using System.ComponentModel.DataAnnotations;

WebApplicationBuilder builder = WebApplication.CreateBuilder(args);

builder.Services.AddValidation();

WebApplication app = builder. Build();

app.MapPost("/employees", (Employee employee) =>
{
    return Results.Ok(employee);
});

app.Run();

public class Employee : IValidatableObject
{
    public string Name { get; set; }

    public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
    {
        if (string.IsNullOrEmpty(Name))
        {
            yield return new ValidationResult("Name cannot be null or empty.", [nameof(Name)]);
        }
    }
}

app.MapPost("/employees", (Employee employee) =>
{
    var validationResults = new List<ValidationResult>();
    var validationContext = new ValidationContext(employee);

    if (!Validator.TryValidateObject(employee, validationContext, validationResults, validateAllProperties: true))
    {
        return Results.ValidationProblem(validationResults.ToDictionary(
            x => x.MemberNames.FirstOrDefault() ?? "",
            x => new[] { x.ErrorMessage ?? "Invalid value." }));
    }

    return Results.Ok(employee);
});