/*
 * 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.iotdb.db.queryengine.execution.operator;

import org.apache.iotdb.tsfile.read.common.block.TsBlock;

import com.google.common.util.concurrent.ListenableFuture;

import static com.google.common.util.concurrent.Futures.immediateVoidFuture;

public interface Operator extends AutoCloseable {

  ListenableFuture<?> NOT_BLOCKED = immediateVoidFuture();

  OperatorContext getOperatorContext();

  /**
   * Returns a future that will be completed when the operator becomes unblocked. If the operator is
   * not blocked, this method should return {@code NOT_BLOCKED}.
   */
  @SuppressWarnings("squid:S1452")
  default ListenableFuture<?> isBlocked() {
    return NOT_BLOCKED;
  }

  default TsBlock nextWithTimer() throws Exception {
    OperatorContext context = getOperatorContext();
    long startTime = System.nanoTime();

    try {
      return next();
    } finally {
      context.recordExecutionTime(System.nanoTime() - startTime);
      context.recordNextCalled();
    }
  }

  /**
   * Gets next tsBlock from this operator. If no data is currently available, return null.
   *
   * @throws Exception Error happened while fetching next batch
   */
  @SuppressWarnings("squid:S112")
  TsBlock next() throws Exception;

  default boolean hasNextWithTimer() throws Exception {
    OperatorContext context = getOperatorContext();
    long startTime = System.nanoTime();

    try {
      return hasNext();
    } finally {
      context.recordExecutionTime(System.nanoTime() - startTime);
    }
  }

  /**
   * return true if the operator has more data, otherwise false.
   *
   * @throws Exception Error happened while judging whether there exists next batch
   */
  @SuppressWarnings("squid:S112")
  boolean hasNext() throws Exception;

  /**
   * The close method cleans up the resources occupied by this Operator. This method will always be
   * called before releasing the Operator reference.
   *
   * <p><b>Note:</b> If this Operator has child Operators, please ensure that child operators are
   * also closed.
   *
   * @throws Exception An exception occurred during the close operation.
   */
  @Override
  void close() throws Exception;

  /**
   * Is this operator completely finished processing and no more output TsBlock will be produced.
   *
   * @throws Exception Error happened while judging whether operator is finished
   */
  @SuppressWarnings("squid:S112")
  boolean isFinished() throws Exception;

  /**
   * We should also consider the memory used by its children operator, so the calculation logic may
   * be like: long estimatedOfCurrentOperator = XXXXX; return max(estimatedOfCurrentOperator,
   * child1.calculateMaxPeekMemory(), child2.calculateMaxPeekMemory(), ....).
   *
   * <p>Each operator's MaxPeekMemory should also take retained size of each child operator into
   * account.
   *
   * @return estimated max memory footprint that the Operator Tree(rooted from this operator) will
   *     use while doing its own read processing
   */
  long calculateMaxPeekMemory();

  /** return estimated max memory footprint for returned TsBlock when calling operator.next(). */
  long calculateMaxReturnSize();

  /**
   * return each operator's retained size(including all its children's retained size) after calling
   * its next() method.
   */
  long calculateRetainedSizeAfterCallingNext();
}
