/*
    *
    * 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.filter;
  
  
  import java.io.IOException;
  import java.util.ArrayList;
  import java.util.Objects;
  
  import org.apache.hadoop.hbase.Cell;
  import org.apache.hadoop.hbase.KeyValue;
  import org.apache.hadoop.hbase.KeyValueUtil;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.classification.InterfaceStability;
  import org.apache.hadoop.hbase.exceptions.DeserializationException;
  import org.apache.hadoop.hbase.protobuf.generated.FilterProtos;
  import org.apache.hadoop.hbase.util.Bytes;
  
  import com.google.common.base.Preconditions;
  import com.google.protobuf.InvalidProtocolBufferException;
  
  /**
   * A filter that will only return the key component of each KV (the value will
   * be rewritten as empty).
   * <p>
   * This filter can be used to grab all of the keys without having to also grab
   * the values.
   */
  @InterfaceAudience.Public
  @InterfaceStability.Stable
  public class KeyOnlyFilter extends FilterBase {
  
    boolean lenAsVal;
    public KeyOnlyFilter() { this(false); }
    public KeyOnlyFilter(boolean lenAsVal) { this.lenAsVal = lenAsVal; }
  
    @Override
    public Cell transformCell(Cell cell) {
      return createKeyOnlyCell(cell);
    }
  
    private Cell createKeyOnlyCell(Cell c) {
      // KV format: <keylen:4><valuelen:4><key:keylen><value:valuelen>
      // Rebuild as: <keylen:4><0:4><key:keylen>
      int dataLen = lenAsVal ? Bytes.SIZEOF_INT : 0;
      int keyOffset = (2 * Bytes.SIZEOF_INT);
      int keyLen = KeyValueUtil.keyLength(c);
      byte[] newBuffer = new byte[keyLen + keyOffset + dataLen];
      Bytes.putInt(newBuffer, 0, keyLen);
      Bytes.putInt(newBuffer, Bytes.SIZEOF_INT, dataLen);
      KeyValueUtil.appendKeyTo(c, newBuffer, keyOffset);
      if (lenAsVal) {
        Bytes.putInt(newBuffer, newBuffer.length - dataLen, c.getValueLength());
      }
      return new KeyValue(newBuffer);
    }
  
    @Override
    public ReturnCode filterKeyValue(Cell ignored) throws IOException {
      return ReturnCode.INCLUDE;
    }
    
    public static Filter createFilterFromArguments(ArrayList<byte []> filterArguments) {
      Preconditions.checkArgument((filterArguments.size() == 0 || filterArguments.size() == 1),
                                  "Expected: 0 or 1 but got: %s", filterArguments.size());
      KeyOnlyFilter filter = new KeyOnlyFilter();
      if (filterArguments.size() == 1) {
        filter.lenAsVal = ParseFilter.convertByteArrayToBoolean(filterArguments.get(0));
      }
      return filter;
    }
  
    /**
     * @return The filter serialized using pb
     */
    @Override
    public byte [] toByteArray() {
      FilterProtos.KeyOnlyFilter.Builder builder =
        FilterProtos.KeyOnlyFilter.newBuilder();
      builder.setLenAsVal(this.lenAsVal);
      return builder.build().toByteArray();
    }
  
   /**
    * @param pbBytes A pb serialized {@link KeyOnlyFilter} instance
    * @return An instance of {@link KeyOnlyFilter} made from <code>bytes</code>
    * @throws DeserializationException
    * @see #toByteArray
    */
   public static KeyOnlyFilter parseFrom(final byte [] pbBytes)
   throws DeserializationException {
     FilterProtos.KeyOnlyFilter proto;
     try {
       proto = FilterProtos.KeyOnlyFilter.parseFrom(pbBytes);
     } catch (InvalidProtocolBufferException e) {
       throw new DeserializationException(e);
     }
     return new KeyOnlyFilter(proto.getLenAsVal());
   }
 
   /**
    * @param other
    * @return true if and only if the fields of the filter that are serialized
    * are equal to the corresponding fields in other.  Used for testing.
    */
   @Override
   boolean areSerializedFieldsEqual(Filter o) {
     if (o == this) return true;
     if (!(o instanceof KeyOnlyFilter)) return false;
 
     KeyOnlyFilter other = (KeyOnlyFilter)o;
     return this.lenAsVal == other.lenAsVal;
   }
 
   @Override
   public boolean equals(Object obj) {
     return obj instanceof Filter && areSerializedFieldsEqual((Filter) obj);
   }
 
   @Override
   public int hashCode() {
     return Objects.hash(this.lenAsVal);
   }
 }