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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.action.search;

import org.apache.logging.log4j.util.Strings;
import org.elasticsearch.ExceptionsHelper;
import org.elasticsearch.action.ActionListener;
import org.elasticsearch.common.document.DocumentField;
import org.elasticsearch.common.util.Maps;
import org.elasticsearch.common.util.concurrent.AtomicArray;
import org.elasticsearch.search.SearchHit;
import org.elasticsearch.search.SearchPhaseResult;
import org.elasticsearch.search.fetch.subphase.LookupField;
import org.elasticsearch.search.internal.InternalSearchResponse;
import org.elasticsearch.transport.RemoteClusterService;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

/**
 * Asynchronously resolves {@link LookupField} that are specified {@link DocumentField#getLookupFields()}
 *
 * @see org.elasticsearch.index.mapper.LookupRuntimeFieldType
 */
final class FetchLookupFieldsPhase extends SearchPhase {
    private final SearchPhaseContext context;
    private final InternalSearchResponse searchResponse;
    private final AtomicArray queryResults;

    FetchLookupFieldsPhase(SearchPhaseContext context, InternalSearchResponse searchResponse, AtomicArray queryResults) {
        super("fetch_lookup_fields");
        this.context = context;
        this.searchResponse = searchResponse;
        this.queryResults = queryResults;
    }

    private record Cluster(String clusterAlias, List hitsWithLookupFields, List lookupFields) {

    }

    private static List groupLookupFieldsByClusterAlias(InternalSearchResponse response) {
        final Map> perClusters = new HashMap<>();
        for (SearchHit hit : response.hits.getHits()) {
            String clusterAlias = hit.getClusterAlias() != null ? hit.getClusterAlias() : RemoteClusterService.LOCAL_CLUSTER_GROUP_KEY;
            if (hit.hasLookupFields()) {
                perClusters.computeIfAbsent(clusterAlias, k -> new ArrayList<>()).add(hit);
            }
        }
        final List clusters = new ArrayList<>(perClusters.size());
        for (Map.Entry> e : perClusters.entrySet()) {
            final List lookupFields = e.getValue()
                .stream()
                .flatMap(h -> h.getDocumentFields().values().stream())
                .flatMap(doc -> doc.getLookupFields().stream())
                .distinct()
                .toList();
            clusters.add(new Cluster(e.getKey(), e.getValue(), lookupFields));
        }
        return clusters;
    }

    @Override
    public void run() {
        final List clusters = groupLookupFieldsByClusterAlias(searchResponse);
        if (clusters.isEmpty()) {
            context.sendSearchResponse(searchResponse, queryResults);
            return;
        }
        final MultiSearchRequest multiSearchRequest = new MultiSearchRequest();
        for (Cluster cluster : clusters) {
            // Do not prepend the clusterAlias to the targetIndex if the search request is already on the remote cluster.
            final String clusterAlias = context.getRequest().getLocalClusterAlias() == null ? cluster.clusterAlias : null;
            assert Strings.isEmpty(clusterAlias) || TransportSearchAction.shouldMinimizeRoundtrips(context.getRequest()) == false
                : "lookup across clusters only if [ccs_minimize_roundtrips] is disabled";
            for (LookupField lookupField : cluster.lookupFields) {
                final SearchRequest searchRequest = lookupField.toSearchRequest(clusterAlias);
                searchRequest.setCcsMinimizeRoundtrips(false);
                multiSearchRequest.add(searchRequest);
            }
        }
        context.getSearchTransport().sendExecuteMultiSearch(multiSearchRequest, context.getTask(), new ActionListener<>() {
            @Override
            public void onResponse(MultiSearchResponse items) {
                Exception failure = null;
                int index = 0;
                for (Cluster cluster : clusters) {
                    final Map> lookupResults = Maps.newMapWithExpectedSize(cluster.lookupFields.size());
                    for (LookupField lookupField : cluster.lookupFields) {
                        final MultiSearchResponse.Item item = items.getResponses()[index];
                        if (item.isFailure()) {
                            failure = ExceptionsHelper.useOrSuppress(failure, item.getFailure());
                        } else if (failure == null) {
                            final List