From 9a7b37282a31e86ca51c53e46855e54c23950020 Mon Sep 17 00:00:00 2001
From: Andrew Horth <andrew@horth.co.uk>
Date: Thu, 28 Sep 2023 17:33:32 +0100
Subject: [PATCH] Add tag helper to render empty content as a hyphen

---
 .../TagHelpers/UseEmptyFallbackTagHelper.cs   | 23 +++++++++++++++++++
 1 file changed, 23 insertions(+)
 create mode 100644 TeachingRecordSystem/src/TeachingRecordSystem.SupportUi/TagHelpers/UseEmptyFallbackTagHelper.cs

diff --git a/TeachingRecordSystem/src/TeachingRecordSystem.SupportUi/TagHelpers/UseEmptyFallbackTagHelper.cs b/TeachingRecordSystem/src/TeachingRecordSystem.SupportUi/TagHelpers/UseEmptyFallbackTagHelper.cs
new file mode 100644
index 0000000000..a99465d55b
--- /dev/null
+++ b/TeachingRecordSystem/src/TeachingRecordSystem.SupportUi/TagHelpers/UseEmptyFallbackTagHelper.cs
@@ -0,0 +1,23 @@
+using System.Text.Encodings.Web;
+using Microsoft.AspNetCore.Mvc.TagHelpers;
+using Microsoft.AspNetCore.Razor.TagHelpers;
+
+namespace TeachingRecordSystem.SupportUi.TagHelpers;
+
+[HtmlTargetElement("*", Attributes = "use-empty-fallback")]
+public class UseEmptyFallbackTagHelper : TagHelper
+{
+    public override int Order => -1;
+
+    public override async Task ProcessAsync(TagHelperContext context, TagHelperOutput output)
+    {
+        var content = await output.GetChildContentAsync();
+        output.Attributes.RemoveAll("use-empty-fallback");
+
+        if (content.IsEmptyOrWhiteSpace)
+        {
+            output.AddClass("trs-subtle-emphasis", HtmlEncoder.Default);
+            output.Content.SetContent("-");
+        }
+    }
+}