/*
 * 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.rel.rules;

import org.apache.calcite.plan.RelOptCluster;
import org.apache.calcite.plan.RelOptRule;
import org.apache.calcite.plan.RelOptRuleCall;
import org.apache.calcite.plan.RelOptUtil;
import org.apache.calcite.rel.RelNode;
import org.apache.calcite.rel.core.Aggregate;
import org.apache.calcite.rel.core.Join;
import org.apache.calcite.rel.core.JoinInfo;
import org.apache.calcite.rel.core.Project;
import org.apache.calcite.rel.core.RelFactories;
import org.apache.calcite.rex.RexBuilder;
import org.apache.calcite.rex.RexNode;
import org.apache.calcite.tools.RelBuilder;
import org.apache.calcite.tools.RelBuilderFactory;
import org.apache.calcite.util.ImmutableBitSet;
import org.apache.calcite.util.ImmutableIntList;

import java.util.ArrayList;
import java.util.List;
import java.util.function.Predicate;

/**
 * Planner rule that creates a {@code SemiJoin} from a
 * {@link org.apache.calcite.rel.core.Join} on top of a
 * {@link org.apache.calcite.rel.logical.LogicalAggregate}.
 */
public abstract class SemiJoinRule extends RelOptRule implements TransformationRule {
  private static final Predicate<Join> NOT_GENERATE_NULLS_ON_LEFT =
      join -> !join.getJoinType().generatesNullsOnLeft();

  /* Tests if an Aggregate always produces 1 row and 0 columns. */
  private static final Predicate<Aggregate> IS_EMPTY_AGGREGATE =
      aggregate -> aggregate.getRowType().getFieldCount() == 0;

  public static final SemiJoinRule PROJECT =
      new ProjectToSemiJoinRule(Project.class, Join.class, Aggregate.class,
          RelFactories.LOGICAL_BUILDER, "SemiJoinRule:project");

  public static final SemiJoinRule JOIN =
      new JoinToSemiJoinRule(Join.class, Aggregate.class,
          RelFactories.LOGICAL_BUILDER, "SemiJoinRule:join");

  protected SemiJoinRule(Class<Project> projectClass, Class<Join> joinClass,
      Class<Aggregate> aggregateClass, RelBuilderFactory relBuilderFactory,
      String description) {
    super(
        operand(projectClass,
            some(
                operandJ(joinClass, null, NOT_GENERATE_NULLS_ON_LEFT,
                    some(operand(RelNode.class, any()),
                        operand(aggregateClass, any()))))),
        relBuilderFactory, description);
  }

  protected SemiJoinRule(Class<Join> joinClass, Class<Aggregate> aggregateClass,
      RelBuilderFactory relBuilderFactory, String description) {
    super(
        operandJ(joinClass, null, NOT_GENERATE_NULLS_ON_LEFT,
            some(operand(RelNode.class, any()),
                operand(aggregateClass, any()))),
        relBuilderFactory, description);
  }

  protected void perform(RelOptRuleCall call, Project project,
      Join join, RelNode left, Aggregate aggregate) {
    final RelOptCluster cluster = join.getCluster();
    final RexBuilder rexBuilder = cluster.getRexBuilder();
    if (project != null) {
      final ImmutableBitSet bits =
          RelOptUtil.InputFinder.bits(project.getProjects(), null);
      final ImmutableBitSet rightBits =
          ImmutableBitSet.range(left.getRowType().getFieldCount(),
              join.getRowType().getFieldCount());
      if (bits.intersects(rightBits)) {
        return;
      }
    } else {
      if (join.getJoinType().projectsRight()
          && !IS_EMPTY_AGGREGATE.test(aggregate)) {
        return;
      }
    }
    final JoinInfo joinInfo = join.analyzeCondition();
    if (!joinInfo.rightSet().equals(
        ImmutableBitSet.range(aggregate.getGroupCount()))) {
      // Rule requires that aggregate key to be the same as the join key.
      // By the way, neither a super-set nor a sub-set would work.
      return;
    }
    if (!joinInfo.isEqui()) {
      return;
    }
    final RelBuilder relBuilder = call.builder();
    relBuilder.push(left);
    switch (join.getJoinType()) {
    case SEMI:
    case INNER:
      final List<Integer> newRightKeyBuilder = new ArrayList<>();
      final List<Integer> aggregateKeys = aggregate.getGroupSet().asList();
      for (int key : joinInfo.rightKeys) {
        newRightKeyBuilder.add(aggregateKeys.get(key));
      }
      final ImmutableIntList newRightKeys = ImmutableIntList.copyOf(newRightKeyBuilder);
      relBuilder.push(aggregate.getInput());
      final RexNode newCondition =
          RelOptUtil.createEquiJoinCondition(relBuilder.peek(2, 0),
              joinInfo.leftKeys, relBuilder.peek(2, 1), newRightKeys,
              rexBuilder);
      relBuilder.semiJoin(newCondition);
      break;

    case LEFT:
      // The right-hand side produces no more than 1 row (because of the
      // Aggregate) and no fewer than 1 row (because of LEFT), and therefore
      // we can eliminate the semi-join.
      break;

    default:
      throw new AssertionError(join.getJoinType());
    }
    if (project != null) {
      relBuilder.project(project.getProjects(), project.getRowType().getFieldNames());
    }
    final RelNode relNode = relBuilder.build();
    call.transformTo(relNode);
  }

  /** SemiJoinRule that matches a Project on top of a Join with an Aggregate
   * as its right child. */
  public static class ProjectToSemiJoinRule extends SemiJoinRule {

    /** Creates a ProjectToSemiJoinRule. */
    public ProjectToSemiJoinRule(Class<Project> projectClass,
        Class<Join> joinClass, Class<Aggregate> aggregateClass,
        RelBuilderFactory relBuilderFactory, String description) {
      super(projectClass, joinClass, aggregateClass,
          relBuilderFactory, description);
    }

    @Override public void onMatch(RelOptRuleCall call) {
      final Project project = call.rel(0);
      final Join join = call.rel(1);
      final RelNode left = call.rel(2);
      final Aggregate aggregate = call.rel(3);
      perform(call, project, join, left, aggregate);
    }
  }

  /** SemiJoinRule that matches a Join with an empty Aggregate as its right
   * child. */
  public static class JoinToSemiJoinRule extends SemiJoinRule {

    /** Creates a JoinToSemiJoinRule. */
    public JoinToSemiJoinRule(
        Class<Join> joinClass, Class<Aggregate> aggregateClass,
        RelBuilderFactory relBuilderFactory, String description) {
      super(joinClass, aggregateClass, relBuilderFactory, description);
    }
  }

  @Override public void onMatch(RelOptRuleCall call) {
    final Join join = call.rel(0);
    final RelNode left = call.rel(1);
    final Aggregate aggregate = call.rel(2);
    perform(call, null, join, left, aggregate);
  }
}