Use the new Rune API for handling emoji code points

DiscordChatExporter.Core.Models/Emoji.cs

@@ -1,5 +1,6 @@
 using System.Collections.Generic;
 using System.Linq;
+using System.Text;
 using Tyrrrz.Extensions;
 
 namespace DiscordChatExporter.Core.Models
@@ -28,14 +29,21 @@ namespace DiscordChatExporter.Core.Models
 
     public partial class Emoji
     {
-        private static IEnumerable<int> GetCodePoints(string emoji)
+        private static IEnumerable<Rune> GetRunes(string emoji)
         {
-            for (var i = 0; i < emoji.Length; i += char.IsHighSurrogate(emoji[i]) ? 2 : 1)
-                yield return char.ConvertToUtf32(emoji, i);
+            var lastIndex = 0;
+            while (lastIndex < emoji.Length && Rune.TryGetRuneAt(emoji, lastIndex, out var rune))
+            {
+                // Skip variant selector rune
+                if (rune.Value != 0xfe0f)
+                    yield return rune;
+
+                lastIndex += rune.Utf16SequenceLength;
+            }
         }
 
-        private static string GetTwemojiName(string emoji) =>
-            GetCodePoints(emoji).Select(i => i.ToString("x")).JoinToString("-");
+        private static string GetTwemojiName(IEnumerable<Rune> runes) =>
+            runes.Select(r => r.Value.ToString("x")).JoinToString("-");
 
         public static string GetImageUrl(string? id, string name, bool isAnimated)
         {
@@ -50,9 +58,17 @@ namespace DiscordChatExporter.Core.Models
                 return $"https://cdn.discordapp.com/emojis/{id}.png";
             }
 
-            // Standard unicode emoji (via twemoji)
-            var twemojiName = GetTwemojiName(name);
-            return $"https://twemoji.maxcdn.com/2/72x72/{twemojiName}.png";
+            // Standard unicode emoji
+            var emojiRunes = GetRunes(name).ToArray();
+            if (emojiRunes.Any())
+            {
+                // Get corresponding Twemoji image
+                var twemojiName = GetTwemojiName(emojiRunes);
+                return $"https://twemoji.maxcdn.com/2/72x72/{twemojiName}.png";
+            }
+
+            // Fallback in case of failure
+            return name;
         }
     }
 }