Handle invalid dates more gracefully

Closes #766

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

@@ -159,12 +159,18 @@ internal partial class HtmlMarkdownVisitor : MarkdownVisitor
 
     protected override MarkdownNode VisitUnixTimestamp(UnixTimestampNode timestamp)
     {
+        var dateString = timestamp.Date is not null
+            ? _context.FormatDate(timestamp.Date.Value)
+            : "Invalid date";
+
         // Timestamp tooltips always use full date regardless of the configured format
-        var longDateString = timestamp.Value.ToLocalString("dddd, MMMM d, yyyy h:mm tt");
+        var longDateString = timestamp.Date is not null
+            ? timestamp.Date.Value.ToLocalString("dddd, MMMM d, yyyy h:mm tt")
+            : "Invalid date";
 
         _buffer
             .Append($"<span class=\"timestamp\" title=\"{HtmlEncode(longDateString)}\">")
-            .Append(HtmlEncode(_context.FormatDate(timestamp.Value)))
+            .Append(HtmlEncode(dateString))
             .Append("</span>");
 
         return base.VisitUnixTimestamp(timestamp);

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

@@ -73,7 +73,9 @@ internal partial class PlainTextMarkdownVisitor : MarkdownVisitor
     protected override MarkdownNode VisitUnixTimestamp(UnixTimestampNode timestamp)
     {
         _buffer.Append(
-            _context.FormatDate(timestamp.Value)
+            timestamp.Date is not null
+                ? _context.FormatDate(timestamp.Date.Value)
+                : "Invalid date"
         );
 
         return base.VisitUnixTimestamp(timestamp);

DiscordChatExporter.Core/Markdown/Parsing/MarkdownParser.cs

@@ -235,7 +235,7 @@ internal static partial class MarkdownParser
 
     // Capture <t:12345678> or <t:12345678:R>
     private static readonly IMatcher<MarkdownNode> UnixTimestampNodeMatcher = new RegexMatcher<MarkdownNode>(
-        new Regex("<t:(\\d+)(?::\\w)?>", DefaultRegexOptions),
+        new Regex("<t:(-?\\d+)(?::\\w)?>", DefaultRegexOptions),
         (_, m) =>
         {
             // TODO: support formatting parameters
@@ -244,17 +244,19 @@ internal static partial class MarkdownParser
             if (!long.TryParse(m.Groups[1].Value, NumberStyles.Integer, CultureInfo.InvariantCulture,
                     out var offset))
             {
-                return null;
+                return new UnixTimestampNode(null);
             }
 
-            // Bound check
+            try
+            {
+                return new UnixTimestampNode(DateTimeOffset.UnixEpoch + TimeSpan.FromSeconds(offset));
+            }
             // https://github.com/Tyrrrz/DiscordChatExporter/issues/681
-            if (offset < TimeSpan.MinValue.TotalSeconds || offset > TimeSpan.MaxValue.TotalSeconds)
+            // https://github.com/Tyrrrz/DiscordChatExporter/issues/766
+            catch (Exception ex) when (ex is ArgumentOutOfRangeException or OverflowException)
             {
-                return null;
+                return new UnixTimestampNode(null);
             }
-
-            return new UnixTimestampNode(DateTimeOffset.UnixEpoch + TimeSpan.FromSeconds(offset));
         }
     );
 

DiscordChatExporter.Core/Markdown/UnixTimestampNode.cs

@@ -2,4 +2,5 @@
 
 namespace DiscordChatExporter.Core.Markdown;
 
-internal record UnixTimestampNode(DateTimeOffset Value) : MarkdownNode;
+// Null means invalid date
+internal record UnixTimestampNode(DateTimeOffset? Date) : MarkdownNode;