/*
 * 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.metadata;

import org.apache.calcite.adapter.enumerable.EnumerableLimit;
import org.apache.calcite.plan.RelOptPredicateList;
import org.apache.calcite.plan.volcano.RelSubset;
import org.apache.calcite.rel.RelNode;
import org.apache.calcite.rel.core.Aggregate;
import org.apache.calcite.rel.core.Calc;
import org.apache.calcite.rel.core.Exchange;
import org.apache.calcite.rel.core.Filter;
import org.apache.calcite.rel.core.Intersect;
import org.apache.calcite.rel.core.Join;
import org.apache.calcite.rel.core.Minus;
import org.apache.calcite.rel.core.Project;
import org.apache.calcite.rel.core.Sort;
import org.apache.calcite.rel.core.TableModify;
import org.apache.calcite.rel.core.TableScan;
import org.apache.calcite.rel.core.Union;
import org.apache.calcite.rel.core.Values;
import org.apache.calcite.rex.RexBuilder;
import org.apache.calcite.rex.RexLiteral;
import org.apache.calcite.util.Bug;
import org.apache.calcite.util.Util;

import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * RelMdMaxRowCount supplies a default implementation of
 * {@link RelMetadataQuery#getMaxRowCount} for the standard logical algebra.
 */
public class RelMdMaxRowCount
    implements MetadataHandler<BuiltInMetadata.MaxRowCount> {
  public static final RelMetadataProvider SOURCE =
      ReflectiveRelMetadataProvider.reflectiveSource(
          new RelMdMaxRowCount(), BuiltInMetadata.MaxRowCount.Handler.class);

  //~ Methods ----------------------------------------------------------------

  @Override public MetadataDef<BuiltInMetadata.MaxRowCount> getDef() {
    return BuiltInMetadata.MaxRowCount.DEF;
  }

  public @Nullable Double getMaxRowCount(Union rel, RelMetadataQuery mq) {
    double rowCount = 0.0;
    for (RelNode input : rel.getInputs()) {
      Double partialRowCount = mq.getMaxRowCount(input);
      if (partialRowCount == null) {
        return null;
      }
      rowCount += partialRowCount;
    }
    return rowCount;
  }

  public @Nullable Double getMaxRowCount(Intersect rel, RelMetadataQuery mq) {
    // max row count is the smallest of the inputs
    Double rowCount = null;
    for (RelNode input : rel.getInputs()) {
      Double partialRowCount = mq.getMaxRowCount(input);
      if (rowCount == null
          || partialRowCount != null && partialRowCount < rowCount) {
        rowCount = partialRowCount;
      }
    }
    return rowCount;
  }

  public @Nullable Double getMaxRowCount(Minus rel, RelMetadataQuery mq) {
    return mq.getMaxRowCount(rel.getInput(0));
  }

  public @Nullable Double getMaxRowCount(Filter rel, RelMetadataQuery mq) {
    if (rel.getCondition().isAlwaysFalse()) {
      return 0D;
    }
    return mq.getMaxRowCount(rel.getInput());
  }

  public @Nullable Double getMaxRowCount(Calc rel, RelMetadataQuery mq) {
    return mq.getMaxRowCount(rel.getInput());
  }

  public @Nullable Double getMaxRowCount(Project rel, RelMetadataQuery mq) {
    return mq.getMaxRowCount(rel.getInput());
  }

  public @Nullable Double getMaxRowCount(Exchange rel, RelMetadataQuery mq) {
    return mq.getMaxRowCount(rel.getInput());
  }

  public Double getMaxRowCount(Sort rel, RelMetadataQuery mq) {
    Double rowCount = mq.getMaxRowCount(rel.getInput());
    if (rowCount == null) {
      rowCount = Double.POSITIVE_INFINITY;
    }

    final int offset = rel.offset instanceof RexLiteral ? RexLiteral.intValue(rel.offset) : 0;
    rowCount = Math.max(rowCount - offset, 0D);

    final double limit =
        rel.fetch instanceof RexLiteral ? RexLiteral.intValue(rel.fetch) : rowCount;
    return limit < rowCount ? limit : rowCount;
  }

  public Double getMaxRowCount(EnumerableLimit rel, RelMetadataQuery mq) {
    Double rowCount = mq.getMaxRowCount(rel.getInput());
    if (rowCount == null) {
      rowCount = Double.POSITIVE_INFINITY;
    }

    final int offset = rel.offset instanceof RexLiteral ? RexLiteral.intValue(rel.offset) : 0;
    rowCount = Math.max(rowCount - offset, 0D);

    final double limit =
        rel.fetch instanceof RexLiteral ? RexLiteral.intValue(rel.fetch) : rowCount;
    return limit < rowCount ? limit : rowCount;
  }

  public @Nullable Double getMaxRowCount(Aggregate rel, RelMetadataQuery mq) {
    if (rel.getGroupSet().isEmpty()) {
      // Aggregate with no GROUP BY always returns 1 row (even on empty table).
      return 1D;
    }

    // Aggregate with constant GROUP BY always returns 1 row
    if (rel.getGroupType() == Aggregate.Group.SIMPLE) {
      final RelOptPredicateList predicateList =
          mq.getPulledUpPredicates(rel.getInput());
      if (!RelOptPredicateList.isEmpty(predicateList)
          && allGroupKeysAreConstant(rel, predicateList)) {
        return 1D;
      }
    }
    final Double rowCount = mq.getMaxRowCount(rel.getInput());
    if (rowCount == null) {
      return null;
    }
    return rowCount * rel.getGroupSets().size();
  }

  private static boolean allGroupKeysAreConstant(Aggregate aggregate,
      RelOptPredicateList predicateList) {
    final RexBuilder rexBuilder = aggregate.getCluster().getRexBuilder();
    for (int key : aggregate.getGroupSet()) {
      if (!predicateList.constantMap.containsKey(
          rexBuilder.makeInputRef(aggregate.getInput(), key))) {
        return false;
      }
    }
    return true;
  }

  public @Nullable Double getMaxRowCount(Join rel, RelMetadataQuery mq) {
    Double left = mq.getMaxRowCount(rel.getLeft());
    Double right = mq.getMaxRowCount(rel.getRight());
    if (left == null || right == null) {
      return null;
    }
    if (left < 1D && rel.getJoinType().generatesNullsOnLeft()) {
      left = 1D;
    }
    if (right < 1D && rel.getJoinType().generatesNullsOnRight()) {
      right = 1D;
    }
    return left * right;
  }

  public @Nullable Double getMaxRowCount(TableScan rel, RelMetadataQuery mq) {
    final BuiltInMetadata.MaxRowCount.Handler handler =
        rel.getTable().unwrap(BuiltInMetadata.MaxRowCount.Handler.class);
    if (handler != null) {
      return handler.getMaxRowCount(rel, mq);
    }
    // For typical tables, there is no upper bound to the number of rows.
    return Double.POSITIVE_INFINITY;
  }

  public Double getMaxRowCount(Values values, RelMetadataQuery mq) {
    // For Values, the maximum row count is the actual row count.
    // This is especially useful if Values is empty.
    return (double) values.getTuples().size();
  }

  public @Nullable Double getMaxRowCount(TableModify rel, RelMetadataQuery mq) {
    return mq.getMaxRowCount(rel.getInput());
  }

  public Double getMaxRowCount(RelSubset rel, RelMetadataQuery mq) {
    // FIXME This is a short-term fix for [CALCITE-1018]. A complete
    // solution will come with [CALCITE-1048].
    Util.discard(Bug.CALCITE_1048_FIXED);
    for (RelNode node : rel.getRels()) {
      if (node instanceof Sort) {
        Sort sort = (Sort) node;
        if (sort.fetch instanceof RexLiteral) {
          return (double) RexLiteral.intValue(sort.fetch);
        }
      }
    }

    return Double.POSITIVE_INFINITY;
  }

  // Catch-all rule when none of the others apply.
  public @Nullable Double getMaxRowCount(RelNode rel, RelMetadataQuery mq) {
    return null;
  }
}
