Web API

[ApiController]
[Route("api/[controller]")]
public class OrdersController(
    IOrderService orderService,
    ILogger<OrdersController> logger) : ControllerBase
{
    [HttpGet("{id:guid}")]
    [ProducesResponseType<OrderDto>(StatusCodes.Status200OK)]
    [ProducesResponseType(StatusCodes.Status404NotFound)]
    public async Task<IActionResult> GetById(Guid id, CancellationToken ct)
    {
        var order = await orderService.GetByIdAsync(id, ct);
        return order is null ? NotFound() : Ok(order);
    }

    [HttpPost]
    [ProducesResponseType<OrderDto>(StatusCodes.Status201Created)]
    [ProducesResponseType<ValidationProblemDetails>(StatusCodes.Status400BadRequest)]
    public async Task<IActionResult> Create(CreateOrderRequest request, CancellationToken ct)
    {
        var order = await orderService.CreateAsync(request, ct);
        return CreatedAtAction(nameof(GetById), new { id = order.Id }, order);
    }
}

[HttpGet("{id:guid}")]
public async Task<IActionResult> GetWithOptions(
    [FromRoute] Guid id,
    [FromQuery] bool includeDeleted = false,
    [FromHeader(Name = "X-Correlation-Id")] string? correlationId = null,
    CancellationToken ct = default)
{
    // Route: id, Query: includeDeleted, Header: X-Correlation-Id
}

public record CreateProductRequest
{
    public required string Name { get; init; }
    public required decimal Price { get; init; }
    public string? Description { get; init; }
    public IReadOnlyList<string> Tags { get; init; } = [];
}

public class CreateOrderRequestValidator : AbstractValidator<CreateOrderRequest>
{
    public CreateOrderRequestValidator(IProductRepository products)
    {
        RuleFor(x => x.CustomerId)
            .NotEmpty()
            .WithMessage("Customer ID is required");

        RuleFor(x => x.Items)
            .NotEmpty()
            .WithMessage("Order must contain at least one item");

        RuleForEach(x => x.Items).ChildRules(item =>
        {
            item.RuleFor(i => i.ProductId)
                .NotEmpty()
                .MustAsync(async (id, ct) => await products.ExistsAsync(id, ct))
                .WithMessage("Product does not exist");

            item.RuleFor(i => i.Quantity)
                .GreaterThan(0)
                .LessThanOrEqualTo(100);
        });
    }
}

builder.Services.Configure<ApiBehaviorOptions>(options =>
{
    options.InvalidModelStateResponseFactory = context =>
    {
        var problemDetails = new ValidationProblemDetails(context.ModelState)
        {
            Type = "https://tools.ietf.org/html/rfc7231#section-6.5.1",
            Title = "One or more validation errors occurred.",
            Status = StatusCodes.Status400BadRequest,
            Instance = context.HttpContext.Request.Path
        };

        return new BadRequestObjectResult(problemDetails);
    };
});

builder.Services.AddApiVersioning(options =>
{
    options.DefaultApiVersion = new ApiVersion(1, 0);
    options.AssumeDefaultVersionWhenUnspecified = true;
    options.ReportApiVersions = true;
    options.ApiVersionReader = new UrlSegmentApiVersionReader();
})
.AddApiExplorer(options =>
{
    options.GroupNameFormat = "'v'VVV";
    options.SubstituteApiVersionInUrl = true;
});

[ApiController]
[Route("api/v{version:apiVersion}/products")]
[ApiVersion("1.0")]
public class ProductsV1Controller(IProductService productService) : ControllerBase
{
    [HttpGet("{id}")]
    public async Task<IActionResult> Get(int id, CancellationToken ct)
    {
        var product = await productService.GetAsync(id, ct);
        return Ok(product);
    }
}

public class GlobalExceptionHandler(
    ILogger<GlobalExceptionHandler> logger) : IExceptionHandler
{
    public async ValueTask<bool> TryHandleAsync(
        HttpContext httpContext,
        Exception exception,
        CancellationToken cancellationToken)
    {
        logger.LogError(exception, "Unhandled exception occurred");

        var problemDetails = exception switch
        {
            ValidationException validationEx => new ProblemDetails
            {
                Status = StatusCodes.Status400BadRequest,
                Title = "Validation Error",
                Detail = validationEx.Message
            },
            NotFoundException notFoundEx => new ProblemDetails
            {
                Status = StatusCodes.Status404NotFound,
                Title = "Resource Not Found",
                Detail = notFoundEx.Message
            },
            _ => new ProblemDetails
            {
                Status = StatusCodes.Status500InternalServerError,
                Title = "Internal Server Error"
            }
        };

        problemDetails.Extensions["traceId"] = httpContext.TraceIdentifier;

        httpContext.Response.StatusCode = problemDetails.Status ?? 500;
        await httpContext.Response.WriteAsJsonAsync(problemDetails, cancellationToken);

        return true;
    }
}