Emit MediatR Events to EventGrid

gistfile1.txt

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using MyApp.AppServices.Configuration;
using MyApp.AppServices.EventBus.Command;
using MyApp.AppServices.Model.EventGrid;
using Framework.EventBus.Command;
using Framework.Model;
using MediatR;
using Microsoft.Azure.EventGrid;
using Microsoft.Azure.EventGrid.Models;

namespace MyApp.AppServices.EventBus.PipelineBehaviors
{
    /// <summary>
    /// Post-response logic for emitting events to event grid
    /// </summary>
    /// <typeparam name="TRequest"></typeparam>
    /// <typeparam name="TResponse"></typeparam>
    internal class EmitEventPipelineBehavior<TRequest, TResponse> : IPipelineBehavior<TRequest, TResponse>
    {
        private const string EventTypeFormat = "MyApp.{0}";
        private const string EventSubjectFormat = "AppServices/{0}";
        private const string EventDataVersion = "1.0";

        private readonly EventGridClient _eventGridClient;
        private readonly EventGridConfig _eventGridConfig;

        public EmitEventPipelineBehavior(EventGridClient eventGridClient,
            EventGridConfig eventGridConfig)
        {
            _eventGridClient = eventGridClient;
            _eventGridConfig = eventGridConfig;
        }

        public async Task<TResponse> Handle(TRequest request, CancellationToken cancellationToken,
            RequestHandlerDelegate<TResponse> next)
        {
            var response = await next();

            // Emit event to EventGrid
            if (response is CommandResult<CommandEventData> commandResult
                && commandResult.Outcome == Outcome.Success
                && commandResult.EventList != null
                && commandResult.EventList.Count > 0)
            {
                var eventGridEvents = ToEventGridEventList(commandResult.EventList);

                // For Azure Function development using Postman
                // var eventsJson = eventGridEvents.ToJson();

                // Fire and forget - results are discarded
                _ = _eventGridClient.PublishEventsAsync(_eventGridConfig.TopicHostname, eventGridEvents, cancellationToken);
            }

            return response;
        }

        private List<EventGridEvent> ToEventGridEventList(List<CommandEventData> eventList)
        {
            return eventList
                .Select(eventData =>
                    new EventGridEvent
                    {
                        Id = Guid.NewGuid().ToString(),
                        Data = new EventGridEventData
                        {
                            UserSecurityInfo = eventData.UserSecurityInfo,
                            EventType = eventData.EventType,
                            Target = eventData.Target,
                            Context = eventData.Context
                        },
                        DataVersion = EventDataVersion,
                        EventTime = eventData.EventTimeUtc,
                        EventType = string.Format(EventTypeFormat, eventData.EventType.ToString()),
                        Subject = string.Format(EventSubjectFormat, eventData.Source)
                    }).ToList();
        }
    }
}