PI-2876 Sort results manually in Kotlin

Due to bug in current OpenSearch version

Author: marcus-bcl

src/main/kotlin/uk/gov/justice/hmpps/probationsearch/contactsearch/ContactSearchService.kt

@@ -33,8 +33,7 @@ import org.springframework.data.elasticsearch.core.query.IndexQuery
 import org.springframework.security.core.context.SecurityContextHolder
 import org.springframework.stereotype.Service
 import uk.gov.justice.hmpps.probationsearch.contactsearch.ContactSearchService.SortType
-import uk.gov.justice.hmpps.probationsearch.contactsearch.ContactSearchService.SortType.LAST_UPDATED_DATETIME
-import uk.gov.justice.hmpps.probationsearch.contactsearch.ContactSearchService.SortType.SCORE
+import uk.gov.justice.hmpps.probationsearch.contactsearch.ContactSearchService.SortType.*
 import uk.gov.justice.hmpps.probationsearch.services.DeliusService
 import uk.gov.justice.hmpps.sqs.audit.HmppsAuditService
 import java.time.Instant
@@ -111,14 +110,9 @@ class ContactSearchService(
         .trackTotalHits(TrackHits.of { it.count(5000) })
         .size(pageable.pageSize)
         .from(pageable.offset.toInt())
-        .sort { sort ->
-          // Note: Hybrid query does not allow sorting by multiple fields including score
-          val order = pageable.sort.singleOrNull() ?: Sort.Order.desc(SCORE.searchField)
-          sort.field {
-            it.field(order.property)
-              .order(if (order.isDescending) JavaClientSortOrder.Desc else JavaClientSortOrder.Asc)
-          }
-        }
+        // Note: We're currently unable to reliably sort hybrid results until OpenSearch 2.19, so we re-sort the results later
+        // See https://github.com/opensearch-project/neural-search/issues/1067
+        .sort { sort -> sort.field { it.field(SCORE.searchField).order(JavaClientSortOrder.Desc) } }
         .highlight { highlight ->
           highlight
             .encoder(HighlighterEncoder.Html)
@@ -143,7 +137,17 @@ class ContactSearchService(
       response.pageable.pageNumber,
       response.totalElements,
       response.totalPages,
-      results,
+      results.sortedWith(
+        SortType.entries
+          .flatMap { type -> type.aliases.mapNotNull { alias -> pageable.sort.getOrderFor(alias)?.let { type to it } } }
+          .fold(Comparator { _, _ -> 0 }) { comparator, (type, order) ->
+            val selector = when (type) {
+              DATE -> { contact: ContactSearchResult -> contact.date }
+              else -> { contact: ContactSearchResult -> contact.score }
+            }
+            if (order.isDescending) comparator.thenByDescending(selector) else comparator.thenBy(selector)
+          },
+      ),
     )
   }