prefab-page-detail/Prefab.Web/Shared/ExceptionHandler.cs

using System.Text.Json;
using FluentValidation;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Options;
using Prefab.Handler;
using Prefab.Catalog.Domain.Exceptions;
using Prefab.Shared;
using Microsoft.EntityFrameworkCore;

namespace Prefab.Web.Shared;

public class ExceptionHandler(RequestDelegate next, ILogger<ExceptionHandler> logger, IOptions<Microsoft.AspNetCore.Http.Json.JsonOptions> jsonOptions)
{
    private readonly JsonSerializerOptions _jsonOptions = jsonOptions?.Value?.SerializerOptions ?? new JsonSerializerOptions(JsonSerializerDefaults.Web);

    public async Task InvokeAsync(HttpContext context)
    {
        try
        {
            await next(context);
        }
        catch (Exception ex)
        {
            if (context.Response.HasStarted)
            {
                logger.LogWarning("Response already started for {Method} {Path}. Rethrowing exception.", context.Request.Method, context.Request.Path);
                throw;
            }

            await HandleExceptionAsync(context, ex);
        }
    }

    private async Task HandleExceptionAsync(HttpContext context, Exception exception)
    {
        var (status, problem) = MapException(context, exception);
        problem.Status ??= status;

        problem.Instance ??= context.Request.Path;
        problem.Extensions["traceId"] = context.TraceIdentifier;

        if (!problem.Extensions.ContainsKey("method"))
        {
            problem.Extensions["method"] = context.Request.Method;
        }

        if (context.RequestServices.GetService<IHandlerContextAccessor>()?.Current is { } handlerContext)
        {
            if (!string.IsNullOrWhiteSpace(handlerContext.CorrelationId))
            {
                problem.Extensions["correlationId"] = handlerContext.CorrelationId;
            }

            if (!string.IsNullOrWhiteSpace(handlerContext.RequestId))
            {
                problem.Extensions["requestId"] = handlerContext.RequestId;
            }
        }
        else if (context.Items.TryGetValue(HandlerContextItems.HttpContextKey, out var ctxObj) && ctxObj is HandlerContext storedContext)
        {
            if (!string.IsNullOrWhiteSpace(storedContext.CorrelationId))
            {
                problem.Extensions["correlationId"] = storedContext.CorrelationId;
            }

            if (!string.IsNullOrWhiteSpace(storedContext.RequestId))
            {
                problem.Extensions["requestId"] = storedContext.RequestId;
            }
        }
        else if (!problem.Extensions.ContainsKey("correlationId"))
        {
            problem.Extensions["correlationId"] = context.TraceIdentifier;
        }

        if (problem is ValidationProblemDetails validation)
        {
            if (!problem.Extensions.ContainsKey("errors"))
            {
                problem.Extensions["errors"] = validation.Errors;
            }

            if (string.IsNullOrWhiteSpace(problem.Detail))
            {
                var firstError = validation.Errors.Values.SelectMany(values => values)
                    .FirstOrDefault(message => !string.IsNullOrWhiteSpace(message));
                if (!string.IsNullOrWhiteSpace(firstError))
                {
                    problem.Detail = firstError;
                }
            }
        }

        context.Response.StatusCode = status;
        context.Response.ContentType = "application/problem+json";

        await context.Response.WriteAsync(JsonSerializer.Serialize(problem, _jsonOptions));
    }

    private (int StatusCode, ProblemDetails Problem) MapException(HttpContext context, Exception exception) =>
        exception switch
        {
            ValidationException validationException => MapValidationException(validationException),
            CatalogNotFoundException notFound => MapNotFoundException(notFound),
            RemoteProblemException remoteException => MapRemoteProblemException(remoteException),
            DomainException domainException => MapDomainException(domainException),
            DbUpdateConcurrencyException concurrencyException => MapConcurrencyException(concurrencyException),
            _ => MapUnexpectedException(exception)
        };

    private static (int StatusCode, ProblemDetails Problem) MapValidationException(ValidationException exception)
    {
        var errors = exception.Errors
            .GroupBy(error => string.IsNullOrWhiteSpace(error.PropertyName) ? string.Empty : error.PropertyName)
            .ToDictionary(
                group => group.Key,
                group => group.Select(error => error.ErrorMessage ?? string.Empty).ToArray());

        var details = new ValidationProblemDetails(errors)
        {
            Title = "Validation failed.",
            Type = "https://prefab.dev/problems/validation-error",
            Status = StatusCodes.Status400BadRequest
        };

        return (details.Status.Value, details);
    }

    private static (int StatusCode, ProblemDetails Problem) MapNotFoundException(CatalogNotFoundException exception)
    {
        var details = new ProblemDetails
        {
            Title = "Resource not found.",
            Detail = exception.Message,
            Type = "https://prefab.dev/problems/not-found",
            Status = StatusCodes.Status404NotFound
        };

        details.Extensions["resource"] = exception.Resource;
        details.Extensions["identifier"] = exception.Identifier;

        return (details.Status.Value, details);
    }

    private (int StatusCode, ProblemDetails Problem) MapRemoteProblemException(RemoteProblemException exception)
    {
        var status = (int)exception.StatusCode;
        ProblemDetails details;

        if (!string.IsNullOrWhiteSpace(exception.ResponseBody))
        {
            try
            {
                details = JsonSerializer.Deserialize<ProblemDetails>(exception.ResponseBody, new JsonSerializerOptions(JsonSerializerDefaults.Web)) ?? new ProblemDetails();
            }
            catch (JsonException)
            {
                details = new ProblemDetails
                {
                    Detail = exception.ResponseBody
                };
            }
        }
        else
        {
            details = new ProblemDetails();
        }

        details.Status ??= status;
        details.Title ??= "Remote request failed.";
        details.Detail ??= "The downstream service returned an error.";
        details.Type ??= "https://prefab.dev/problems/remote-error";

        return (details.Status.Value, details);
    }

    private static (int StatusCode, ProblemDetails Problem) MapDomainException(DomainException exception)
    {
        var details = new ProblemDetails
        {
            Title = "Request could not be processed.",
            Detail = exception.Message,
            Type = "https://prefab.dev/problems/domain-error",
            Status = StatusCodes.Status400BadRequest
        };

        return (details.Status.Value, details);
    }

    private (int StatusCode, ProblemDetails Problem) MapConcurrencyException(DbUpdateConcurrencyException exception)
    {
        logger.LogWarning(exception, "Concurrency conflict encountered.");

        var details = new ProblemDetails
        {
            Title = "Concurrency conflict.",
            Detail = "The resource was modified by another process. Refresh and retry your request.",
            Type = "https://prefab.dev/problems/concurrency-conflict",
            Status = StatusCodes.Status409Conflict
        };

        return (details.Status.Value, details);
    }

    private (int StatusCode, ProblemDetails Problem) MapUnexpectedException(Exception exception)
    {
        logger.LogError(exception, "Unhandled exception encountered.");

        var details = new ProblemDetails
        {
            Title = "An unexpected error occurred.",
            Detail = exception.Message,
            Type = "https://prefab.dev/problems/unexpected-error",
            Status = StatusCodes.Status500InternalServerError
        };

        return (details.Status.Value, details);
    }
}

public static class ExceptionHandlingExtensions
{
    public static IApplicationBuilder UseExceptionHandling(this IApplicationBuilder app)
    {
        return app.UseMiddleware<ExceptionHandler>();
    }
}