DeutschLernen/GermanApp/Shared/Middleware/ExceptionMiddleware.cs

using System.Net;
using System.Text.Json;
using GermanApp.Shared.Models;

namespace GermanApp.Shared.Middleware;

/// <summary>
/// Global exception handling middleware.
/// Catches exceptions and returns consistent error responses.
/// </summary>
public class ExceptionMiddleware
{
    private readonly RequestDelegate _next;
    private readonly ILogger<ExceptionMiddleware> _logger;

    public ExceptionMiddleware(RequestDelegate next, ILogger<ExceptionMiddleware> logger)
    {
        _next = next;
        _logger = logger;
    }

    public async Task InvokeAsync(HttpContext httpContext)
    {
        try
        {
            await _next(httpContext);
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Unhandled exception occurred: {Message}", ex.Message);
            await HandleExceptionAsync(httpContext, ex);
        }
    }

    private static Task HandleExceptionAsync(HttpContext context, Exception exception)
    {
        context.Response.ContentType = "application/json";
        context.Response.StatusCode = (int)HttpStatusCode.InternalServerError;

        var response = new ApiErrorResponse(
            "An unexpected error occurred. Please try again later.",
            context.Response.StatusCode,
            exception.Message
        );

        var options = new JsonSerializerOptions
        {
            PropertyNamingPolicy = JsonNamingPolicy.CamelCase
        };

        return context.Response.WriteAsync(JsonSerializer.Serialize(response, options));
    }
}

/// <summary>
/// Extension method to add exception middleware.
/// </summary>
public static class ExceptionMiddlewareExtensions
{
    public static IApplicationBuilder UseExceptionMiddleware(this IApplicationBuilder builder) =>
        builder.UseMiddleware<ExceptionMiddleware>();
}