/**
    *
    * 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.Objects;
  import java.util.Random;
  
  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.protobuf.InvalidProtocolBufferException;
  
  /**
   * A filter that includes rows based on a chance.
   * 
   */
  @InterfaceAudience.Public
  @InterfaceStability.Stable
  public class RandomRowFilter extends FilterBase {
    protected static final Random random = new Random();
  
    protected float chance;
    protected boolean filterOutRow;
  
    /**
     * Create a new filter with a specified chance for a row to be included.
     * 
     * @param chance
     */
    public RandomRowFilter(float chance) {
      this.chance = chance;
    }
  
    /**
     * @return The chance that a row gets included.
     */
    public float getChance() {
      return chance;
    }
  
    /**
     * Set the chance that a row is included.
     * 
     * @param chance
     */
    public void setChance(float chance) {
      this.chance = chance;
    }
  
    @Override
    public boolean filterAllRemaining() {
      return false;
    }
  
    @Override
    public ReturnCode filterKeyValue(Cell v) {
      if (filterOutRow) {
        return ReturnCode.NEXT_ROW;
      }
      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;
    }
  
    @Override
    public boolean filterRow() {
      return filterOutRow;
    }
  
    @Override
    public boolean hasFilterRow() {
      return true;
    }
  
   @Override
   public boolean filterRowKey(byte[] buffer, int offset, int length) {
     if (chance < 0) {
       // with a zero chance, the rows is always excluded
       filterOutRow = true;
     } else if (chance > 1) {
       // always included
       filterOutRow = false;
     } else {
       // roll the dice
       filterOutRow = !(random.nextFloat() < chance);
     }
     return filterOutRow;
   }
 
   @Override
   public void reset() {
     filterOutRow = false;
   }
 
   /**
    * @return The filter serialized using pb
    */
   @Override
   public byte [] toByteArray() {
     FilterProtos.RandomRowFilter.Builder builder =
       FilterProtos.RandomRowFilter.newBuilder();
     builder.setChance(this.chance);
     return builder.build().toByteArray();
   }
 
   /**
    * @param pbBytes A pb serialized {@link RandomRowFilter} instance
    * @return An instance of {@link RandomRowFilter} made from <code>bytes</code>
    * @throws DeserializationException
    * @see #toByteArray
    */
   public static RandomRowFilter parseFrom(final byte [] pbBytes)
   throws DeserializationException {
     FilterProtos.RandomRowFilter proto;
     try {
       proto = FilterProtos.RandomRowFilter.parseFrom(pbBytes);
     } catch (InvalidProtocolBufferException e) {
       throw new DeserializationException(e);
     }
     return new RandomRowFilter(proto.getChance());
   }
 
   /**
    * @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 RandomRowFilter)) return false;
 
     RandomRowFilter other = (RandomRowFilter)o;
     return this.getChance() == other.getChance();
   }
 
   @Override
   public boolean equals(Object obj) {
     return obj instanceof Filter && areSerializedFieldsEqual((Filter) obj);
   }
 
   @Override
   public int hashCode() {
     return Objects.hash(this.getChance());
   }
 }