Improve performance (#162)

DiscordChatExporter.Core.Models/Emoji.cs

@@ -0,0 +1,58 @@
+using System.Collections.Generic;
+using System.Linq;
+using Tyrrrz.Extensions;
+
+namespace DiscordChatExporter.Core.Models
+{
+    // https://discordapp.com/developers/docs/resources/emoji#emoji-object
+
+    public partial class Emoji
+    {
+        public string Id { get; }
+
+        public string Name { get; }
+
+        public bool IsAnimated { get; }
+
+        public string ImageUrl { get; }
+
+        public Emoji(string id, string name, bool isAnimated)
+        {
+            Id = id;
+            Name = name;
+            IsAnimated = isAnimated;
+
+            ImageUrl = GetImageUrl(id, name, isAnimated);
+        }
+    }
+
+    public partial class Emoji
+    {
+        private static IEnumerable<int> GetCodePoints(string emoji)
+        {
+            for (var i = 0; i < emoji.Length; i += char.IsHighSurrogate(emoji[i]) ? 2 : 1)
+                yield return char.ConvertToUtf32(emoji, i);
+        }
+
+        private static string GetTwemojiName(string emoji) =>
+            GetCodePoints(emoji).Select(i => i.ToString("x")).JoinToString("-");
+
+        public static string GetImageUrl(string id, string name, bool isAnimated)
+        {
+            // Custom emoji
+            if (id != null)
+            {
+                // Animated
+                if (isAnimated)
+                    return $"https://cdn.discordapp.com/emojis/{id}.gif";
+
+                // Non-animated
+                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";
+        }
+    }
+}