/// <summary>
    /// Validates requests and responses.
    /// </summary>
    public static ServiceDelegator Validate(object inner)
    {
        if (inner is null)
        {
            throw new ArgumentNullException(nameof(inner));
        }

        return(async(method, request, cancellationToken) =>
        {
            if (!request.Validate(out var requestErrorMessage))
            {
                return ServiceResult.Failure(ServiceErrors.CreateInvalidRequest(requestErrorMessage));
            }

            var response = await method.InvokeAsync(inner, request, cancellationToken).ConfigureAwait(false);

            if (!response.Validate(out var responseErrorMessage))
            {
                return ServiceResult.Failure(ServiceErrors.CreateInvalidResponse(responseErrorMessage));
            }

            return response;
        });
    }
    /// <summary>
    /// Attempts to handle a service method.
    /// </summary>
    protected async Task <HttpResponseMessage?> TryHandleServiceMethodAsync <TRequest, TResponse>(HttpMethodMapping <TRequest, TResponse> mapping, HttpRequestMessage httpRequest, Func <TRequest, CancellationToken, Task <ServiceResult <TResponse> > > invokeMethodAsync, CancellationToken cancellationToken)
        where TRequest : ServiceDto, new()
        where TResponse : ServiceDto, new()
    {
        if (mapping == null)
        {
            throw new ArgumentNullException(nameof(mapping));
        }
        if (httpRequest == null)
        {
            throw new ArgumentNullException(nameof(httpRequest));
        }
        if (invokeMethodAsync == null)
        {
            throw new ArgumentNullException(nameof(invokeMethodAsync));
        }
        if (httpRequest.RequestUri == null)
        {
            throw new ArgumentException("RequestUri must be specified.", nameof(httpRequest));
        }

        if (httpRequest.Method != mapping.HttpMethod)
        {
            return(null);
        }

        var pathParameters = TryMatchHttpRoute(httpRequest.RequestUri, m_rootPath + mapping.Path);

        if (pathParameters == null)
        {
            return(null);
        }

        var context = new ServiceHttpContext();

        ServiceHttpContext.SetContext(httpRequest, context);

        var aspectHttpResponse = await AdaptTask(RequestReceivedAsync(httpRequest, cancellationToken)).ConfigureAwait(true);

        if (aspectHttpResponse != null)
        {
            return(aspectHttpResponse);
        }

        ServiceErrorDto?error = null;

        object?requestBody = null;

        if (mapping.RequestBodyType != null)
        {
            try
            {
                var serializer    = GetHttpContentSerializer(mapping.RequestBodyType);
                var requestResult = await AdaptTask(serializer.ReadHttpContentAsync(mapping.RequestBodyType, httpRequest.Content, cancellationToken)).ConfigureAwait(true);

                if (requestResult.IsFailure)
                {
                    error = requestResult.Error;
                }
                else
                {
                    requestBody = requestResult.Value;
                }
            }
            catch (Exception exception) when(ShouldCreateErrorFromException(exception))
            {
                // cancellation can cause the wrong exception
                cancellationToken.ThrowIfCancellationRequested();

                // error reading request body
                error = CreateErrorFromException(exception);
            }
        }

        TResponse?response = null;

        if (error == null)
        {
            var request = mapping.CreateRequest(requestBody);

            var uriParameters = new Dictionary <string, string?>(StringComparer.OrdinalIgnoreCase);
            foreach (var queryParameter in ParseQueryString(httpRequest.RequestUri.Query))
            {
                uriParameters[queryParameter.Key] = queryParameter.Value[0];
            }
            foreach (var pathParameter in pathParameters)
            {
                uriParameters[pathParameter.Key] = pathParameter.Value;
            }
            request = mapping.SetUriParameters(request, uriParameters);
            request = mapping.SetRequestHeaders(request, HttpServiceUtility.CreateDictionaryFromHeaders(httpRequest.Headers, httpRequest.Content?.Headers) !);

            context.Request = request;

            if (!m_skipRequestValidation && !request.Validate(out var requestErrorMessage))
            {
                error = ServiceErrors.CreateInvalidRequest(requestErrorMessage);
            }
            else
            {
                var methodResult = await invokeMethodAsync(request, cancellationToken).ConfigureAwait(true);

                if (methodResult.IsFailure)
                {
                    error = methodResult.Error;
                }
                else
                {
                    response = methodResult.Value;

                    if (!m_skipResponseValidation && !response.Validate(out var responseErrorMessage))
                    {
                        error    = ServiceErrors.CreateInvalidResponse(responseErrorMessage);
                        response = null;
                    }
                }
            }

            context.Result = error != null?ServiceResult.Failure(error) : ServiceResult.Success <ServiceDto>(response !);
        }

        HttpResponseMessage httpResponse;

        if (error == null)
        {
            var responseMappingGroups = mapping.ResponseMappings
                                        .GroupBy(x => x.MatchesResponse(response !))
                                        .Where(x => x.Key != false)
                                        .OrderByDescending(x => x.Key)
                                        .ToList();
            if (responseMappingGroups.Count >= 1 && responseMappingGroups[0].Count() == 1)
            {
                var responseMapping = responseMappingGroups[0].Single();
                httpResponse = new HttpResponseMessage(responseMapping.StatusCode);

                var responseHeaders = mapping.GetResponseHeaders(response !);
                var headersResult   = HttpServiceUtility.TryAddNonContentHeaders(httpResponse.Headers, responseHeaders);
                if (headersResult.IsFailure)
                {
                    throw new InvalidOperationException(headersResult.Error !.Message);
                }

                if (responseMapping.ResponseBodyType != null)
                {
                    var serializer = GetHttpContentSerializer(responseMapping.ResponseBodyType);
                    var mediaType  = responseMapping.ResponseBodyContentType ?? responseHeaders?.GetContentType() ?? GetAcceptedMediaType(httpRequest, serializer);
                    httpResponse.Content = serializer.CreateHttpContent(responseMapping.GetResponseBody(response !) !, mediaType);
                    if (m_disableChunkedTransfer)
                    {
                        await httpResponse.Content.LoadIntoBufferAsync().ConfigureAwait(false);
                    }
                }
            }
            else
            {
                throw new InvalidOperationException($"Found {responseMappingGroups.Sum(x => x.Count())} valid HTTP responses for {typeof(TResponse).Name}: {response}");
            }
        }
        else
        {
            var statusCode = error.Code == null ? HttpStatusCode.InternalServerError :
                             (TryGetCustomHttpStatusCode(error.Code) ?? HttpServiceErrors.TryGetHttpStatusCode(error.Code) ?? HttpStatusCode.InternalServerError);
            httpResponse = new HttpResponseMessage(statusCode);
            if (statusCode != HttpStatusCode.NoContent && statusCode != HttpStatusCode.NotModified)
            {
                var mediaType = GetAcceptedMediaType(httpRequest, m_contentSerializer);
                httpResponse.Content = m_contentSerializer.CreateHttpContent(error, mediaType);
                if (m_disableChunkedTransfer)
                {
                    await httpResponse.Content.LoadIntoBufferAsync().ConfigureAwait(false);
                }
            }
        }

        httpResponse.RequestMessage = httpRequest;
        await AdaptTask(ResponseReadyAsync(httpResponse, cancellationToken)).ConfigureAwait(true);

        return(httpResponse);
    }
    /// <summary>
    /// Sends an HTTP request and processes the response.
    /// </summary>
    protected async Task <ServiceResult <TResponse> > TrySendRequestAsync <TRequest, TResponse>(HttpMethodMapping <TRequest, TResponse> mapping, TRequest request, CancellationToken cancellationToken)
        where TRequest : ServiceDto, new()
        where TResponse : ServiceDto, new()
    {
        if (mapping == null)
        {
            throw new ArgumentNullException(nameof(mapping));
        }
        if (request == null)
        {
            throw new ArgumentNullException(nameof(request));
        }

        try
        {
            // validate the request DTO
            if (!m_skipRequestValidation && !request.Validate(out var requestErrorMessage))
            {
                return(ServiceResult.Failure(ServiceErrors.CreateInvalidRequest(requestErrorMessage)));
            }

            // make sure the request DTO doesn't violate any HTTP constraints
            var requestValidation = mapping.ValidateRequest(request);
            if (requestValidation.IsFailure)
            {
                return(requestValidation.ToFailure());
            }

            // create the HTTP request with the right method, path, query string, and headers
            var requestHeaders    = mapping.GetRequestHeaders(request);
            var httpRequestResult = TryCreateHttpRequest(mapping.HttpMethod, mapping.Path, mapping.GetUriParameters(request), requestHeaders);
            if (httpRequestResult.IsFailure)
            {
                return(httpRequestResult.ToFailure());
            }

            // create the request body if necessary
            using var httpRequest = httpRequestResult.Value;
            var requestBody = mapping.GetRequestBody(request);
            if (requestBody != null)
            {
                var contentType = mapping.RequestBodyContentType ?? requestHeaders?.GetContentType();
                httpRequest.Content = GetHttpContentSerializer(requestBody.GetType()).CreateHttpContent(requestBody, contentType);
                if (m_disableChunkedTransfer)
                {
                    await httpRequest.Content.LoadIntoBufferAsync().ConfigureAwait(false);
                }
            }

            // send the HTTP request and get the HTTP response
            using var httpResponse = await SendRequestAsync(httpRequest, request, cancellationToken).ConfigureAwait(false);

            // find the response mapping for the status code
            var statusCode      = httpResponse.StatusCode;
            var responseMapping = mapping.ResponseMappings.FirstOrDefault(x => x.StatusCode == statusCode);

            // fail if no response mapping can be found for the status code
            if (responseMapping == null)
            {
                return(ServiceResult.Failure(await CreateErrorFromHttpResponseAsync(httpResponse, cancellationToken).ConfigureAwait(false)));
            }

            // read the response body if necessary
            object?responseBody = null;
            if (responseMapping.ResponseBodyType != null)
            {
                var serializer     = GetHttpContentSerializer(responseMapping.ResponseBodyType);
                var responseResult = await serializer.ReadHttpContentAsync(
                    responseMapping.ResponseBodyType, httpResponse.Content, cancellationToken).ConfigureAwait(false);

                if (responseResult.IsFailure)
                {
                    var error = responseResult.Error !;
                    error.Code = ServiceErrors.InvalidResponse;
                    return(ServiceResult.Failure(error));
                }
                responseBody = responseResult.Value;
            }

            // create the response DTO
            var response = responseMapping.CreateResponse(responseBody);
            response = mapping.SetResponseHeaders(response, HttpServiceUtility.CreateDictionaryFromHeaders(httpResponse.Headers, httpResponse.Content.Headers) !);

            // validate the response DTO
            if (!m_skipResponseValidation && !response.Validate(out var responseErrorMessage))
            {
                return(ServiceResult.Failure(ServiceErrors.CreateInvalidResponse(responseErrorMessage)));
            }

            return(ServiceResult.Success(response));
        }
        catch (OperationCanceledException) when(!cancellationToken.IsCancellationRequested)
        {
            // HttpClient timeout
            return(ServiceResult.Failure(ServiceErrors.CreateTimeout()));
        }
        catch (Exception exception) when(ShouldCreateErrorFromException(exception))
        {
            // cancellation can cause the wrong exception
            cancellationToken.ThrowIfCancellationRequested();

            // error contacting service
            return(ServiceResult.Failure(CreateErrorFromException(exception)));
        }
    }