fix: fix datettime formatting

Author: igorrylko

src/Rh.MessageFormat.CldrGenerator/Generators/LocaleDataCollector.DatePatterns.cs

@@ -91,18 +91,33 @@ private async Task CollectDatePatternsAsync(Dictionary<string, LocaleData> local
             return icuPattern;
 
         var result = icuPattern;
-        result = Regex.Replace(result, @"y{5,}", "yyyy");
-        result = Regex.Replace(result, @"y{4}", "yyyy");
-        result = Regex.Replace(result, @"y{3}", "yyyy");
-        result = Regex.Replace(result, @"y{2}", "yy");
-        result = Regex.Replace(result, @"y{1}(?!y)", "yyyy");
+
+        // Remove ICU optional section markers [...] - keep the content, remove brackets
+        result = Regex.Replace(result, @"\[([^\]]*)\]", "$1");
+
+        // Remove ICU numeric prefix '#' (used for non-padded numbers)
+        result = Regex.Replace(result, @"#(?=[yMdHhms])", "");
+
+        // Convert year patterns: ICU y -> .NET y
+        // Use a single regex to avoid double-replacement issues
+        result = Regex.Replace(result, @"y+", m => m.Length == 2 ? "yy" : "yyyy");
+
+        // Convert day of week patterns
         result = Regex.Replace(result, @"E{4,}", "dddd");
         result = Regex.Replace(result, @"E{1,3}", "ddd");
         result = Regex.Replace(result, @"c{4,}", "dddd");
         result = Regex.Replace(result, @"c{1,3}", "ddd");
+
+        // Convert day period patterns
         result = Regex.Replace(result, @"a+", "tt");
+        // ICU 'B' (flexible day period like "in the morning") -> .NET 'tt' (AM/PM)
+        result = Regex.Replace(result, @"B+", "tt");
+
+        // Convert era patterns
         result = Regex.Replace(result, @"G{4,}", "gg");
         result = Regex.Replace(result, @"G{1,3}", "g");
+
+        // Convert standalone month patterns (L -> M)
         result = Regex.Replace(result, @"L{4,}", "MMMM");
         result = Regex.Replace(result, @"L{3}", "MMM");
         result = Regex.Replace(result, @"L{2}", "MM");

tests/Rh.MessageFormat.Tests/Ast/DateTimeTypeConversionTests.cs

@@ -123,6 +123,35 @@ public void Date_FromUnixMilliseconds_String_FormatsCorrectly()
         Assert.Contains("1", result); // January
     }
 
+    [Fact]
+    public void Date_FromUnixMilliseconds_NoExtraZeroInYear()
+    {
+        // Verify that formatting doesn't add extra zeros before the year
+        // 1704067200000 = January 1, 2024 00:00:00 UTC
+        var args = new Dictionary<string, object?> { { "d", 1704067200000L } };
+
+        var result = _formatter.FormatMessage("{d, date, short}", args);
+
+        // Should be like "1/1/24" or "1/1/2024", NOT "1/1/02024"
+        Assert.DoesNotContain("02024", result);
+        Assert.DoesNotContain("002024", result);
+    }
+
+    [Fact]
+    public void Date_FromUnixMilliseconds_UkrainianLocale_NoExtraZeroInYear()
+    {
+        // Bug fix: Ukrainian locale was generating "dd.MM.yyyyy" instead of "dd.MM.yy"
+        // This caused dates like "01.01.02024" instead of "01.01.24"
+        var ukFormatter = new MessageFormatter("uk", TestOptions.WithCommonLocales());
+        var args = new Dictionary<string, object?> { { "expiringDate", "1704067200000" } };
+
+        var result = ukFormatter.FormatMessage("{expiringDate, date, short}", args);
+
+        // Should be "01.01.24", NOT "01.01.02024"
+        Assert.DoesNotContain("02024", result);
+        Assert.Contains("24", result); // 2-digit year
+    }
+
     [Fact]
     public void Date_FromDateString_StillWorks()
     {