Fix 3D format detection when the tag is the last token of the path

Format3DParser drops the last character of the final path token: when
IndexOfAny finds no more delimiters, the slice is taken with
'index = path.Length - 1', so e.g. "hsbs" is compared as "hsb" and
never matches any rule.

File paths are unaffected because the extension is always the final
token, but directory based media have no extension. For DVD/BluRay
folder rips (BaseVideoResolver parses the folder path via
Set3DFormat), a trailing 3D tag such as
"Gravity (2013) 3d hsbs/BDMV" is silently ignored and Video3DFormat
is never set.

This is a regression from 42a2cc174 which replaced the string.Split
based FlagParser with span slicing; the Split implementation kept the
final token intact.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

2 files changed, 30 insertions, 4 deletions

diff --git a/Emby.Naming/Video/Format3DParser.cs b/Emby.Naming/Video/Format3DParser.cs
index eb5e71d78f..a287a2525b 100644
--- a/Emby.Naming/Video/Format3DParser.cs
+++ b/Emby.Naming/Video/Format3DParser.cs
@@ -52,13 +52,18 @@ namespace Emby.Naming.Video
             while (path.Length > 0)
             {
                 var index = path.IndexOfAny(delimiters);
+                ReadOnlySpan<char> currentSlice;
                 if (index == -1)
                 {
-                    index = path.Length - 1;
+                    // No delimiter left, the last token is the remainder of the path
+                    currentSlice = path;
+                    path = default;
+                }
+                else
+                {
+                    currentSlice = path[..index];
+                    path = path[(index + 1)..];
                 }
-
-                var currentSlice = path[..index];
-                path = path[(index + 1)..];
 
                 if (!foundPrefix)
                 {
diff --git a/tests/Jellyfin.Naming.Tests/Video/Format3DTests.cs b/tests/Jellyfin.Naming.Tests/Video/Format3DTests.cs
index d42bd66a1c..0e35071dd4 100644
--- a/tests/Jellyfin.Naming.Tests/Video/Format3DTests.cs
+++ b/tests/Jellyfin.Naming.Tests/Video/Format3DTests.cs
@@ -20,6 +20,27 @@ namespace Jellyfin.Naming.Tests.Video
         }
 
         [Fact]
+        public void TestFormat3DAtEndOfPath()
+        {
+            // Directory based media (eg. DVD or BluRay folder rips) have no file extension,
+            // so the 3D tag can be the last token of the path.
+            Test("Super movie (2009) 3d hsbs", true, "hsbs");
+            Test("Super movie (2009).3d.sbs", true, "sbs");
+            Test("Super movie (2009) 3d htab", true, "htab");
+            Test("Super movie (2009).hsbs", true, "hsbs");
+            Test("Super movie (2009) 3d", false, null);
+        }
+
+        [Fact]
+        public void TestResolveDirectory3D()
+        {
+            var result = VideoResolver.ResolveDirectory("/movies/Oblivion (2013) 3d hsbs", _namingOptions);
+
+            Assert.True(result?.Is3D);
+            Assert.Equal("hsbs", result?.Format3D, true);
+        }
+
+        [Fact]
         public void Test3DName()
         {
             var result = VideoResolver.ResolveFile("C:/Users/media/Desktop/Video Test/Movies/Oblivion/Oblivion.3d.hsbs.mkv", _namingOptions);