Add wrong answer follow-up prompts

api/QuestionsApi/Controllers/QuestionsController.cs

@@ -220,6 +220,9 @@ public class QuestionsController : ControllerBase
             return "explanation required";
         if (req.ChoiceSelectionPercentages.Any(entry => entry.Value is < 0 or > 100))
             return "choiceSelectionPercentages values must be between 0 and 100";
+        var followupValidation = ValidateWrongAnswerFollowups(req);
+        if (followupValidation is not null)
+            return followupValidation;
         if (string.IsNullOrWhiteSpace(req.System))
             return "system required";
         if (string.IsNullOrWhiteSpace(req.Discipline))
@@ -230,6 +233,28 @@ public class QuestionsController : ControllerBase
         return null;
     }
 
+    private static string? ValidateWrongAnswerFollowups(UpsertQuestionRequest req)
+    {
+        var choiceIds = req.Choices.Select(c => c.Id).Where(id => !string.IsNullOrWhiteSpace(id)).ToHashSet();
+        foreach (var entry in req.WrongAnswerFollowups)
+        {
+            if (!choiceIds.Contains(entry.Key))
+                return "wrongAnswerFollowups keys must match a choice id";
+            if (entry.Key == req.CorrectChoiceId)
+                return "wrongAnswerFollowups should only target incorrect choices";
+            if (string.IsNullOrWhiteSpace(entry.Value.Prompt))
+                return "wrongAnswerFollowups prompt required";
+            if (string.IsNullOrWhiteSpace(entry.Value.TeachingPoint))
+                return "wrongAnswerFollowups teachingPoint required";
+            if (entry.Value.Choices.Count == 0)
+                return "wrongAnswerFollowups choices required";
+            if (!entry.Value.Choices.Any(c => c.Id == entry.Value.CorrectChoiceId))
+                return "wrongAnswerFollowups correctChoiceId must match a follow-up choice id";
+        }
+
+        return null;
+    }
+
     private string CurrentUserId() =>
         User.FindFirstValue(ClaimTypes.NameIdentifier)
         ?? User.FindFirstValue(ClaimTypes.Name)