BulkPrintingAPI/BulkPrintingAPI/Middleware/ExceptionHan...

using MAX;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.Logging;
using Newtonsoft.Json;
using System;
using System.Threading.Tasks;

namespace BulkPrintingAPI.Middleware
{
    public class ExceptionHandlerMiddleware
    {
        private readonly RequestDelegate _next;
        private ILogger _logger;

        private class ErrorResponse
        {
            public ErrorResponse(string message)
            {
                code = null;
                error = message;
            }

            public ErrorResponse(MAXException e)
            {
                code = e.ErrorCode;
                error = e.Message;
            }

            public int? code { get; set; }

            public string error { get; set; }
        }

        public ExceptionHandlerMiddleware(RequestDelegate next, ILoggerFactory loggerFactory)
        {
            _next = next;
            _logger = loggerFactory.CreateLogger(GetType().FullName);
        }

        public async Task Invoke(HttpContext context)
        {
            try
            {
                await _next(context);
            }
            catch (Exception e)
            {
                if (context.Response.HasStarted)
                {
                    _logger.LogWarning("Response has already started; exception will be rethrown");
                    throw;
                }

                _logger.LogError(0, e, "Unhandled exception");

                ErrorResponse response;
                if (e is MAXException)
                {
                    response = new ErrorResponse((MAXException)e);
                }
                else
                {
                    // Don't want to leak arbitrary exception messages to the user
                    response = new ErrorResponse("The server encountered an unexpected error");
                }

                context.Response.StatusCode = 500;
                context.Response.ContentType = "application/json";
                await context.Response.WriteAsync(JsonConvert.SerializeObject(response));
            }
        }
    }
}