Add post and event cards, shared calendar sheet and per-event ICS; rework past events and next-event card

Elternbeirat.Web/Features/Events/EventDateFormat.cs

@@ -7,8 +7,10 @@ namespace Elternbeirat.Web.Features.Events;
 ///     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.
+///     Shared by the full event list, the home-page events embed and the next-event
+///     card, so all render dates the same way: <see cref="Range"/> as the full date,
+///     the <c>Sheet…</c> methods and <see cref="Span"/> for the calendar sheet and the
+///     time line beside it, <see cref="PastDays"/> and <see cref="PastTime"/> for the list of past events.
 ///     <para>
 ///         This is the event counterpart to
 ///         <see cref="Posts.PostDateFormat"/>, which formats a plain
@@ -27,6 +29,11 @@ public static class EventDateFormat
     /// </summary>
     private const string ShortDate = "d. MMMM yyyy";
 
+    /// <summary>
+    ///     Date format for the list of past events, which is grouped by year.
+    /// </summary>
+    private const string DayMonth = "d. MMMM";
+
     /// <summary>
     ///     Formats the date range of an event.
     /// </summary>
@@ -54,13 +61,136 @@ public static class EventDateFormat
             (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",
+                => $"{start.ToString(LongDate, Cultures.German)}, {Clock(start)}–{Clock(end)} 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>
+    ///     The short month for the top band of a calendar sheet.
+    /// </summary>
+    /// <param name="value">The event's start.</param>
+    /// <returns>The German short month without its period, e.g. <c>Okt</c> or <c>März</c>.</returns>
+    /// <remarks>
+    ///     Returned in normal case; the sheet's CSS sets it in capitals. The period of the
+    ///     abbreviation (<c>Okt.</c>) is dropped because on a sheet it reads as a stray dot.
+    /// </remarks>
+    /// <seealso cref="CalendarSheet"/>
+    public static string SheetMonth(DateTime value)
+        => value.ToString("MMM", Cultures.German).TrimEnd('.');
+
+    /// <summary>
+    ///     The day of the month for the large number on a calendar sheet.
+    /// </summary>
+    /// <param name="value">The event's start.</param>
+    /// <returns>The day without a leading zero, e.g. <c>8</c>.</returns>
+    public static string SheetDay(DateTime value)
+        => value.Day.ToString(Cultures.German);
+
+    /// <summary>
+    ///     The short weekday for the bottom of a calendar sheet.
+    /// </summary>
+    /// <param name="value">The event's start.</param>
+    /// <returns>The German short weekday without its period, e.g. <c>Do</c>.</returns>
+    public static string SheetWeekday(DateTime value)
+        => value.ToString("ddd", Cultures.German).TrimEnd('.');
+
+    /// <summary>
+    ///     The time line beside a calendar sheet: what the sheet itself cannot show.
+    /// </summary>
+    /// <param name="event">The event to format.</param>
+    /// <returns>
+    ///     Depending on <see cref="Event.End"/> and <see cref="Event.HasTime"/>:
+    ///     <list type="bullet">
+    ///         <item><description>No end: <c>19:30 Uhr</c></description></item>
+    ///         <item><description>Same day: <c>19:30–21:00 Uhr</c></description></item>
+    ///         <item><description>Several days: <c>09:00 Uhr bis Sonntag, 11. Oktober 2026, 13:00 Uhr</c></description></item>
+    ///         <item><description>Several days, no time: <c>bis Sonntag, 11. Oktober 2026</c></description></item>
+    ///         <item><description>One day, no time: an empty string; the sheet says it all.</description></item>
+    ///     </list>
+    /// </returns>
+    /// <remarks>
+    ///     The sheet shows the start day only, so a multi-day event must name its last
+    ///     day here, with the weekday, as the sheet does for the first one.
+    /// </remarks>
+    public static string Span(Event @event)
+        => (@event.Start, @event.End, @event.HasTime) switch
+        {
+            (var start, { } end, var hasTime) when end.Date != start.Date
+                => (hasTime ? Clock(start) + " Uhr " : "") + "bis " + Stamp(end, LongDate, hasTime),
+            (var start, null, true)
+                => $"{Clock(start)} Uhr",
+            (var start, { } end, true)
+                => $"{Clock(start)}–{Clock(end)} Uhr",
+            _ => "",
+        };
+
+    /// <summary>
+    ///     The day column of a past event in the folded-up list on the events page.
+    /// </summary>
+    /// <param name="event">The event to format.</param>
+    /// <returns>
+    ///     Day and full month, depending on <see cref="Event.End"/>:
+    ///     <list type="bullet">
+    ///         <item><description>One day: <c>13. November</c></description></item>
+    ///         <item><description>Several days in one month: <c>8.–9. Februar</c></description></item>
+    ///         <item><description>Across a month: <c>30. Januar – 2. Februar</c></description></item>
+    ///         <item><description>Across a year: <c>30. Dezember – 2. Januar 2027</c></description></item>
+    ///     </list>
+    /// </returns>
+    /// <remarks>
+    ///     The list is grouped by the start year under its own small heading, so the
+    ///     year is only named where the end leaves that year. The weekday is left out
+    ///     to keep the column short; the time follows the title (<see cref="PastTime"/>).
+    /// </remarks>
+    public static string PastDays(Event @event)
+        => (@event.Start, @event.End) switch
+        {
+            (var start, { } end) when end.Year != start.Year
+                => $"{start.ToString(DayMonth, Cultures.German)} – {end.ToString(ShortDate, Cultures.German)}",
+            (var start, { } end) when end.Month != start.Month
+                => $"{start.ToString(DayMonth, Cultures.German)} – {end.ToString(DayMonth, Cultures.German)}",
+            (var start, { } end) when end.Day != start.Day
+                => $"{start.Day.ToString(Cultures.German)}.–{end.ToString(DayMonth, Cultures.German)}",
+            (var start, _)
+                => start.ToString(DayMonth, Cultures.German),
+        };
+
+    /// <summary>
+    ///     The time after the title of a past event in the folded-up list.
+    /// </summary>
+    /// <param name="event">The event to format.</param>
+    /// <returns>
+    ///     Depending on <see cref="Event.HasTime"/> and <see cref="Event.End"/>:
+    ///     <list type="bullet">
+    ///         <item><description>No time: an empty string; nothing is shown.</description></item>
+    ///         <item><description>No end: <c>19:00 Uhr</c></description></item>
+    ///         <item><description>Same day: <c>19:00–21:00 Uhr</c></description></item>
+    ///         <item><description>Several days: the start time only, <c>09:00 Uhr</c></description></item>
+    ///     </list>
+    /// </returns>
+    /// <remarks>
+    ///     For several days the day column already shows the span; a time range beside
+    ///     it would read as the daily hours, so only the start time is given.
+    /// </remarks>
+    public static string PastTime(Event @event)
+        => (@event.HasTime, @event.End) switch
+        {
+            (false, _) => "",
+            (true, { } end) when end.Date != @event.Start.Date => $"{Clock(@event.Start)} Uhr",
+            _ => Span(@event),
+        };
+
+    /// <summary>
+    ///     Formats the clock time of a point in time.
+    /// </summary>
+    /// <param name="value">The date and time.</param>
+    /// <returns>The time as e.g. <c>19:30</c>.</returns>
+    private static string Clock(DateTime value)
+        => value.ToString("HH:mm", Cultures.German);
+
     /// <summary>
     ///     Formats a single point in time as a date with an optional time.
     /// </summary>