/**
 * Copyright (C) 2014-2016 LinkedIn Corp. (pinot-core@linkedin.com)
 *
 * Licensed 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.linkedin.pinot.core.plan.maker;

import com.linkedin.pinot.common.data.MetricFieldSpec;
import com.linkedin.pinot.common.request.AggregationInfo;
import com.linkedin.pinot.common.request.BrokerRequest;
import com.linkedin.pinot.common.segment.SegmentMetadata;
import com.linkedin.pinot.core.indexsegment.IndexSegment;
import java.util.List;
import java.util.Objects;


/**
 * The <code>BrokerRequestPreProcessor</code> class provides the utility to pre-process the {@link BrokerRequest}.
 * <p>After the pre-process, the {@link BrokerRequest} should not be further changed.
 */
public class BrokerRequestPreProcessor {
  private BrokerRequestPreProcessor() {
  }

  /**
   * Pre-process the {@link BrokerRequest}.
   * <p>Will apply the changes directly to the passed in object.
   * <p>The following steps are performed:
   * <ul>
   *   <li>Rewrite 'fasthll' column name.</li>
   * </ul>
   *
   * @param indexSegments list of index segments.
   * @param brokerRequest broker request.
   */
  public static void preProcess(List<IndexSegment> indexSegments, BrokerRequest brokerRequest) {
    if (brokerRequest.isSetAggregationsInfo()) {
      List<AggregationInfo> aggregationsInfo = brokerRequest.getAggregationsInfo();
      rewriteFastHllColumnName(indexSegments, aggregationsInfo);
    }
  }

  /**
   * Rewrite 'fasthll' column name.
   *
   * @param indexSegments list of index segments.
   * @param aggregationsInfo list of aggregation info.
   */
  private static void rewriteFastHllColumnName(List<IndexSegment> indexSegments,
      List<AggregationInfo> aggregationsInfo) {
    // Consistent check.
    for (AggregationInfo aggregationInfo : aggregationsInfo) {
      if (aggregationInfo.getAggregationType().equalsIgnoreCase("fasthll")) {
        String column = aggregationInfo.getAggregationParams().get("column").trim();
        boolean isFirstSegment = true;
        String firstSegmentName = null;
        String hllDerivedColumn = null;
        for (IndexSegment indexSegment : indexSegments) {
          SegmentMetadata segmentMetadata = indexSegment.getSegmentMetadata();
          if (isFirstSegment) {
            // Use metadata from first index segment to perform rewrite.
            isFirstSegment = false;
            firstSegmentName = segmentMetadata.getName();
            hllDerivedColumn = segmentMetadata.getDerivedColumn(column, MetricFieldSpec.DerivedMetricType.HLL);
            if (hllDerivedColumn != null) {
              aggregationInfo.getAggregationParams().put("column", hllDerivedColumn);
            }
          } else {
            // Perform consistency check on other index segments.
            String hllDerivedColumnToCheck =
                segmentMetadata.getDerivedColumn(column, MetricFieldSpec.DerivedMetricType.HLL);
            if (!Objects.equals(hllDerivedColumn, hllDerivedColumnToCheck)) {
              throw new RuntimeException(
                  "Found inconsistency HLL derived column name. In segment " + firstSegmentName + ": "
                      + hllDerivedColumn + "; In segment " + segmentMetadata.getName() + ": "
                      + hllDerivedColumnToCheck);
            }
          }
        }
      }
    }
  }
}