public class PersonInput
{
    public string? Name { get; set; }
    public int? Age { get; set; }
    public string? Gender { get; set; }
}
public class PersonEntity
{
    public string Name { get; set; }
    public int Age { get; set; }
    public string Gender { get; set; }
}

[HttpPatch]
[Route("patch")]
public ActionResult Patch([FromForm] PersonInput input)
{
    // 測試代碼暫時(shí)將 AutoMapper 配置放在方法內(nèi)。
    var config = new MapperConfiguration(cfg =>
    {
        cfg.CreateMap<PersonInput, PersonEntity>());
    });
    var mapper = config.CreateMapper();
    // entity 從數(shù)據(jù)庫讀取，這里僅演示。
    var entity = new PersonEntity
    {
        Name = "姓名", // 可能會(huì)被改變
        Age = 18, // 可能會(huì)被改變
        Gender = "我可能會(huì)被改變",
    };
    // 如果客戶端只輸入 Name 字段，entity 的 Age 和 Gender 將不能被正確映射或被置為 null。
    mapper.Map(input, entity);
    return Ok();
}

curl --location --request PATCH 'http://localhost:5094/test/patch' \
--form 'Name="foo"'

var keys = _httpContextAccessor.HttpContext.Request.Form.Keys;
if(keys.Contains("Name"))
{
    // 更新 Name(這里忽略合法性判斷)
    entity.Name = input.Name!;
}
if (keys.Contains("Age"))
{
    // 更新 Age(這里忽略合法性判斷)
    entity.Age = input.Age!;
}
// ...

public abstract class PatchInput
{
    [BindNever]
    public ICollection<string>? PatchKeys { get; set; }
}

public class PersonInput : PatchInput
{
    public string? Name { get; set; }
    public int? Age { get; set; }
    public string? Gender { get; set; }
}

public class PatchModelBinder : IModelBinder
{
    private readonly IModelBinder _internalModelBinder;
    public PatchModelBinder(IModelBinder internalModelBinder)
    {
        _internalModelBinder = internalModelBinder;
    }
    public async Task BindModelAsync(ModelBindingContext bindingContext)
    {
        await _internalModelBinder.BindModelAsync(bindingContext);
        if (bindingContext.Model is PatchInput model)
        {
            // 將 Form 中的 Keys 保存在 PatchKeys 中
            model.PatchKeys = bindingContext.HttpContext.Request.Form.Keys;
        }
    }
}

public class PatchModelBinderFactory : IModelBinderFactory
{
    private ModelBinderFactory _modelBinderFactory;
    public PatchModelBinderFactory(
        IModelMetadataProvider metadataProvider,
        IOptions<MvcOptions> options,
        IServiceProvider serviceProvider)
    {
        _modelBinderFactory = new ModelBinderFactory(metadataProvider, options, serviceProvider);
    }
    public IModelBinder CreateBinder(ModelBinderFactoryContext context)
    {
        var modelBinder = _modelBinderFactory.CreateBinder(context);
        // ComplexObjectModelBinder 是 internal 類
        if (typeof(PatchInput).IsAssignableFrom(context.Metadata.ModelType)
            && modelBinder.GetType().ToString().EndsWith("ComplexObjectModelBinder"))
        {
            modelBinder = new PatchModelBinder(modelBinder);
        }
        return modelBinder;
    }
}

var builder = WebApplication.CreateBuilder(args);
// Add services to the container.
builder.Services.AddPatchMapper();

public static class PatchMapperExtensions
{
    public static IServiceCollection AddPatchMapper(this IServiceCollection services)
    {
        services.Replace(ServiceDescriptor.Singleton<IModelBinderFactory, PatchModelBinderFactory>());
        return services;
    }
}

[HttpPatch]
[Route("patch")]
public ActionResult Patch([FromForm] PersonInput input)
{
    // 不需要手工給 input.PatchKeys 賦值。
    return Ok();
}

public class PatchConverter<T> : ITypeConverter<PatchInput, T> where T : new()
{
    /// <inheritdoc />
    public T Convert(PatchInput source, T destination, ResolutionContext context)
    {
        destination ??= new T();
        var sourceType = source.GetType();
        var destinationType = typeof(T);
        foreach (var key in source.PatchKeys ?? Enumerable.Empty<string>())
        {
            var sourcePropertyInfo = sourceType.GetProperty(key, BindingFlags.IgnoreCase | BindingFlags.Public | BindingFlags.Instance);
            if (sourcePropertyInfo != null)
            {
                var destinationPropertyInfo = destinationType.GetProperty(key, BindingFlags.IgnoreCase | BindingFlags.Public | BindingFlags.Instance);
                if (destinationPropertyInfo != null)
                {
                    var sourceValue = sourcePropertyInfo.GetValue(source);
                    destinationPropertyInfo.SetValue(destination, sourceValue);
                }
            }
        }
        return destination;
    }
}

[HttpPatch]
[Route("patch")]
public ActionResult Patch([FromForm] PersonInput input)
{
    // 1. 目前僅支持 `FromForm`，即 `x-www-form_urlencoded` 和 `form-data`；暫不支持 `FromBody` 如 `raw` 等。
    // 2. 使用 ModelBinderFractory 創(chuàng)建 ModelBinder 而不是 ModelBinderProvider 以便于未來支持更多的輸入格式。
    // 3. 目前還沒有支持多級結(jié)構(gòu)。
    // 4. 測試代碼暫時(shí)將 AutoMapper 配置放在方法內(nèi)。
    var config = new MapperConfiguration(cfg =>
    {
        cfg.CreateMap<PersonInput, PersonEntity>().ConvertUsing(new PatchConverter<PersonEntity>());
    });
    var mapper = config.CreateMapper();
    // PersonEntity 有 3 個(gè)屬性，客戶端如果提供的參數(shù)參數(shù)不足 3 個(gè)，在 Map 時(shí)未提供參數(shù)的屬性值不會(huì)被改變。
    var entity = new PersonEntity
    {
        Name = "姓名",
        Age = 18,
        Gender = "如果客戶端沒有提供本參數(shù)，那我的值不會(huì)被改變"
    };
    mapper.Map(input, entity);
    return Ok();
}

curl --location --request PATCH 'http://localhost:5094/test/patch' \
--form 'Name="foo"'

curl --location --request PATCH 'http://localhost:5094/test/patch' \
--header 'Content-Type: application/x-www-form-urlencoded' \
--data-urlencode 'Name=foo'