private Parameter CreateParameter(ApiParameterDescription paramDesc, bool inPath, SchemaRegistry schemaRegistry)
        {
            var @in = (inPath)
                ? "path"
                : (paramDesc.Source == ApiParameterSource.FromUri) ? "query" : "body";

            var parameter = new Parameter
            {
                name = paramDesc.Name,
                @in = @in
            };

            if (paramDesc.ParameterDescriptor == null)
            {
                parameter.type = "string";
                parameter.required = true;
                return parameter; 
            }

            parameter.required = inPath || !paramDesc.ParameterDescriptor.IsOptional;
            parameter.@default = paramDesc.ParameterDescriptor.DefaultValue;

            var schema = schemaRegistry.GetOrRegister(paramDesc.ParameterDescriptor.ParameterType);
            if (parameter.@in == "body")
                parameter.schema = schema;
            else
                parameter.PopulateFrom(schema);

            return parameter;
        }
        private Operation CreateOperation(ApiDescription apiDescription, SchemaRegistry schemaRegistry)
        {
            var parameters = apiDescription.ParameterDescriptions
                .Select(paramDesc =>
                    {
                        var inPath = apiDescription.RelativePathSansQueryString().Contains("{" + paramDesc.Name + "}");
                        return CreateParameter(paramDesc, inPath, schemaRegistry);
                    })
                 .ToList();

            var responses = new Dictionary<string, Response>();
            var responseType = apiDescription.ResponseType();
            if (responseType == null || responseType == typeof(void))
                responses.Add("204", new Response { description = "No Content" });
            else
                responses.Add("200", new Response { description = "OK", schema = schemaRegistry.GetOrRegister(responseType) });

            var operation = new Operation
            { 
                tags = new [] { _options.GroupingKeySelector(apiDescription) },
                operationId = apiDescription.FriendlyId(),
                produces = apiDescription.Produces().ToList(),
                consumes = apiDescription.Consumes().ToList(),
                parameters = parameters.Any() ? parameters : null, // parameters can be null but not empty
                responses = responses,
                deprecated = apiDescription.IsObsolete()
            };

            foreach (var filter in _options.OperationFilters)
            {
                filter.Apply(operation, schemaRegistry, apiDescription);
            }

            return operation;
        }