132 lines
5.0 KiB
C#
132 lines
5.0 KiB
C#
using System.Globalization;
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using System.Text.Json;
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using System.Text.Json.Serialization;
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namespace Elternbeirat.PocketBase;
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/// <summary>
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/// Converts between PocketBase date strings and Europe/Berlin wall-clock time.
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/// </summary>
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/// <remarks>
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/// PocketBase stores every date in UTC and serializes it with a trailing <c>Z</c>
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/// (e.g. <c>"2026-10-08 17:30:00.000Z"</c>). The values produced here are local
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/// wall-clock numbers: an editor who typed 19:30 in the admin form gets 19:30 back,
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/// with daylight saving applied by the time zone. They carry
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/// <see cref="DateTimeKind.Unspecified"/> so that no later formatting shifts them again.
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/// </remarks>
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internal static class WallClock
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{
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/// <summary>
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/// IANA id; resolves on every platform .NET supports, Windows included.
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/// </summary>
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private static readonly TimeZoneInfo Berlin =
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TimeZoneInfo.FindSystemTimeZoneById("Europe/Berlin");
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/// <summary>
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/// Parses a PocketBase UTC date string into Berlin wall-clock time.
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/// </summary>
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/// <param name="raw">
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/// The raw PocketBase value; may be <see langword="null"/> or empty.
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/// </param>
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/// <returns>
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/// The Berlin wall-clock time with <see cref="DateTimeKind.Unspecified"/>, or
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/// <see langword="null"/> if <paramref name="raw"/> is <see langword="null"/> or empty
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/// (PocketBase's representation of an unset date).
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/// </returns>
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/// <exception cref="FormatException">
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/// <paramref name="raw"/> is not a valid date string.
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/// </exception>
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public static DateTime? Parse(string? raw) =>
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string.IsNullOrEmpty(raw)
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? null
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: TimeZoneInfo.ConvertTime(
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DateTimeOffset.Parse(raw, CultureInfo.InvariantCulture), Berlin).DateTime;
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/// <summary>
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/// Formats a Berlin wall-clock time as the UTC string PocketBase stores.
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/// Inverse of <see cref="Parse"/>.
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/// </summary>
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/// <param name="berlin">
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/// A Berlin wall-clock time. Its <see cref="DateTime.Kind"/> is ignored, and the
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/// value is always interpreted as Berlin local time.
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/// </param>
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/// <returns>
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/// The UTC value in PocketBase format, e.g. <c>"2026-10-08 17:30:00.000Z"</c>.
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/// </returns>
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/// <exception cref="ArgumentException">
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/// <paramref name="berlin"/> does not exist in Berlin, because it falls in the
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/// daylight-saving gap in spring.
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/// </exception>
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public static string Format(DateTime berlin) =>
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TimeZoneInfo.ConvertTimeToUtc(DateTime.SpecifyKind(berlin, DateTimeKind.Unspecified), Berlin)
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.ToString("yyyy-MM-dd HH:mm:ss.fff'Z'", CultureInfo.InvariantCulture);
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}
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/// <summary>
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/// JSON converter that reads and writes PocketBase dates as Europe/Berlin
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/// wall-clock <see cref="DateTime"/> values.
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/// </summary>
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/// <remarks>
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/// An empty string (unset date) is read as <see langword="default"/>(<see cref="DateTime"/>).
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/// For optional dates, use <see cref="NullableLocalDateTimeConverter"/> instead.
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/// </remarks>
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/// <example>
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/// <code>
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/// [JsonConverter(typeof(LocalDateTimeConverter))]
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/// public DateTime Start { get; init; }
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/// </code>
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/// </example>
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/// <seealso cref="WallClock"/>
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public sealed class LocalDateTimeConverter : JsonConverter<DateTime>
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{
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/// <inheritdoc/>
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public override DateTime Read(
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ref Utf8JsonReader reader,
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Type typeToConvert,
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JsonSerializerOptions options)
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=> WallClock.Parse(reader.GetString()) ?? default;
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/// <inheritdoc/>
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public override void Write(
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Utf8JsonWriter writer,
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DateTime value,
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JsonSerializerOptions options)
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=> writer.WriteStringValue(WallClock.Format(value));
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}
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/// <summary>
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/// JSON converter that reads and writes optional PocketBase dates as Europe/Berlin
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/// wall-clock <see cref="DateTime"/> values.
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/// </summary>
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/// <remarks>
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/// PocketBase sends an empty string for an unset optional date (e.g. an event
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/// without an end). This value, like JSON <c>null</c>, is read as <see langword="null"/>.
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/// </remarks>
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/// <example>
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/// <code>
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/// [JsonConverter(typeof(NullableLocalDateTimeConverter))]
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/// public DateTime? End { get; init; }
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/// </code>
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/// </example>
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/// <seealso cref="WallClock"/>
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public sealed class NullableLocalDateTimeConverter : JsonConverter<DateTime?>
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{
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/// <inheritdoc/>
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public override DateTime? Read(
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ref Utf8JsonReader reader,
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Type typeToConvert,
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JsonSerializerOptions options)
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=> WallClock.Parse(reader.GetString());
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/// <inheritdoc/>
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/// <remarks>
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/// Only called for non-null values: <see cref="JsonConverter{T}.HandleNull"/> is
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/// <see langword="false"/>, so the serializer writes <see langword="null"/> itself.
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/// </remarks>
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public override void Write(
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Utf8JsonWriter writer,
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DateTime? value,
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JsonSerializerOptions options)
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=> writer.WriteStringValue(WallClock.Format(value ?? throw new ArgumentNullException(nameof(value))));
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}
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