DocumentService/DocumentOperator.API/Middleware/ExceptionHandlingMiddleware.cs

using DocumentOperator.Domain.Common.Exceptions;
using FluentValidation;
using Microsoft.AspNetCore.Mvc;
using System.Net;
using System.Text.Json;

namespace DocumentOperator.API.Middleware;

/// <summary>
/// Central exception handling middleware
/// Maps exceptions to HTTP status codes and RFC 7807 Problem Details
/// </summary>
/// <remarks>
/// Initializes a new instance of the <see cref="ExceptionHandlingMiddleware"/> class.
/// </remarks>
/// <param name="Next">The next middleware in the pipeline.</param>
public class ExceptionHandlingMiddleware(RequestDelegate Next)
{
    private static readonly JsonSerializerOptions ProbDetailsJsonOpt = new()
    {
        PropertyNamingPolicy = JsonNamingPolicy.CamelCase
    };

    /// <summary>
    /// Invokes the middleware to handle incoming HTTP requests and catch exceptions.
    /// </summary>
    /// <param name="context">The HTTP context for the current request.</param>
    public async Task InvokeAsync(HttpContext context)
    {
        try
        {
            await Next(context);
        }
        catch (Exception ex)
        {
            await HandleExceptionAsync(context, ex);
        }
    }

    private static async Task HandleExceptionAsync(HttpContext context, Exception exception)
    {
        var (statusCode, problemDetails) = MapExceptionToProblemDetails(exception, context);

        context.Response.StatusCode = (int)statusCode;
        context.Response.ContentType = "application/problem+json";

        await context.Response.WriteAsync(JsonSerializer.Serialize(problemDetails, ProbDetailsJsonOpt));
    }

    private static (HttpStatusCode StatusCode, ProblemDetails ProblemDetails) MapExceptionToProblemDetails(
        Exception exception,
        HttpContext context)
    {
        return exception switch
        {
            // FluentValidation (400 Bad Request)
            ValidationException validationEx => (
                HttpStatusCode.BadRequest,
                new ProblemDetails
                {
                    Type = "https://datatracker.ietf.org/doc/html/rfc7231#section-6.5.1",
                    Title = "Validation Error",
                    Status = (int)HttpStatusCode.BadRequest,
                    Detail = string.Join("; ", validationEx.Errors.Select(e => e.ErrorMessage)),
                    Instance = context.Request.Path
                }
            ),

            // Bad Request Exception (400 Bad Request)
            BadRequestException badReqEx => (
                HttpStatusCode.BadRequest,
                new ProblemDetails
                {
                    Type = "https://datatracker.ietf.org/doc/html/rfc7231#section-6.5.4",
                    Title = "Bad Request",
                    Status = (int)HttpStatusCode.BadRequest,
                    Detail = badReqEx.Message,
                    Instance = context.Request.Path
                }
            ),

            // Not Found Exception (404 Not Found)
            NotFoundException notFoundEx => (
                HttpStatusCode.NotFound,
                new ProblemDetails
                {
                    Type = "https://datatracker.ietf.org/doc/html/rfc7231#section-6.5.4",
                    Title = "Resource Not Found",
                    Status = (int)HttpStatusCode.NotFound,
                    Detail = notFoundEx.Message,
                    Instance = context.Request.Path
                }
            ),

            // Generic Exception (500 Internal Server Error)
            _ => (
                HttpStatusCode.InternalServerError,
                new ProblemDetails
                {
                    Type = "https://datatracker.ietf.org/doc/html/rfc7231#section-6.6.1",
                    Title = "Internal Server Error",
                    Status = (int)HttpStatusCode.InternalServerError,
                    Detail = "An unexpected error occurred. Please contact support.",
                    Instance = context.Request.Path
                }
            )
        };
    }
}