/**
 * 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.pinot.core.plan;

import java.util.HashMap;
import java.util.Map;
import java.util.Set;
import javax.annotation.Nullable;
import org.apache.pinot.core.operator.DocIdSetOperator;
import org.apache.pinot.core.operator.ProjectionOperator;
import org.apache.pinot.core.operator.filter.BaseFilterOperator;
import org.apache.pinot.core.query.request.context.QueryContext;
import org.apache.pinot.segment.spi.IndexSegment;
import org.apache.pinot.segment.spi.datasource.DataSource;


/**
 * The <code>ProjectionPlanNode</code> class provides the execution plan for fetching projection columns' data source
 * on a single segment.
 */
public class ProjectionPlanNode implements PlanNode {
  private final IndexSegment _indexSegment;
  private final QueryContext _queryContext;
  private final Set<String> _projectionColumns;
  private final int _maxDocsPerCall;
  private final BaseFilterOperator _filterOperator;

  public ProjectionPlanNode(IndexSegment indexSegment, QueryContext queryContext, Set<String> projectionColumns,
      int maxDocsPerCall, @Nullable BaseFilterOperator filterOperator) {
    _indexSegment = indexSegment;
    _queryContext = queryContext;
    _projectionColumns = projectionColumns;
    _maxDocsPerCall = maxDocsPerCall;
    _filterOperator = filterOperator;
  }

  @Override
  public ProjectionOperator run() {
    Map<String, DataSource> dataSourceMap = new HashMap<>(_projectionColumns.size());
    for (String column : _projectionColumns) {
      dataSourceMap.put(column, _indexSegment.getDataSource(column));
    }
    // NOTE: Skip creating DocIdSetOperator when maxDocsPerCall is 0 (for selection query with LIMIT 0)
    DocIdSetOperator docIdSetOperator =
        _maxDocsPerCall > 0 ? new DocIdSetPlanNode(_indexSegment, _queryContext, _maxDocsPerCall, _filterOperator).run()
            : null;
    return new ProjectionOperator(dataSourceMap, docIdSetOperator);
  }
}