Reject saved state with save boundaries outside the commands

UndoRedo.Test/SerializationTests.cs

@@ -467,6 +467,84 @@
 		Assert.HasCount(1, stack.SaveBoundaries, "A failed restore should keep the existing save boundaries");
 	}
 
+	[TestMethod]
+	[DataRow(-7, DisplayName = "boundary before the start")]
+	[DataRow(-2, DisplayName = "boundary one before the start")]
+	[DataRow(2, DisplayName = "boundary at the command count")]
+	[DataRow(42, DisplayName = "boundary far past the last command")]
+	public void UndoRedoService_RestoreFromStateInvalidBoundaryPosition_ReturnsFalseAndKeepsHistory(int boundaryPosition)
+	{
+		// Arrange
+		UndoRedoService stack = CreateService();
+		stack.Execute(new DelegateCommand("A", () => { }, () => { }));
+		stack.MarkAsSaved();
+
+		UndoRedoStackState state = new(
+			[new DelegateCommand("X", () => { }, () => { }), new DelegateCommand("Y", () => { }, () => { })],
+			1,
+			[new SaveBoundary(boundaryPosition)],
+			"1.0",
+			DateTime.UtcNow);
+
+		// Act
+		bool success = stack.RestoreFromState(state);
+
+		// Assert
+		Assert.IsFalse(success, "RestoreFromState should reject a save boundary outside the commands");
+		Assert.AreEqual(1, stack.CommandCount, "A failed restore should keep the existing commands");
+		Assert.AreEqual(0, stack.CurrentPosition, "A failed restore should keep the existing position");
+		Assert.HasCount(1, stack.SaveBoundaries, "A failed restore should keep the existing save boundaries");
+		Assert.AreEqual(0, stack.SaveBoundaries[0].Position, "A failed restore should keep the existing save boundary position");
+	}
+
+	[TestMethod]
+	[DataRow(-1, DisplayName = "boundary at the initial position")]
+	[DataRow(1, DisplayName = "boundary at the last command")]
+	public void UndoRedoService_RestoreFromStateBoundaryAtEdge_Restores(int boundaryPosition)
+	{
+		// Arrange
+		UndoRedoService stack = CreateService();
+		UndoRedoStackState state = new(
+			[new DelegateCommand("X", () => { }, () => { }), new DelegateCommand("Y", () => { }, () => { })],
+			1,
+			[new SaveBoundary(boundaryPosition)],
+			"1.0",
+			DateTime.UtcNow);
+
+		// Act
+		bool success = stack.RestoreFromState(state);
+
+		// Assert
+		Assert.IsTrue(success, "RestoreFromState should accept a save boundary at -1 or at the last command");
+		Assert.HasCount(1, stack.SaveBoundaries);
+		Assert.AreEqual(boundaryPosition, stack.SaveBoundaries[0].Position);
+	}
+
+	[TestMethod]
+	public async Task UndoRedoService_LoadStateAsyncInvalidBoundaryPosition_ReturnsFalseAndKeepsHistory()
+	{
+		// Arrange
+		JsonUndoRedoSerializer serializer = new();
+		byte[] data = await serializer.SerializeAsync(
+			[new TestSerializableCommand("X")],
+			0,
+			[new SaveBoundary(-7), new SaveBoundary(42)]).ConfigureAwait(false);
+
+		UndoRedoService stack = CreateService();
+		stack.SetSerializer(new JsonUndoRedoSerializer());
+		stack.Execute(new DelegateCommand("A", () => { }, () => { }));
+		stack.MarkAsSaved();
+
+		// Act
+		bool success = await stack.LoadStateAsync(data).ConfigureAwait(false);
+
+		// Assert
+		Assert.IsFalse(success, "LoadStateAsync should reject save boundaries outside the commands");
+		Assert.AreEqual(1, stack.CommandCount, "A failed load should keep the existing commands");
+		Assert.HasCount(1, stack.SaveBoundaries, "A failed load should keep the existing save boundaries");
+		Assert.AreEqual(0, stack.SaveBoundaries[0].Position, "A failed load should keep the existing save boundary position");
+	}
+
 	private sealed class ConstructorOnlySerializableCommand(string value)
 		: BaseCommand(ChangeType.Modify, ["test"]), ISerializableCommand
 	{

UndoRedo/Services/UndoRedoService.cs

@@ -172,7 +172,7 @@
 
 			try
 			{
 				await _navigationProvider.NavigateToAsync(command.NavigationContext!, cts.Token).ConfigureAwait(false);
 			}
 			catch (OperationCanceledException)
 			{
@@ -208,7 +208,7 @@
 
 			try
 			{
 				await _navigationProvider.NavigateToAsync(command.NavigationContext!, cts.Token).ConfigureAwait(false);
 			}
 			catch (OperationCanceledException)
 			{
@@ -274,7 +274,7 @@
 
 			try
 			{
 				await _navigationProvider.NavigateToAsync(lastCommand.NavigationContext!, cts.Token).ConfigureAwait(false);
 			}
 			catch (OperationCanceledException)
 			{
@@ -396,6 +396,7 @@
 		state.SaveBoundaries is not null &&
 		!state.Commands.Any(command => command is null) &&
 		!state.SaveBoundaries.Any(boundary => boundary is null) &&
+		state.SaveBoundaries.All(boundary => boundary.Position >= -1 && boundary.Position < state.Commands.Count) &&
 		state.CurrentPosition >= -1 &&
 		state.CurrentPosition < state.Commands.Count;
 }