DigitalData.TaskFlow/src/presentation/DigitalData.TaskFlow.API/Middleware/ExceptionHandlingMiddleware.cs

using DigitalData.TaskFlow.Application.Common.Exceptions;
using DigitalData.TaskFlow.API.Contracts.Common;
using DigitalData.TaskFlow.Domain.Common;
using DigitalData.TaskFlow.Domain.Enums;
using FluentValidation;
using System.Text.Json;

namespace DigitalData.TaskFlow.API.Middleware;

/// <summary>
/// Handles exceptions globally and returns ticket-compatible API envelopes.
/// </summary>
public sealed class ExceptionHandlingMiddleware(RequestDelegate next, ILogger<ExceptionHandlingMiddleware> logger)
{
    private static readonly JsonSerializerOptions JsonOptions = new(JsonSerializerDefaults.Web);

    /// <summary>
    /// Executes the middleware.
    /// </summary>
    /// <param name="context">HTTP context.</param>
    public async Task InvokeAsync(HttpContext context)
    {
        try
        {
            await next(context);
        }
        catch (ApiException apiException)
        {
            logger.LogWarning(apiException, "API exception intercepted.");

            context.Response.StatusCode = apiException.StatusCode;
            context.Response.ContentType = "application/json";

            var response = new MetaOnlyResponse
            {
                Meta =
                [
                    new MetaEntry
                    {
                        Code = (int)apiException.MetaCode,
                        Message = apiException.Message
                    }
                ]
            };
            await context.Response.WriteAsync(JsonSerializer.Serialize(response, JsonOptions));
        }
        catch (ValidationException validationException)
        {
            logger.LogWarning(validationException, "Validation failed.");

            context.Response.StatusCode = StatusCodes.Status400BadRequest;
            context.Response.ContentType = "application/json";

            var message = validationException.Errors.FirstOrDefault()?.ErrorMessage
                          ?? "Ungultiger Request";

            var response = new MetaOnlyResponse
            {
                Meta =
                [
                    new MetaEntry
                    {
                        Code = (int)MetaCode.InvalidRequest,
                        Message = message
                    }
                ]
            };
            await context.Response.WriteAsync(JsonSerializer.Serialize(response, JsonOptions));
        }
        catch (NotSupportedException notSupportedException)
        {
            logger.LogWarning(notSupportedException, "Operation not supported yet.");

            context.Response.StatusCode = StatusCodes.Status500InternalServerError;
            context.Response.ContentType = "application/json";

            var response = new MetaOnlyResponse
            {
                Meta =
                [
                    new MetaEntry
                    {
                        Code = (int)MetaCode.InternalError,
                        Message = notSupportedException.Message
                    }
                ]
            };
            await context.Response.WriteAsync(JsonSerializer.Serialize(response, JsonOptions));
        }
        catch (Exception exception)
        {
            logger.LogError(exception, "Unhandled exception.");

            context.Response.StatusCode = StatusCodes.Status500InternalServerError;
            context.Response.ContentType = "application/json";

            var response = new MetaOnlyResponse
            {
                Meta =
                [
                    new MetaEntry
                    {
                        Code = (int)MetaCode.InternalError,
                        Message = "Interner Fehler"
                    }
                ]
            };
            await context.Response.WriteAsync(JsonSerializer.Serialize(response, JsonOptions));
        }
    }
}