Document and Operation Transformers

using System.Threading.RateLimiting;
using Microsoft.AspNetCore.RateLimiting;
using Microsoft.OpenApi;

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddRateLimiter(options =>
{
    options.RejectionStatusCode = StatusCodes.Status429TooManyRequests;
    // The middleware never sets Retry-After itself; without this the documented header is a lie.
    options.OnRejected = (context, cancellationToken) =>
    {
        if (context.Lease.TryGetMetadata(MetadataName.RetryAfter, out var retryAfter))
        {
            context.HttpContext.Response.Headers.RetryAfter = ((int)retryAfter.TotalSeconds).ToString();
        }
        return ValueTask.CompletedTask;
    };
    options.AddFixedWindowLimiter("checkout", limiter =>
    {
        limiter.PermitLimit = 20;
        limiter.Window = TimeSpan.FromMinutes(1);
        limiter.QueueLimit = 0;
    });
});

builder.Services.AddOpenApi(options =>
{
    options.AddOperationTransformer((operation, context, cancellationToken) =>
    {
        var limited = context.Description.ActionDescriptor.EndpointMetadata
            .OfType<EnableRateLimitingAttribute>().Any();
        if (!limited)
        {
            return Task.CompletedTask;
        }

        operation.Responses ??= new OpenApiResponses();
        operation.Responses.TryAdd("429", new OpenApiResponse
        {
            Description = "Rate limit exceeded; retry after the number of seconds in Retry-After.",
            Headers = new Dictionary<string, IOpenApiHeader>
            {
                ["Retry-After"] = new OpenApiHeader
                {
                    Description = "Seconds to wait before retrying.",
                    Schema = new OpenApiSchema { Type = JsonSchemaType.Integer }
                }
            }
        });
        return Task.CompletedTask;
    });
});

var app = builder.Build();
app.UseRateLimiter();
if (app.Environment.IsDevelopment())
{
    app.MapOpenApi();
}

app.MapPost("/checkout", (CheckoutRequest request) => TypedResults.Accepted($"/orders/{request.CartId}"))
    .WithName("Checkout")
    .RequireRateLimiting("checkout");

app.Run();

record CheckoutRequest(Guid CartId, string PaymentMethodId);

using System.Text.Json.Nodes;
using Microsoft.OpenApi;

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddOpenApi(options =>
{
    options.AddSchemaTransformer((schema, context, cancellationToken) =>
    {
        // Every decimal in the API is money: say so instead of the default "double".
        if (context.JsonTypeInfo.Type == typeof(decimal))
        {
            schema.Format = "decimal";
        }

        // One property only: the ISO 4217 currency code on payment types.
        if (context.JsonPropertyInfo is { Name: "currency" }
            && context.JsonPropertyInfo.DeclaringType == typeof(PaymentResponse))
        {
            schema.Pattern = "^[A-Z]{3}$";
            schema.Example = JsonValue.Create("EUR");
        }
        return Task.CompletedTask;
    });
});

var app = builder.Build();
if (app.Environment.IsDevelopment())
{
    app.MapOpenApi();
}

app.MapGet("/payments/{id:guid}", (Guid id) =>
        TypedResults.Ok(new PaymentResponse(id, 129.50m, "EUR", "Captured")))
    .WithName("GetPayment");

app.Run();

public record PaymentResponse(Guid Id, decimal Amount, string Currency, string Status);

using Microsoft.AspNetCore.OpenApi;
using Microsoft.Extensions.Options;
using Microsoft.OpenApi;

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddOptions<ApiDocsOptions>()
    .BindConfiguration("ApiDocs")
    .ValidateDataAnnotations()
    .ValidateOnStart();

builder.Services.AddOpenApi(options => options.AddDocumentTransformer<ApiInfoTransformer>());

var app = builder.Build();
if (app.Environment.IsDevelopment())
{
    app.MapOpenApi();
}
app.MapGet("/customers/{id:int}", (int id) => TypedResults.Ok(new { id, name = "Dana Ruiz" }))
    .WithName("GetCustomer");
app.Run();

public sealed class ApiDocsOptions
{
    [System.ComponentModel.DataAnnotations.Required]
    public string Title { get; set; } = "";
    public string? PublicUrl { get; set; }
    public string SupportEmail { get; set; } = "[email protected]";
}

internal sealed class ApiInfoTransformer(IOptions<ApiDocsOptions> options) : IOpenApiDocumentTransformer
{
    public Task TransformAsync(OpenApiDocument document, OpenApiDocumentTransformerContext context,
        CancellationToken cancellationToken)
    {
        var docs = options.Value;
        document.Info.Title = $"{docs.Title} ({context.DocumentName})";
        document.Info.Contact = new OpenApiContact { Name = "Orders team", Email = docs.SupportEmail };
        document.Servers = docs.PublicUrl is null ? [] : [new OpenApiServer { Url = docs.PublicUrl }];
        return Task.CompletedTask;
    }
}