Refine hasPrevious/hasNext for keyset scrolling

Closes gh-843

Author: rstoyanchev

spring-graphql/src/main/java/org/springframework/graphql/data/query/WindowConnectionAdapter.java

@@ -18,6 +18,7 @@
 
 import java.util.Collection;
 
+import org.springframework.data.domain.KeysetScrollPosition;
 import org.springframework.data.domain.ScrollPosition;
 import org.springframework.data.domain.Window;
 import org.springframework.graphql.data.pagination.ConnectionAdapter;
@@ -53,12 +54,31 @@ public <T> Collection<T> getContent(Object container) {
 	@Override
 	public boolean hasPrevious(Object container) {
 		Window<?> window = window(container);
-		return (window.size() > 0 && !window.positionAt(0).isInitial());
+		if (!window.isEmpty()) {
+			ScrollPosition position = window.positionAt(0);
+			if (position instanceof KeysetScrollPosition keysetPosition) {
+				return (keysetPosition.scrollsBackward() && window.hasNext());
+			}
+			else {
+				return !position.isInitial();
+			}
+		}
+		return false;
 	}
 
 	@Override
 	public boolean hasNext(Object container) {
-		return window(container).hasNext();
+		Window<?> window = window(container);
+		if (!window.isEmpty()) {
+			ScrollPosition pos = window.positionAt(0);
+			if (pos instanceof KeysetScrollPosition keysetPos) {
+				return (keysetPos.scrollsForward() && window.hasNext());
+			}
+			else {
+				return window.hasNext();
+			}
+		}
+		return false;
 	}
 
 	@Override

spring-graphql/src/test/java/org/springframework/graphql/data/query/WindowConnectionAdapterTests.java

@@ -16,6 +16,7 @@
 
 package org.springframework.graphql.data.query;
 
+import java.util.Collections;
 import java.util.List;
 
 import org.junit.jupiter.api.Test;
@@ -60,4 +61,28 @@ void unpaged() {
 		assertThat(this.adapter.cursorAt(window, 3)).isEqualTo("O_3");
 	}
 
+	@Test
+	void hasNextPreviousWithKeysetScrollForward() {
+
+		Window<Book> window = Window.from(
+				BookSource.books(),
+				index -> ScrollPosition.of(Collections.singletonMap("id", index), ScrollPosition.Direction.FORWARD),
+				true);
+
+		assertThat(this.adapter.hasPrevious(window)).isFalse();
+		assertThat(this.adapter.hasNext(window)).isEqualTo(true);
+	}
+
+	@Test
+	void hasNextPreviousWithKeysetScrollBackward() {
+
+		Window<Book> window = Window.from(
+				BookSource.books(),
+				index -> ScrollPosition.of(Collections.singletonMap("id", index), ScrollPosition.Direction.BACKWARD),
+				true);
+
+		assertThat(this.adapter.hasPrevious(window)).isEqualTo(true);
+		assertThat(this.adapter.hasNext(window)).isFalse();
+	}
+
 }