using System.Text.Json;
using System.Text.Json.Serialization;

namespace Elternbeirat.Contracts;

/// <summary>
///     JSON converter that reads and writes a PocketBase date as a calendar date
///     (<see cref="DateOnly"/>), keeping the day and dropping the time-of-day.
/// </summary>
/// <remarks>
///     PocketBase has no date-only field type: it stores every date as a UTC
///     instant with a time-of-day (e.g. an editor's <c>2 Jan 00:00</c> Berlin is
///     stored as <c>"2026-01-01 22:00:00.000Z"</c>). The day the editor meant is
///     therefore the day <em>in Berlin</em>, not the day of the raw UTC string. This
///     converter reuses the same UTC-&gt;Berlin conversion as
///     <see cref="LocalDateTimeConverter"/> and then keeps only the date, so the day
///     shown is the day that was entered -- with no time-of-day and no off-by-one.
/// </remarks>
/// <example>
///     Apply it to a calendar-day field of a contract:
/// <code>
///     [JsonConverter(typeof(DateOnlyConverter))]
///     public DateOnly Date { get; init; }
/// </code>
/// </example>
/// <seealso cref="WallClock"/>
public sealed class DateOnlyConverter : JsonConverter<DateOnly>
{
    /// <inheritdoc/>
    /// <exception cref="FormatException">
    ///     The stored value is not a valid date string.
    /// </exception>
    public override DateOnly Read(
        ref Utf8JsonReader reader,
        Type typeToConvert,
        JsonSerializerOptions options)
        => WallClock.Parse(reader.GetString()) is { } berlin
            ? DateOnly.FromDateTime(berlin)
            : default;

    /// <inheritdoc/>
    public override void Write(
        Utf8JsonWriter writer,
        DateOnly value,
        JsonSerializerOptions options)
        => writer.WriteStringValue(WallClock.Format(value.ToDateTime(TimeOnly.MinValue)));
}