Resolve "Relevance Ranking in Metadata"

Required MRs to be merged before

• codeabilitysharingpluginapi!2 (merged)
• !217 (merged)
• codeabilitysharingpluginapi!3 (merged)

Related to #439 (closed)

src/main/java/at/ac/uibk/gitsearch/repository/search/MetaDataRepository.java

@@ -7,12 +7,19 @@ import at.ac.uibk.gitsearch.repository.jpa.StatisticsRepository;
 import at.ac.uibk.gitsearch.service.dto.AutoCompleteEntry;
 import at.ac.uibk.gitsearch.service.dto.StatisticsDTO;
 import co.elastic.clients.elasticsearch.ElasticsearchClient;
-import co.elastic.clients.elasticsearch._types.FieldValue;
 import co.elastic.clients.elasticsearch._types.SortOptions;
 import co.elastic.clients.elasticsearch._types.SortOptionsBuilders;
 import co.elastic.clients.elasticsearch._types.SortOrder;
 import co.elastic.clients.elasticsearch._types.mapping.FieldType;
-import co.elastic.clients.elasticsearch._types.query_dsl.*;
+import co.elastic.clients.elasticsearch._types.query_dsl.BoolQuery;
+import co.elastic.clients.elasticsearch._types.query_dsl.ExistsQuery;
+import co.elastic.clients.elasticsearch._types.query_dsl.MatchPhrasePrefixQuery;
+import co.elastic.clients.elasticsearch._types.query_dsl.MatchQuery;
+import co.elastic.clients.elasticsearch._types.query_dsl.MultiMatchQuery;
+import co.elastic.clients.elasticsearch._types.query_dsl.PrefixQuery;
+import co.elastic.clients.elasticsearch._types.query_dsl.RangeQuery;
+import co.elastic.clients.elasticsearch._types.query_dsl.TermQuery;
+import co.elastic.clients.elasticsearch._types.query_dsl.TextQueryType;
 import co.elastic.clients.elasticsearch.core.search.Hit;
 import co.elastic.clients.json.JsonData;
 import co.elastic.clients.transport.rest_client.RestClientTransport;
@@ -26,8 +33,22 @@ import java.net.ConnectException;
 import java.text.ParseException;
 import java.time.Instant;
 import java.time.format.DateTimeFormatter;
-import java.util.*;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.ConcurrentModificationException;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Locale;
+import java.util.Map;
 import java.util.Map.Entry;
+import java.util.NoSuchElementException;
+import java.util.Optional;
+import java.util.Spliterator;
+import java.util.Spliterators;
+import java.util.StringTokenizer;
+import java.util.TreeMap;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicInteger;
@@ -573,6 +594,29 @@ public class MetaDataRepository {
     }
 
     private List<SortOptions> getDefaultSortStrategy() {
+        /** todo try this
+         * GET /my_index/_search
+         * {
+         *  "query": {
+         *    "match_all": {}
+         *  },
+         *  "sort": {
+         *    "_script": {
+         *      "type": "number",
+         *      "script": {
+         *        "lang": "painless",
+         *        "source": "doc['fieldA'].value * params.factorA + doc['fieldB'].value * params.factorB",
+         *        "params": {
+         *          "factorA": 1.0,
+         *          "factorB": 100.0
+         *        }
+         *      },
+         *      "order": "desc"
+         *    }
+         *  }
+         * }
+         */
+
         return List.of(
             getSortOptionForFieldAndOrder(SearchRepositoryConstants.SEARCHSTATISTICS_BADGEREWARDED, SortOrder.Desc, FieldType.Boolean),
             getSortOptionForFieldAndOrder(SearchRepositoryConstants.SEARCHSTATISTICS_DOWNLOADS, SortOrder.Desc, FieldType.Integer),
@@ -581,7 +625,7 @@ public class MetaDataRepository {
     }
 
     private SortOptions getSortOptionForFieldAndOrder(String field, SortOrder order, FieldType fieldType) {
-        return SortOptionsBuilders.field(sb -> sb.field(field).unmappedType(fieldType).order(order).missing(FieldValue.NULL));
+        return SortOptionsBuilders.field(sb -> sb.field(field).unmappedType(fieldType).order(order).missing("_last"));
     }
 
     /**