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/*
 * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
 * or more contributor license agreements. Licensed under the Elastic License
 * 2.0 and the Server Side Public License, v 1; you may not use this file except
 * in compliance with, at your election, the Elastic License 2.0 or the Server
 * Side Public License, v 1.
 */

package org.elasticsearch.search.dfs;

import com.carrotsearch.hppc.ObjectObjectHashMap;
import org.apache.lucene.index.Term;
import org.apache.lucene.search.CollectionStatistics;
import org.apache.lucene.search.IndexSearcher;
import org.apache.lucene.search.Query;
import org.apache.lucene.search.ScoreMode;
import org.apache.lucene.search.TermStatistics;
import org.elasticsearch.common.collect.HppcMaps;
import org.elasticsearch.search.internal.SearchContext;
import org.elasticsearch.search.rescore.RescoreContext;
import org.elasticsearch.tasks.TaskCancelledException;

import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

/**
 * Dfs phase of a search request, used to make scoring 100% accurate by collecting additional info from each shard before the query phase.
 * The additional information is used to better compare the scores coming from all the shards, which depend on local factors (e.g. idf)
 */
public class DfsPhase {

    public void execute(SearchContext context) {
        try {
            ObjectObjectHashMap fieldStatistics = HppcMaps.newNoNullKeysMap();
            Map stats = new HashMap<>();
            IndexSearcher searcher = new IndexSearcher(context.searcher().getIndexReader()) {
                @Override
                public TermStatistics termStatistics(Term term, int docFreq, long totalTermFreq) throws IOException {
                    if (context.isCancelled()) {
                        throw new TaskCancelledException("cancelled");
                    }
                    TermStatistics ts = super.termStatistics(term, docFreq, totalTermFreq);
                    if (ts != null) {
                        stats.put(term, ts);
                    }
                    return ts;
                }

                @Override
                public CollectionStatistics collectionStatistics(String field) throws IOException {
                    if (context.isCancelled()) {
                        throw new TaskCancelledException("cancelled");
                    }
                    CollectionStatistics cs = super.collectionStatistics(field);
                    if (cs != null) {
                        fieldStatistics.put(field, cs);
                    }
                    return cs;
                }
            };

            searcher.createWeight(context.searcher().rewrite(context.query()), ScoreMode.COMPLETE, 1);
            for (RescoreContext rescoreContext : context.rescore()) {
                for (Query query : rescoreContext.getQueries()) {
                    searcher.createWeight(context.searcher().rewrite(query), ScoreMode.COMPLETE, 1);
                }
            }

            Term[] terms = stats.keySet().toArray(new Term[0]);
            TermStatistics[] termStatistics = new TermStatistics[terms.length];
            for (int i = 0; i < terms.length; i++) {
                termStatistics[i] = stats.get(terms[i]);
            }

            context.dfsResult().termsStatistics(terms, termStatistics)
                    .fieldStatistics(fieldStatistics)
                    .maxDoc(context.searcher().getIndexReader().maxDoc());
        } catch (Exception e) {
            throw new DfsPhaseExecutionException(context.shardTarget(), "Exception during dfs phase", e);
        }
    }

}