Fix PageUp and PageDown wrapping past result boundaries

Flow.Launcher.Test/ResultsViewModelNavigationTest.cs

@@ -0,0 +1,101 @@
+using System.Threading;
+using Flow.Launcher.Infrastructure.UserSettings;
+using Flow.Launcher.Plugin;
+using Flow.Launcher.ViewModel;
+using NUnit.Framework;
+
+namespace Flow.Launcher.Test;
+
+[TestFixture]
+[Apartment(ApartmentState.STA)]
+public class ResultsViewModelNavigationTest
+{
+    [TestCase(17, 15, 0, 15)]
+    [TestCase(17, 15, 15, 16)]
+    [TestCase(17, 15, 16, 16)]
+    [TestCase(3, 15, 0, 2)]
+    [TestCase(1, 15, 0, 0)]
+    [TestCase(0, 15, -1, -1)]
+    public void NextPageStopsAtLastResult(int count, int pageSize, int selectedIndex, int expected)
+    {
+        var viewModel = CreateViewModel(count, pageSize, selectedIndex);
+
+        viewModel.SelectNextPage();
+
+        Assert.That(viewModel.SelectedIndex, Is.EqualTo(expected));
+    }
+
+    [TestCase(17, 15, 16, 1)]
+    [TestCase(17, 15, 1, 0)]
+    [TestCase(17, 15, 0, 0)]
+    [TestCase(3, 15, 2, 0)]
+    [TestCase(1, 15, 0, 0)]
+    [TestCase(0, 15, -1, -1)]
+    public void PreviousPageStopsAtFirstResult(int count, int pageSize, int selectedIndex, int expected)
+    {
+        var viewModel = CreateViewModel(count, pageSize, selectedIndex);
+
+        viewModel.SelectPrevPage();
+
+        Assert.That(viewModel.SelectedIndex, Is.EqualTo(expected));
+    }
+
+    [Test]
+    public void RepeatedPageDownReachesAndKeepsLastResult()
+    {
+        var viewModel = CreateViewModel(17, 15, 0);
+
+        viewModel.SelectNextPage();
+        Assert.That(viewModel.SelectedIndex, Is.EqualTo(15));
+        viewModel.SelectNextPage();
+        Assert.That(viewModel.SelectedIndex, Is.EqualTo(16));
+        viewModel.SelectNextPage();
+        Assert.That(viewModel.SelectedIndex, Is.EqualTo(16));
+    }
+
+    [Test]
+    public void RepeatedPageUpReachesAndKeepsFirstResult()
+    {
+        var viewModel = CreateViewModel(17, 15, 16);
+
+        viewModel.SelectPrevPage();
+        Assert.That(viewModel.SelectedIndex, Is.EqualTo(1));
+        viewModel.SelectPrevPage();
+        Assert.That(viewModel.SelectedIndex, Is.Zero);
+        viewModel.SelectPrevPage();
+        Assert.That(viewModel.SelectedIndex, Is.Zero);
+    }
+
+    [Test]
+    public void DownArrowStillWrapsFromLastResult()
+    {
+        var viewModel = CreateViewModel(17, 15, 16);
+
+        viewModel.SelectNextResult();
+
+        Assert.That(viewModel.SelectedIndex, Is.Zero);
+    }
+
+    [Test]
+    public void UpArrowStillWrapsFromFirstResult()
+    {
+        var viewModel = CreateViewModel(17, 15, 0);
+
+        viewModel.SelectPrevResult();
+
+        Assert.That(viewModel.SelectedIndex, Is.EqualTo(16));
+    }
+
+    private static ResultsViewModel CreateViewModel(int count, int pageSize, int selectedIndex)
+    {
+        var settings = new Settings { MaxResultsToShow = pageSize };
+        var viewModel = new ResultsViewModel(settings, null);
+        for (var index = 0; index < count; index++)
+        {
+            viewModel.Results.Add(new ResultViewModel(new Result { Title = $"Result {index}" }, settings));
+        }
+
+        viewModel.SelectedIndex = selectedIndex;
+        return viewModel;
+    }
+}

Flow.Launcher/ViewModel/ResultsViewModel.cs

@@ -138,12 +138,16 @@ public void SelectPrevResult()
 
         public void SelectNextPage()
         {
-            SelectedIndex = NewIndex(SelectedIndex + MaxResults);
+            SelectedIndex = Results.Count > 0
+                ? Math.Clamp(SelectedIndex + MaxResults, 0, Results.Count - 1)
+                : -1;
         }
 
         public void SelectPrevPage()
         {
-            SelectedIndex = NewIndex(SelectedIndex - MaxResults);
+            SelectedIndex = Results.Count > 0
+                ? Math.Clamp(SelectedIndex - MaxResults, 0, Results.Count - 1)
+                : -1;
         }
 
         public void SelectFirstResult()