Add PocketBase client with contracts and sharp build tooling

Elternbeirat.PocketBase/LocalDateTimeConverter.cs

@@ -0,0 +1,75 @@
+using System.Globalization;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace Elternbeirat.PocketBase;
+
+/// <summary>
+/// Shared parsing of a PocketBase date string as wall-clock time. The trailing
+/// "Z" is stripped rather than honoured, so the number is taken at face value and
+/// the result carries <see cref="DateTimeKind.Unspecified"/> -- no timezone shift.
+/// </summary>
+internal static class WallClock
+{
+    public static DateTime Parse(string raw)
+    {
+        // Drop a trailing "Z" so DateTime.Parse does not treat the value as UTC
+        // and convert it to local time (which would shift 19:30 to 20:30/21:30).
+        var value = raw.EndsWith('Z') ? raw[..^1] : raw;
+        var parsed = DateTime.Parse(value, CultureInfo.InvariantCulture,
+            DateTimeStyles.None);
+        return DateTime.SpecifyKind(parsed, DateTimeKind.Unspecified);
+    }
+}
+
+/// <summary>
+/// Reads PocketBase date values as local wall-clock time.
+/// <para>
+/// PocketBase stores every date in UTC and serializes it with a trailing "Z"
+/// (e.g. "2026-10-08 19:30:00.000Z"). By project convention the stored number
+/// IS the local time (Europe/Berlin) and the "Z" is ignored -- see the timezone
+/// decision in the data model. This converter therefore parses the value and
+/// returns it as an <see cref="DateTimeKind.Unspecified"/> instant, so no
+/// timezone shift is ever applied when the value is later formatted.
+/// </para>
+/// </summary>
+public sealed class LocalDateTimeConverter : JsonConverter<DateTime>
+{
+    public override DateTime Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+    {
+        var raw = reader.GetString();
+        return string.IsNullOrEmpty(raw) 
+            ? default 
+            : WallClock.Parse(raw);
+    }
+
+    public override void Write(Utf8JsonWriter writer, DateTime value, JsonSerializerOptions options)
+        => writer.WriteStringValue(value.ToString("yyyy-MM-dd HH:mm:ss.fff'Z'",
+            CultureInfo.InvariantCulture));
+}
+
+/// <summary>
+/// Nullable counterpart of <see cref="LocalDateTimeConverter"/>. PocketBase sends
+/// an empty string for an unset optional date (e.g. an event without an end);
+/// that maps to null.
+/// </summary>
+public sealed class NullableLocalDateTimeConverter : JsonConverter<DateTime?>
+{
+    public override DateTime? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+    {
+        var raw = reader.GetString();
+        if (string.IsNullOrEmpty(raw))
+            return null;
+
+        return WallClock.Parse(raw);
+    }
+
+    public override void Write(Utf8JsonWriter writer, DateTime? value, JsonSerializerOptions options)
+    {
+        if (value is null)
+            writer.WriteStringValue("");
+        else
+            writer.WriteStringValue(value.Value.ToString("yyyy-MM-dd HH:mm:ss.fff'Z'",
+                CultureInfo.InvariantCulture));
+    }
+}