#toString()
   */
  @Override
  public String toString() {
    return "" + this.region;
  }

  public static boolean isTopFileRegion(final Range r) {
    return r.equals(Range.top);
  }

  /**
   * @deprecated Writables are going away. Use the pb serialization methods instead. Remove in a
   *             release after 0.96 goes out. This is here only to migrate old Reference files
   *             written with Writables before 0.96.
   */
  @Deprecated
  public void readFields(DataInput in) throws IOException {
    boolean tmp = in.readBoolean();
    // If true, set region to top.
    this.region = tmp ? Range.top : Range.bottom;
    this.splitkey = Bytes.readByteArray(in);
  }

  public Path write(final FileSystem fs, final Path p) throws IOException {
    FSDataOutputStream out = fs.create(p, false);
    try {
      out.write(toByteArray());
    } finally {
      out.close();
    }
    return p;
  }

  /**
   * Read a Reference from FileSystem. nn * @return New Reference made from passed <code>p</code> n
   */
  public static Reference read(final FileSystem fs, final Path p) throws IOException {
    InputStream in = fs.open(p);
    try {
      // I need to be able to move back in the stream if this is not a pb serialization so I can
      // do the Writable decoding instead.
      in = in.markSupported() ? in : new BufferedInputStream(in);
      int pblen = ProtobufUtil.lengthOfPBMagic();
      in.mark(pblen);
      byte[] pbuf = new byte[pblen];
      IOUtils.readFully(in, pbuf, 0, pblen);
      // WATCHOUT! Return in middle of function!!!
      if (ProtobufUtil.isPBMagicPrefix(pbuf)) return convert(FSProtos.Reference.parseFrom(in));
      // Else presume Writables. Need to reset the stream since it didn't start w/ pb.
      // We won't bother rewriting thie Reference as a pb since Reference is transitory.
      in.reset();
      Reference r = new Reference();
      DataInputStream dis = new DataInputStream(in);
      // Set in = dis so it gets the close below in the finally on our way out.
      in = dis;
      r.readFields(dis);
      return r;
    } finally {
      in.close();
    }
  }

  public FSProtos.Reference convert() {
    FSProtos.Reference.Builder builder = FSProtos.Reference.newBuilder();
    builder.setRange(isTopFileRegion(getFileRegion())
      ? FSProtos.Reference.Range.TOP
      : FSProtos.Reference.Range.BOTTOM);
    builder.setSplitkey(UnsafeByteOperations.unsafeWrap(getSplitKey()));
    return builder.build();
  }

  public static Reference convert(final FSProtos.Reference r) {
    Reference result = new Reference();
    result.splitkey = r.getSplitkey().toByteArray();
    result.region = r.getRange() == FSProtos.Reference.Range.TOP ? Range.top : Range.bottom;
    return result;
  }

  /**
   * Use this when writing to a stream and you want to use the pb mergeDelimitedFrom (w/o the
   * delimiter, pb reads to EOF which may not be what you want).
   * @return This instance serialized as a delimited protobuf w/ a magic pb prefix. n
   */
  byte[] toByteArray() throws IOException {
    return ProtobufUtil.prependPBMagic(convert().toByteArray());
  }

  @Override
  public int hashCode() {
    return Arrays.hashCode(splitkey) + region.hashCode();
  }

  @Override
  public boolean equals(Object o) {
    if (this == o) return true;
    if (o == null) return false;
    if (!(o instanceof Reference)) return false;

    Reference r = (Reference) o;
    if (splitkey != null && r.splitkey == null) return false;
    if (splitkey == null && r.splitkey != null) return false;
    if (splitkey != null && !Arrays.equals(splitkey, r.splitkey)) return false;

    return region.equals(r.region);
  }
}