using FluentValidation;
using FluentValidation.AspNetCore;
using MicroElements.Swashbuckle.FluentValidation.AspNetCore;

var builder = WebApplication.CreateBuilder(args);
var services = builder.Services;

// Asp.Net stuff
services.AddControllers();
services.AddEndpointsApiExplorer();

// Add Swagger
services.AddSwaggerGen();

// Add FV
services.AddFluentValidationAutoValidation();
services.AddFluentValidationClientsideAdapters();

// Add FV validators
services.AddValidatorsFromAssemblyContaining<Program>();

// Add FV Rules to swagger
services.AddFluentValidationRulesToSwagger();

var app = builder.Build();

// Use Swagger
app.UseSwagger();
app.UseSwaggerUI();

app.MapControllers();

app.Run();

// This method gets called by the runtime. Use this method to add services to the container.
public void ConfigureServices(IServiceCollection services)
{
    // Asp.net stuff
    services.AddControllers();
    
    // HttpContextValidatorRegistry requires access to HttpContext
    services.AddHttpContextAccessor();

    // Register FV validators
    services.AddValidatorsFromAssemblyContaining<Startup>(lifetime: ServiceLifetime.Scoped);

    // Add FV to Asp.net
    services.AddFluentValidationAutoValidation();

    // Add swagger
    services.AddSwaggerGen(c =>
    {
        c.SwaggerDoc("v1", new OpenApiInfo { Title = "My API", Version = "v1" });
    });

    // [Optional] Add INameResolver (SystemTextJsonNameResolver will be registered by default)
    // services.AddSingleton<INameResolver, CustomNameResolver>();

    // Adds FluentValidationRules staff to Swagger. (Minimal configuration)
    services.AddFluentValidationRulesToSwagger();

    // [Optional] Configure generation options for your needs. Also can be done with services.Configure<SchemaGenerationOptions>
    // services.AddFluentValidationRulesToSwagger(options =>
    // {
    //     options.SetNotNullableIfMinLengthGreaterThenZero = true;
    //     options.UseAllOffForMultipleRules = true;
    // });

    // Adds logging
    services.AddLogging(builder => builder.AddConsole());
}

// This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
    app.UseRouting();

    app.UseEndpoints(endpoints =>
    {
        endpoints.MapControllers();
    });

    // Adds swagger
    app.UseSwagger();

    // Adds swagger UI
    app.UseSwaggerUI(c =>
    {
        c.SwaggerEndpoint("/swagger/v1/swagger.json", "My API V1");
    });
}

using MicroElements.OpenApi.FluentValidation.FileUpload;

public class UploadProductImageRequestValidator : AbstractValidator<UploadProductImageRequest>
{
    public UploadProductImageRequestValidator()
    {
        RuleFor(x => x.File)
            .NotNull()                                    // required
            .FileContentType("image/jpeg", "image/png")   // allowed media types
            .MaxFileSize(2 * 1024 * 1024);                // 2 MB
    }
}

new FluentValidationRule("Pattern")
{
    Matches = propertyValidator => propertyValidator is IRegularExpressionValidator,
    Apply = context =>
    {
        var regularExpressionValidator = (IRegularExpressionValidator)context.PropertyValidator;
        context.Schema.Properties[context.PropertyKey].Pattern = regularExpressionValidator.Expression;
    }
},

public class Sample
{
    public string PropertyWithNoRules { get; set; }

    public string NotNull { get; set; }
    public string NotEmpty { get; set; }
    public string EmailAddress { get; set; }
    public string RegexField { get; set; }

    public int ValueInRange { get; set; }
    public int ValueInRangeExclusive { get; set; }

    public float ValueInRangeFloat { get; set; }
    public double ValueInRangeDouble { get; set; }
}

public class SampleValidator : AbstractValidator<Sample>
{
    public SampleValidator()
    {
        RuleFor(sample => sample.NotNull).NotNull();
        RuleFor(sample => sample.NotEmpty).NotEmpty();
        RuleFor(sample => sample.EmailAddress).EmailAddress();
        RuleFor(sample => sample.RegexField).Matches(@"(\d{4})-(\d{2})-(\d{2})");

        RuleFor(sample => sample.ValueInRange).GreaterThanOrEqualTo(5).LessThanOrEqualTo(10);
        RuleFor(sample => sample.ValueInRangeExclusive).GreaterThan(5).LessThan(10);

        // WARNING: Swashbuckle implements minimum and maximim as int so you will loss fraction part of float and double numbers
        RuleFor(sample => sample.ValueInRangeFloat).InclusiveBetween(1.1f, 5.3f);
        RuleFor(sample => sample.ValueInRangeDouble).ExclusiveBetween(2.2, 7.5f);
    }
}

public class CustomerValidator : AbstractValidator<Customer>
{
    public CustomerValidator()
    {
        RuleFor(customer => customer.Surname).NotEmpty();
        RuleFor(customer => customer.Forename).NotEmpty().WithMessage("Please specify a first name");

        Include(new CustomerAddressValidator());
    }
}

internal class CustomerAddressValidator : AbstractValidator<Customer>
{
    public CustomerAddressValidator()
    {
        RuleFor(customer => customer.Address).Length(20, 250);
    }
}

public class CreateUserRequest
{
    public CreateUserParams User { get; set; }
}

public class CreateUserParams
{
    public string Email { get; set; }
    public string Name { get; set; }
}

public class CreateUserRequestValidator : AbstractValidator<CreateUserRequest>
{
    public CreateUserRequestValidator()
    {
        // Inline child rules — no separate validator class required
        RuleFor(x => x.User)
            .NotEmpty()
            .ChildRules(user =>
            {
                user.RuleFor(u => u.Email).NotEmpty().EmailAddress();
                user.RuleFor(u => u.Name).NotEmpty().MaximumLength(510);
            });

        // Equivalent with a standalone validator:
        // RuleFor(x => x.User).NotEmpty().SetValidator(new CreateUserParamsValidator());
    }
}

services.AddFluentValidationRulesToSwagger(
    configureRegistration: options => options.UseDocumentFilter = true);

public void ConfigureServices(IServiceCollection services)
{
    // HttpContextServiceProviderValidatorFactory requires access to HttpContext
    services.AddHttpContextAccessor();

    services
        .AddMvc()
        // Adds fluent validators to Asp.net
        .AddFluentValidation(c =>
        {
            c.RegisterValidatorsFromAssemblyContaining<Startup>();
            // Optionally set validator factory if you have problems with scope resolve inside validators.
            c.ValidatorFactoryType = typeof(HttpContextServiceProviderValidatorFactory);
        });

public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
    app
        .UseMvc()
        // Use scoped swagger if you have problems with scoped services in validators
        .UseScopedSwagger();

public static IWebHost BuildWebHost(string[] args) =>
    WebHost.CreateDefaultBuilder(args)
        // Needed for using scoped services (for example DbContext) in validators
        .UseDefaultServiceProvider(options => options.ValidateScopes = false)
        .UseStartup<Startup>()
        .Build();

services.TryAddTransient<IValidatorFactory, ServiceProviderValidatorFactory>();
services.AddFluentValidationRulesToSwagger();

Startup.cs:

    .AddJsonOptions(options =>
    {
        options.JsonSerializerOptions.PropertyNamingPolicy = new NewtonsoftJsonNamingPolicy(new SnakeCaseNamingStrategy());
        //options.JsonSerializerOptions.DictionaryKeyPolicy = new NewtonsoftJsonNamingPolicy(new SnakeCaseNamingStrategy());
    })


    /// <summary>
    /// Allows use Newtonsoft <see cref="NamingStrategy"/> as System.Text <see cref="JsonNamingPolicy"/>.
    /// </summary>
    public class NewtonsoftJsonNamingPolicy : JsonNamingPolicy
    {
        private readonly NamingStrategy _namingStrategy;

        /// <summary>
        /// Creates new instance of <see cref="NewtonsoftJsonNamingPolicy"/>.
        /// </summary>
        /// <param name="namingStrategy">Newtonsoft naming strategy.</param>
        public NewtonsoftJsonNamingPolicy(NamingStrategy namingStrategy)
        {
            _namingStrategy = namingStrategy;
        }

        /// <inheritdoc />
        public override string ConvertName(string name)
        {
            return _namingStrategy.GetPropertyName(name, false);
        }
    }