Initial commit

src/PowderCoating.Web/Extensions/DateTimeExtensions.cs

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+namespace PowderCoating.Web.Extensions;
+
+/// <summary>
+/// Converts UTC DateTimes to a specific IANA or Windows timezone for display.
+/// .NET 6+ accepts both timezone ID formats on all platforms.
+/// Falls back to the original value when the ID is null, empty, or unrecognised.
+/// </summary>
+public static class DateTimeExtensions
+{
+    /// <summary>Converts a UTC DateTime to the specified timezone (IANA or Windows ID).</summary>
+    public static DateTime Tz(this DateTime utc, string? ianaTimeZone)
+    {
+        if (string.IsNullOrWhiteSpace(ianaTimeZone)) return utc;
+        try
+        {
+            var tzi = TimeZoneInfo.FindSystemTimeZoneById(ianaTimeZone);
+            var normalized = utc.Kind == DateTimeKind.Unspecified
+                ? DateTime.SpecifyKind(utc, DateTimeKind.Utc)
+                : utc.ToUniversalTime();
+            return TimeZoneInfo.ConvertTimeFromUtc(normalized, tzi);
+        }
+        catch
+        {
+            return utc;
+        }
+    }
+}