/*
    *
    * 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.util.ArrayList;
  import java.util.Objects;
  
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.classification.InterfaceStability;
  import org.apache.hadoop.hbase.Cell;
  import org.apache.hadoop.hbase.exceptions.DeserializationException;
  import org.apache.hadoop.hbase.protobuf.generated.FilterProtos;
  
  import com.google.common.base.Preconditions;
  import com.google.protobuf.InvalidProtocolBufferException;
  
  /**
   * A filter that will only return the first KV from each row.
   * <p>
   * This filter can be used to more efficiently perform row count operations.
   */
  @InterfaceAudience.Public
  @InterfaceStability.Stable
  public class FirstKeyOnlyFilter extends FilterBase {
    private boolean foundKV = false;
  
    public FirstKeyOnlyFilter() {
    }
  
    @Override
    public void reset() {
      foundKV = false;
    }
  
    @Override
    public ReturnCode filterKeyValue(Cell v) {
      if(foundKV) return ReturnCode.NEXT_ROW;
      foundKV = true;
      return ReturnCode.INCLUDE;
    }
  
    // Override here explicitly as the method in super class FilterBase might do a KeyValue recreate.
    // See HBASE-12068
    @Override
    public Cell transformCell(Cell v) {
      return v;
    }
  
    public static Filter createFilterFromArguments(ArrayList<byte []> filterArguments) {
      Preconditions.checkArgument(filterArguments.size() == 0,
                                  "Expected 0 but got: %s", filterArguments.size());
      return new FirstKeyOnlyFilter();
    }
  
    /**
     * @return true if first KV has been found.
     */
    protected boolean hasFoundKV() {
      return this.foundKV;
    }
  
    /**
     *
     * @param value update {@link #foundKV} flag with value.
     */
    protected void setFoundKV(boolean value) {
      this.foundKV = value;
    }
  
    /**
     * @return The filter serialized using pb
     */
    @Override
    public byte [] toByteArray() {
      FilterProtos.FirstKeyOnlyFilter.Builder builder =
        FilterProtos.FirstKeyOnlyFilter.newBuilder();
      return builder.build().toByteArray();
    }
  
    /**
     * @param pbBytes A pb serialized {@link FirstKeyOnlyFilter} instance
     * @return An instance of {@link FirstKeyOnlyFilter} made from <code>bytes</code>
     * @throws org.apache.hadoop.hbase.exceptions.DeserializationException
    * @see #toByteArray
    */
   public static FirstKeyOnlyFilter parseFrom(final byte [] pbBytes)
   throws DeserializationException {
     // There is nothing to deserialize.  Why do this at all?
     try {
       FilterProtos.FirstKeyOnlyFilter.parseFrom(pbBytes);
     } catch (InvalidProtocolBufferException e) {
       throw new DeserializationException(e);
     }
     // Just return a new instance.
     return new FirstKeyOnlyFilter();
   }
 
   /**
    * @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 FirstKeyOnlyFilter)) return false;
 
     return true;
   }
 
   @Override
   public boolean equals(Object obj) {
     return obj instanceof Filter && areSerializedFieldsEqual((Filter) obj);
   }
 
   @Override
   public int hashCode() {
     return Objects.hashCode(foundKV);
   }
 }