MilliSim/backend/MilliSim.Api/Common/Models/BeijingTimeConverter.cs

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

namespace MilliSim.Common.Models;

/// <summary>
/// 北京时间（UTC+8）JSON转换器
/// 将 DateTime 序列化为北京时间格式 "yyyy-MM-dd HH:mm:ss"
/// </summary>
public class BeijingTimeConverter : JsonConverter<DateTime>
{
    /// <summary>
    /// 北京时区信息（UTC+8）
    /// </summary>
    private static readonly TimeZoneInfo BeijingTimeZone = TimeZoneInfo.FindSystemTimeZoneById(
        OperatingSystem.IsWindows() ? "China Standard Time" : "Asia/Shanghai");

    /// <summary>
    /// 北京时间格式
    /// </summary>
    private const string DateTimeFormat = "yyyy-MM-dd HH:mm:ss";

    /// <summary>
    /// 读取JSON并转换为DateTime
    /// </summary>
    /// <param name="reader">JSON读取器</param>
    /// <param name="typeToConvert">要转换的类型</param>
    /// <param name="options">序列化选项</param>
    /// <returns>DateTime对象</returns>
    public override DateTime Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
        // 读取字符串值
        var dateString = reader.GetString();
        if (string.IsNullOrEmpty(dateString))
            return DateTime.MinValue;

        // 尝试解析为北京时间
        if (DateTime.TryParseExact(dateString, DateTimeFormat, CultureInfo.InvariantCulture, DateTimeStyles.None, out var result))
        {
            // 将北京时间转换为本地时间（按Kind处理）
            return DateTime.SpecifyKind(result, DateTimeKind.Local);
        }

        // 兜底：使用默认解析
        return DateTime.Parse(dateString, CultureInfo.InvariantCulture);
    }

    /// <summary>
    /// 将DateTime写入JSON（转换为北京时间格式）
    /// </summary>
    /// <param name="writer">JSON写入器</param>
    /// <param name="value">DateTime值</param>
    /// <param name="options">序列化选项</param>
    public override void Write(Utf8JsonWriter writer, DateTime value, JsonSerializerOptions options)
    {
        // 将DateTime转换为北京时间
        DateTime beijingTime;
        if (value.Kind == DateTimeKind.Utc)
        {
            // UTC时间转换为北京时间
            beijingTime = TimeZoneInfo.ConvertTimeFromUtc(value, BeijingTimeZone);
        }
        else if (value.Kind == DateTimeKind.Unspecified)
        {
            // 未指定类型的时间，假定为本地时间并转换为北京时间
            beijingTime = TimeZoneInfo.ConvertTime(value, BeijingTimeZone);
        }
        else
        {
            // 已经是本地时间，转换为北京时间
            beijingTime = TimeZoneInfo.ConvertTime(value, BeijingTimeZone);
        }

        // 格式化为 "yyyy-MM-dd HH:mm:ss" 并写入
        writer.WriteStringValue(beijingTime.ToString(DateTimeFormat, CultureInfo.InvariantCulture));
    }
}

/// <summary>
/// 可空DateTime的北京时间JSON转换器
/// </summary>
public class NullableBeijingTimeConverter : JsonConverter<DateTime?>
{
    /// <summary>
    /// 北京时区信息（UTC+8）
    /// </summary>
    private static readonly TimeZoneInfo BeijingTimeZone = TimeZoneInfo.FindSystemTimeZoneById(
        OperatingSystem.IsWindows() ? "China Standard Time" : "Asia/Shanghai");

    /// <summary>
    /// 北京时间格式
    /// </summary>
    private const string DateTimeFormat = "yyyy-MM-dd HH:mm:ss";

    /// <summary>
    /// 读取JSON并转换为可空DateTime
    /// </summary>
    public override DateTime? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
        if (reader.TokenType == JsonTokenType.Null)
            return null;

        var dateString = reader.GetString();
        if (string.IsNullOrEmpty(dateString))
            return null;

        if (DateTime.TryParseExact(dateString, DateTimeFormat, CultureInfo.InvariantCulture, DateTimeStyles.None, out var result))
        {
            return DateTime.SpecifyKind(result, DateTimeKind.Local);
        }

        return DateTime.Parse(dateString, CultureInfo.InvariantCulture);
    }

    /// <summary>
    /// 将可空DateTime写入JSON（转换为北京时间格式）
    /// </summary>
    public override void Write(Utf8JsonWriter writer, DateTime? value, JsonSerializerOptions options)
    {
        if (value == null)
        {
            writer.WriteNullValue();
            return;
        }

        // 将DateTime转换为北京时间
        DateTime beijingTime;
        var dt = value.Value;
        if (dt.Kind == DateTimeKind.Utc)
        {
            beijingTime = TimeZoneInfo.ConvertTimeFromUtc(dt, BeijingTimeZone);
        }
        else if (dt.Kind == DateTimeKind.Unspecified)
        {
            beijingTime = TimeZoneInfo.ConvertTime(dt, BeijingTimeZone);
        }
        else
        {
            beijingTime = TimeZoneInfo.ConvertTime(dt, BeijingTimeZone);
        }

        writer.WriteStringValue(beijingTime.ToString(DateTimeFormat, CultureInfo.InvariantCulture));
    }
}