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 * 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.
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package org.apache.iotdb.db.mpp.plan.planner.distribution;

import org.apache.iotdb.common.rpc.thrift.TRegionReplicaSet;
import org.apache.iotdb.commons.partition.DataPartition;
import org.apache.iotdb.db.mpp.plan.analyze.Analysis;
import org.apache.iotdb.db.mpp.plan.planner.plan.node.PlanNode;
import org.apache.iotdb.db.mpp.plan.planner.plan.node.PlanVisitor;
import org.apache.iotdb.db.mpp.plan.planner.plan.node.WritePlanNode;
import org.apache.iotdb.db.mpp.plan.planner.plan.node.metedata.read.AbstractSchemaMergeNode;
import org.apache.iotdb.db.mpp.plan.planner.plan.node.metedata.read.CountSchemaMergeNode;
import org.apache.iotdb.db.mpp.plan.planner.plan.node.metedata.read.SchemaFetchMergeNode;
import org.apache.iotdb.db.mpp.plan.planner.plan.node.metedata.read.SchemaFetchScanNode;
import org.apache.iotdb.db.mpp.plan.planner.plan.node.metedata.read.SchemaQueryMergeNode;
import org.apache.iotdb.db.mpp.plan.planner.plan.node.metedata.read.SchemaQueryOrderByHeatNode;
import org.apache.iotdb.db.mpp.plan.planner.plan.node.metedata.read.SchemaQueryScanNode;
import org.apache.iotdb.db.mpp.plan.planner.plan.node.process.AggregationNode;
import org.apache.iotdb.db.mpp.plan.planner.plan.node.process.DeviceMergeNode;
import org.apache.iotdb.db.mpp.plan.planner.plan.node.process.DeviceViewNode;
import org.apache.iotdb.db.mpp.plan.planner.plan.node.process.ExchangeNode;
import org.apache.iotdb.db.mpp.plan.planner.plan.node.process.FilterNode;
import org.apache.iotdb.db.mpp.plan.planner.plan.node.process.GroupByLevelNode;
import org.apache.iotdb.db.mpp.plan.planner.plan.node.process.GroupByTagNode;
import org.apache.iotdb.db.mpp.plan.planner.plan.node.process.MultiChildProcessNode;
import org.apache.iotdb.db.mpp.plan.planner.plan.node.process.SlidingWindowAggregationNode;
import org.apache.iotdb.db.mpp.plan.planner.plan.node.process.TimeJoinNode;
import org.apache.iotdb.db.mpp.plan.planner.plan.node.process.TransformNode;
import org.apache.iotdb.db.mpp.plan.planner.plan.node.process.last.LastQueryCollectNode;
import org.apache.iotdb.db.mpp.plan.planner.plan.node.process.last.LastQueryMergeNode;
import org.apache.iotdb.db.mpp.plan.planner.plan.node.process.last.LastQueryNode;
import org.apache.iotdb.db.mpp.plan.planner.plan.node.source.AlignedLastQueryScanNode;
import org.apache.iotdb.db.mpp.plan.planner.plan.node.source.AlignedSeriesAggregationScanNode;
import org.apache.iotdb.db.mpp.plan.planner.plan.node.source.AlignedSeriesScanNode;
import org.apache.iotdb.db.mpp.plan.planner.plan.node.source.LastQueryScanNode;
import org.apache.iotdb.db.mpp.plan.planner.plan.node.source.SeriesAggregationScanNode;
import org.apache.iotdb.db.mpp.plan.planner.plan.node.source.SeriesScanNode;
import org.apache.iotdb.db.mpp.plan.planner.plan.node.source.SourceNode;
import org.apache.iotdb.db.mpp.plan.statement.crud.QueryStatement;

import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

import static com.google.common.collect.ImmutableList.toImmutableList;

public class ExchangeNodeAdder extends PlanVisitor<PlanNode, NodeGroupContext> {

  private final Analysis analysis;

  public ExchangeNodeAdder(Analysis analysis) {
    this.analysis = analysis;
  }

  @Override
  public PlanNode visitPlan(PlanNode node, NodeGroupContext context) {
    // TODO: (xingtanzjr) we apply no action for IWritePlanNode currently
    if (node instanceof WritePlanNode) {
      return node;
    }
    // Visit all the children of current node
    List<PlanNode> children =
        node.getChildren().stream()
            .map(child -> child.accept(this, context))
            .collect(toImmutableList());

    // Calculate the node distribution info according to its children

    // Put the node distribution info into context
    // NOTICE: we will only process the PlanNode which has only 1 child here. For the other
    // PlanNode, we need to process
    // them with special method
    context.putNodeDistribution(
        node.getPlanNodeId(),
        new NodeDistribution(NodeDistributionType.SAME_WITH_ALL_CHILDREN, null));

    return node.cloneWithChildren(children);
  }

  @Override
  public PlanNode visitSchemaQueryMerge(SchemaQueryMergeNode node, NodeGroupContext context) {
    return internalVisitSchemaMerge(node, context);
  }

  private PlanNode internalVisitSchemaMerge(
      AbstractSchemaMergeNode node, NodeGroupContext context) {
    node.getChildren()
        .forEach(
            child -> {
              visit(child, context);
            });
    NodeDistribution nodeDistribution =
        new NodeDistribution(NodeDistributionType.DIFFERENT_FROM_ALL_CHILDREN);
    PlanNode newNode = node.clone();
    nodeDistribution.region = calculateSchemaRegionByChildren(node.getChildren(), context);
    context.putNodeDistribution(newNode.getPlanNodeId(), nodeDistribution);
    node.getChildren()
        .forEach(
            child -> {
              if (!nodeDistribution.region.equals(
                  context.getNodeDistribution(child.getPlanNodeId()).region)) {
                ExchangeNode exchangeNode =
                    new ExchangeNode(context.queryContext.getQueryId().genPlanNodeId());
                exchangeNode.setChild(child);
                exchangeNode.setOutputColumnNames(child.getOutputColumnNames());
                newNode.addChild(exchangeNode);
              } else {
                newNode.addChild(child);
              }
            });
    return newNode;
  }

  @Override
  public PlanNode visitCountMerge(CountSchemaMergeNode node, NodeGroupContext context) {
    return internalVisitSchemaMerge(node, context);
  }

  @Override
  public PlanNode visitSchemaFetchMerge(SchemaFetchMergeNode node, NodeGroupContext context) {
    return internalVisitSchemaMerge(node, context);
  }

  @Override
  public PlanNode visitSchemaQueryScan(SchemaQueryScanNode node, NodeGroupContext context) {
    return processNoChildSourceNode(node, context);
  }

  @Override
  public PlanNode visitSchemaFetchScan(SchemaFetchScanNode node, NodeGroupContext context) {
    return processNoChildSourceNode(node, context);
  }

  @Override
  public PlanNode visitSeriesScan(SeriesScanNode node, NodeGroupContext context) {
    return processNoChildSourceNode(node, context);
  }

  @Override
  public PlanNode visitAlignedSeriesScan(AlignedSeriesScanNode node, NodeGroupContext context) {
    return processNoChildSourceNode(node, context);
  }

  @Override
  public PlanNode visitLastQueryScan(LastQueryScanNode node, NodeGroupContext context) {
    return processNoChildSourceNode(node, context);
  }

  @Override
  public PlanNode visitAlignedLastQueryScan(
      AlignedLastQueryScanNode node, NodeGroupContext context) {
    return processNoChildSourceNode(node, context);
  }

  @Override
  public PlanNode visitSeriesAggregationScan(
      SeriesAggregationScanNode node, NodeGroupContext context) {
    return processNoChildSourceNode(node, context);
  }

  @Override
  public PlanNode visitAlignedSeriesAggregationScan(
      AlignedSeriesAggregationScanNode node, NodeGroupContext context) {
    return processNoChildSourceNode(node, context);
  }

  private PlanNode processNoChildSourceNode(SourceNode node, NodeGroupContext context) {
    context.putNodeDistribution(
        node.getPlanNodeId(),
        new NodeDistribution(NodeDistributionType.NO_CHILD, node.getRegionReplicaSet()));
    return node.clone();
  }

  @Override
  public PlanNode visitDeviceView(DeviceViewNode node, NodeGroupContext context) {
    // A temporary way to decrease the FragmentInstance for aggregation with device view.
    if (isAggregationQuery()) {
      return processDeviceViewWithAggregation(node, context);
    }
    return processMultiChildNode(node, context);
  }

  @Override
  public PlanNode visitDeviceMerge(DeviceMergeNode node, NodeGroupContext context) {
    return processMultiChildNode(node, context);
  }

  @Override
  public PlanNode visitLastQueryMerge(LastQueryMergeNode node, NodeGroupContext context) {
    return processMultiChildNode(node, context);
  }

  @Override
  public PlanNode visitLastQueryCollect(LastQueryCollectNode node, NodeGroupContext context) {
    return processMultiChildNode(node, context);
  }

  @Override
  public PlanNode visitLastQuery(LastQueryNode node, NodeGroupContext context) {
    return processMultiChildNode(node, context);
  }

  @Override
  public PlanNode visitTimeJoin(TimeJoinNode node, NodeGroupContext context) {
    return processMultiChildNode(node, context);
  }

  @Override
  public PlanNode visitAggregation(AggregationNode node, NodeGroupContext context) {
    return processMultiChildNode(node, context);
  }

  @Override
  public PlanNode visitSchemaQueryOrderByHeat(
      SchemaQueryOrderByHeatNode node, NodeGroupContext context) {
    return processMultiChildNode(node, context);
  }

  @Override
  public PlanNode visitGroupByLevel(GroupByLevelNode node, NodeGroupContext context) {
    return processMultiChildNode(node, context);
  }

  @Override
  public PlanNode visitTransform(TransformNode node, NodeGroupContext context) {
    return processOneChildNode(node, context);
  }

  @Override
  public PlanNode visitFilter(FilterNode node, NodeGroupContext context) {
    return processOneChildNode(node, context);
  }

  public PlanNode visitGroupByTag(GroupByTagNode node, NodeGroupContext context) {
    return processMultiChildNode(node, context);
  }

  private PlanNode processDeviceViewWithAggregation(DeviceViewNode node, NodeGroupContext context) {
    // group all the children by DataRegion distribution
    Map<TRegionReplicaSet, DeviceViewGroup> deviceViewGroupMap = new HashMap<>();
    for (int i = 0; i < node.getDevices().size(); i++) {
      String device = node.getDevices().get(i);
      PlanNode rawChildNode = node.getChildren().get(i);
      PlanNode visitedChild = visit(rawChildNode, context);
      TRegionReplicaSet region = context.getNodeDistribution(visitedChild.getPlanNodeId()).region;
      DeviceViewGroup group = deviceViewGroupMap.computeIfAbsent(region, DeviceViewGroup::new);
      group.addChild(device, visitedChild);
    }

    // Generate DeviceViewNode for each group
    List<DeviceViewNode> deviceViewNodeList = new ArrayList<>();
    for (DeviceViewGroup group : deviceViewGroupMap.values()) {
      DeviceViewNode deviceViewNode =
          new DeviceViewNode(
              context.queryContext.getQueryId().genPlanNodeId(),
              node.getMergeOrderParameter(),
              node.getOutputColumnNames(),
              node.getDeviceToMeasurementIndexesMap());
      for (int i = 0; i < group.devices.size(); i++) {
        deviceViewNode.addChildDeviceNode(group.devices.get(i), group.children.get(i));
      }
      context.putNodeDistribution(
          deviceViewNode.getPlanNodeId(),
          new NodeDistribution(
              NodeDistributionType.SAME_WITH_ALL_CHILDREN,
              context.getNodeDistribution(deviceViewNode.getChildren().get(0).getPlanNodeId())
                  .region));
      deviceViewNodeList.add(deviceViewNode);
    }

    if (deviceViewNodeList.size() == 1) {
      return deviceViewNodeList.get(0);
    }

    DeviceMergeNode deviceMergeNode =
        new DeviceMergeNode(
            context.queryContext.getQueryId().genPlanNodeId(),
            node.getMergeOrderParameter(),
            node.getDevices());

    // Each child of deviceMergeNode has different TRegionReplicaSet, so we can select any one from
    // its child
    deviceMergeNode.addChild(deviceViewNodeList.get(0));
    context.putNodeDistribution(
        deviceMergeNode.getPlanNodeId(),
        new NodeDistribution(
            NodeDistributionType.SAME_WITH_SOME_CHILD,
            context.getNodeDistribution(deviceViewNodeList.get(0).getPlanNodeId()).region));

    // Add ExchangeNode for any other child except first one
    for (int i = 1; i < deviceViewNodeList.size(); i++) {
      PlanNode child = deviceViewNodeList.get(i);
      ExchangeNode exchangeNode =
          new ExchangeNode(context.queryContext.getQueryId().genPlanNodeId());
      exchangeNode.setChild(child);
      exchangeNode.setOutputColumnNames(child.getOutputColumnNames());
      deviceMergeNode.addChild(exchangeNode);
    }
    return deviceMergeNode;
  }

  private static class DeviceViewGroup {
    public TRegionReplicaSet regionReplicaSet;
    public List<PlanNode> children;
    public List<String> devices;

    public DeviceViewGroup(TRegionReplicaSet regionReplicaSet) {
      this.regionReplicaSet = regionReplicaSet;
      this.children = new LinkedList<>();
      this.devices = new LinkedList<>();
    }

    public void addChild(String device, PlanNode child) {
      devices.add(device);
      children.add(child);
    }

    public int hashCode() {
      return regionReplicaSet.hashCode();
    }

    public boolean equals(Object o) {
      if (o instanceof DeviceViewGroup) {
        return regionReplicaSet.equals(((DeviceViewGroup) o).regionReplicaSet);
      }
      return false;
    }
  }

  private PlanNode processMultiChildNode(MultiChildProcessNode node, NodeGroupContext context) {
    MultiChildProcessNode newNode = (MultiChildProcessNode) node.clone();
    List<PlanNode> visitedChildren = new ArrayList<>();
    node.getChildren()
        .forEach(
            child -> {
              visitedChildren.add(visit(child, context));
            });

    TRegionReplicaSet dataRegion = calculateDataRegionByChildren(visitedChildren, context);
    NodeDistributionType distributionType =
        nodeDistributionIsSame(visitedChildren, context)
            ? NodeDistributionType.SAME_WITH_ALL_CHILDREN
            : NodeDistributionType.SAME_WITH_SOME_CHILD;
    context.putNodeDistribution(
        newNode.getPlanNodeId(), new NodeDistribution(distributionType, dataRegion));

    // If the distributionType of all the children are same, no ExchangeNode need to be added.
    if (distributionType == NodeDistributionType.SAME_WITH_ALL_CHILDREN) {
      newNode.setChildren(visitedChildren);
      return newNode;
    }

    // Otherwise, we need to add ExchangeNode for the child whose DataRegion is different from the
    // parent.
    visitedChildren.forEach(
        child -> {
          // If the child's region is NOT_ASSIGNED, it means the child do not belong to any
          // existing DataRegion. We make it belong to its parent and no ExchangeNode will be added.
          if (context.getNodeDistribution(child.getPlanNodeId()).region
                  != DataPartition.NOT_ASSIGNED
              && !dataRegion.equals(context.getNodeDistribution(child.getPlanNodeId()).region)) {
            ExchangeNode exchangeNode =
                new ExchangeNode(context.queryContext.getQueryId().genPlanNodeId());
            exchangeNode.setChild(child);
            exchangeNode.setOutputColumnNames(child.getOutputColumnNames());
            newNode.addChild(exchangeNode);
          } else {
            newNode.addChild(child);
          }
        });
    return newNode;
  }

  @Override
  public PlanNode visitSlidingWindowAggregation(
      SlidingWindowAggregationNode node, NodeGroupContext context) {
    return processOneChildNode(node, context);
  }

  private PlanNode processOneChildNode(PlanNode node, NodeGroupContext context) {
    PlanNode newNode = node.clone();
    PlanNode child = visit(node.getChildren().get(0), context);
    newNode.addChild(child);
    TRegionReplicaSet dataRegion = context.getNodeDistribution(child.getPlanNodeId()).region;
    context.putNodeDistribution(
        newNode.getPlanNodeId(),
        new NodeDistribution(NodeDistributionType.SAME_WITH_ALL_CHILDREN, dataRegion));
    return newNode;
  }

  private TRegionReplicaSet calculateDataRegionByChildren(
      List<PlanNode> children, NodeGroupContext context) {
    // Step 1: calculate the count of children group by DataRegion.
    Map<TRegionReplicaSet, Long> groupByRegion =
        children.stream()
            .collect(
                Collectors.groupingBy(
                    child -> {
                      TRegionReplicaSet region =
                          context.getNodeDistribution(child.getPlanNodeId()).region;
                      if (region == null
                          && context.getNodeDistribution(child.getPlanNodeId()).type
                              == NodeDistributionType.SAME_WITH_ALL_CHILDREN) {
                        return calculateSchemaRegionByChildren(child.getChildren(), context);
                      }
                      return region;
                    },
                    Collectors.counting()));
    if (groupByRegion.entrySet().size() == 1) {
      return groupByRegion.entrySet().iterator().next().getKey();
    }
    // Step 2: return the RegionReplicaSet with max count
    return Collections.max(
            groupByRegion.entrySet().stream()
                .filter(e -> e.getKey() != DataPartition.NOT_ASSIGNED)
                .collect(Collectors.toList()),
            Map.Entry.comparingByValue())
        .getKey();
  }

  private TRegionReplicaSet calculateSchemaRegionByChildren(
      List<PlanNode> children, NodeGroupContext context) {
    // We always make the schemaRegion of MetaMergeNode to be the same as its first child.
    return context.getNodeDistribution(children.get(0).getPlanNodeId()).region;
  }

  private boolean nodeDistributionIsSame(List<PlanNode> children, NodeGroupContext context) {
    // The size of children here should always be larger than 0, or our code has Bug.
    NodeDistribution first = context.getNodeDistribution(children.get(0).getPlanNodeId());
    for (int i = 1; i < children.size(); i++) {
      NodeDistribution next = context.getNodeDistribution(children.get(i).getPlanNodeId());
      if (first.region == null || !first.region.equals(next.region)) {
        return false;
      }
    }
    return true;
  }

  private boolean isAggregationQuery() {
    return ((QueryStatement) analysis.getStatement()).isAggregationQuery();
  }

  public PlanNode visit(PlanNode node, NodeGroupContext context) {
    return node.accept(this, context);
  }
}
