internal async ValueTask PrepareRequestMessageAsync()

in Microsoft.Azure.Cosmos/src/GatewayStoreClient.cs [269:369]
85 lines of code
25 McCabe index (conditional complexity)

        internal async ValueTask<HttpRequestMessage> PrepareRequestMessageAsync(
            DocumentServiceRequest request,
            Uri physicalAddress)
        {
            HttpMethod httpMethod = HttpMethod.Head;
            if (request.OperationType == OperationType.Create ||
                request.OperationType == OperationType.Upsert ||
                request.OperationType == OperationType.Query ||
                request.OperationType == OperationType.SqlQuery ||
                request.OperationType == OperationType.Batch ||
                request.OperationType == OperationType.ExecuteJavaScript ||
                request.OperationType == OperationType.QueryPlan ||
                (request.ResourceType == ResourceType.PartitionKey && request.OperationType == OperationType.Delete))
            {
                httpMethod = HttpMethod.Post;
            }
            else if (ChangeFeedHelper.IsChangeFeedWithQueryRequest(request.OperationType, request.Body != null))
            {
                // ChangeFeed with payload is a CF with query support and will
                // be a query POST request.
                httpMethod = HttpMethod.Post;
            }
            else if (request.OperationType == OperationType.Read
                || request.OperationType == OperationType.ReadFeed)
            {
                httpMethod = HttpMethod.Get;
            }
            else if ((request.OperationType == OperationType.Replace)
                || (request.OperationType == OperationType.CollectionTruncate))
            {
                httpMethod = HttpMethod.Put;
            }
            else if (request.OperationType == OperationType.Delete)
            {
                httpMethod = HttpMethod.Delete;
            }
            else if (request.OperationType == OperationType.Patch)
            {
                // There isn't support for PATCH method in .NetStandard 2.0
                httpMethod = httpPatchMethod;
            }
            else
            {
                throw new NotImplementedException();
            }

            HttpRequestMessage requestMessage = new HttpRequestMessage(httpMethod, physicalAddress);

            // The StreamContent created below will own and dispose its underlying stream, but we may need to reuse the stream on the 
            // DocumentServiceRequest for future requests. Hence we need to clone without incurring copy cost, so that when
            // HttpRequestMessage -> StreamContent -> MemoryStream all get disposed, the original stream will be left open.
            if (request.Body != null)
            {
                await request.EnsureBufferedBodyAsync();
                MemoryStream clonedStream = new MemoryStream();
                // WriteTo doesn't use and update Position of source stream. No point in setting/restoring it.
                request.CloneableBody.WriteTo(clonedStream);
                clonedStream.Position = 0;

                requestMessage.Content = new StreamContent(clonedStream);
            }

            if (request.Headers != null)
            {
                foreach (string key in request.Headers)
                {
                    if (GatewayStoreClient.IsAllowedRequestHeader(key))
                    {
                        if (key.Equals(HttpConstants.HttpHeaders.ContentType, StringComparison.OrdinalIgnoreCase))
                        {
                            requestMessage.Content.Headers.ContentType = new MediaTypeHeaderValue(request.Headers[key]);
                        }
                        else
                        {
                            requestMessage.Headers.TryAddWithoutValidation(key, request.Headers[key]);
                        }
                    }
                }
            }

            if (request.Properties != null)
            {
                foreach (KeyValuePair<string, object> property in request.Properties)
                {
                    requestMessage.Properties.Add(property);
                }
            }

            // add activityId
            Guid activityId = System.Diagnostics.Trace.CorrelationManager.ActivityId;
            Debug.Assert(activityId != Guid.Empty);
            requestMessage.Headers.Add(HttpConstants.HttpHeaders.ActivityId, activityId.ToString());

            string regionName = request?.RequestContext?.RegionName;
            if (regionName != null)
            {
                requestMessage.Properties.Add(ClientSideRequestStatisticsTraceDatum.HttpRequestRegionNameProperty, regionName);
            }

            return requestMessage;
        }