Retain scroll direction across keyset scroll requests.

Closes #4413

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/ScrollUtils.java

@@ -61,7 +61,8 @@ class ScrollUtils {
 
 		Document sortObject = query.getSortObject();
 		KeysetScrollPosition keyset = query.getKeyset();
-		KeysetScrollDirector director = KeysetScrollDirector.of(keyset.getDirection());
+		Direction direction = keyset.getDirection();
+		KeysetScrollDirector director = KeysetScrollDirector.of(direction);
 
 		List<T> resultsToUse = director.postPostProcessResults(result, query.getLimit());
 
@@ -71,7 +72,7 @@ class ScrollUtils {
 			Entity<T> entity = operations.forEntity(last);
 
 			Map<String, Object> keys = entity.extractKeys(sortObject, sourceType);
-			return ScrollPosition.forward(keys);
+			return ScrollPosition.of(keys, direction);
 		};
 
 		return Window.from(resultsToUse, positionFunction, hasMoreElements(result, query.getLimit()));

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/MongoTemplateScrollTests.java

@@ -190,9 +190,30 @@ class MongoTemplateScrollTests {
 		window = template.scroll(q.with(window.positionAt(0)).limit(2), Person.class);
 
 		assertThat(window).hasSize(2);
-		assertThat(window).containsOnly(john20, john40_1);
-		assertThat(window.hasNext()).isTrue();
-		assertThat(window.isLast()).isFalse();
+		assertThat(window).containsOnly(jane_20, jane_40);
+		assertThat(window.hasNext()).isFalse();
+		assertThat(window.isLast()).isTrue();
+	}
+
+	@Test // GH-4413
+	void shouldAllowInitialBackwardSort() {
+
+		Person jane_20 = new Person("Jane", 20);
+		Person jane_40 = new Person("Jane", 40);
+		Person jane_42 = new Person("Jane", 42);
+		Person john20 = new Person("John", 20);
+		Person john40_1 = new Person("John", 40);
+		Person john40_2 = new Person("John", 40);
+
+		template.insertAll(Arrays.asList(john20, john40_1, john40_2, jane_20, jane_40, jane_42));
+		Query q = new Query(where("firstName").regex("J.*")).with(Sort.by("firstName", "age"));
+		q.with(ScrollPosition.keyset().backward()).limit(3);
+
+		Window<Person> window = template.scroll(q, Person.class);
+		assertThat(window).containsExactly(john20, john40_1, john40_2);
+
+		window = template.scroll(q.with(window.positionAt(0)).limit(3), Person.class);
+		assertThat(window).containsExactly(jane_20, jane_40, jane_42);
 	}
 
 	@ParameterizedTest // GH-4308

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/ScrollUtilsUnitTests.java

@@ -0,0 +1,56 @@
+/*
+ * Copyright 2023 the original author or authors.
+ *
+ * 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
+ *
+ *      https://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 org.springframework.data.mongodb.core;
+
+import static org.assertj.core.api.AssertionsForClassTypes.*;
+import static org.mockito.Mockito.*;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+
+import org.junit.jupiter.api.Test;
+import org.springframework.data.domain.KeysetScrollPosition;
+import org.springframework.data.domain.ScrollPosition;
+import org.springframework.data.domain.Window;
+import org.springframework.data.mongodb.core.EntityOperations.Entity;
+import org.springframework.data.mongodb.core.query.Query;
+
+/**
+ * Unit tests for {@link ScrollUtils}.
+ *
+ * @author Mark Paluch
+ */
+class ScrollUtilsUnitTests {
+
+	@Test // GH-4413
+	void positionShouldRetainScrollDirection() {
+
+		Query query = new Query();
+		query.with(ScrollPosition.keyset().backward());
+		EntityOperations entityOperationsMock = mock(EntityOperations.class);
+		Entity entityMock = mock(Entity.class);
+
+		when(entityOperationsMock.forEntity(any())).thenReturn(entityMock);
+		when(entityMock.extractKeys(any(), any())).thenReturn(Map.of("k", "v"));
+
+		Window<Integer> window = ScrollUtils.createWindow(query, new ArrayList<>(List.of(1, 2, 3)), Integer.class,
+				entityOperationsMock);
+
+		assertThat(window.positionAt(0)).isInstanceOf(KeysetScrollPosition.class);
+		assertThat(((KeysetScrollPosition) window.positionAt(0)).scrollsBackward()).isTrue();
+	}
+}