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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.
 */
package com.hazelcast.org.apache.calcite.rel.rules;

import com.hazelcast.org.apache.calcite.plan.RelOptRule;
import com.hazelcast.org.apache.calcite.plan.RelOptRuleCall;
import com.hazelcast.org.apache.calcite.plan.RelOptUtil;
import com.hazelcast.org.apache.calcite.rel.RelNode;
import com.hazelcast.org.apache.calcite.rel.core.Aggregate;
import com.hazelcast.org.apache.calcite.rel.core.AggregateCall;
import com.hazelcast.org.apache.calcite.rel.core.Join;
import com.hazelcast.org.apache.calcite.rel.core.JoinRelType;
import com.hazelcast.org.apache.calcite.rel.core.RelFactories;
import com.hazelcast.org.apache.calcite.rel.logical.LogicalAggregate;
import com.hazelcast.org.apache.calcite.rel.logical.LogicalJoin;
import com.hazelcast.org.apache.calcite.tools.RelBuilder;
import com.hazelcast.org.apache.calcite.tools.RelBuilderFactory;
import com.hazelcast.org.apache.calcite.util.ImmutableBitSet;
import com.hazelcast.org.apache.calcite.util.mapping.Mappings;

import com.hazelcast.com.google.common.collect.ImmutableList;

import java.util.HashMap;
import java.util.Map;
import java.util.Set;

/**
 * Planner rule that matches an {@link com.hazelcast.org.apache.calcite.rel.core.Aggregate}
 * on a {@link com.hazelcast.org.apache.calcite.rel.core.Join} and removes the join
 * provided that the join is a left join or right join and it computes no
 * aggregate functions or all the aggregate calls have distinct.
 *
 * For instance,
 *
 * 
 * select distinct s.product_id from
 * sales as s
 * left join product as p
 * on s.product_id = p.product_id
 *
 * becomes
 *
 * 

 * select distinct s.product_id from sales as s
 *
 */
public class AggregateJoinRemoveRule extends RelOptRule implements TransformationRule {
  public static final AggregateJoinRemoveRule INSTANCE =
      new AggregateJoinRemoveRule(LogicalAggregate.class, LogicalJoin.class,
          RelFactories.LOGICAL_BUILDER);

  /** Creates an AggregateJoinRemoveRule. */
  public AggregateJoinRemoveRule(
      Class aggregateClass,
      Class joinClass, RelBuilderFactory relBuilderFactory) {
    super(
        operand(aggregateClass,
            operandJ(joinClass, null,
                join -> join.getJoinType() == JoinRelType.LEFT
                    || join.getJoinType() == JoinRelType.RIGHT, any())),
        relBuilderFactory, null);
  }

  @Override public void onMatch(RelOptRuleCall call) {
    final Aggregate aggregate = call.rel(0);
    final Join join = call.rel(1);
    boolean isLeftJoin = join.getJoinType() == JoinRelType.LEFT;
    int lower = isLeftJoin
        ? join.getLeft().getRowType().getFieldCount() - 1 : 0;
    int upper = isLeftJoin ? join.getRowType().getFieldCount()
        : join.getLeft().getRowType().getFieldCount();

    // Check whether the aggregate uses columns whose index is between
    // lower(included) and upper(excluded).
    final Set allFields = RelOptUtil.getAllFields(aggregate);
    if (allFields.stream().anyMatch(i -> i >= lower && i < upper)) {
      return;
    }

    if (aggregate.getAggCallList().stream().anyMatch(
        aggregateCall -> !aggregateCall.isDistinct())) {
      return;
    }

    RelNode node;
    if (isLeftJoin) {
      node = aggregate.copy(aggregate.getTraitSet(), join.getLeft(),
          aggregate.getGroupSet(), aggregate.getGroupSets(),
          aggregate.getAggCallList());
    } else {
      final Map map = new HashMap<>();
      allFields.forEach(index -> map.put(index, index - upper));
      final ImmutableBitSet groupSet = aggregate.getGroupSet().permute(map);

      final ImmutableList.Builder aggCalls =
          ImmutableList.builder();
      final int sourceCount = aggregate.getInput().getRowType().getFieldCount();
      final Mappings.TargetMapping targetMapping =
          Mappings.target(map, sourceCount, sourceCount);
      aggregate.getAggCallList().forEach(aggregateCall ->
          aggCalls.add(aggregateCall.transform(targetMapping)));

      final RelBuilder relBuilder = call.builder();
      node = relBuilder.push(join.getRight())
          .aggregate(relBuilder.groupKey(groupSet), aggCalls.build())
          .build();
    }
    call.transformTo(node);
  }
}