content: /*
   * 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.cassandra.cql3.functions;
  
  import java.nio.ByteBuffer;
  
  import org.apache.cassandra.exceptions.InvalidRequestException;
  import org.apache.cassandra.transport.ProtocolVersion;
  
  /**
   * Performs a calculation on a set of values and return a single value.
   */
  public interface AggregateFunction extends Function
  {
      /**
       * Creates a new <code>Aggregate</code> instance.
       *
       * @return a new <code>Aggregate</code> instance.
       */
      public Aggregate newAggregate() throws InvalidRequestException;
  
      /**
       * An aggregation operation.
       */
      interface Aggregate
      {
          /**
           * Adds the specified input to this aggregate.
           *
           * @param arguments the values to add to the aggregate.
           */
          public void addInput(Arguments arguments) throws InvalidRequestException;
  
          /**
           * Computes and returns the aggregate current value.
           *
           * @param protocolVersion native protocol version
           * @return the aggregate current value.
           */
          public ByteBuffer compute(ProtocolVersion protocolVersion) throws InvalidRequestException;
  
          /**
           * Reset this aggregate.
           */
          public void reset();
      }
  }
  