Extract date rendering into per-feature Date components

Elternbeirat.Web/Features/Events/EventDateFormat.cs

@@ -0,0 +1,83 @@
+using Elternbeirat.Contracts;
+using Elternbeirat.Web.Shared;
+
+namespace Elternbeirat.Web.Features.Events;
+
+/// <summary>
+///     Formats the date range of an <see cref="Event"/> for display in German.
+/// </summary>
+/// <remarks>
+///     Shared by the full event list and the home-page events embed, so both render
+///     dates the same way.
+///     <para>
+///         This is the event counterpart to
+///         <see cref="Posts.PostDateFormat"/>, which formats a plain
+///         <see cref="DateOnly"/> day instead of a point-in-time range.
+///     </para>
+/// </remarks>
+public static class EventDateFormat
+{
+    /// <summary>
+    ///     Date format for the start, and for a single-day event.
+    /// </summary>
+    private const string LongDate = "dddd, d. MMMM yyyy";
+
+    /// <summary>
+    ///     Date format for the end of a multi-day event; the weekday is omitted.
+    /// </summary>
+    private const string ShortDate = "d. MMMM yyyy";
+
+    /// <summary>
+    ///     Formats the date range of an event.
+    /// </summary>
+    /// <param name="event">
+    ///     The event to format.
+    /// </param>
+    /// <returns>
+    ///     The formatted range, depending on <see cref="Event.End"/> and <see cref="Event.HasTime"/>:
+    ///     <list type="bullet">
+    ///         <item>
+    ///             <description>No end: <c>Donnerstag, 8. Oktober 2026, 19:30 Uhr</c></description>
+    ///         </item>
+    ///         <item>
+    ///             <description>Same day: <c>Donnerstag, 8. Oktober 2026, 19:30–21:00 Uhr</c></description>
+    ///         </item>
+    ///         <item>
+    ///             <description>Several days: <c>Freitag, 9. Oktober 2026 – 11. Oktober 2026</c></description>
+    ///         </item>
+    ///     </list>
+    ///     Without a time, the time parts are omitted.
+    /// </returns>
+    public static string Range(Event @event)
+        => (@event.Start, @event.End, @event.HasTime) switch
+        {
+            (var start, null, var hasTime)
+                => Stamp(start, LongDate, hasTime),
+            (var start, { } end, true) when end.Date == start.Date
+                => $"{start.ToString(LongDate, Cultures.German)}, {start.ToString("HH:mm", Cultures.German)}–{end.ToString("HH:mm", Cultures.German)} Uhr",
+            (var start, { } end, false) when end.Date == start.Date
+                => Stamp(start, LongDate, withTime: false),
+            (var start, { } end, var hasTime)
+                => $"{Stamp(start, LongDate, hasTime)} – {Stamp(end, ShortDate, hasTime)}",
+        };
+
+    /// <summary>
+    ///     Formats a single point in time as a date with an optional time.
+    /// </summary>
+    /// <param name="value">
+    ///     The date and time to format.
+    /// </param>
+    /// <param name="dateFormat">
+    ///     The date format, e.g. <see cref="LongDate"/>.
+    /// </param>
+    /// <param name="withTime">
+    ///     <see langword="true"/> to append the time, e.g. <c>, 19:30 Uhr</c>.
+    /// </param>
+    /// <returns>
+    ///     The formatted date, with the time if requested.
+    /// </returns>
+    private static string Stamp(DateTime value, string dateFormat, bool withTime)
+        => withTime
+            ? value.ToString(dateFormat + ", HH:mm", Cultures.German) + " Uhr"
+            : value.ToString(dateFormat, Cultures.German);
+}