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

namespace FoodLabeling.Application.Contracts.Json;

/// <summary>
/// 反序列化时兼容 JSON 字符串或字符串数组（取首个非空元素），用于前端误把单选字段传成数组的场景（如 <c>partnerId</c>）。
/// </summary>
public sealed class StringOrFirstArrayItemJsonConverter : JsonConverter<string?>
{
    public override string? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
        switch (reader.TokenType)
        {
            case JsonTokenType.Null:
                return null;
            case JsonTokenType.String:
                return reader.GetString();
            case JsonTokenType.StartArray:
            {
                string? first = null;
                while (reader.Read())
                {
                    if (reader.TokenType == JsonTokenType.EndArray)
                    {
                        break;
                    }

                    if (reader.TokenType == JsonTokenType.Null)
                    {
                        continue;
                    }

                    if (reader.TokenType != JsonTokenType.String)
                    {
                        throw new JsonException("partnerId 数组元素必须是字符串");
                    }

                    var item = reader.GetString()?.Trim();
                    if (first is null && !string.IsNullOrWhiteSpace(item))
                    {
                        first = item;
                    }
                }

                return first;
            }
            default:
                throw new JsonException($"无法将 JSON token {reader.TokenType} 转为字符串（partnerId）");
        }
    }

    public override void Write(Utf8JsonWriter writer, string? value, JsonSerializerOptions options)
    {
        if (value is null)
        {
            writer.WriteNullValue();
        }
        else
        {
            writer.WriteStringValue(value);
        }
    }
}