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.calcite.adapter.enumerable;
  
  import org.apache.calcite.linq4j.tree.Expression;
  
  import java.lang.reflect.Type;
  import java.util.List;
  
  /**
   * Implements an aggregate function by generating expressions to
   * initialize, add to, and get a result from, an accumulator.
   *
   * @see org.apache.calcite.adapter.enumerable.StrictAggImplementor
   * @see org.apache.calcite.adapter.enumerable.StrictWinAggImplementor
   * @see org.apache.calcite.adapter.enumerable.RexImpTable.CountImplementor
   * @see org.apache.calcite.adapter.enumerable.RexImpTable.SumImplementor
   */
  public interface AggImplementor {
    /**
     * Returns the types of the intermediate variables used by the aggregate
     * implementation.
     *
     * <p>For instance, for "concatenate to string" this can be
     * {@link java.lang.StringBuilder}.
     * Calcite calls this method before all other {@code implement*} methods.
     *
     * @param info Aggregate context
     * @return Types of the intermediate variables used by the aggregate
     *   implementation
     */
    List<Type> getStateType(AggContext info);
  
    /**
     * Implements reset of the intermediate variables to the initial state.
     * {@link AggResetContext#accumulator()} should be used to reference
     * the state variables.
     * For instance, to zero the count, use the following code:
     *
     * <blockquote><code>reset.currentBlock().add(<br>
     *   Expressions.statement(<br>
     *     Expressions.assign(reset.accumulator().get(0),<br>
     *       Expressions.constant(0)));</code></blockquote>
     *
     * @param info Aggregate context
     * @param reset Reset context
     */
    void implementReset(AggContext info, AggResetContext reset);
  
    /**
     * Updates intermediate values to account for the newly added value.
     * {@link AggResetContext#accumulator()} should be used to reference
     * the state variables.
     *
     * @param info Aggregate context
     * @param add Add context
     */
    void implementAdd(AggContext info, AggAddContext add);
  
    /**
     * Calculates the resulting value based on the intermediate variables.
     * Note: this method must NOT destroy the intermediate variables as
     * calcite might reuse the state when calculating sliding aggregates.
     * {@link AggResetContext#accumulator()} should be used to reference
     * the state variables.
     *
     * @param info Aggregate context
     * @param result Result context
     * @return Expression that is a result of calculating final value of
     *   the aggregate being implemented
     */
    Expression implementResult(AggContext info, AggResultContext result);
  }
  