proposal-system/api/src/ProposalSystem.Api/Middleware/GlobalExceptionHandler.cs

using System.Net;
using System.Text.Json;
using FluentValidation;
using Microsoft.AspNetCore.Mvc;

namespace ProposalSystem.Api.Middleware;

public class GlobalExceptionHandler : IMiddleware
{
    private readonly ILogger<GlobalExceptionHandler> _logger;

    public GlobalExceptionHandler(ILogger<GlobalExceptionHandler> logger)
    {
        _logger = logger;
    }

    public async Task InvokeAsync(HttpContext context, RequestDelegate next)
    {
        try
        {
            await next(context);
        }
        catch (Exception ex)
        {
            await HandleExceptionAsync(context, ex);
        }
    }

    private async Task HandleExceptionAsync(HttpContext context, Exception exception)
    {
        var (statusCode, problemDetails) = exception switch
        {
            ValidationException validationEx => (
                HttpStatusCode.BadRequest,
                new ProblemDetails
                {
                    Status = 400,
                    Title = "Validation Error",
                    Detail = string.Join("; ", validationEx.Errors.Select(e => e.ErrorMessage)),
                }
            ),
            KeyNotFoundException => (
                HttpStatusCode.NotFound,
                new ProblemDetails
                {
                    Status = 404,
                    Title = "Not Found",
                    Detail = exception.Message,
                }
            ),
            UnauthorizedAccessException => (
                HttpStatusCode.Unauthorized,
                new ProblemDetails
                {
                    Status = 401,
                    Title = "Unauthorized",
                    Detail = "Authentication required",
                }
            ),
            InvalidOperationException => (
                HttpStatusCode.BadRequest,
                new ProblemDetails
                {
                    Status = 400,
                    Title = "Invalid Operation",
                    Detail = exception.Message,
                }
            ),
            _ => (
                HttpStatusCode.InternalServerError,
                new ProblemDetails
                {
                    Status = 500,
                    Title = "Internal Server Error",
                    Detail = "An unexpected error occurred",
                }
            ),
        };

        if (statusCode == HttpStatusCode.InternalServerError)
        {
            _logger.LogError(exception, "Unhandled exception");
        }

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

        await context.Response.WriteAsync(
            JsonSerializer.Serialize(problemDetails, new JsonSerializerOptions
            {
                PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
            }));
    }
}