components/LiteCharms.Features/Mediator/TelemetryPipelineBehavior.cs

namespace LiteCharms.Features.Mediator;

public sealed class TelemetryPipelineBehavior<TRequest, TResponse> :
    IPipelineBehavior<TRequest, TResponse?>
    where TRequest : IRequest<TResponse>
    where TResponse : ResultBase, new()
{
    public async ValueTask<TResponse?> Handle(TRequest message, MessageHandlerDelegate<TRequest, TResponse?> next, CancellationToken cancellationToken)
    {
        var requestName = typeof(TRequest).Name;

        using var activity = MediatorTelemetry.Source.StartActivity(requestName);

        activity?.SetTag("mediator.request_type", typeof(TRequest).FullName);

        var stopWatch = Stopwatch.StartNew();
        var status = "Success";

        try
        {
            TResponse? response = await next(message, cancellationToken);

            if (response is null)
            {
                status = "NullResponse";
                activity?.SetStatus(ActivityStatusCode.Error, "Response was null");

                return response;
            }

            if (response.IsFailed)
            {
                status = "Failed";
                activity?.SetStatus(ActivityStatusCode.Error, "Request failed");

                var firstError = response.Errors.FirstOrDefault()?.Message ?? "Unknown Error";
                activity?.SetTag("error.message", firstError);

                foreach (var error in response.Errors)
                    activity?.AddEvent(new ActivityEvent("Result Error", tags: new() { { "message", error.Message } }));
            }
            else
                activity?.SetStatus(ActivityStatusCode.Ok);

            return response;
        }
        catch (Exception ex)
        {
            status = "Exception";
            activity?.SetStatus(ActivityStatusCode.Error, ex.Message);
            
            activity?.AddException(ex);

            throw;
        }
        finally
        {
            stopWatch.Stop();

            var tags = new TagList { { "request", requestName }, { "status", status } };

            MediatorTelemetry.RequestCounter.Add(1, tags);
            MediatorTelemetry.RequestDuration.Record(stopWatch.Elapsed.TotalMilliseconds, tags);
        }
    }
}