Don't crash on invalid mentions

Fixes #816

DiscordChatExporter.Core/Exporting/Writers/MarkdownVisitors/HtmlMarkdownVisitor.cs

@@ -107,27 +107,34 @@ internal partial class HtmlMarkdownVisitor : MarkdownVisitor
 
     protected override MarkdownNode VisitMention(MentionNode mention)
     {
-        if (mention.Kind == MentionKind.Meta)
+        if (mention.Kind == MentionKind.Everyone)
         {
             _buffer
                 .Append("<span class=\"mention\">")
-                .Append("@").Append(HtmlEncode(mention.Id.ToString()))
+                .Append("@everyone")
+                .Append("</span>");
+        }
+        else if (mention.Kind == MentionKind.Here)
+        {
+            _buffer
+                .Append("<span class=\"mention\">")
+                .Append("@here")
                 .Append("</span>");
         }
         else if (mention.Kind == MentionKind.User)
         {
-            var member = _context.TryGetMember(mention.Id);
+            var member = mention.TargetId?.Pipe(_context.TryGetMember);
             var fullName = member?.User.FullName ?? "Unknown";
             var nick = member?.Nick ?? "Unknown";
 
             _buffer
                 .Append($"<span class=\"mention\" title=\"{HtmlEncode(fullName)}\">")
-                .Append("@").Append(HtmlEncode(nick))
+                .Append('@').Append(HtmlEncode(nick))
                 .Append("</span>");
         }
         else if (mention.Kind == MentionKind.Channel)
         {
-            var channel = _context.TryGetChannel(mention.Id);
+            var channel = mention.TargetId?.Pipe(_context.TryGetChannel);
             var symbol = channel?.IsVoiceChannel == true ? "🔊" : "#";
             var name = channel?.Name ?? "deleted-channel";
 
@@ -138,7 +145,7 @@ internal partial class HtmlMarkdownVisitor : MarkdownVisitor
         }
         else if (mention.Kind == MentionKind.Role)
         {
-            var role = _context.TryGetRole(mention.Id);
+            var role = mention.TargetId?.Pipe(_context.TryGetRole);
             var name = role?.Name ?? "deleted-role";
             var color = role?.Color;
 
@@ -148,7 +155,7 @@ internal partial class HtmlMarkdownVisitor : MarkdownVisitor
 
             _buffer
                 .Append($"<span class=\"mention\" style=\"{style}\">")
-                .Append("@").Append(HtmlEncode(name))
+                .Append('@').Append(HtmlEncode(name))
                 .Append("</span>");
         }
 

DiscordChatExporter.Core/Exporting/Writers/MarkdownVisitors/PlainTextMarkdownVisitor.cs

@@ -1,6 +1,7 @@
 using System.Text;
 using DiscordChatExporter.Core.Markdown;
 using DiscordChatExporter.Core.Markdown.Parsing;
+using DiscordChatExporter.Core.Utils.Extensions;
 
 namespace DiscordChatExporter.Core.Exporting.Writers.MarkdownVisitors;
 
@@ -34,20 +35,24 @@ internal partial class PlainTextMarkdownVisitor : MarkdownVisitor
 
     protected override MarkdownNode VisitMention(MentionNode mention)
     {
-        if (mention.Kind == MentionKind.Meta)
+        if (mention.Kind == MentionKind.Everyone)
         {
-            _buffer.Append($"@{mention.Id}");
+            _buffer.Append("@everyone");
+        }
+        else if (mention.Kind == MentionKind.Here)
+        {
+            _buffer.Append("@here");
         }
         else if (mention.Kind == MentionKind.User)
         {
-            var member = _context.TryGetMember(mention.Id);
+            var member = mention.TargetId?.Pipe(_context.TryGetMember);
             var name = member?.User.Name ?? "Unknown";
 
             _buffer.Append($"@{name}");
         }
         else if (mention.Kind == MentionKind.Channel)
         {
-            var channel = _context.TryGetChannel(mention.Id);
+            var channel =mention.TargetId?.Pipe(_context.TryGetChannel);
             var name = channel?.Name ?? "deleted-channel";
 
             _buffer.Append($"#{name}");
@@ -58,7 +63,7 @@ internal partial class PlainTextMarkdownVisitor : MarkdownVisitor
         }
         else if (mention.Kind == MentionKind.Role)
         {
-            var role = _context.TryGetRole(mention.Id);
+            var role = mention.TargetId?.Pipe(_context.TryGetRole);
             var name = role?.Name ?? "deleted-role";
 
             _buffer.Append($"@{name}");

DiscordChatExporter.Core/Markdown/MentionKind.cs

@@ -2,7 +2,8 @@
 
 internal enum MentionKind
 {
-    Meta,
+    Everyone,
+    Here,
     User,
     Channel,
     Role

DiscordChatExporter.Core/Markdown/MentionNode.cs

@@ -2,4 +2,5 @@
 
 namespace DiscordChatExporter.Core.Markdown;
 
-internal record MentionNode(Snowflake Id, MentionKind Kind) : MarkdownNode;
+// Null ID means it's a meta mention or an invalid mention
+internal record MentionNode(Snowflake? TargetId, MentionKind Kind) : MarkdownNode;

DiscordChatExporter.Core/Markdown/Parsing/MarkdownParser.cs

@@ -124,31 +124,31 @@ internal static partial class MarkdownParser
     // Capture @everyone
     private static readonly IMatcher<MarkdownNode> EveryoneMentionNodeMatcher = new StringMatcher<MarkdownNode>(
         "@everyone",
-        _ => new MentionNode(Snowflake.Zero, MentionKind.Meta)
+        _ => new MentionNode(null, MentionKind.Everyone)
     );
 
     // Capture @here
     private static readonly IMatcher<MarkdownNode> HereMentionNodeMatcher = new StringMatcher<MarkdownNode>(
         "@here",
-        _ => new MentionNode(Snowflake.Zero, MentionKind.Meta)
+        _ => new MentionNode(null, MentionKind.Here)
     );
 
     // Capture <@123456> or <@!123456>
     private static readonly IMatcher<MarkdownNode> UserMentionNodeMatcher = new RegexMatcher<MarkdownNode>(
         new Regex("<@!?(\\d+)>", DefaultRegexOptions),
-        (_, m) => new MentionNode(Snowflake.Parse(m.Groups[1].Value), MentionKind.User)
+        (_, m) => new MentionNode(Snowflake.TryParse(m.Groups[1].Value), MentionKind.User)
     );
 
     // Capture <#123456>
     private static readonly IMatcher<MarkdownNode> ChannelMentionNodeMatcher = new RegexMatcher<MarkdownNode>(
         new Regex("<#!?(\\d+)>", DefaultRegexOptions),
-        (_, m) => new MentionNode(Snowflake.Parse(m.Groups[1].Value), MentionKind.Channel)
+        (_, m) => new MentionNode(Snowflake.TryParse(m.Groups[1].Value), MentionKind.Channel)
     );
 
     // Capture <@&123456>
     private static readonly IMatcher<MarkdownNode> RoleMentionNodeMatcher = new RegexMatcher<MarkdownNode>(
         new Regex("<@&(\\d+)>", DefaultRegexOptions),
-        (_, m) => new MentionNode(Snowflake.Parse(m.Groups[1].Value), MentionKind.Role)
+        (_, m) => new MentionNode(Snowflake.TryParse(m.Groups[1].Value), MentionKind.Role)
     );
 
     /* Emoji */
@@ -179,7 +179,7 @@ internal static partial class MarkdownParser
     private static readonly IMatcher<MarkdownNode> CustomEmojiNodeMatcher = new RegexMatcher<MarkdownNode>(
         new Regex("<(a)?:(.+?):(\\d+?)>", DefaultRegexOptions),
         (_, m) => new EmojiNode(
-            Snowflake.Parse(m.Groups[3].Value),
+            Snowflake.TryParse(m.Groups[3].Value),
             m.Groups[2].Value,
             !string.IsNullOrWhiteSpace(m.Groups[1].Value)
         )

DiscordChatExporter.Core/Markdown/UnixTimestampNode.cs

@@ -2,5 +2,5 @@
 
 namespace DiscordChatExporter.Core.Markdown;
 
-// Null means invalid date
+// Null date means invalid timestamp
 internal record UnixTimestampNode(DateTimeOffset? Date) : MarkdownNode;