Fixed some issues highlighted by CoPilot PR review agent

src/HackerNews.BestStories.Api/UtcIso8601DateTimeOffsetConverter.cs

@@ -5,8 +5,27 @@ namespace HackerNews.BestStories.Api;
 
 internal sealed class UtcIso8601DateTimeOffsetConverter : JsonConverter<DateTimeOffset>
 {
+    private static readonly string[] Iso8601Formats =
+    [
+        "yyyy-MM-dd'T'HH:mm:ssK",
+        "yyyy-MM-dd'T'HH:mm:ss.FFFFFFFK"
+    ];
+
     public override DateTimeOffset Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
-        => DateTimeOffset.Parse(reader.GetString()!);
+    {
+        var value = reader.GetString()!;
+        if (!DateTimeOffset.TryParseExact(
+                value,
+                Iso8601Formats,
+                System.Globalization.CultureInfo.InvariantCulture,
+                System.Globalization.DateTimeStyles.None,
+                out var result))
+        {
+            throw new FormatException($"The value '{value}' is not a valid ISO-8601 date/time offset.");
+        }
+
+        return result;
+    }
 
     public override void Write(Utf8JsonWriter writer, DateTimeOffset value, JsonSerializerOptions options)
         => writer.WriteStringValue(value.ToUniversalTime()

src/HackerNews.BestStories.Blazor/Components/Pages/Home.razor

@@ -1,5 +1,6 @@
 @page "/"
 @rendermode InteractiveServer
+@using System.Globalization
 @inject BestStoriesClient Api
 
 <PageTitle>Hacker News Best Stories</PageTitle>
@@ -143,5 +144,5 @@
     private void LastPage() => page = PageCount;
 
     private static string FormatTime(DateTimeOffset value)
-        => value.ToUniversalTime().ToString("yyyy-MM-dd'T'HH:mm:ss+00:00");
+        => value.ToUniversalTime().ToString("yyyy-MM-dd'T'HH:mm:ss+00:00", CultureInfo.InvariantCulture);
 }

src/HackerNews.BestStories.React/Directory.Build.props

@@ -1,6 +1,6 @@
 <Project>
-    <!-- Do not inherit TargetFramework / TreatWarningsAsErrors from the repo root. -->
-    <!-- Repo-level Directory.Build.props sets <TargetFramework>net10.0</TargetFramework> for every project. That is wrong for an .esproj -->
+    <!-- MSBuild automatically loads only the nearest Directory.Build.props. -->
+    <!-- This file does not import the repo root props, keeping their TargetFramework and warning settings out of the .esproj. -->
     <PropertyGroup Condition="'$(MSBuildProjectExtension)' == '.esproj'">
         <TreatWarningsAsErrors>false</TreatWarningsAsErrors>
     </PropertyGroup>

tests/HackerNews.BestStories.Api.Tests/Serialization/UtcIso8601DateTimeOffsetConverterTests.cs

@@ -54,10 +54,60 @@ public void Read_ParsesIso8601ValueWithExplicitOffset()
         Assert.Equal(new DateTimeOffset(2025, 1, 2, 3, 4, 5, TimeSpan.FromHours(2)), result);
     }
 
-    [Fact]
-    public void Read_ThrowsFormatException_ForMalformedValue()
+    [Theory]
+    [InlineData("en-US")]
+    [InlineData("ar-SA")]
+    [InlineData("th-TH")]
+    public void Read_ParsesInvariantValues_PreservingInstantAndOffset(string culture)
+    {
+        var previous = System.Globalization.CultureInfo.CurrentCulture;
+        try
+        {
+            System.Globalization.CultureInfo.CurrentCulture = new System.Globalization.CultureInfo(culture);
+            (string Text, int OffsetMinutes, long FractionTicks)[] cases =
+            [
+                ("2025-01-02T03:04:05Z", 0, 0),
+                ("2025-01-02T03:04:05+02:00", 120, 0),
+                ("2025-01-02T03:04:05.1234567Z", 0, 1234567),
+                ("2025-01-02T03:04:05.1234567+02:00", 120, 1234567),
+                ("2025-01-02T03:04:05.123-05:30", -330, 1230000)
+            ];
+
+            foreach (var (text, offsetMinutes, fractionTicks) in cases)
+            {
+                var expected = new DateTimeOffset(2025, 1, 2, 3, 4, 5, TimeSpan.FromMinutes(offsetMinutes))
+                    .AddTicks(fractionTicks);
+                var result = DeserializeDateTimeOffset(JsonSerializer.Serialize(text));
+
+                Assert.Equal(expected, result);
+                Assert.Equal(expected.Offset, result.Offset);
+            }
+        }
+        finally
+        {
+            System.Globalization.CultureInfo.CurrentCulture = previous;
+        }
+    }
+
+    [Theory]
+    [InlineData("en-US")]
+    [InlineData("ar-SA")]
+    [InlineData("th-TH")]
+    public void Read_ThrowsFormatException_ForMalformedValue(string culture)
     {
-        Assert.Throws<FormatException>(() => DeserializeDateTimeOffset("\"not-a-date\""));
+        var previous = System.Globalization.CultureInfo.CurrentCulture;
+        try
+        {
+            System.Globalization.CultureInfo.CurrentCulture = new System.Globalization.CultureInfo(culture);
+            Assert.Throws<FormatException>(() =>
+            {
+                DeserializeDateTimeOffset("\"not-a-date\"");
+            });
+        }
+        finally
+        {
+            System.Globalization.CultureInfo.CurrentCulture = previous;
+        }
     }
 
     private DateTimeOffset DeserializeDateTimeOffset(string json)

tests/HackerNews.BestStories.Blazor.Tests/Components/HomeTests.cs

@@ -1,3 +1,4 @@
+using System.Globalization;
 using System.Net;
 using System.Text;
 using AwesomeAssertions;
@@ -70,27 +71,43 @@ public void Renders_error_state_when_service_throws()
         cut.Markup.Should().Contain("No stories to display.");
     }
 
-    [Fact]
-    public void Renders_story_time_in_utc_format()
+    [Theory]
+    [InlineData("en-US")]
+    [InlineData("ar-SA")]
+    [InlineData("th-TH")]
+    public void Renders_story_time_in_utc_format(string cultureName)
     {
-        const string json = """
-                            [{
-                              "title":"Story",
-                              "uri":"https://example.com/1",
-                              "postedBy":"author",
-                              "time":"2024-01-02T03:04:05+02:00",
-                              "score":10,
-                              "commentCount":2
-                            }]
-                            """;
-        var handler = new StaticHandler(HttpStatusCode.OK, json);
-        Services.AddSingleton(new BestStoriesClient(
-            new HttpClient(handler) { BaseAddress = new Uri("http://api/") },
-            _ => TimeSpan.Zero));
-
-        var cut = Render<Home>();
-
-        cut.Markup.Should().Contain("2024-01-02T01:04:05+00:00");
+        var originalCulture = CultureInfo.CurrentCulture;
+        var originalUiCulture = CultureInfo.CurrentUICulture;
+        try
+        {
+            CultureInfo.CurrentCulture = CultureInfo.GetCultureInfo(cultureName);
+            CultureInfo.CurrentUICulture = CultureInfo.GetCultureInfo(cultureName);
+
+            const string json = """
+                                [{
+                                  "title":"Story",
+                                  "uri":"https://example.com/1",
+                                  "postedBy":"author",
+                                  "time":"2024-01-02T03:04:05+02:00",
+                                  "score":10,
+                                  "commentCount":2
+                                }]
+                                """;
+            var handler = new StaticHandler(HttpStatusCode.OK, json);
+            Services.AddSingleton(new BestStoriesClient(
+                new HttpClient(handler) { BaseAddress = new Uri("http://api/") },
+                _ => TimeSpan.Zero));
+
+            var cut = Render<Home>();
+
+            cut.Find("tbody td.mono").TextContent.Should().Be("2024-01-02T01:04:05+00:00");
+        }
+        finally
+        {
+            CultureInfo.CurrentCulture = originalCulture;
+            CultureInfo.CurrentUICulture = originalUiCulture;
+        }
     }
 
     [Fact]