content: /*
   * 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.adapter.mongodb;
  
  import org.apache.calcite.plan.RelOptCluster;
  import org.apache.calcite.plan.RelTraitSet;
  import org.apache.calcite.rel.InvalidRelException;
  import org.apache.calcite.rel.RelNode;
  import org.apache.calcite.rel.core.Aggregate;
  import org.apache.calcite.rel.core.AggregateCall;
  import org.apache.calcite.sql.SqlAggFunction;
  import org.apache.calcite.sql.fun.SqlStdOperatorTable;
  import org.apache.calcite.sql.fun.SqlSumAggFunction;
  import org.apache.calcite.sql.fun.SqlSumEmptyIsZeroAggFunction;
  import org.apache.calcite.util.ImmutableBitSet;
  import org.apache.calcite.util.Util;
  
  import com.google.common.collect.ImmutableList;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  import java.util.AbstractList;
  import java.util.ArrayList;
  import java.util.List;
  
  /**
   * Implementation of
   * {@link org.apache.calcite.rel.core.Aggregate} relational expression
   * in MongoDB.
   */
  public class MongoAggregate
      extends Aggregate
      implements MongoRel {
    public MongoAggregate(
        RelOptCluster cluster,
        RelTraitSet traitSet,
        RelNode input,
        ImmutableBitSet groupSet,
        @Nullable List<ImmutableBitSet> groupSets,
        List<AggregateCall> aggCalls)
        throws InvalidRelException {
      super(cluster, traitSet, ImmutableList.of(), input, groupSet, groupSets, aggCalls);
      assert getConvention() == MongoRel.CONVENTION;
      assert getConvention() == input.getConvention();
  
      for (AggregateCall aggCall : aggCalls) {
        if (aggCall.isDistinct()) {
          throw new InvalidRelException(
              "distinct aggregation not supported");
        }
      }
      switch (getGroupType()) {
      case SIMPLE:
        break;
      default:
        throw new InvalidRelException("unsupported group type: "
            + getGroupType());
      }
    }
  
    @Deprecated // to be removed before 2.0
    public MongoAggregate(RelOptCluster cluster, RelTraitSet traitSet,
        RelNode input, boolean indicator, ImmutableBitSet groupSet,
        List<ImmutableBitSet> groupSets, List<AggregateCall> aggCalls)
        throws InvalidRelException {
      this(cluster, traitSet, input, groupSet, groupSets, aggCalls);
      checkIndicator(indicator);
    }
  
    @Override public Aggregate copy(RelTraitSet traitSet, RelNode input,
        ImmutableBitSet groupSet, @Nullable List<ImmutableBitSet> groupSets,
        List<AggregateCall> aggCalls) {
      try {
        return new MongoAggregate(getCluster(), traitSet, input,
            groupSet, groupSets, aggCalls);
      } catch (InvalidRelException e) {
        // Semantic error not possible. Must be a bug. Convert to
        // internal error.
        throw new AssertionError(e);
      }
    }
  
    @Override public void implement(Implementor implementor) {
      implementor.visitChild(0, getInput());
      List<String> list = new ArrayList<>();
      final List<String> inNames =
          MongoRules.mongoFieldNames(getInput().getRowType());
      final List<String> outNames = MongoRules.mongoFieldNames(getRowType());
      int i = 0;
      if (groupSet.cardinality() == 1) {
        final String inName = inNames.get(groupSet.nth(0));
        list.add("_id: " + MongoRules.maybeQuote("$" + inName));
        ++i;
      } else {
        List<String> keys = new ArrayList<>();
        for (int group : groupSet) {
          final String inName = inNames.get(group);
          keys.add(inName + ": " + MongoRules.quote("$" + inName));
          ++i;
        }
        list.add("_id: " + Util.toString(keys, "{", ", ", "}"));
      }
      for (AggregateCall aggCall : aggCalls) {
        list.add(
            MongoRules.maybeQuote(outNames.get(i++)) + ": "
            + toMongo(aggCall.getAggregation(), inNames, aggCall.getArgList()));
      }
      implementor.add(null,
          "{$group: " + Util.toString(list, "{", ", ", "}") + "}");
      final List<String> fixups;
      if (groupSet.cardinality() == 1) {
        fixups = new AbstractList<String>() {
          @Override public String get(int index) {
            final String outName = outNames.get(index);
            return MongoRules.maybeQuote(outName) + ": "
                + MongoRules.maybeQuote("$" + (index == 0 ? "_id" : outName));
          }
  
          @Override public int size() {
            return outNames.size();
          }
        };
      } else {
        fixups = new ArrayList<>();
        fixups.add("_id: 0");
        i = 0;
        for (int group : groupSet) {
          fixups.add(
              MongoRules.maybeQuote(outNames.get(group))
              + ": "
              + MongoRules.maybeQuote("$_id." + outNames.get(group)));
          ++i;
        }
        for (AggregateCall ignored : aggCalls) {
          final String outName = outNames.get(i++);
          fixups.add(
              MongoRules.maybeQuote(outName) + ": " + MongoRules.maybeQuote(
                  "$" + outName));
        }
      }
      if (!groupSet.isEmpty()) {
        implementor.add(null,
            "{$project: " + Util.toString(fixups, "{", ", ", "}") + "}");
      }
    }
  
    private static String toMongo(SqlAggFunction aggregation, List<String> inNames,
        List<Integer> args) {
      if (aggregation == SqlStdOperatorTable.COUNT) {
        if (args.isEmpty()) {
          return "{$sum: 1}";
        } else {
          assert args.size() == 1;
          final String inName = inNames.get(args.get(0));
          return "{$sum: {$cond: [ {$eq: ["
              + MongoRules.quote(inName)
              + ", null]}, 0, 1]}}";
        }
      } else if (aggregation instanceof SqlSumAggFunction
          || aggregation instanceof SqlSumEmptyIsZeroAggFunction) {
        assert args.size() == 1;
        final String inName = inNames.get(args.get(0));
        return "{$sum: " + MongoRules.maybeQuote("$" + inName) + "}";
      } else if (aggregation == SqlStdOperatorTable.MIN) {
        assert args.size() == 1;
        final String inName = inNames.get(args.get(0));
        return "{$min: " + MongoRules.maybeQuote("$" + inName) + "}";
      } else if (aggregation == SqlStdOperatorTable.MAX) {
        assert args.size() == 1;
        final String inName = inNames.get(args.get(0));
        return "{$max: " + MongoRules.maybeQuote("$" + inName) + "}";
      } else if (aggregation == SqlStdOperatorTable.AVG) {
        assert args.size() == 1;
        final String inName = inNames.get(args.get(0));
        return "{$avg: " + MongoRules.maybeQuote("$" + inName) + "}";
      } else {
        throw new AssertionError("unknown aggregate " + aggregation);
      }
    }
  }
  