From eee7f09e9068794af6e4ff1d55e1b222ce7e1063 Mon Sep 17 00:00:00 2001
From: rstoyanchev <rstoyanchev@vmware.com>
Date: Thu, 26 Oct 2023 12:28:02 +0100
Subject: [PATCH] Refine hasPrevious/hasNext for keyset scrolling

Closes gh-843
---
 .../data/query/WindowConnectionAdapter.java   | 24 ++++++++++++++++--
 .../query/WindowConnectionAdapterTests.java   | 25 +++++++++++++++++++
 2 files changed, 47 insertions(+), 2 deletions(-)

diff --git a/spring-graphql/src/main/java/org/springframework/graphql/data/query/WindowConnectionAdapter.java b/spring-graphql/src/main/java/org/springframework/graphql/data/query/WindowConnectionAdapter.java
index 8d8edf82..44534947 100644
--- a/spring-graphql/src/main/java/org/springframework/graphql/data/query/WindowConnectionAdapter.java
+++ b/spring-graphql/src/main/java/org/springframework/graphql/data/query/WindowConnectionAdapter.java
@@ -18,6 +18,7 @@ package org.springframework.graphql.data.query;
 
 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 final class WindowConnectionAdapter
 	@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
diff --git a/spring-graphql/src/test/java/org/springframework/graphql/data/query/WindowConnectionAdapterTests.java b/spring-graphql/src/test/java/org/springframework/graphql/data/query/WindowConnectionAdapterTests.java
index 8ee611cb..e8d8f65c 100644
--- a/spring-graphql/src/test/java/org/springframework/graphql/data/query/WindowConnectionAdapterTests.java
+++ b/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 @@ public class WindowConnectionAdapterTests {
 		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();
+	}
+
 }